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Applications of LA-ICP-MS analysis to zircon : assessing downhole fractionation and pre-treatment effects… Ver Hoeve, Thomas James 2016

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APPLICATIONS OF LA-ICP-MS ANALYSIS TO ZIRCON: ASSESSING DOWNHOLE FRACTIONATION AND PRE-TREATMENT EFFECTS FOR U-Pb GEOCHRONOLOGY AND TRACE ELEMENT VARIATIONS IN ACCESSORY MINERALS FROM THE BUSHVELD COMPLEXbyTHOMAS JAMES VER HOEVEB.Sc.H., The University of British Columbia, 2013A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEinTHE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES(Geological Sciences)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)December 2016© Thomas James Ver Hoeve, 2016iiAbstractAbstractZircon and other U-Th-Pb-bearing minerals are now recognized as key geochemical and geochronological tracers of the evolution of late-stage fractionated interstitial melt in mafic layered intrusions. Two separate, yet complementary, applications of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) on zircon from layered intrusions are presented with the goals of advancing the analytical capabilities of LA-ICP-MS and showcasing the powerful geochemical fingerprinting of zircon. The effects of downhole fractionation, the time-dependent evolution of Pb-U ratios during laser ablation, represents a significant limitation on the accuracy of U-Th-Pb zircon geochronology by LA-ICP-MS. Exponential downhole correction models developed from the analyses of three common zircon reference materials (Plešovice, Temora-2, 91500) and applied to low-U zircon from Precambrian mafic intrusions (Laramie, Bushveld, Stillwater) indicate that successful correction requires careful matrix-matching the reference zircon to the unknowns. Pre-treatment protocols, including annealing and leaching, applied to all analyzed zircon produces strong effects on downhole fractionation with correlative impact on the relative accuracy of the calculated ages as a function of the downhole behaviour in the reference material used. In the Paleoproterozoic Bushveld Complex, the world’s largest layered intrusion, the trace element systematics of zircon provide temperature-composition constraints on the near-solidus crystallization of mafic-ultramafic cumulates and overlying granitic rocks. Zircon occurs with other late-stage interstitial minerals (e.g., quartz, biotite, Na-plagioclase) and crystallized at temperatures ranging from 950°C down to 690°C based on Ti-in-zircon thermometry. Forward modeling using rhyolite-MELTS of proposed Bushveld parental magmas yields similar zircon saturation temperatures from melts of intermediate-silicic composition, representing less than ~15% remaining melt, and reproduces the observed mineral assemblages. Anomalously high and variable Th/U in zircon from the Critical Zone (e.g., UG2 chromitite, Merensky Reef) reflects U loss to late, oxidized Cl-rich fluids that exsolved from the fractionated interstitial melt, a process that may be a characteristic feature of large open-system layered intrusions (e.g., Neoarchean Stillwater Complex). The presence of late-stage interstitial zircon and other accessory minerals in layered intrusions provides new in situ geochemical and geochronological tools for evaluating the origin and evolution of mafic-ultramafic magmatism in the Earth’s crust throughout geological time.iiiPrefacePrefaceThis thesis contains two research chapters (Chapter 2 and Chapter 3) that have been targeted for submission to international peer-reviewed geoscience journals and that include co-authors who aided in their development. I am the lead author on both chapters and my co-supervisors Dr. James Scoates and Dr. Dominique Weis are co-authors on both studies, each of whom provided extensive feedback and editing for both projects. Dr. Corey Wall provided substantial preparatory and analytical help for both studies and contributed significantly to the ideas presented in Chapter 3. Dr. Margharelay Amini is also a co-author and provided expertise related to LA-ICP-MS analysis and interpretation.  Funding for both studies was provided through an NSERC CREATE (MAGNET – Multidisciplinary Applied Geochemistry Network) grant to Tom Ver Hoeve with additional support for research and analytical work from NSERC Discovery Grants to Drs. Scoates and Weis. The excimer laser ablation system consisting of a Resonetics (now Australian Scientific Instruments, ASI) RESOlution M-50LR coupled to an Agilent 7700x quadrupole ICP-MS at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) was integral to the research carried out for both studies. Funding for PCIGR has been derived in part by NSERC MFA and NSERC MRSP grants over the years.Details of the work carried out by others for the analyses presented in each chapter are indicated below along with co-authors and the journals targeted for submission. Collection and processing of samples are also attributed. I performed all other analytical work for these studies including mineral picking, puck making, SEM imaging, electron probe microanalysis, LA-ICP-MS analysis, data reduction, and interpretation.Chapter 2Matrix Matching Downhole U-Pb Fractionation in Zircon Reference Materials Analyzed by LA-ICP-MSAuthors: Thomas J. Ver Hoeve, James S. Scoates, Corey J. Wall, Margharelay Amini, Dominique WeisSamples SR336 and SA04-13 were provided by Dr. Scoates; sample ST05-03 was collected ivPrefaceby Dr. Scoates and Dr. William Meurer. Processing (sample crushing, mineral separation) was performed by Dr. Wall and the LA-ICP-MS analytical sessions were designed and conducted in collaboration with Dr. Wall.Chapter 3Trace Element Systematics of Zircon and Rutile from the Bushveld Complex, South AfricaAuthors: Thomas J. Ver Hoeve, James S. Scoates, Corey J. Wall, Margharelay Amini, Dominique WeisMost samples were provided by Drs. Edmund Mathez and Jill VanTongeren from the extensive collection of Bushveld Complex materials at the American Museum of Natural History; select samples were contributed by Dr. Scoates from a 2004 field trip to the Bushveld Complex. Processing (sample crushing, mineral separation) was performed by Dr. Wall and the LA-ICP-MS analytical sessions were designed and conducted in collaboration with Dr. Wall.vTable of contentsTable of contentsAbstract  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . iiPreface  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . iiiTable of contents  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . vList of tables .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . xList of figures  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . xiiList of abbreviations  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . xviiAcknowledgements  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .xixDedication   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . xxChapter 1 Introduction to Laser Ablation-ICP-MS and Accessory Minerals in Mafic Layered Intrusions  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 11.1. Introduction and scope of the project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2. LA-ICP-MS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.1.  Overview of LA-ICP-MS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2.2. Advancements in LA-ICP-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.2.3. Downhole fractionation and pre-treatment in LA-ICP-MS . . . . . . . . . . . . . . . . 71.2.4. LA-ICP-MS at PCIGR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.3. Geochemistry of zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.3.1. Zircon composition and structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.3.2. Zircon geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111.3.3. Trace elements in zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141.3.4. High field strength elements and Ti-in-zircon thermometry . . . . . . . . . . . . . . . 16viTable of contents1.4. Mafic layered intrusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181.5. The Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191.5.1. Overview of geology and mineral resources  . . . . . . . . . . . . . . . . . . . . . . . . . . 191.5.2. Previous work on zircon and rutile from the Bushveld Complex . . . . . . . . . . . 241.6. Overview of the thesis  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Chapter 2 Matrix Matching Downhole U-Pb Fractionation in Zircon Reference Materials Analyzed by LA-ICP-MS   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 292.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302.2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312.2.1. Standardization in LA-ICP-MS and downhole fractionation . . . . . . . . . . . . . . 312.3. Pre-treatment of zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322.3.1. Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.3.1.1. Plešovice  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.3.1.2. Temora-2  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.3.1.3. 91500 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.3.1.4. In-house zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.4. Analytical procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362.4.1. Sample preparation and pre-treatment  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362.4.2. Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362.4.3. LA-ICP-MS experimental design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372.4.4. Data reduction and downhole correction  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392.5. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402.5.1. Cathodoluminescence imagery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402.5.2. Characterizing downhole fractionation between samples . . . . . . . . . . . . . . . . . 44viiTable of contents2.5.3. Application of exponential downhole fractionation correction  . . . . . . . . . . . . 522.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542.6.1. Effect of pre-treatment on downhole fractionation  . . . . . . . . . . . . . . . . . . . . . 542.6.2. Impact on LA-ICP-MS methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652.7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Chapter 3 Trace Element Systematics of Zircon and Rutile from the Bushveld Complex, South Africa  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 683.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693.2. Geologic setting of the Bushveld Complex  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703.2.1. Geology of the Rustenburg Layered Suite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733.2.2. Geology of the felsic roof rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 773.2.3. Previous work on zircon and rutile in the Bushveld Complex . . . . . . . . . . . . . 773.3. Samples and analytical techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 783.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833.4.1. Textural setting and internal structure of zircon and rutile in the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833.5. Trace element geochemistry of zircon  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883.5.1. Hafnium and titanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 883.5.2. Thorium and uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.5.3. Rare earth elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 933.5.4. Trace element geochemistry of rutile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 953.6.1. Mapping the solidus of cumulates and granites from the Bushveld Complex using Ti-in-zircon thermometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99viiiTable of contents3.6.2. Forward modelling of zircon saturation in fractionated interstitial melts during crystallization of the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003.6.3. High-Th/U zircon in the Critical Zone: a signal of late-stage fluid saturation 1063.6.4. Origin of LREE-enriched signature of zircon from the roof of the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1083.6.5. Zircon trace element constraints on the relationship between the Upper Zone magmas and felsic magmas in the roof of the Bushveld Complex . . . . . . . . . . . . . . . 1103.6.6. Rutile as a petrogenetic indicator in the Bushveld Complex and other mafic layered intrusions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1133.7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Chapter 4 Conclusions  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 1194.1. Summary of the thesis and key findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1204.2. Correcting for downhole fractionation in U-Pb zircon geochronology by LA-ICP-MS 1204.3. Implications of trace element systematics in zircon in layered intrusions . . . . . . . 1214.3.1. Comparison to the Stillwater Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1234.3.2. Tectono-magmatic implications of zircon chemistry . . . . . . . . . . . . . . . . . . . 1264.4. Directions for future research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1264.4.1. Pre-treatment of zircon for LA-ICP-MS analysis . . . . . . . . . . . . . . . . . . . . . . 1264.4.2. Recommendations for improving methodology . . . . . . . . . . . . . . . . . . . . . . . 1294.4.3. Future of accessory mineral trace element studies in mafic-ultramafic plutonic rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Bibliography   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 131Appendices  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 149ixTable of contentsAppendix A . Trace element results for zircon reference materials and in-house                   zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149Appendix B . MATLAB code for processing downhole fractionation data . . . . . . . . 155Appendix C . Cathodoluminescence (CL) images of untreated and treated zircon reference materials and in-house zircon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Appendix D . Thin section scans and petrographic descriptions of samples from the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171Appendix E . Major and minor element oxides of zircon in the Bushveld Complex determined by EPMA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183Appendix F . LA-ICP-MS results for reference materials determined during analysis of zircon and rutile from the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187Appendix G . Cathodoluminescence images of zircon grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicated . . . . . . . . . . . . . . . . . . . . . . . 191Appendix H . Backscattered electron images of rutile grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicated . . . . . . . . . . . . . . . . . . . . . . . 218Appendix I . Complete trace element analyses of zircon from the Bushveld Complex determined by LA-ICP-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226Appendix J . Chondrite-normalized REE patterns of zircon from the Bushveld                    Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253Appendix K . Complete trace element analyses of rutile from the Bushveld Complex determined by LA-ICP-MS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257Appendix L . Trace element variation diagrams for rutile from the Bushveld Complex used to assess U-Pb concentrations and dating of rutile . . . . . . . . . . . . . . . . . . . . . . . 264Appendix M . Rhyolite-MELTS modeling results for crystallization of proposed Bushveld parent magmas  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266Appendix N . Trace element zonation in zircon from the Bushveld Complex . . . . . . 276xList of tablesTable 1 .1 . Overview of possible substitutions in zircon  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 13Table 2 .1 . Summary of zircon materials used to examine the effects of downhole                         fractionation   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 34Table 2 .2 . Procedure for LA-ICP-MS analysis of zircon at PCIGR   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 38Table 2 .3 . Summary of downhole fractionation for all reference materials and samples in this study  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 48Table 2 .4 . Coefficients determined for exponential correction of downhole fractionation during zircon analysis by LA-ICP-MS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 50Table 2 .5 . Summary of ages of zircon from the in-house samples based on different pre-treatment protocols  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 63Table 3 .1 . Summary of samples examined from the Bushveld Complex for zircon and rutile trace element geochemistry  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 79Table 3 .2 . Procedure for LA-ICP-MS analysis of zircon and rutile  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 82Table 3 .3 . Summary of ranges of trace element concentrations of zircon from the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 90Table 3 .4 . Summary of ranges of trace element concentrations of rutile from the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 97Table A .1 . Summary of ranges of trace element concentrations in untreated, annealed, and leached zircon reference materials and unknowns  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 150Table E .1 . Major and minor element oxides in zircon from the Bushveld Complex  .  .  .  .  .  .  . 184Table I .1 . Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 227Table K .1 . Trace element concentrations of rutile from the Bushveld Complex measured by laser ablation ICP-MS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 258List of tablesxiList of tablesTable M .1 . Results from crystallization of B1 parental Bushveld magmas using                              rhyolite-MELTS   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 267Table M .2 . Results from crystallization of B2 parental Bushveld magmas using                             rhyolite-MELTS   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 269Table M .3 . Results from crystallization of B3 parental Bushveld magmas using                             rhyolite-MELTS   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 271Table M .4 . Results from crystallization of a 60:40 mix of B1 and B2 parental Bushveld magmas using rhyolite-MELTS   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 273xiiList of figuresFigure 1 .1 . Overview of the LA-ICP-MS methodology at PCIGR  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 5Figure 1 .2 . Schematic comparison between a 1-volume and a 2-volume cell  .  .  .  .  .  .  .  .  .  .  .  .  .  . 6Figure 1 .3 . Schematic illustrations of the signal smoothing effect of a “squid” device   .  .  .  .  .  . 8Figure 1 .4 . Comparison of spot and raster analysis techniques by LA-ICP-MS  .  .  .  .  .  .  .  .  .  .  .  . 9Figure 1 .5 . Summary of the physical properties and geochemical applications of zircon . . . . 12Figure 1 .6 . Overview of the U-Th-Pb dating system  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 15Figure 1 .7 . Examples of chondrite-normalized rare earth element (REE) patterns for zircon from the Upper Group Chromitite 2 (sample B00-1-6)  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 17Figure 1 .8 . Schematic diagrams showing the textural setting of zircon within three types of plagioclase cumulates in layered intrusions  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 20Figure 1 .9 . Scanned thin section images showing samples from the Merensky Reef in the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 21Figure 1 .10 . Generalized geologic map of the Bushveld Complex in South Africa   .  .  .  .  .  .  .  . 22Figure 1 .11 . Stratigraphic column of the Bushveld Complex showing major stratigraphic divisions and cumulus mineralogy  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 23Figure 1 .12 . Photomicrographs showing the textural setting of interstitial minerals in samples from the Merensky Reef of the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 25Figure 2 .1 . Diagrams of ablation time vs. 206Pb/238U showing an exponential downhole fractionation correction applied to the analysis of Plešovice  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 41Figure 2 .2 . Cathodoluminescence images of zircon grains from three zircon reference     materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Figure 2 .3 . Cathodoluminescence images of zircon grains from three different in-house               samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43List of figuresxiiiList of figuresFigure 2 .4 . Cathodoluminescence images comparing the differences in CL intensity for untreated and annealed zircon grains  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 45Figure 2 .5 . Ablation time vs. raw 206Pb/238U and 207Pb/235U for untreated grains of the zircon reference materials   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 46Figure 2 .6 . Ablation time vs. raw 206Pb/238U and 207Pb/235U for untreated grains of in-house zircon from samples SR336, SA04-13, and ST05-03  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 47Figure 2 .7 . Diagrams of ablation time vs. 206Pb/238U showing modelled exponential fits for average 206Pb/238U in zircon  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 49Figure 2 .8 . Diagrams of ablation time vs. 206Pb/238U showing time-resolved ratios for untreated and treated grains of the three reference materials  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 53Figure 2 .9 . Diagrams of ablation time vs. 206Pb/238U showing downhole-corrected time-resolved ratios for untreated in-house zircon grains  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 55Figure 2 .10 . Concordia diagrams for the U-Pb results for zircon from the three in-house samples reduced using Plešovice as the reference zircon  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 57Figure 2 .11 . Concordia diagrams for the U-Pb results for zircon from the three in-house samples reduced using Temora-2 as the reference zircon  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 58Figure 2 .12 . Concordia diagrams for the U-Pb results for zircon from the three in-house samples reduced using 91500 as the reference zircon   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 59Figure 2 .13 . Concordia diagrams for the U-Pb results for untreated and treated grains of zircon from SR336 (Laramie) reduced using each of the three reference zircon materials   .  .  .  .  .  .  .  . 60Figure 2 .14 . Concordia diagrams for the U-Pb results for untreated and treated grains of zircon from SA04-13(Bushveld) reduced using each of the three reference zircon materials   .  .  .  .  .  . 61Figure 2 .15 . Concordia diagrams for the U-Pb results for untreated and treated grains of zircon from ST05-03 (Stillwater) reduced using each of the three reference zircon materials  .  .  .  .  .  . 62Figure 2 .16 . Summary figure showing the final ages for the untreated and treated zircon grains from three samples (SR336, SA04-13, ST05-03)  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 64xivList of figuresFigure 3 .1 . Generalized geologic map of the Bushveld Complex in South Africa with                  sample locations  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 71Figure 3 .2 . Schematic stratigraphic sections of the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 72Figure 3 .3 . Geologic map of the Eastern Limb of the Bushveld Complex   .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 74Figure 3 .4 . Photomicrographs showing the textural setting of accessory minerals in rocks from the Rustenburg Layered Suite  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 85Figure 3 .5 . Thin section scan and photomicrographs showing the distribution, shape, and mineralogy of interstitial pockets in sample TW477-661 (Lower Critical Zone)   .  .  .  .  .  .  .  .  .  . 86Figure 3 .6 . Representative scanning electron microscope-cathodoluminescence images of zircon from the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 87Figure 3 .7 . Backscattered electron (BSE) images of representative rutile grains from                     the Critical Zone  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 89Figure 3 .8 . Trace element variations of select high field strength elements and actinides in zircon from the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 92Figure 3 .9 . Chondrite-normalized rare earth element patterns of zircon from the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 94Figure 3 .10 . Trace element ratio variations in zircon from the Bushveld Complex   .  .  .  .  .  .  .  . 96Figure 3 .11 . Trace element variations in rutile from the Bushveld Complex   .  .  .  .  .  .  .  .  .  .  .  .  . 98Figure 3 .12 . Ti vs. Hf diagrams for zircon from all samples analyzed from the Bushveld Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100Figure 3 .13 . Summary of thermometry results for zircon from the Bushveld Complex  .  .  .  . 101Figure 3 .14 . Zr vs. temperature plots summarizing zircon saturation modelling using rhyolite-MELTS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 104Figure 3 .15 . Predicted temperature vs. mineral abundance modeled with rhyolite-MELTS for Bushveld parental magma B1:B2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105Figure 3 .16 . Modelling results for the Nebo granite sample  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 109xvList of figuresFigure 3 .17 . Box-and-whisker diagrams showing trace element variations in zircon vs. stratigraphic height in the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 111Figure 3 .18 . Box-and-whisker diagrams showing trace element ratio variations in zircon vs. stratigraphic height in the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 112Figure 3 .19 . Summary of thermometry results for rutile from the Bushveld Complex  .  .  .  .  . 115Figure 4 .1 . Summary concordia diagrams showing the LA-ICP-MS U-Pb zircon results and age interpretations for Precambrian zircon  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 122Figure 4 .2 . Comparison of Th vs. U for zircon from mafic layered intrusions  .  .  .  .  .  .  .  .  .  .  . 124Figure 4 .3 . Comparison of the distribution of Ti-in-zircon temperatures determined from mafic layered intrusions   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 125Figure 4 .4 . Trace element distribution diagrams for zircon from the Bushveld Complex compared to classification schemes from global zircon datasets  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 127Figure 4 .5 . Trace element discrimination diagrams comparing zircon chemistry from the Bushveld Complex and Stillwater Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 128Figure A .1 . Chondrite-normalized rare earth element patterns in the reference materials and in-house zircon samples analyzed by LA-ICP-MS for Chapter 2 of this thesis  .  .  .  .  .  .  .  .  .  .  .  .  . 153Figure A .2 . Trace element variations of in zircon from the reference materials and in-house zircon samples analyzed by LA-ICP-MS for Chapter 2 of this thesis   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 154Figure E .1 . Major and minor element oxide variations in zircon from the Bushveld Complex measured by EPMA   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 186Figure F .1 . Compilation of trace element results for reference material NIST610 analyzed by LA-ICP-MS .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 188Figure F .2. Chondrite-normalized rare earth element patterns in the 91500 and Plešovice zircon reference materials analyzed by LA-ICP-MS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 189Figure F .3 . Chondrite-normalized rare earth element patterns in the FC-1 and ST05-03 (AN2) zircon reference materials analyzed by LA-ICP-MS  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 190xviList of figuresFigure J .1 . Chondrite-normalized rare earth element patterns in zircon from the Lower Zone and Critical Zone of the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 254Figure J .2 . Chondrite-normalized rare earth element patterns in zircon from the Critical Zone, Main Zone, and Upper Zone of the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 255Figure J .3 . Chondrite-normalized rare earth element patterns in zircon from the felsic roof rocks of Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 256Figure L .1 . Lead and uranium variations in rutile from the Bushveld Complex  .  .  .  .  .  .  .  .  .  . 265Figure M .1 . Mineral crystallization sequences modelled in rhyolite-MELTS for four proposed parental magmas to the Bushveld Complex  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 275Figure N .1 . Hafnium and titanium variations in representative zircon grains from the Rustenburg Layered Suite of the Bushveld Complex   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 277Figure N .2 . Uranium and Th/U variations in representative zircon grains from the Rustenburg Layered Suite of the Bushveld Complex   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 278xviiList of abbreviationsList of abbreviationsAnalytical: BSE: backscattered electronCA-TIMS: chemical abrasion-thermal ionization mass spectrometryCL: cathodoluminescenceEDS: Energy-dispersive X-ray spectroscopyGa: billion yearsID-TIMS: isotope dilution-thermal ionization mass spectrometrykm: kilometersLA-ICP-MS: laser ablation-inductively coupled plasma-mass spectrometrym: metersMa: million yearsMC-ICP-MS: multicollector-inductively coupled plasma-mass spectrometrymJ: millijoule mL: milliliterNIST SRM 610: National Institute of Standards and Technology Standard Reference Material 610 (glass)NIST SRM 612: National Institute of Standards and Technology Standard Reference Material 612 (glass)ppm: parts per millionSEM: scanning electron microscope/microscopySIMS: secondary ion mass spectrometryTIMS: thermal ionization mass spectrometrya: thermodynamic activity of an element (used in Ti-in-zircon and Zr-in-rutile thermometry, eg., a SiO2)σ: standard deviation (sigma) analytical uncertainty (usually reported as 2σ)xviiiList of abbreviationsBushveld Complex:B1, B2, B3: Proposed Bushveld parental magmas (Bushveld-1, Bushveld-2, Bushveld-3)BR: Bastard ReefCZ: Critical ZoneLCZ: Lower Critical ZoneLG: Lower Group chromititeLZ: Lower ZoneMG: Middle Group chromititeMML: Main Magnetite LayerMR: Merensky ReefMZ: Main ZoneTML: Thabazimbi-Murchison LineamentUCZ: Upper Critical ZoneUG: Upper Group chromititeUG2: Upper Group chromitite 2UUMZ: Upper Upper Main ZoneUZ: Upper ZoneMinerals and Element Groups:bt: biotitechr: chromitecpx: clinopyroxenegrn: granophyre (quartz + alkali feldspar)HFSE: high field strength elements (Hf, Zr, Ti, Nb, Ta)HREE: heavy rare earth elements (Gd-Lu)ksp: K-feldsparLREE: light rare earth elements (La-Sm)opx: orthopyroxenePGE: platinum group elements (Ru, Rh, Pd, Os, Ir, Pt)plag: plagioclaseqtz: quartzREE: rare earth elements (La-Lu)zrc: zirconxixAcknowledgementsAcknowledgementsThis thesis has been a long and fulfilling experience that has been shaped and guided both directly and indirectly by many people. I first and foremost thank my advisors, Drs. James Scoates and Dominique Weis, to whom I owe many thanks (and blue pens) for the incalculable time, guidance, feedback, and editing they put forth in helping me to complete this degree. Training and expertise from Dr. Marg Amini on working with the laser ablation system at PCIGR has been invaluable. An indescribable amount of thanks goes to Corey Wall (now Dr.), not only for the work involved in my sample processing, but for his advice and comradery throughout the tenure on our projects. Additional thanks to Anaïs Fourny, June Cho, Nichole Moerhuis, and Laura Bilenker for their helpful feedback and discussion during our Layered Mafic Intrusions group meetings. To every other grad student in room 305 and elsewhere that has provided support, friendship, or joined on a coffee-run throughout my degree, many thanks are also owed.I am grateful to Drs. Ed Mathez and Jill VanTongeren their careful field work on the Bushveld Complex and for providing most of the samples used in Chapter 3 from the collection at the American Museum of Natural History (New York). A special thanks to Dr, Mati Raudsepp and to Elisabetta Pani, Jenny Lai, Lan Kato, and Edith Czech from the Electron Microbeam and X-ray Diffraction Facility for assistance with the SEM and electron microprobe. Funding for this project came from an NSERC CREATE (MAGNET – Multidisciplinary Applied Geochemistry Network) grant to Tom Ver Hoeve and additional support for research and analytical work was provided by NSERC Discovery Grants to James Scoates and Dominique Weis.xxDedicationDedicationTo my family, Who I know will always be there no matter how far I am from home. Thank you for your continued love and support.1Chapter 1 Chapter 1Chapter 1Introduction to Laser Ablation-ICP-MS and Accessory Minerals in Mafic Layered Intrusions2Chapter 11 .1 . Introduction and scope of the projectContinuous improvements in our analytical capabilities and understanding of the behaviour of geochemical systems have led to broad applications of geochemical methods in the geological, chemical, biological, and environmental sciences. The modern geochemist is equipped with an analytical toolbox that allows for analysis of major and minor element concentrations in a wide range of sample materials (e.g., rock, mineral, soil), including X-ray fluorescence (XRF) and electron probe microanalysis (EPMA), as well as analysis of small variations in isotopic ratios using thermal ionisation mass spectrometry (TIMS) or multiple-collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) (e.g., per mil to parts per million) (e.g., Jenner et al., 1990; Black et al., 2004; Jackson et al., 2004; Weis et al., 2011; Schoene et al., 2012). Each of these techniques has been refined for specific geological applications with the goal of balancing time, cost, and sample integrity (destructive vs. non-destructive) with relative accuracy and precision. A key addition to the geochemical arsenal is laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). In the past decade, LA-ICP-MS has become an essential in situ analytical tool in laboratories worldwide for fast, accurate, and relatively inexpensive data acquisition without the need for chemical clean laboratory dissolution (e.g., Horn et al., 2000; Jackson et al., 2004; Liu et al., 2008; Yuan et al., 2008; Fisher et al., 2010). Originally developed out of a desire to determine lower concentrations in samples than was possible by EPMA (Gray, 1985), and informally referred to as a “laser microprobe”, LA-ICP-MS has today become an important method for rapid U-Th-Pb zircon geochronology (Jackson et al., 1992; Longerich et al., 1993; Košler, 2003). In addition to U-Th-Pb zircon analysis, LA-ICP-MS can be used to determine a suite of trace elements from geological materials (Hoskin and Ireland, 2000; Rubatto, 2002; Ulrich and Kamber, 2009) and to analyze them for a variety of isotopic systems (e.g., Yuan et al., 2008; Deng et al., 2013; Ibanez-Mejia et al., 2014). Recent innovations are pushing the boundaries of LA-ICP-MS applications in the geosciences, anthropology (Prohaska et al., 2002; Brumm et al., 2016), and biology (e.g., Becker et al., 2007), amongst other disciplines. The research conducted for this thesis involved two separate yet intertwined applications 3Chapter 1of LA-ICP-MS analysis of zircon – one technical and one practical – with the goals of advancing the analytical capability of LA-ICP-MS and showcasing the power of in situ analytical techniques in mineral studies. First, the problem of downhole fractionation – the mass dependent fractionation of lighter Pb and heavier U isotopes as an ablation pit deepens – in U-Th-Pb zircon dating was addressed by comparing ablation characteristics in different zircon reference materials of variable ages in an effort to improve methods for analyzing unknown samples. Second, a high-resolution trace element study was conducted using zircon and rutile from the Bushveld Complex, South Africa, the world’s largest layered intrusion. The spatial resolution and high-throughput capabilities of LA-ICP-MS were applied to a suite of samples that cover the 8 km thick stratigraphy of the intrusion. Trace element concentrations and variations recorded by these two accessory minerals were then used to constrain the late-stage crystallization history of fractionated interstitial melt in cumulates from this highly influential intrusion in petrology and geochemistry.This chapter contains background information on the development and refinement of the LA-ICP-MS technique along with details about the instrumentation and methodologies applied in these studies. It also provides a review of the key geochemical properties of zircon, the mineral of focus in Chapter 2 and Chapter 3, including the U-Th-Pb system and various trace element systematics. An overview of the role of downhole fractionation in LA-ICP-MS provides context for Chapter 2. The Bushveld Complex is the focus of Chapter 3 and an overview of the research questions as well as a description of previous work on accessory minerals in the intrusion is included below. Finally, the main conclusions from Chapters 2 and 3 as well as suggestions for future work are presented in Chapter 4.1 .2 . LA-ICP-MS1 .2 .1 .  Overview of LA-ICP-MSA key distinction between LA-ICP-MS and other geoanalytical techniques lies in the method of sample introduction (Arevalo, 2013; Sylvester and Jackson, 2016). Laser ablation involves focusing a powerful laser beam directly onto a sample surface and delivering enough energy to excavate sample material from the ablation site via a carrier gas (typically helium) 4Chapter 1(Eggins et al., 1998) mixed with a plasma gas (typically argon) (Fig. 1.1). Measurement of atomic masses by laser ablation can be done using quadrupole, magnetic sector, and multi-collector mass spectrometers. Modern laser systems are capable of collecting data with spatial resolution at the micrometer scale with ablation pits ranging from 1-100 μm in diameter (Sylvester and Jackson, 2016). This allows for mapping and studying processes that are typically obscured by dissolution techniques such as dating crystal zoning (Barboni and Schoene, 2014; Schaltegger et al., 2015), growth rings in bivalves (Fuge et al., 1993), or even bioimaging in the brain tissues of mice (Drescher et al., 2012). Although data collection by LA-ICP-MS has undergone major improvements since its inception, inherent issues related to the physical ablation process remain, and technical advancements in standardization and downhole fractionation corrections are needed.1 .2 .2 . Advancements in LA-ICP-MSRecent instrument developments and software-based innovations have impacted the precision and accuracy of LA-ICP-MS. One of the most notable design evolutions has been modification of the laser ablation source to minimize and normalize fractionation effects. Laser ablation systems initially used a 1064 nm Nd:YAG laser, which evolved towards the shorter 266 nm ND:YAG wavelength, then the 213 nm Nd:YAG, and finally the 193 nm ArF excimer lasers that are most prominent today (Günther et al., 1997; Günther and Heinrich, 1999; Arevalo, 2013). Shorter wavelength laser sources are able to deliver a more powerful impact on a material surface (without heating or melting), resulting in cleaner and more consistent ablation pit walls and bottoms, and most importantly, they produce an aerosol of homogeneous nanoparticles small enough to be efficiently ionized by the plasma source (Jackson and Günther, 2003; Sylvester and Jackson, 2016). Physical changes to the set-up and geometry of the laser systems have also improved analytical stability. For example, instability of the laser signal due to turbulence and uneven flow of the carrier gas in the sample cell can result in major differences in sensitivity depending on the location of grains in the sample cell (Gurevich and Hergenröder, 2007; Fricker et al., 2011). Implementation of a 2-volume sample cell (Eggins et al., 2005; Müller et al., 2009), with a moving cone centered above the ablation site to ensure identical carrier gas flow in each analysis can help limit this issue (Fig. 1.2). 5Chapter 140s ablation20s gas blankpre-ablation shot20s gas blankAgilent 7700xQuadrupole ICP-MSResoneticsRESOlutionM50-LRAr torch gassquid(signal smoothing)He carrier gassample cell(ablation)ArF laser sourceLA-ICP-MS Setupat PCIGRlaser opticsplasmaionizationmass separation and detectionhigh purity N2 for increased sensitivityHe carrier gassecondcelllaserSample outdual-volume cell6:14:30 PM 6:14:45 PM 6:15:00 PM 6:15:15 PM 6:15:30 PM 6:15:45 PM 6:16:00 PM54210 counts per second (x103 )integration windowz91500total beamHfUThsingle shot pre-ablation cleaningLubaselinebaselineAnalysis TimeFigure 1 .1 . Overview of the LA-ICP-MS methodology at PCIGR used in this study. (a) Photograph of the Resonetics (now Australian Scientific Instruments) RESOlution M50-LR Class 1 excimer laser ablation system coupled to an Agilent 7700x quadrupole ICP-MS. The path of the laser from the source to the ablation site is shown in pink. Carrier gas (He) and the path of the sample material from the ablation site are indicated in blue. Argon torch gas (orange) and high purity N2 (green) are added to the carrier gas and sample prior to signal smoothing with a “squid” and plasma ionization in the ICP-MS (dashed purple line). (b) Photograph of the Laurin-Technic dual-volume ablation chamber (Photo: D. Weis). The conical second chamber is centered over each analysis site, ensuring that carrier gas flow is consistent within the sample chamber. The paths of the carrier gas and sample output are shown as blue lines and the white dashed line represents the ability of the second cell to travel in X-Y space. (c) Example of raw LA-ICP-MS data for a 40-second analysis of 91500 reference zircon showing counts per second (CPS) for the total beam and select masses (175Lu, 177Hf, 232Th, 238U) vs. time (hours/minutes/seconds). The integration window that will be used to reduce the CPS data to concentrations (ppm) is shown as the dashed box. The time of the analysis is bounded by the right and left edges, the upper and lower bounds of the box represent the deviation of the mean value (not show) within the selected time frame. Each analysis is preceded by a single shot to ensure that the sample surface is clean prior to analysis. Baseline values for the gas blank are indicated. 6Chapter 1Carrier gas inSample outTurbulent and uneven gas flow within sample cellCarrier gas inSample outIsolated cell equalizes carrier gas flow at each ablation siteOne-Volume Sample Cell Two-Volume Sample Cella) b)plan viewcross sectionFigure 1 .2 . Schematic comparison between a 1-volume and a 2-volume cell for sampling by LA-ICP-MS. The upper diagrams show plan views and the lower diagrams show vertical sections. (a) 1-volume cell. The traditional design of a sample cell with carrier gas input and sample output results in heterogeneous sampling spatially within the sample chamber due to turbulence in the carrier gas flow. The resulting ICP-MS signal may be variable in sample intensity and mass bias. (b) 2-volume cell. A conical device is centered above each ablation site and the ablated sample material is directly excavated to the ICP-MS. The carrier gas floods the main sample chamber and enters the second volume above and below the ablation site to regulate gas behaviour and homogenize sampling efficiency. 7Chapter 1Another instrumental improvement in analytical precision was achieved using a device known as a “squid” (Fig. 1.3a). In the typical ICP-MS carrier setup, laser pulses delivered to the sample surface at a rate of typically 5-10 Hz (Müller et al., 2009) yield a “bumpy” signal (Fig. 1.3b). The squid includes a series of tubes of slightly different lengths that smooth the sample signal (Fig. 1.3c). Other major advancements, such as single-shot ablations (Cottle et al., 2010) and split-stream ablations (Kylander-Clark et al., 2013) continue to expand the capabilities of this technique. Additionally, software-based innovations, including exponential downhole correction modelling (Paton et al., 2010) using programs such as Iolite (Paton et al., 2011), allow for improvement of the precision and accuracy of LA-ICP-MS.1 .2 .3 . Downhole fractionation and pre-treatment in LA-ICP-MSThe most prominent cause of elemental fractionation during analysis by LA-ICP-MS is downhole fractionation, the process by which certain elements are more efficiently evacuated from an ablation site than others due to a combination of properties including volatility and isotopic mass (Košler et al., 2005; Hergenröder, 2006; Paton et al., 2010). In a spot analysis, fractionation occurs as the ablation pit deepens with each laser pulse, resulting in progressively changing elemental ratios (Fig. 1.4a). To deal with this problem, initial forays into U-Pb geochronology focussed solely on 207Pb/206Pb dates rather than attempting to calculate parent-daughter ratios (e.g., Feng et al., 1993; Fryer et al., 1993; Hirata and Nesbitt, 1995). An alternative method that circumvents downhole fractionation requires performing a raster analysis, a process that involves moving the laser in a sequence over the surface of a sample with a constant pit depth (Fig. 1.4b). A raster analysis minimizes downhole fractionation, however, this method also reduces the ability to assess spatial variation within a sample when compared with a spot analysis.Another intrinsic problem in U-Pb zircon dating is damage to the zircon crystal structure (metamictization) due to alpha recoil, the result of radioactive decay of isotopes of U and Th to their daughter Pb products. To overcome this problem and to improve U-Pb TIMS results, researchers in the 1970s-1980s innovated techniques, including the critical physical abrasion method, to remove metamict and altered high-U rims (Krogh, 1982a, 1982b; Davis et al., 2003). More recently, Mattinson (2005) outlined the “chemical abrasion” technique, a process 8Chapter 1Laser pulse repetitions produce “bumpy” signal in ICP-MS analysisto ICP-MSto ICP-MSSquidWithout SquidTubing of different lengths smoothes sample signalSample inSample inWithout Squid SquidOscillation in signal strength at frequency of laser pulseSmoothed signal(a)(b) (c)time timesignal intensitysignal intensityFigure 1 .3 . Schematic illustrations of the signal smoothing effect of a “squid” device placed between a laser ablation sample cell and an ICP-MS. (a) Repetitions of the laser beam produce pulses of material that travel to the ICP-MS. Placement of a squid, consisting of tubing of slightly varying lengths, separates the pulses and merges them back together to produce a smooth signal. (b) Representation of a noisy signal in an ICP-MS as each repetition reaches the detector in a system with simple tubing. (c) A smoother ICP-MS signal from a system with a squid that smooths the sample signal and reduces the effect of each laser pulse.9Chapter 1t=1206Pb 238Ut=1206Pb 238Ut=40206Pb 238Ut=40206Pb 238UDownhole fractionation of masses as lighter isotopes are excavated more efficiently as ablation pit deepens(a) Spot analysis(b) Raster analysisMoving laser during analysis removes downhole fractionation (but limits spatial resolution)Figure 1 .4 . Comparison of spot and raster analysis techniques by LA-ICP-MS. (a) Spot analysis. Successive laser pulses produce a pit within the sample material that is progressively deepened with each pulse. Differences in elemental properties result in preferential excavation of certain isotopes over others producing downhole fractionation of element ratios (e.g., Pb/U) over the analysis time (e.g., t = 1 second vs. t = 40 seconds), however, high spatial resolution in the x-y dimension is retained. (b) Raster analysis. Progressive scanning of the laser pulse results in equal pit depth throughout the duration of the analysis, thus significantly reducing the effects of downhole fractionation, however, the benefits of high spatial resolution are lost.10Chapter 1of thermal annealing that involves heating the grains to 900°C to recrystallize their structure and subsequently subjecting them to acid leaching, a process by which most damaged zones are systematically leached away leaving only pristine zircon, free of Pb loss, for analysis (Mattinson, 2005; Schoene, 2013). This process greatly improves precision and accuracy in ID-TIMS and has been investigated as a potential method for improving standardization in LA-ICP-MS (Crowley et al., 2014; Solari et al., 2015; Marillo-Sialer et al., 2016). Pre-treatment of reference materials and unknown zircon could potentially improve the accuracy and precision of zircon dating by standardizing the behaviour of the materials during ablation, which requires that the pre-treatment effects have been sufficiently quantified.1 .2 .4 . LA-ICP-MS at PCIGRThe Pacific Centre for Isotopic and Geochemical Research (PCIGR) has an array of state-of-the-art instruments that provide exceptional tools for a variety of trace element and isotopic applications in the Earth and environmental sciences. The ablation system used in this study is a Resonetics (now Australian Scientific Instruments, ASI) Resolution ArF excimer (193 nm) Class I laser coupled to an Agilent 7700x quadrupole ICP-MS (Fig. 1.1). This system utilizes a 2-volume sample cell from Laurin Technic that includes a configuration of either four pucks or a thin section and two pucks, allowing for easy input of reference materials along with unknown samples. Additionally, the laser uses a Z-focus that ensures optimal laser focus on sample surfaces, even in samples with irregular topography. The laser optics and aperture allow for spot ablations ranging from 5-380 μm in diameter. Helium is used as carrier gas in all analyses at 700-900 mL/s, and the sample and carrier gases are mixed with Ar for the plasma torch prior to introduction into the ICP-MS. The addition of high purity N2 at 1-2 mL/s greatly increases measurement sensitivity. All gases are homogenized using a squid composed of high-quality nylon tubing (Fig. 1.1.). 1 .3 . Geochemistry of zircon1 .3 .1 . Zircon composition and structureZircon (ZrSiO4) is a nesosilicate, or orthosilicate, that commonly occurs as an accessory mineral in felsic igneous rocks (Harley and Kelly, 2007). Zircon is also found in rocks of 11Chapter 1mafic-ultramafic composition (Scoates and Chamberlain, 1995; Scoates and Friedman, 2008; Scoates and Wall, 2015; Zeh et al., 2015) (Fig. 1.5a) and in rocks from metamorphic and hydrothermal settings (Rubin et al., 1989; Hoskin and Schaltegger, 2003; Schaltegger, 2007). The tetragonal structure of zircon consists of ZrO8 dodecahedra coupled to SiO4 tetrahedra (Fig. 1.5b). As a result, zircon is remarkably resilient through surficial weathering processes and notably refractory under high-grade metamorphic conditions (Finch and Hanchar, 2003; Harley and Kelly, 2007). Typically growing to only a few hundred microns in size, zircon has gained a reputation in the geosciences over the past decades as a “giant” in U-Pb geochronology (Schoene, 2013; Valley et al., 2014; Samperton et al., 2015) and, more recently, in isotopic and trace element fingerprinting (Fig. 1.5) (Belousova et al., 2002; Hawkesworth and Kemp, 2006; Grimes et al., 2015). 1 .3 .2 . Zircon geochronologyU-Th-Pb zircon geochronology represents the “gold standard” within the age dating community, providing the most precise and reliable mineral chronometer available (see summary in Schoene, 2013). The substitution of U4+ (and Th4+) for Zr4+ into the zircon crystal structure at the 1-1000 ppm level (Table 1.1), combined with the near-complete exclusion of Pb (i.e., common Pb) during crystallization and zircon’s robust and refractory nature, make it a virtual time capsule. Over geologic time, the predictable radioactive decay of the parent isotopes of uranium and thorium to their respective daughter isotopes of lead (e.g., 232Th→208Pb, 235U→207Pb, 238U→206Pb) allows for the precise calculation of the age at which Pb diffusion ceased in zircon, which corresponds to temperatures >950 °C (Cherniak and Watson, 2001). U-Th-Pb geochronology of zircon has been applied to zircon from less than 1 Ma in age (Bishop Tuff, USA; Crowley et al., 2007) to the oldest zircon on earth at 4.4 Ga (Jack Hills, Australia; Valley et al., 2005). Currently, the most accurate and precise method for conducting U-Pb zircon geochronology is chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) (Schoene, 2013). This method allows for determination of high-precision dates with uncertainties below 0.01% (Mattinson, 2005). However, due to the relatively large amount of time and cost associated with CA-ID-TIMS, and because of the many recent advancements in 12Chapter 1ZrO8SiO40.5 mmZirconXPLElongated ZrO4 shortened ZrO4cba(a)(b)Figure 1 .5 . Summary of the physical properties and geochemical applications of zircon. (a) Photomicrograph of a euhedral, doubly terminated zircon crystal from the Upper Zone of the Bushveld Complex demonstrating crystal habit, high relief, and the 4th-order interference colors of zircon in thin section (XPL, cross-polarized light). (b) Polyhedral model of the crystal structure of zircon produced using CrystalMaker projected from the a axis. Dodecahedrons of ZrO8 are shown in orange and SiO4 tetrahedra are shown in blue. The internal structure of the ZrO8 dodecahedron is constructed of two distorted ZrO4 tetrahedra – one shortened (outlined in red) and one elongated (outlined in green). Figure based on Finch and Hanchar (2003) and Harley and Kelly (2007).ZirconFormula: ZrSiO4System: tetragonalSilicate Class: nesosilicateHardness: 7.5Cleavage / Twinning {110},{111} / {101}Specific Gravity 4.6-4.7Cell Parameters a = 6.607 Å, c = 5.982 ÅUnit Cell Volume 261.13 Å3Birefringence: high, up to 4th orderRelief: very highGeochemical Applicationsδ18O crustal recycling, low-T processesImportant SubstitutionsTetravalent             Ti4+→ Si4+ Ti-in-zircon thermometry            Hf4+→ Zr4+176Hf/177Hf, magma sourcing,concentration, magma evolution    Th4+, U4+→ Zr4+ U-Th-Pb geochronology,Th/U ratio, magma evolutionTrivalentSc, Y, REE3+ + P5+→ Zr4++Si4+fingerprinting magmatic processes13Chapter 1Table 1 .1 . Overview of possible substitutions in zirconElement Equation ReferenceXenotime SubstitutionsY3+ (Y, REE)3+ + P5+ = Zr4+ + Si4+Sc3+ Sc3+ + P5+ = Zr4+ + Si4+ Halden et al. (1993)Simple SubstitutionsHf4+ Hf4+ = Zr4+ Frondel (1953)U4+, Th4+, , Sn4+(U, Th, Ti, Sn)4+ = Zr4+ Frondel (1953)Ti4+ Ti4+= Si4+ (~95%),  Zr4+ (~5%) Harrison (2005), Ferry and Watson (2007)(OH)4 (OH)4 = SiO4 Frondel (1953)Coupled SubstitutionsLi+ Li+(interstitial) + REE3+ = Zr4+ Finch et al. (2001), Hanchar et al. (2001)Nb5+, Ta5+ (Y, REE)3+ + (Nb, Ta)5+ = 2Zr4+ Es’kova (1959)(OH)- Mn+ + n(OH)- + (4 - n)H2O = Zr4+ + Zr4+ + (SiO4)4-* Caruba and Iacconi (1983)Mg2+, Fe2+ (Mg, Fe)2+(interstitial) + 3(Y, REE)3+ +P5+ = 3Zr4+ + Si4+ Hoskin et al. (2000)Al3+, Fe3+ (Al, Fe)3+(interstitial) + 4(Y, REE)3+ +P5+ = 4Zr4+ + Si4+ Hoskin et al. (2000)S6+ S6+ + 2(Y, REE)3+ = Si4+ + 2Zr4+ Based on Romans et al. (1975)Ca2+ Ca2+(interstitial) + 2(Y, REE)3+ = 2Zr4+ Based on Romans et al. (1975)Zr4+ Zr4+(interstitial) + 4REE3+ = 4Zr4+ Finch et al. (2001)Mo6+ Mo6+ + 2REE3+ = Si4+ + 2Zr4+ Speer (1982)Mo6+ + 2REE3+ = 3Zr4+ Speer (1982)Mo6+ + 6REE3+ = 6Zr4+ Finch et al. (2001)*M = metal cation, n = integerTable adapted from Bouvier et al. (2012) with information from Harley and Kelly (2007).14Chapter 1LA-ICP-MS technology detailed previously, many researchers are now choosing to implement laser ablation analyses of zircon. This procedure allows fast, accurate (±1% relative), and relatively precise ages at a fraction of the time and cost of CA-ID-TIMS (Jackson et al., 2004). The Wetherill (1956) concordia diagram is the most commonly implemented visualization of the U-Pb decay schemes and is used extensively in Chapter 2 to illustrate the effects of downhole fractionation corrections on final U-Pb ratios determined in situ by LA-ICP-MS. This diagram of 206Pb/238U versus 207Pb/235U, where 206Pb and 207Pb are the radiogenic isotopes, displays the concordia curve, which represents the locus of points at which the two decay schemes correspond to identical ages (Schoene, 2013). The concordia line is curved due to the large difference in half-lives of 238U (0.704 Ga) and 235U (4.468 Ga). Analysis of a sample that has not experienced any Pb loss or open-system behaviour yields a result that plots directly on the concordia line and is referred to as “concordant” (Fig. 1.6a). Any Pb loss that occurs to a material (e.g., zircon) post-crystallization results in a “reset” U-Pb age, with the analysis plotting below concordia and resulting in a “discordant” analysis (Fig. 1.6b). Growth of new zircon during periods of metamorphism or subsequent hydrothermal activity corresponds to the time of new crystallization, and analysis of the entire grain will result in a discordant mixed age that defines a line between the primary growth age and the secondary age for the metamorphic zircon (Fig. 1.6c). 1 .3 .3 . Trace elements in zirconIn addition to U and Th, a wide variety of minor and trace elements partition into zircon during crystallization and can be used as powerful geochemical tools for magmatic fingerprinting and process identification (Table 1.1). Among other accessory minerals (e.g., apatite, xenotime, monazite), zircon provides a sink for many highly incompatible elements via simple and coupled substitutions (Belousova et al., 2002; Bouvier et al., 2012; Nardi et al., 2013). Trace element concentrations in zircon can be analyzed relatively rapidly by LA-ICP-MS, which also provides spatial context at the grain (micrometer) scale while capturing magmatic evolution over the entire time of zircon growth (e.g., Rubatto, 2002; Yudovskaya et al., 2013; Schaltegger et al., 2015). Interpretation of the results, however, may be complicated by the complex partitioning behaviour of trace elements into zircon, which is controlled by temperature (Ferry and Watson, 15Chapter 1238U4.5 Ga235U0.7 Ga234U246 ka234Pa234Th232Th14 Ga231Th230Th75 ka231Pa34 ka228Ra228Ac228Th226Ra1.61 ka227Ac22 a227Th224Ra223Fr222Rn223Ra220Rn219At218Po219Rn218At218Rn216Po215Bi214Pb215Po214Bi212Pb214Po215At212Po212Bi211Pb210Tl208Tl210Pb22 a210Bi210Po208Pb207Pb206Tl206Pb207Tl206Hg211Po211Bi230Th75 kaIndicates beta decay(to isotope diagonal in indicateddirection and same mass)~Half-life(only indicated if >10 a)Indicates alpha decay(to isotope diagonal in indicateddirection and 4 a.m.u. less)238U 206Pb + 8α + 6β + Q; λ238 = 1.55125e-10 a-1Atomic Number (Z)Hg 80Tl 81Pb 82Bi 83Po 84At 85Rn 86Fr 87Ra 88Ac 89Th 90Pa 91U 92 Neutron Number (N)124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146235U 207Pb + 7α + 4β + Q; λ235 = 9.8485e-10 a-1232Th 208Pb + 6α + 4β + Q; λ232 = 4.9475e-11 a-1206 Pb/238 U207Pb/235U206Pb/238U date207Pb/235U dateUpper intercept: 207Pb/206Pb date = minimum age“concordia curve”discordant grainfrom Pb loss206Pb/238U date ≠ 207Pb/235U date200030003500400045001.00.80.60.40.20.00 20 40 60 80concordant grain206Pb/238U date = 207Pb/235U date1000207Pb/235U200030003500400045000 20 40 60 801000path defined by ingrowth of Pb*age of zircon after ~3800 Maof ingrowth of Pb*discordant date between 3800 Maand the lower interceptdiscordant date between 3800 Maand the lower interceptdate of new zircon or Pb loss definedby lower intercept(c)(b)(a)Figure 1 .6 . Overview of the U-Th-Pb dating system. Figure from Wall (2016) and modified from Schoene (2013). (a) Illustration of the decay chains of parental 232Th (orange), 235U (yellow), and 238U (green) through their intermediate products via alpha and beta radioactive decay to their stable daughter isotopes of 208Pb, 207Pb, and 206Pb, respectively. The decay schemes are indicated, where α represents an alpha particle, β a beta particle, and Q the energy released during decay. (b) A Wetherill concordia diagram of 206Pb/238U vs. 207Pb/235U showing an example of a concordant zircon analysis at 3800 Ma (red ellipse) and a discordant zircon analysis (green ellipse) with an upper intercept of 3800 Ma that is discordant due to Pb loss or mixing with metamorphic overgrowths. (c) A Wetherill concordia diagram (Wetherill, 1956) depicting the derivation of a discordia line. The blue ellipse at the origin represents a recent Pb loss or zircon overgrowth event. The green ellipses are zircon grains that have experienced Pb loss and define a discordia line between the primary crystallization age (red) and the blue ellipse.16Chapter 12007), oxygen fugacity (Burnham and Berry, 2012; Trail et al., 2012), and melt chemistry (Rubatto, 2002; Luo and Ayers, 2009), all of which are likely to vary during crystallization. Some of the most commonly used geochemical tracers in zircon include trivalent Sc, Y, and the rare earth elements or REE (La, Ce, Pr, Nd, (Pm), Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), which enter zircon using a coupled “xenotime” substitution with P5+ to fill the vacancies of a Si4+ + Zr4+ (Hoskin and Schaltegger, 2003; Hanchar and van Westrenen, 2007) (Table 1.1). The systematic decrease in the atomic radius of the REE from La to Lu (mainly as 3+ cations) allows for a progressive increase in the abundance of REE in zircon with increasing atomic number when normalized to chondritic values (Fig. 1.7), with the exception of Ce and Eu. For cerium, there may also be Ce4+ in addition to Ce3+, with the Ce4+/Ce3+ ratio serving as a function of oxidation state in a melt. The preferred substitution of Ce4+ results in a prominent positive Ce anomaly in most chondrite-normalized REE patterns of zircon (Trail et al., 2012; Burnham and Berry, 2014). Conversely, Eu in magmas is mostly present as Eu2+, which is readily substituted for Ca2+ in plagioclase. Plagioclase crystallization results in Eu depletion of a melt, leading to large negative Eu anomalies in minerals that crystallize later from the same melt. Oxidation state will also control Eu2+/Eu3+ in a melt, leading to larger negative anomalies in zircon that crystallize from reduced melts, however, this signal can easily be eclipsed by the effect of feldspar crystallization (Belousova et al., 2002; Dilles et al., 2015). The ratios of rare earth elements, the magnitudes of the Eu and Ce anomalies, and the slopes of chondrite-normalized REE patterns all reflect the geochemistry of the parental magma to the zircon grains and, collectively, can be used to identify distinctive populations of grains in a single sample as well as infer information about magma petrogenesis (Belousova et al., 2006). 1 .3 .4 . High field strength elements and Ti-in-zircon thermometryThe behaviour of the tetravalent cations of U, Th, Hf, and Ti forms much of the basis of trace element studies in zircon (e.g., Harley and Kelly, 2007). One of the most significant substitutions in zircon is tetravalent Hf4+ for Zr4+. The matching charge and near identical ionic radii of these elements make Hf substitution in zircon nearly entirely dependent on the Hf concentration in the melt, typically resulting in Hf contents ranging from 0.5-1.5 wt. % in zircon, although much higher concentrations have been observed (Cherniak et al., 1997; Wang 17Chapter 1La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb10-310-210-1100101102103104decreasing ionic radiiincreasing compatibility in zirconpositive Ce anomaly Ce/Ce* = CeN / NdNinferred Pm valuenegative Eu anomaly Eu/Eu* = EuN /   SmN*GdN Sample / ChondriteLa typically below detection limitsEnriched HREEDepleted LREEFigure 1 .7 . Examples of chondrite-normalized rare earth element (REE) patterns for zircon from sample B00-1-6 from the Upper Group Chromitite II (UG2) unit of the Bushveld Complex (n=26). Decreasing ionic radii with increasing atomic numbers for the trivalent REE cations result in increasing compatibility in zircon from the light REE (LREE) to heavy REE (HREE). Substitutions vary over five orders of magnitude from La to Lu. Exceptions include Ce and Eu due to their presence in multiple oxidation states (Ce4+/Ce3+ and Eu2+/Eu3+). Equations to calculate the magnitudes of these anomalies are shown; the equation for the Ce anomaly is simplified to account for the lack of La information in many analyses. Normalization values are from McDonough and Sun (1995).18Chapter 1et al., 2010). Hafnium is incompatible in most primary igneous minerals and is concentrated in the melt as crystallization progresses and the melt composition evolves. This means that the Hf concentration in zircon is an indicator of relative melt evolution (Grimes et al., 2009). The simple substitution of Ti4+ for Si4+ occurs predictably based on a thermodynamic equilibrium between zircon (ZrSiO4), rutile (TiO2), and quartz (SiO2). The Ti-in-zircon thermometer was initially proposed by Watson and Harrison (2005), with later refinement by Ferry and Watson (2007), and it has been extensively tested and applied (e.g., Harrison et al., 2007; Fu et al., 2008; Grimes et al., 2009; Tailby et al., 2011; Yudovskaya et al., 2013; Barboni and Schoene, 2014). The thermometer is a function of Ti concentration and the activities of SiO2 and TiO2 following the equation:log (ppm Ti-in-zircon) = (5.711 ± 0.072) – (4800 ± 86) / Tzrc (K)– log aSiO2 + log aTiO2Application of the thermometer requires knowledge of the crystallization assemblage with zircon or robust estimates of the activities of interest in the absence of rutile or quartz. There is also a pressure dependency that may account for a shift of -5°C per kbar at pressures below 10 kbars (Ferry and Watson, 2007; Ferriss et al., 2008). Temperature trends with trace elements are critical for providing indexes of cooling in relation to evolving magmatic processes and Ti-in-zircon thermometry can yield important insights even when ideal conditions for the system are not fully met (Watson et al., 2006; Harrison et al., 2007; Chamberlain et al., 2013).1 .4 . Mafic layered intrusionsMafic-ultramafic layered intrusions have been emplaced and crystallized in the Earth’s crust throughout geologic time and have been studied for over a century for their enigmatic textures and structures as well as their associations with economic deposits of chromium, platinum group elements (PGE), and vanadium (Bowen, 1928; Wager and Brown, 1968; Parsons, 1987; Eales and Cawthorn, 1996; Charlier et al., 2015). The layered sequences of cumulates preserved in these intrusions are considered to be the product of magmatic differentiation in basaltic magma chambers, resulting in fractionated crystals of higher density that settled and accumulated at the base of the intrusions. Variations in the mineralogy and chemistry of layered intrusions form much of the basis for our understanding of magmatic differentiation and igneous 19Chapter 1petrology. As a magma cools, minerals crystallize at the liquidus and systematically remove certain elements from the melt (i.e., compatible elements) and concentrate other elements in the residual melt (i.e., incompatible elements). This process is key to the saturation of incompatible element-rich accessory minerals in mafic layered intrusions, whereby pockets of interstitial melt between the high-temperature cumulus minerals (e.g., pyroxene, olivine, plagioclase) continue to evolve and fractionate to eventually reach intermediate to granitic compositions (Fig. 1.7) (Scoates and Wall, 2015). It is in these areas where minerals such as zircon are found associated with quartz, alkali feldspar, and biotite (Fig. 1.8, 1.9). The trace element signatures of zircon and other late-stage accessory minerals reflect the cooling history of the parental magmas from which they formed and provide a novel approach to the study of near-solidus crystallization in mafic layered intrusions.1 .5 . The Bushveld Complex1 .5 .1 . Overview of geology and mineral resourcesThe Paleoproterozoic Bushveld Complex in South Africa is the world’s largest layered intrusion.  Its world-renowned wealth of mineral resources accounts for major contributions to the global supply of the platinum group elements (PGE; Pt, Pd, Os, Ir, Rh, Ru), chromium, and vanadium (Eales and Cawthorn, 1996; Cawthorn et al., 2005; Maier et al., 2013). The Bushveld Complex is exposed over >90,000 km2 (Finn et al., 2015), with outcroppings in five major limbs – Eastern, Southeastern, Western, Far Western, and Northern – and the vertical succession of rocks that comprises the igneous stratigraphy of the Rustenburg Layered Suite reaches nearly 8 km in thickness (Fig. 1.10; Fig. 1.11) (Eales and Cawthorn, 1996; Cawthorn and Walraven, 1998).The mineral succession observed in the Bushveld Complex, from chromite-bearing ultramafic rocks in the lower part through to magnetite gabbro and diorite at the top, represents the product of fractional crystallization of mafic and ultramafic magmas, a process that forms the cornerstone to much of our current understanding of igneous petrology and mafic-ultramafic magmatism (Bowen, 1928; Wager and Brown, 1968; Parsons, 1987; Eales and Cawthorn, 1996; Charlier et al., 2015). The chemical evolution of cumulates of layered intrusions like the 20Chapter 1Pyroxene 1A. B. C.Pyroxene 2Pyroxene 3OlivineFe-Ti OxidesQuartz + KspPlagioclaseBoundaries of the original primocrysts shown by the innermost rectangle; lower temperature zones shown by the outer dashed linesMay be zonedMay be zonedTitanomagnetite± ilmenitezzzzBiotiteFractionated interstitial melt with apatite ± zirconCommon association with zirconzzFigure 1 .8 . Schematic diagrams showing the textural setting of zircon within three types of plagioclase cumulates in layered intrusions. Diagrams adapted from Wager et al. (1960) as illustrated in Scoates and Wall (2015). (a) Plagioclase cumulate with poikilitic pyroxene, olivine, and Fe-Ti oxides. Zircon (z) may be found within the most highly fractionated portions of interstitial melt that now contain quartz and alkali feldspar with late biotite overgrowths. (b) Plagioclase cumulate with minor interstitial pyroxene, olivine, and Fe-Ti oxides. Smaller patches of minerals crystallized from fractionated interstitial melt (quartz/alkali feldspar) may contain zircon. (c) Nearly pure plagioclase cumulate (adcumulate) with crystallized pockets of highly fractionated melt that are ideal for targeting zircon (e.g., Scoates and Chamberlain, 1995; Wall et al., 2016).21Chapter 1bt + zirconplagopxcpxSA04-08A XPLplagbt+zirconcpxolivineopxSA04-08B XPLchromiteopxplagzirconsulfideopxapatitebtSA04-11B PPL SA04-11B XPL(a) (b)(c) (d)Figure 1 .9 . Scanned thin section images showing samples from the Merensky Reef in the Bushveld Complex that yielded abundant zircon (modified from Scoates and Wall, 2015). All sections are standard size, 45 × 25 mm. (a) Section SA04-08A (XPL) from Farm Driekop in the Eastern Limb of the Bushveld Complex. The sample contains equigranular orthopyroxene (opx) and clinopyroxene (cpx) with interstitial plagioclase (plag). Zircon is associated with late interstitial biotite (bt), outlined in the white box. (b) SA04-08B (XPL), also from Farm Driekop, a feldspathic pyroxenite (opx and cpx) with abundant interstitial patches of plagioclase. Zircon is found with minor late-stage interstitial biotite (white box). (c) SA04-11B (PPL) from the West Mine, Western Limb. The sample is a very coarse-grained (pegmatitic) feldspathic orthopyroxenite with variable grain sizes and distribution of main minerals (opx, plag, bt, chromite); the locations of zircon and apatite are indicated. (d) SA04-11B (XPL) showing alteration along fractures in orthopyroxene and bent twins within interstitial plagioclase indicating deformation; white box indicates location of zircon on the rim of a large sulphide clot. Abbreviations: XPL, cross-polarized light; PPL, plane-polarized light. Scale bars are 0.5 cm in each panel.22Chapter 1NAlkaline intrusionsRooiberg GroupTransvaal Supergroupfaultskimberlitesmajor cityRashoop Granophyre SuiteRustenburg Layered SuiteBCLebowa Granite SuiteTMLPretoriaJohannesburgRustenburgPietersburgLydenburgEastern LimbWestern LimbFar Western LimbSoutheastern LimbNorthern Limb100 km26°E 27°E26°E 27°E28°E 29°E26°S25°S24°S28°E 29°E 30°ECape TownJohannesburg Pretoria32°S24°S20 28°ESouth AfricaIndianOceanFigure 1 .10 . Generalized geologic map of the Bushveld Complex (BC) in South Africa (modified from Scoates and Friedman, 2008). The Rustenburg Layered Suite is shown in purple (ultramafic rocks) and green (mafic rocks) with the PGE-rich Merensky Reef indicated by a dashed white line. The locations of the Eastern, Southeastern, Northern, Western, and Far Western limbs of the complex are noted. The Bushveld Complex intruded into metasedimentary rocks of the Transvaal Supergroup (tan colour) and volcanic rocks of the Rooiberg Group (grey colour); overlying felsic rocks of the contemporaneous Rashoop Granophyre Suite and Lebowa Granite Suite are shown in pink and red, respectively. Major faults and fault segments related to the transpressional Thabazimbi-Murchison lineament (TML) are also indicated (Good and de Wit, 1997). The inset in the upper left shows the regional placement and scale of the intrusion within South Africa with relation to major cities.23Chapter 15354377-81(w)(w) 81-8383-8985Fo306068-7258-64758079-8381-8583-89mg#74069-72607578-8078-80AnOlivine Opx Plag CpxMtApCr1700 1700300 8002800 14001300 800520 1000780 800300 500520 800West EastMarkersLOWERZONEPyrox-enitePyrox-eniteHarz-burg-iteNoriteNoriteGabbronoriteGab-bronoriteGabbronoriteMtOlivApatite DioriteCRITICALZONEMAINZONEUPPERZONEUZ CUZ bUZ aMUZMLZUCZLCZLZMARGINAL ZONE (Norite)17-218-14Main + 1-7MagnetitePyroxeniteUpper and MainMottledAnorthositesMerenskyUGMgLG chromititesMagnetites7200 (West) - 8100 (East) metersFigure 1 .11 . Stratigraphic column of the Bushveld Complex showing major stratigraphic divisions, dominant rock types, and notable marker horizons adapted from Cawthorn (1996). Unit thicknesses for the Western and Eastern limbs in meters are indicated. The occurrence and compositions of the main cumulus minerals olivine, orthopyroxene (opx), plagioclase (plag), and clinopyroxene (cpx) are shown on the right side of the diagram along with significant oxide phases chromite (cr) and magnetite (mt). The occurrence of cumulus apatite in the upper part of the Upper Zone is also indicated. 24Chapter 1Bushveld Complex has traditionally been approached through the bulk chemistry (i.e., major, trace, isotope) of whole rocks or from the major and minor element variations of the major high-temperature phases (e.g., olivine, pyroxene, spinel, plagioclase). Little appreciated until recently (e.g., Scoates and Wall, 2015) are the late-crystallized minerals (e.g., quartz, K-feldspar, biotite, zircon) found in cumulates between the major cumulus minerals and the record of magma evolution preserved in their chemistry (Fig. 1.9; Fig. 1.12). 1 .5 .2 . Previous work on zircon and rutile from the Bushveld ComplexThe textural setting of zircon from the Merensky Reef in the Western Limb of the Bushveld Complex was first described by Scoates and Friedman (2008) who reported a U-Pb CA-ID-TIMS age of 2054.4 ± 1.3 Ma (weighted mean 207Pb/206Pb), subsequently revised to 2057.04 ± 0.55 Ma (Scoates and Wall, 2015). A separate sample of the Merensky Reef in the Eastern Limb, nearly 300 km to the east yielded a statistically identical age of 2056.88 ± 0.41 Ma (Scoates and Wall, 2015) providing additional evidence that the limbs of the Bushveld Complex are likely connected at depth (Cawthorn and Webb, 2001). Zircon from chromitites in the Critical Zone of the Bushveld Complex was analyzed by Yudovskaya et al. (2013) for U-Pb ages (SHRIMP) and trace element variations (LA-ICP-MS). They identified high Th/U = 1-4 in zircon from the Merensky Reef and documented relatively low Ti-in-zircon temperatures of 930-760 °C. Yudovskaya et al. (2013) proposed that trace element variations between relatively enriched cores and depleted rims reflected inputs of less evolved magmas during the late stages of crystallization. More recently, Zeh et al. (2015) published a high-precision U-Pb CA-ID-TIMS dataset of zircon ages from a suite of samples that covered much of the Bushveld stratigraphy and argued that the intrusion may have cooled in less than 1 million years at ca. 2055 Ma. Their Ti-in-zircon thermometry results indicated zircon crystallization temperatures from 940-670 °C, similar to the range in Yudovskaya et al. (2013), and they found Th/U ratios in zircon were unusually high (up to Th/U = 18) in some grains from the UG2 chromitite. Zeh et al. (2015) proposed that the Bushveld Complex cooled much more rapidly than previously considered for such a large intrusion (e.g., ~125 °C/Ma based on combined U-Pb zircon and rutile dating; Scoates and Wall, 2015).Rutile from the Bushveld Complex was documented by Cameron (1979) who described 25Chapter 1(a) (b) (c)(d) (e)rutilechrplag(f)rutilechrchrbiotitezirconbiotitezirconqtzzirconopxbiotitezirconbiotitesulfide(po,pn,cp)(g)rutileopx plagqtz(h)biotiteopxapatiteplagqtz(i) biotiteqtzkspqtzplagzrcFigure 1 .12 . Photomicrographs showing the textural setting of accessory and other interstitial minerals in samples from the Merensky Reef of the Bushveld Complex (adapted from Scoates and Wall, 2015). Scale bar is 200 μm in each panel. (a) Large grain of zircon on the margin of a composite sulphide (po, pyrrhotite; pn, pentlandite; cp, chalcopyrite) encased in biotite (SA04-11B, XPL). (b) Zircon along cleavage plane in biotite with interstitial quartz (qtz) (SA04-11B, XPL). (c) Irregular zircon enclosed in the rim of biotite and in contact with interstitial quartz (SA04-11B, XPL). (d) Euhedral zircon on the margin of biotite in contact with orthopyroxene (opx) (SA04-11B, XPL). (e) Large single grain of rutile (brown-colored, high-relief) enclosed by orthopyroxene from near the base of the pegmatitic feldspathic orthopyroxenite (plagioclase, plag; chromite, chr) (SA04-13, PPL). (f) Rutile on the edges of several chromite grains in contact with orthopyroxene (SA04-13, PPL). (g) Small euhedral crystal of rutile at the contact between orthopyroxene and plagioclase (SA04-08, XPL). (h) Large composite apatite cluster (at extinction) with interstitial biotite, quartz and plagioclase (SA04-11B, XPL). (i) Interstitial biotite, quartz, and granophyre patch (quartz is at extinction, alkali feldspar [ksp] is partially altered to sericite); note zircon in biotite rim (same as panel c) (SA04-11B, XPL).26Chapter 1the occurrence of rutile in association with chromite within the Critical Zone, the ultramafic cumulate sequence that hosts the major chromium and PGE horizons in the Bushveld. Scoates and Friedman (2008) and Scoates and Wall (2015) reported U-Pb rutile dates for the two samples from the Merensky Reef (2052.96 ± 0.61 Ma, 2053.00 ± 2.70 Ma) (Fig. 1.12e). These dates correspond to the closure temperature for Pb diffusion in rutile (~900-950°C) (Schmitz and Schoene, 2007; Scoates and Wall, 2015). Textural relationships between rutile and chromite from the Merensky Reef were described by Vukmanovic et al. (2013) who noted exsolution features of rutile within chromite grains. To date, there are no studies that have analyzed rutile from the Bushveld Complex for trace element concentrations. Rutile is an excellent tracer of magmatic processes as it strongly partitions the high field strength elements (HFSE) (e.g., Zack et al., 2002, 2004) and can also be used as a thermometer (Zr-in-rutile; Watson et al., 2006; Ferry and Watson, 2007).1 .6 . Overview of the thesisThe research in this thesis approached two separate, yet complementary, aspects of zircon analysis by LA-ICP-MS that are both at the forefront of analyzing and interpreting zircon geochemistry. The first goal was to assess and improve the methodology of U-Pb geochronology of zircon through the process of laser ablation-ICP-MS by quantifying differences in downhole fractionation between natural zircon reference materials as a function of different pre-treatment protocols. The second goal was to contribute to the burgeoning field of trace element systematics in zircon with specific application to the Bushveld Complex. Based on samples from all major stratigraphic horizons of this enormous intrusion, the trace element variations were characterized and constraints placed on the late-stage evolution of Bushveld magmas. In Chapter 2, downhole fractionation during U-Pb zircon dating by LA-ICP-MS was assessed through analysis of the ablation characteristics of three established U-Pb zircon reference materials compared to three well-characterized in-house zircon samples. Combined, these six zircon samples range in age from 339 Ma (Carboniferous) to 2709 Ma (Neoarchean). For each sample, three different zircon fractions were analyzed: (1) grains that were untreated, (2) grains that were annealed, and (3) grains that were annealed and leached. An exponential downhole fractionation correction was applied to each sample and was treated as the standard. 27Chapter 1These correction factors were then applied to the unknowns so that U-Pb ages could be calculated for the different populations. Comparisons between the downhole behaviour of these samples and analysis of the effects of the pre-treatments are designed to improve assessments on calculations of final U-Pb ages and allow for recommendations of standardization methodology to enhance accuracy in LA-ICP-MS U-Pb zircon dating.In Chapter 3, the near-solidus chemical history of the Bushveld Complex was examined as recorded in the trace element signatures of two accessory minerals, zircon and rutile. Coupling petrography and SEM-CL (cathodoluminescence) imagery with LA-ICP-MS trace element chemistry, a detailed view of the crystallization sequence of the mafic-ultramafic cumulates was established for the first time. The temperatures of crystallization and the solidus of the Bushveld Complex were defined using Ti-in-zircon and Zr-in-rutile thermometry and the chemistry of zircon and rutile was used to constrain the evolution of interstitial melt of the Bushveld cumulates and then compared with forward crystallization modelling using rhyolite-MELTS (Gualda et al., 2012). The main conclusions from the two research chapters are summarized in Chapter 4 along with the presentation of some ideas for future research. The extensive Appendix to this thesis provides a catalogue of imagery, data, and additional figures used to support the research presented in Chapters 2 and 3. The appendices include: Appendix A, tables of trace element concentrations of zircon reference materials and samples analyzed by LA-ICP-MS in Chapter 2; Appendix B, the MATLAB code used to process and analyze data on downhole fractionation in zircon; Appendix C, a library of all cathodoluminescence (CL) images of untreated and treated zircon reference materials and in-house zircon used in Chapter 2; Appendix D, a comprehensive library of thin section scans and petrographic descriptions of samples from the Bushveld Complex used in Chapter 3; Appendix E, a table of results for EPMA analysis of major and minor element oxides of zircon in the Bushveld Complex; Appendix F, tables of LA-ICP-MS results for analysis of reference materials determined during analysis of zircon and rutile from the Bushveld Complex as described in Chapters 2 and 3; Appendix G, a complete suite of CL images of zircon grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicated; Appendix H, a library of all backscattered electron images (BSE) of rutile grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicated; Appendix I, tables of trace 28Chapter 1element analyses of zircon for each sample from the Bushveld Complex as determined by LA-ICP-MS; Appendix J, individual chondrite-normalized REE patterns in zircon for all analyses from the Bushveld Complex; Appendix K, tables of trace element analyses of rutile for each sample from the Bushveld Complex as determined by LA-ICP-MS; Appendix L, trace element variation diagrams of rutile from the Bushveld Complex assessing Pb concentrations and their potential impact on U-Pb dating of rutile; Appendix M, tables showing results from rhyolite-MELTS modelling for crystallization of proposed Bushveld parent magmas; and Appendix N, figures assessing trace element zoning characteristics of select zircon grains from the Bushveld Complex.29Chapter 2Chapter 2Chapter 2Matrix Matching Downhole U-Pb Fractionation in Zircon Reference Materials Analyzed by LA-ICP-MS 30Chapter 22 .1 . IntroductionLaser ablation-inductively coupled-plasma mass spectrometry (LA-ICP-MS) offers fast, accurate (Klötzli et al., 2009), and relatively precise geochemical analyses for numerous applications with micrometer-scale spatial resolution (Longerich et al., 1993; Norman and Pearson, 1996; Jackson et al., 2004; Klötzli et al., 2009; Arevalo, 2013; Schaltegger et al., 2015a; Sylvester and Jackson, 2016). These features, combined with the absence of a requirement for chemical clean laboratory dissolution, have resulted in the emergence of LA-ICP-MS as a highly utilized tool for geochemical fingerprinting (e.g., Jackson et al., 2004; Belousova et al., 2006; Chamberlain et al., 2013). In the Earth sciences, LA-ICP-MS is perhaps most commonly used for U-Pb zircon geochronology, providing a powerful tool for dating materials at a rate significantly faster than that achievable by isotope dilution-thermal ionization mass spectrometry (ID-TIMS) (Jackson et al., 2004; Cottle et al., 2010; Kylander-Clark et al., 2013; Schoene, 2013; Schaltegger et al., 2015b). In addition, the scope of LA-ICP-MS applications to zircon has broadened to include the analysis of hafnium isotopes (Griffin et al., 2002; Hawkesworth and Kemp, 2006; Zirakparvar et al., 2014; Vervoort and Kemp, 2016) and trace element concentrations (Belousova et al., 2002; Burnham and Berry, 2012; Yudovskaya et al., 2013). Among the most significant challenges involved in maximizing the precision and accuracy of U-Pb LA-ICP-MS zircon geochronology is downhole fractionation, the time-dependent evolution of Pb-U ratios due to complex differences in volatility and mass of the isotopes as they are excavated from the ablation site (Horn et al., 2000; Paton et al., 2010; Chew et al., 2014). To produce meaningful dates for unknown materials, downhole fractionation must be quantified in a reference material and a correction factor then applied to yield constant Pb/U in both standards and unknowns. This methodology operates under the assumption that the ablation characteristics of the two samples behave similarly downhole (Paton et al., 2010; Allen and Campbell, 2012). Yet, many factors control how a zircon grain will ablate, including color, crystallinity, radiation damage, and orientation as well as instrument settings and daily mass bias (Nasdala et al., 2005). Recently, application of annealing (AN) and chemical abrasion (CA) pre-treatment 31Chapter 2protocols for zircon that were developed for U-Pb ID-TIMS geochronology (Mattinson, 2005) were discovered to also improve the accuracy and precision of LA-ICP-MS analysis of zircon (Allen and Campbell, 2012; Crowley et al., 2014; Solari et al., 2015). However, the nature of downhole fractionation in zircon has not yet been sufficiently characterized to validate the assumption that correction models based on reference materials will yield accurate results from unknown zircon. In this study, downhole fractionation patterns are characterized and quantified in three common zircon reference materials (Plešovice, Temora-2, 91500) and in three samples from mafic intrusions (Laramie, Bushveld, Stillwater) for a complete age range from the Phanerozoic (337 Ma) to the Archean (2710 Ma). Using an exponential downhole correction model developed from the reference zircon samples, corrections are applied to determine the effects of variable downhole behaviour on final U-Pb ratios and ages from the “unknown” grains from the mafic intrusions. The results are then used to assess the effects of pre-treatment on the ablation characteristics of zircon and on variations in downhole fractionation between untreated, annealed, and chemically abraded grains. Because fractionation and standardization are among the main limitations on the precision of U-Pb LA-ICP-MS analysis (Klötzli et al., 2009; Allen and Campbell, 2012), understanding the controls of fractionation is a critical step towards improving methodologies.2 .2 . Background2 .2 .1 . Standardization in LA-ICP-MS and downhole fractionationIn LA-ICP-MS, as in most other analytical techniques in geochemistry, well-characterized homogeneous standards or reference materials must be analyzed concurrently with unknowns to obtain accurate results. Attempts at standardization with synthetic materials have been made, including nanoparticulate (e.g., Garbe-Schönberg and Müller, 2014; Tabersky et al., 2014) and solution nebulization (e.g., Horn et al., 2000) for U-Pb and trace element analyses by LA-ICP-MS, however, no synthetic material has yet been deemed sufficient for adoption by the LA-ICP-MS community. Due to the importance of matrix matching (e.g., Norman and Pearson, 1996; Gaboardi and Humayun, 2009; Schaltegger et al., 2015), the procedure of analyzing unknown zircon requires standardization alongside natural reference materials. In U-Pb zircon 32Chapter 2geochronology by LA-ICP-MS, matrix matching is typically accomplished by sample-standard bracketing of the unknown zircon with natural zircon reference materials. This procedure limits the precision of LA-ICP-MS analyses due to the inherent heterogeneity in natural zircon even in the best of cases. However, matrix matching is arguably the most important characteristic of a zircon reference material as factors including crystallinity, clarity, chemistry, and even orientation have been shown to affect ablation characteristics (Gaboardi and Humayun, 2009; Kooijman et al., 2012). 2 .3 . Pre-treatment of zirconWhile robust under most geologic conditions, zircon can be susceptible to open-system Pb loss over time due to metamictization, the process of self-irradiation of the crystal structure following radioactive decay of the parent isotopes 238U, 235U, and 232Th to their respective radiogenic daughter isotopes 206Pb, 207Pb, and 208Pb (e.g., Silver and Deutsch, 1963; Nasdala et al., 2001; Schoene, 2013). As this behaviour can lead to discordant U-Pb results, common treatment methods have been developed to systematically remove damaged zones using both physical and chemical processes (Krogh, 1973, 1982; Mattinson, 2005). The most significant recent advance in U-Pb zircon dating by ID-TIMS is the development of the chemical abrasion method (CA-ID-TIMS) by Mattinson (2005). This process involves two main steps, including 1) thermal annealing, during which grains are subjected to high temperatures (800-1100 °C) to recrystallize zones that have experienced Pb loss, and 2) leaching, where annealed grains undergo a series of partial dissolutions to remove high U+Th damaged domains, leaving only zones that yield concordant U-Pb results by TIMS analysis. The potential benefits of using annealing and chemical abrasion pre-treatment on zircon grains for analysis by LA-ICP-MS have been investigated by Crowley et al. (2014), Marillo-Sialer et al. (2014), and Solari et al. (2015). Both annealing and chemical abrasion techniques have been found to significantly impact the ablation characteristics of zircon, typically by decreasing overall downhole fractionation due to strengthening of the grain structures through the annealing process (Solari et al., 2015). Although pre-treatment may help standardize ablation behaviour between standards and unknowns, and thereby enhance the matrix match, this step adds time and cost to LA-ICP-MS analyses. Additional comparative analyses are needed to quantify the effects of pre-treatment on downhole 33Chapter 2fractionation and to generate recommendations on procedures for optimizing precision and accuracy in U-Pb LA-ICP-MS geochronology.2 .3 .1 . SamplesThe three well-characterized zircon U-Pb reference materials (Plešovice, 337 Ma; Temora-2, 417 Ma; 91500, 1065 Ma) used in this study represent some of the most highly used reference materials in LA-ICP-MS geochronology (Table 2.1). In addition, three in-house zircon samples with previously established U-Pb TIMS ages are utilized as “unknowns” and include SR336 from the 1.43 Ga Laramie anorthosite complex in Wyoming, SA04-13 from the Merensky Reef of the 2.06 Ga Bushveld Complex, and ST05-03, a leucogabbro from the 2.71 Ga Stillwater Complex (Table 2.1). All three of the unknown samples are from, or associated with, mafic layered intrusions that extend the age range of investigated samples from the Mesoproterozoic to the Neoarchean. Mafic intrusions typically yield zircon with simple morphologies and zoning patterns, low U concentrations (typically <300 ppm), and concordant U-Pb isotope systematics (e.g., Scoates and Wall, 2015).2 .3 .1 .1 . PlešovicePlešovice zircon, which was extracted from a potassic granulite from Plešovice (Czech Republic), was proposed as a reference material by Sláma et al. (2008). The accepted 206Pb/238U age is 337.13 ± 0.37 Ma (ID-TIMS) and the relatively homogeneous grains make it a common reference standard for laser ablation (e.g., Cottle et al., 2010; Chew et al., 2011; Crowley et al., 2014). Large variations in trace elements, particularly the actinides, have been observed with U concentrations ranging from a few hundred ppm to >3000 ppm (Sláma et al., 2008). These high-actinide domains are typically metamict and tend to be less reliable for U-Pb dating than the low-actinide domains, although Pb loss is not substantial, even in the damaged zones.2 .3 .1 .2 . Temora-2The Temora-2 zircon is sourced from the Paleozoic Middledale gabbroic diorite in eastern Australia (Black et al., 2004). It is chemically and isotopically similar to its predecessor Temora-1 (206Pb/238U = 416.75 ± 0.24, Black et al., 2003), although the two materials yield slightly, but significant different ages. Zircon from Temora-2 is characterized by relatively 34Chapter 2Table 2 .1 .  Summary of zircon materials used to examine the effects of downhole fractionationZircon Eon / Era / Period Accepted Age (Ma) 206Pb/238U Age (Ma) U (ppm) Average Pb*/U Size (μm) ZoningReference MaterialsPlešovice1 Carboniferous 337.13 ± 0.23 (206Pb/238U) 337.13 ± 0.23 465-1106 0.052 175-300 minor oscillatoryTemora-22 Silurian 416.78 ± 0.33 (206Pb/238U) 416.78 ± 0.33 82-320 0.070 100-200 oscillatory and sector915003 Mesoproterozoic 1065.4 ± 0.3 (concordia) 1062.4 ± 0.4 71-86 0.18 700-1000 very minorIn-house SamplesSR3364,7 Mesoproterozoic 1435.6 ± 2.5 (upper intercept 207Pb/206Pb) 1431.7 ± 1.3 30-35 0.26 70-100 sectorSA04-135,8 Paleoproterozoic2057.04 ± 0.55 (weighted mean 207Pb/206Pb)2054.52 ± 0.79 7-103 0.57 ~100 sectorST05-036,8 Neoarchean2710.44 ± 0.32 (weighted mean 207Pb/206Pb)2709.87 ± 0.81 32-252 0.62 60-115 sectorNote: the U-Pb ID-TIMS results for all samples plot are concordant and there is no evidence for Pb loss; all uncertainties are 2σ1. Slama et al. (2008)2. Black et al. (2004)3. Wiedenbeck et al. (1995)4. Scoates and Chamberlain (2003)5. Scoates and Wall (2015)6. Wall et al. (2016)7. Analyses by ID-TIMS at the University of Wyoming8. Analyses by CA-ID-TIMS at PCIGR, University of British Columbia35Chapter 2low U concentrations (~100-200 ppm) and yields an ID-TIMS 206Pb/238U age of 416.78 ± 0.33 Ma, however LA-ICP-MS analysis of Temora-2 zircon produces significantly younger results (206Pb/238U = 411.8 ± 2.1) (Black et al., 2004). This inconsistency has been correlated with variations in trace element concentrations, especially Nd, and Black et al. (2004) proposed a correction based on rare earth element contents to unify LA-ICP-MS ages with those determined by ID-TIMS. Allen and Campbell (2012) found that the discrepancy was highly correlated with radiogenic Pb contents, and therefore alpha-dose, and suggested that annealing of grains could close the age gap between LA-ICP-MS and TIMS ages.2 .3 .1 .3 . 91500The 91500 zircon is derived from a large single crystal (Royal Ontario Museum) that was broken into grain sizes of ~200 μm and distributed for geochemical analysis (Wiedenbeck et al., 1995, 2004). The sample is presumed to be taken from a porphyroblastic syenite gneiss with cross-cutting syenite pegmatite sills from Kuehl Lake in Ontario, Canada. The accepted ID-TIMS 206Pb/238U age is 1062.4 ± 0.4 Ma with a concordia age of 1065.4 ± 0.3 Ma (Wiedenbeck et al., 2004). The large, weakly zoned fragments of this pristine zircon (U typically <100 ppm) make it an excellent reference material for LA-ICP-MS as grains can easily be re-polished many times and ages are homogeneous across the crystals fragments. 2 .3 .1 .4 . In-house zirconZircon sample SR336 was collected from a monzodiorite dike along the eastern contact of the monzosyenitic Sybille intrusion adjacent to the Poe Mountain anorthosite of the Laramie anorthosite complex in Wyoming, USA (Scoates and Chamberlain, 2003; Scoates et al., 2010). ID-TIMS U-Pb dating of multigrain fractions (U~30-100 ppm) that were untreated or air-abraded yielded an upper concordia 207Pb/206Pb intercept age of 1435.6 ± 2.5 Ma based on the analysis of concordant to slightly discordant results (D = 0.3-0.7%) (Scoates and Chamberlain, 2003). Zircon sample SA04-13 was taken from a pegmatitic feldspathic orthopyroxenite of the Merensky Reef in the Bushveld Complex of South Africa (Scoates and Friedman, 2008; Scoates and Wall, 2015). Analysis of single grains (U = 30-100 ppm) by CA-ID-TIMS yielded a weighted mean 207Pb/206Pb age of 2057.04 ± 0.55 Ma (Scoates and Wall, 2015). Comprehensive trace element analyses by LA-ICP-MS of zircon from this sample are reported in Chapter 3.36Chapter 2Zircon sample ST05-03 is derived from a leucogabbro in the Anorthosite zone II (AN2) of the Stillwater Complex (Montana, USA) (Wall et al., 2016). Analysis of single grains (U = 54-585 ppm) by CA-ID-TIMS yielded concordant results with a weighted mean 207Pb/206Pb age of 2710.44 ± 0.32 Ma and analysis by ID-TIMS and LA-ICP-MS yield indistinguishable results (ID-TIMS = 2710.56 ± 0.32 Ma; LA-ICP-MS = 2715 ± 9 Ma). As a result, this sample has been proposed as a new zircon reference material for the TIMS and LA-ICP-MS community for the dating of Archean zircon (Wall et al., 2016). 2 .4 . Analytical procedure2 .4 .1 . Sample preparation and pre-treatmentZircon from samples SA04-13 and ST05-03 underwent mineral processing techniques at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) as described by Scoates and Wall (2015). Large, clear, inclusion-free grains were picked from these samples under a binocular microscope; the reference materials were acquired as pure zircon separates. From each zircon sample, two-thirds of the population was separated for annealing following the procedure of Scoates and Wall (2015), based on Mattinson (2005), with the remaining third of the grains untreated. Grains selected for annealing were placed in quartz glass crucibles in a muffle furnace at 900⁰C for 60 hours, and following annealing, half of the annealed grains from each sample were selected for chemical abrasion. For chemical abrasion, grains were placed in 10 mL PyrexTM beakers, ultrasonicated in ultrapure 3 N HNO3 for 15 minutes, and brought to 60°C for 30 minutes, followed by a rinse of ultrapure acetone and water. Grains were transferred into 3.5 mL perfluoroalkoxy alkane (PFA) screw-top beakers with ultrapure HF (50%, 500 μL) and HNO3 (14 N, 50 μL) and capped. Beakers were then placed within 125 mL polytetrafluorethylene PTFE Teflon® liners, and 2 mL HF and 0.2 mL concentrated HNO3 was added. Liners were inserted into stainless steel jackets of Parr® high-pressure dissolution devices, sealed, and kept at 200°C for 16 hours. Once cooled, the beakers were removed from the liners and the leached zircon grains were retrieved. 2 .4 .2 . ImagingFollowing treatment, untreated (UT), annealed (AN), and annealed + chemically abraded 37Chapter 2(CA) grains were mounted in epoxy in 2.5 cm diameter pucks that were subsequently ground and polished to reveal the approximate mid-sections of the grains. Grains were imaged for their internal structure using a Robinson cathodoluminescence (CL) detector attached to a Philips XL-30 scanning electron microscope (SEM) at the Electron Microbeam/X-Ray Diffraction Facility (EMXDF) at the University of British Columbia (UBC), Vancouver. During imaging, major differences in the brightness of the CL-response were observed between the untreated and treated populations of each sample, and the brightness and contrast settings were recorded for later comparison. 2 .4 .3 . LA-ICP-MS experimental designAssessment of downhole fractionation of U-Pb isotopes for the analyzed zircon was carried out on a Resonetics RESOlution M-50-LR Class I laser ablation system coupled to an Agilent 7700x quadrupole ICP-MS at the PCIGR. Analyses were conducted using pit diameters of 34 μm at a repetition rate of 5 Hz using a beam energy of 100 mJ. Samples were ablated for 40 seconds followed by 20 seconds of gas blank. Analytical conditions are reported in Table 2.2. Due to the homogeneous nature of the reference materials used in this study, as well as the lack of notable compositional zoning observed in CL imagery, ablation spots were placed on grain surfaces with no location preference to internal structure, only ensuring sufficient distance from grain edges and neighboring ablation sites. The laser beam was calibrated to the height of the grain surface within 1 μm using an adjustable z-focus. Masses of Pb (204Pb, 206Pb, 207Pb, 208Pb), 232Th, and U (235U and 238U) were measured as well as 202Hg (as a monitor). Additionally, the following trace element masses were selected for measurement based on their high abundances and lack of isotopic interferences: 49Ti, 89Y, 90Zr, 140Ce, 146Nd, 147Sm, 153Eu, 157Gd, 163Dy, 165Ho, 166Er, 172Yb, 175Lu, 177Hf.Analyses were carried out over two sessions on consecutive days with the first session involving only 91500, Temora-2, and Plešovice (untreated, annealed, leached), and the second session including 91500, Temora-2, Plešovice (UT), ST05-03, SA04-13, and SR336 (untreated, annealed, leached). The synthetic glass standard NIST612 was also analyzed to allow for later interpretation of trace element variations (results reported in Appendix A). A sample bracketing system was designed that allowed untreated grains of 91500, Temora-2, and Plešovice to be 38Chapter 2Table 2 .2 . Procedure for LA-ICP-MS analysis of zircon at PCIGRParameter ValueResonetics RESOlution M-50 LR Class I LaserWavelength 193 nmEnergy density 5 J cm-2Repetition rate 5 HzSpot diameter 34 μmHelium flow 0.75 L min-1High-purity N2 gas flow 0.002 L min-1Ablation time / gas blank time 40 s / 20 sAgilent 7700x  Quadrupole ICP-MSDay 1 Day 2Argon carrier gas flow 0.57 L min-1  0.57 L min-1Masses measured 22 22Mass sweep time 705 ms 706 ms ThO+/Th+ (NIST612) <0.4 wt.% <0.6 wt.%U238/Th232 sensitivity (NIST612) 108.01% 111.74%39Chapter 2used to reduce the unknowns for both sessions. This procedure followed the repeating sequence: 91500 (UT), Temora-2 (UT), Plešovice (UT), NIST612, followed by 5-6 analyses of either AN and CA grains of 91500, Temora-2, and Plešovice (session 1) or UT, AN, and CA grains of ST05-03, SA04-13, and SR336 (session 2). The sequence was repeated 32 times per session to ensure statistical significance and the calculation of propagated errors.2 .4 .4 . Data reduction and downhole correctionThe Iolite 2.5 extension for Igor Pro (Paton et al., 2011) was used for selecting integrations from the raw data, subtracting baselines, and computing exponential functions to correct for downhole fractionation. Full integrations were selected from the initial peak in signal to the end of the ablation when the signal dropped. This approach was chosen to best standardize the ablation depth when comparing each analysis to fit a downhole fractionation curve. To quantify the downhole fractionation patterns of the samples, the data were then reduced using the U_Pb_Geochron3 data reduction scheme (Paton et al., 2011), and downhole fractionation exponential fit functions were calculated for the raw baseline-subtracted 206Pb/238U, 207Pb/235U, and 208Pb/232Th. Due to the low and noisy 235U signal, 235U was calculated based on a 238U/235U value of 137.88 (Steiger and Jäger, 1977); comparisons of measured and calculated 235U values showed nearly identical averages indicating that this assumption was valid. No significant variation of 204Hg was detected between any analysis and background values, therefore, no common Pb correction was applied.To calculate a fit for downhole fractionation, Iolite stacks each integration of a given sample and calculates an average ratio of Pb/U over each ablation time-slice. The function:            (Equation 1)provides an exponential fit to this average. Data were trimmed at the beginning and end of the ablations to minimize the residuals to the fit and the fit coefficients were recorded as a, b, and c. This process was repeated for each of the in-house zircon and treated zircon samples. Raw time-integrated counts of background-corrected Pb, Th and U isotopes were exported and all further analysis of the ratios was performed outside of Iolite using a MATLAB script (Appendix B). Raw ratios were corrected to the downhole fit by inverting the function to yield corrected ratios ƒ(t) = a + b ⁎ e(-ct) 40Chapter 2by the equation:    (Equation 2)This method produces constant ratios of 206Pb/238U that do not evolve with time (Fig. 2.1). Finally, trimmed raw data for the three unknown samples (UT, AN, CA) were reduced in Iolite using the U_Pb_Geochron3 data reduction scheme with untreated grains of each of 91500, Temora-2, and Plešovice used as the reference standard zircon. The exponential downhole fits determined in Iolite yielded three parallel data sets of final U-Th-Pb ratios.2 .5 . Results2 .5 .1 . Cathodoluminescence imageryThe internal structure and zoning of the three zircon reference materials and in-house unknowns were examined by cathodoluminescence imaging (Figs. 2.2, 2.3). A catalogue of all CL images is found in Appendix C. Plešovice zircon consists mainly of fragments (175-300 μm diameter) that show fine micrometer-scale oscillatory zoning. Temora-2 grains are irregular to euhedral and are typically smaller (100-200 μm diameter) than Plešovice zircon (Fig. 2.2a, d, g). Zoning in Temora-2 zircon is variable, consisting of fine oscillatory bands within larger sector zones, and commonly including CL-dark patches with no zoning (Fig. 2.2b, e, h). Grains from zircon 91500 are very large, up to 1 mm in length, representing fragments of the original single crystal (Fig. 2.2c, f, i). The CL response in zircon 91500 is nearly homogeneous, with some rare fragments showing very minor oscillatory zoning. The cathodoluminescence responses of the three in-house unknown samples are variable (Fig. 2.3). Zircon grains in sample SR336 (Laramie) are small, up to 100 μm in length, with some grains showing variable sector zoning and other grains displaying very little internal structure (Fig. 2.3a, d, g). Grains from sample SA04-13 (Bushveld) are also ~100 μm in length and are dominated by sector zoning and internal oscillatory zones within sectors. Some grains display mottled and irregular CL responses (Fig. 2.3b, e, h). Zircon from ST05-03 (Stillwater) is typically 100 μm long, and shows minimal variation in CL response with minor sector zoning f(t) = 206Pb/238U (t)         1 + (b/a) ⁎ e-ct41Chapter 2206Pb238U206Pb238U0 5 10 15 20 25 30 35 40ablation time (s)0.020.030.040.050.060.070.08(a) Raw Data0 5 10 15 20 25 30 35 40ablation time (s)0.020.030.040.050.060.070.08(b) Downhole CorrectedFigure 2 .1 . Diagrams of ablation time (in seconds) vs. 206Pb/238U showing an exponential downhole fractionation correction applied to the analysis of the Plešovice zircon reference material by LA-ICP-MS. (a) Raw data. The green lines represent the analyzed raw ratios from the 36 different analyses by LA-ICP-MS. The black line is a mean for each collection time-slice. The red line is an exponential fit function to the average ratio of 206Pb/238U. The grey bars indicate time slices that were trimmed from the fit calculation. (b) Downhole-corrected. The downhole-corrected raw ratios (green) and average ratios (black) are flattened by the fit correction. The corrected fit function produces a horizontal line (red).42Chapter 291500 UT 200 ȝm91500 AN 200 ȝm91500 CA 200 ȝmPlešovice UT 80 ȝmPlešovice AN 60 ȝmPlešovice CA 60 ȝmTemora-2 UT 60 ȝmTemora-2 AN 30 ȝmTemora-2 CA 30 ȝmPlešoviceChem AbrasionAnnealedUntreatedTemora-2 91500(a) (b) (c)(d) (e) (f)(g) (h) (i)Figure 2 .2 . Cathodoluminescence (CL) images of representative zircon grains from the three different zircon reference materials used for this study (Plešovice, left column; Temora-2, middle column; 91500, right column). The images show the different emissions for untreated grains (UT, upper row), annealed grains (AN, middle row), and grains that were leached and annealed (chemical abrasion, CA, lower row). Note the zoning patterns for the different zircon reference materials and the substantially enhanced CL emission for the annealed and chemically abraded grains. Scale bars are indicated for each panel.43Chapter 2ST05-03 UT 20 ȝmST05-03 AN 20 ȝmST05-03 CA 40 ȝmSR336 UT 20 ȝmSR336 AN 20 ȝmSR336 CA 20 ȝmSA04-13 UT 30 ȝmSA04-13 AN 30 ȝmSA04-13 CA 20 ȝmSR336AnnealedUntreatedSA04-13 ST05-03(a) (b) (c)(d) (e) (f)(g) (h) (i)Chem AbrasionFigure 2 .3 . Cathodoluminescence images of zircon grains from three different in-house samples used for this study, including SR336 (Mesoproterozoic Laramie anorthosite complex, left column), SA04-13 (Paleoproterozoic Bushveld Complex, middle column), and ST05-03 (Neoarchean Stillwater Complex, right column) showing the different emissions for untreated grains (UT, upper row), annealed grains (AN, middle row), and grains that were leached and annealed (chemical abrasion, CA, lower row). Note the substantially enhanced CL emission for the annealed and chemically abraded grains, especially for SA04-13 and ST05-03. Scale bars are indicated for each panel.44Chapter 2(Fig. 2.3c, f, i).Annealing produced significantly stronger CL responses for all reference and in-house zircon (Figs. 2.2, 2.3, 2.4). Such an increase in CL response following pre-treatment has been recognized in previous studies, and while not incompletely understood, appears to be a function of regained crystallinity that allows for more efficient emission from the CL-activated elements (Dy3+, Tb3+, Gd3+) in zircon (Nasdala et al., 2002). The additional step of chemical abrasion of the annealed grains did not produce any noticeable increase in CL response (Figs. 2.2, 2.3). 2 .5 .2 . Characterizing downhole fractionation between samplesTo quantify the exponential fit parameters for each sample, the time-integrated raw (background-subtracted) 206Pb/238U of each 40-second ablation was aligned and a mean value was calculated for each time slice of the data. This average Pb/U was then used to fit the exponential function (Figs. 2.5, 2.6). This same process was applied to the raw 207Pb/235U (Figs. 2.5, 2.6, right columns). In all cases, the Pb/U of the sample increases throughout the ablation time following an exponential curve, with the most rapidly changing ratios occurring at the beginning of the ablations and more gradual changes characteristic of the later part of each analysis. Variations in Pb/U from the start to the end of each analysis range from 13.6-21.5% for the untreated zircon of each sample (Figs. 2.5a, 2.6e, Table 2.3). To quantitatively compare fractionation, variations in the parameters of the exponential fit equations for each of the six samples are assessed and compared below.Exponential fits and associated coefficients to the averaged downhole fractionation observed in the three zircon reference samples (Plešovice, Temora-2, 91500) show distinct behaviour both between samples and when comparing untreated, annealed, and chemically abraded grains of a single sample (Fig. 2.7, Table 2.4). In the exponential fit equation (Equation 1), the a coefficient defines the asymptote of the fit, and therefore the height of the line, and the b value controls the tilt or slope of the fit line similar to a linear function. The c coefficient is particularly important for interpreting the downhole behaviour as it reflects the curvature of the downhole fit. Higher c values produce more sharply curved fits indicating more rapid changes in Pb/U early in an ablation, whereas lower c values produce fits that continue to evolve for the duration of an ablation. 45Chapter 2annealeduntreated(a) SR336annealeduntreated(b) ST05-03Figure 2 .4 . Cathodoluminescence (CL) images at low magnification comparing the differences in CL intensity for untreated and annealed zircon grains. (a) SR336 Laramie anorthosite complex. (b) ST05-03 Stillwater Complex. The CL intensity is significantly higher for the annealed grains. Scale bars are indicated for each panel.46Chapter 20 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 4500.020.040.060.080.100.120 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 450.040.060.080.100.120.140.160.180.200.220.240 5 10 15 20 25 30 35 40 450 5 10 15 20 25 30 35 40 4500.010.020.030.040.050.060.070.080.090.10(a) Plešovice (UT)(c) Temora-2 (UT)(e) 91500 (UT)ablation time (s)00.20.40.60.81.01.21.4(b) Plešovice (UT)(d) Temora-2 (UT)(f) 91500 (UT)00.51.01.52.02.53.03.54.04.500.20.40.60.81.01.21.41.61.82.0206Pb238U207Pb235UFigure 2 .5 . Ablation time vs. raw 206Pb/238U (left column) and 207Pb/235U (right column) for all untreated grains of the zircon reference materials: (a-b) Plešovice, (c-d), Temora-2, and (e-f) 91500. The analyzed raw ratios are shown as the coloured lines (green, blue, red) in the background of each plot. The black lines represent the mean value for each ratio and the red lines are an exponential fit to the mean using coefficients determined using Iolite 2.5. The grey bars indicate time that was trimmed from the ablations and omitted from the fit calculations. UT = untreated.47Chapter 20 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 450 5 10 15 20 25 30 35 40 45 0 5 10 15 20 25 30 35 40 450 5 10 15 20 25 30 35 40 450 5 10 15 20 25 30 35 40 45(a) SR336 (UT)(c) SA04-13 (UT)(e) ST05-03 (UT)ablation time (s)(b) SR336 (UT)(d) SA04-13 (UT)(f) ST05-03 (UT)206Pb238U207Pb235U0.20.30.40.50.60.70.8681012141618200.10.20.30.40.50.60.70.8051015202500.050.100.150.200.250.300.350.400.450.5001234567Figure 2 .6 . Ablation time vs. raw 206Pb/238U (left column) and 207Pb/235U (right column) for all untreated grains of in-house zircon from samples SR336 (Laramie, panels a-b), SA04-13 (Bushveld, panels c-d), and ST05-03 (Stillwater, panels e-f). The analyzed raw ratios are shown as coloured lines (orange, blue, purple) in the background of each plot. The black lines represent the mean value for each ratio and the red lines are an exponential fit to the mean using coefficients determined using Iolite 2.5. The grey bars indicate time that was trimmed from the ablations and that was omitted from the fit calculation. UT = untreated.48Chapter 2Table 2 .3 . Summary of downhole fractionation for all reference materials and samples in this studySample Treatment1 206Pb/238U initial2 206Pb/238U final3 % change % change from UTReference MaterialsPlešoviceUT 0.0408 0.0493 20.70 N/A4AN 0.0407 0.0482 18.18 -2.51CA 0.0403 0.0476 18.11 -2.58Temora-2UT 0.0518 0.0589 13.62 N/AAN 0.0505 0.0578 14.59 0.97CA 0.0497 0.0578 16.31 2.6991500UT 0.1333 0.1575 18.18 N/AAN 0.1339 0.1575 17.64 -0.54CA 0.1368 0.1577 15.26 -2.91In-house ZirconSR336UT 0.1955 0.2245 14.81 N/AAN 0.1888 0.2207 16.88 2.06CA 0.1884 0.2191 16.28 1.47SA04-13UT 0.2820 0.3359 19.09 N/AAN 0.2793 0.3378 20.95 1.86CA 0.2797 0.3328 18.99 -0.10ST05-03UT 0.3944 0.4792 21.49 N/AAN 0.3939 0.4646 17.94 -3.55CA 0.3969 0.4740 19.44 -2.051. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion2. Initial value taken at 3 seconds into ablation3. Final value taken from 3 seconds before end of ablation4. N/A = not available49Chapter 20.0380.0400.0420.0440.0460.0480.0500.0460.0480.0500.0520.0540.0560.0580.0600.1200.1250.1300.1350.1400.1450.1500.1550.1600.1650.170.180.190.200.210.220.230.270.280.290.300.310.320.330.340.350.360.380.400.420.440.460.480.500 5 10 15 20 25 30 35 400 5 10 15 20 25 30 35 40(a) Plešovice(b) Temora-2(c) 91500 (f) ST05-03(e) SA04-13(d) SR336ablation time (s) ablation time (s)206Pb238UUntreatedAnnealedChemical AbrasionFigure 2 .7 . Diagrams of ablation time (in seconds) vs. 206Pb/238U showing modelled exponential fits for average 206Pb/238U in zircon from the reference materials (left column) and in-house samples (right columns). Solid lines indicate fits for untreated grains, long-dashed lines indicate fits for annealed grains, and short-dashed lines indicate fits for grains that underwent chemical abrasion. The colours of the lines correspond to those used for each sample in Figures 2.5 and 2.6. (a) Plešovice, (b) Temora-2, (c) 91500, (d) SR336 Laramie, (e) SA04-13 Bushveld, (f) ST05-03 Stillwater.50Chapter 2Table 2 .4 . Coefficients determined for exponential correction of downhole fractionation during zircon analysis by LA-ICP-MS206Pb/238U 207Pb/235U 208Pb/232ThSample Treatment1 a2 b c a b c a b cReference MaterialsPlešoviceUT 0.0521 -0.0134 0.0417 0.3790 -0.0852 0.0414 0.0177 0.0004 0.0220AN 0.0502 -0.0114 0.0467 0.4257 -0.1229 0.0190 0.0182 -0.0013 0.0317CA 0.0482 -0.0108 0.0764 0.3512 -0.1101 0.1175 0.0178 -0.0024 0.0548Temora-2UT 0.0595 -0.0104 0.0763 0.4399 -0.0627 0.0642 0.0205 0.0079 0.1333AN 0.0584 -0.0109 0.0812 0.4795 -0.1039 0.0166 0.0195 0.0076 0.2130CA 0.0582 -0.0123 0.0933 0.4232 -0.1009 0.1444 0.0230 -0.0026 0.000691500UT 0.1587 -0.0370 0.0942 1.7260 -0.4639 0.0609 0.0586 -0.0086 0.0162AN 0.1581 -0.0379 0.1121 1.8404 -0.4788 0.0259 0.0610 -0.0120 0.0169CA 0.1600 -0.0307 0.0693 1.7698 -0.4200 0.0356 0.0537 -0.0028 0.0329In-house ZirconPlešovice UT 0.0490 -0.0096 0.0742 0.4027 -0.0962 0.0240 0.0171 0.0550 0.6134Temora-2 UT 0.0601 -0.0121 0.1114 0.4876 -0.0979 0.0189 0.0218 0.0102 0.204991500 UT 0.1613 -0.0353 0.0920 1.7366 -0.3206 0.0411 0.0535 -0.0043 0.0904SR336UT 0.2271 -0.0427 0.0757 2.7071 -1.1248 0.2845 0.0768 0.0010 -0.0057AN 0.2233 -0.0472 0.0786 3.1921 -0.7678 0.0111 0.0759 -0.0035 0.0119CA 0.2211 -0.0458 0.0842 2.8679 -0.0746 0.0606 0.0754 -0.0051 0.0186SA04-13UT 0.3873 -0.1148 0.0217 6.9107 -2.2108 0.0204 0.1296 -0.0317 0.0131AN 0.4035 -0.1341 0.0193 6.9438 -2.1623 0.0193 0.1276 -0.0304 0.0126CA 0.4030 -0.1321 0.0171 6.8545 -1.9136 0.0136 0.1262 -0.0317 0.0135ST05-03UT 0.4916 -0.1247 0.0623 12.4570 -2.9904 0.0697 0.1614 -0.0245 0.0212AN 0.4685 -0.1065 0.0890 12.5545 -2.8794 0.0055 0.0150 -0.0063 0.0059CA 0.4889 -0.1148 0.0552 15.5491 -2.8389 0.0617 0.1530 -0.0183 0.03221. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion2. Coefficients refer to the following Equation (2): (t) = 206Pb/238U (t) / (1 + (b/a) ⁎ e-ct)51Chapter 2In Plešovice zircon, the annealed and chemically abraded grains behave differently from the untreated zircon grains during ablation, especially as the ablation time increases (Fig. 2.7a). Annealed Plešovice zircon has a similar initial ratio, however, the exponential fit is more curved (i.e., both a less negative b value and higher c value). Significantly higher c values for the chemically abraded zircon grains produce a more curved exponential fit than the untreated and annealed grains. Downhole fractionation of 206Pb/238U increases by 20.7% for untreated grains and by 18% for annealed and chemically abraded grains (Table 2.3). Exponential fits for Temora-2 zircon show similar behaviour between the three types of grains that were analyzed (Fig. 2.7b). While the lower values in a result in lower fit functions, the three lines are roughly parallel. Overall, less downhole fractionation is observed during ablation of Temora-2 zircon compared with Plešovice (e.g., 13.6% increase in 206Pb/238U during ablation). Downhole fractionation is 1% higher for annealed grains and 2.7% higher for chemically abraded grains when compared to the untreated grains, which is opposite to the trends observed in Plešovice zircon. Downhole behaviour in 91500 zircon is distinct from that observed in Plešovice and Temora-2 zircon (Fig. 2.7c). The downhole fit for untreated 91500 zircon grains yields a high c value (0.094) and produces a line more sharply curved than that determined for Plešovice or Temora-2. Analyses of the annealed 91500 zircon grains are fit with a higher c value (0.11), however, the c value for the chemically abraded grains is significantly lower (0.069). Net changes in 206Pb/238U include an 18.1% increase for untreated grains and a 17.6% and 15.3% increase for the annealed and chemically abraded grains, respectively. Downhole fractionation patterns for the in-house zircon samples analyzed as unknowns also show variations between treatments similar to those observed in the reference samples with some important differences (Fig. 2.7d-f). The fits for the SR336 grains are similar for the annealed and chemically abraded grains and are parallel to the fit for the untreated grains, comparable to the pattern observed for Temora-2. The downhole fractionation patterns for the SA04-13 grains evolve steeply throughout the entirety of the ablation with no significant tapering of the function within the 40 second ablation; differences due to variable treatment of the grains are minor. Finally, the downhole fit for ST05-03 zircon is similar for all grains for the first half 52Chapter 2of the ablation, but flattens more rapidly for the treated samples during the second half of the ablation, similar to the change observed in the Plešovice grains, but with a reversal of the effect on annealed and chemically abraded grains relative to the untreated.2 .5 .3 . Application of exponential downhole fractionation correctionApplying an ideal downhole fit correction to raw ratios of Pb/U results in flat corrected-Pb/U throughout the entirety of the ablation (Fig. 2.8). While the absolute value of the corrected Pb/U is inconsequential, because the corrected value will be standardized with a reference material with a known ratio, it is important that the corrected value remain constant over the duration of the ablation. Using an improper correction will result in certain portions of the corrected-Pb/U changing over time, resulting in either over- or under-corrected ratios, depending on the time segments chosen for the integrations. The effect of using the downhole correction fit of untreated zircon to correct the analysis of annealed and chemically abraded grains is investigated below by assessing the significance of the differences in corrected ratios (Fig. 2.8).  This approach was chosen because the vast majority of LA-ICP-MS labs operate with untreated reference materials and may consider treatment of their unknowns to potentially improve results. Assessing the effect of correcting treated grains with the patterns of untreated reference materials presents a realistic scenario that has not yet been fully explored.In Plešovice zircon, applying the fit parameters of untreated grains to annealed and chemically abraded zircon results in evolving 206Pb/238U throughout the ablation time (Fig. 2.8a). Analysis of the annealed grains shows a constant increase in 206Pb/238U, whereas 206Pb/238U initially decreases through the first 10 seconds of the ablation for the chemically abraded grains before gradually rising during the remainder of the ablation. The annealed and chemically abraded Temora-2 zircon grains show downhole behaviour similar to the untreated grains (Fig. 2.8b) with overcorrected 206Pb/238U in the first 10 seconds and constant ratios thereafter. Pre-treatment appears to have the most significant impact on the downhole fractionation behaviour of 91500 zircon resulting in corrected annealed and chemically abraded ratios that contain both increasing and decreasing segments (Fig. 2.8c). Fit parameters for downhole fractionation in the three untreated zircon reference materials (Plešovice, Temora-2, 91500) were then applied to the untreated grains of the three 53Chapter 20 5 10 15 20 25 30 35 400 5 10 15 20 25 30 35 400 5 10 15 20 25 30 35 400.0350.0400.0450.0500.0550.060(a) Plešovice(b) Temora-2(c) 91500206Pb238U0.120.130.140.150.160.170.0450.0500.0550.0600.065ablation time (s)UntreatedAnnealedChemical AbrasionFigure 2 .8 . Diagrams of ablation time (in seconds) vs. 206Pb/238U showing time-resolved ratios (coloured lines) for the analysis of untreated grains (solid lines), annealed grains (long-dashed lines), and grains that underwent chemical abrasion (short-dashed lines) for the three zircon reference materials Plešovice (panel a), Temora-2 (panel b), 91500 (panel c). The ratios were corrected using the downhole fit parameters calculated from the analysis of untreated zircon grains from each sample. Black lines represent the exponential fits to each sample as shown in Figure 2.7. The corrected fit for the untreated grains is horizontal in all panels. 54Chapter 2unknown zircon samples (SR336, SA04-13, ST05-03) to assess the effectiveness of the correction (Fig. 2.9a-c). The corrected 206Pb/238U decreases constantly throughout the ablation of SR336 grains when using the Plešovice correction, but is relatively flat when corrected using both Temora-2 and 91500 values (Fig. 2.9a). This result is distinct from the effect of using the three reference zircon samples to correct the analyses of SA04-13. Plešovice-corrected SA04-13 zircon shows the most stable 206Pb/238U throughout the ablation; Temora-2 initially produces decreasing ratios that then gradually increase, and 91500 results in consistently increasing ratios throughout the entire 40 second ablation (Fig. 2.9b). For the ST05-03 zircon grains, no downhole fractionation parameters produce ideal corrected-Pb/U for the full ablation time (Fig. 2.9c). Corrections with Plešovice result in ratios that increase for the first half of the ablation before gradually decreasing, whereas both Temora-2 and 91500 yield similar results to those observed for SA04-13, with increasing 206Pb/238U throughout the entire ablation. 2 .6 . Discussion2 .6 .1 . Effect of pre-treatment on downhole fractionation For optimal U-Pb zircon geochronology by LA-ICP-MS, the impact of downhole fractionation must be characterized, quantified, modelled, and systematically corrected. A critical component of U-Pb zircon analysis by laser ablation involves matching the matrices of the unknowns with externally calibrated natural reference materials. Among the characteristics that have the potential to control the ablation behaviour of zircon (e.g., color, orientation, metamictization), crystallinity has been shown to have the strongest effect on downhole fractionation behaviour (Klötzli et al., 2009; Allen and Campbell, 2012). Pre-treatment protocols that aim to correct for differences in grain crystallinity can be effective in normalizing downhole behaviour between reference materials and unknowns. Specifically, both thermal annealing (i.e., recrystallization) and chemical abrasion can minimize differences in downhole behaviour between reference materials and unknowns, and thereby improve corrections when applied to zircon (Crowley et al., 2014; Solari et al., 2015). This study provides the first and most comprehensive quantitative analysis of the effects of downhole fractionation corrections using a range of reference materials with different degrees 55Chapter 20.160.180.200.220.240.260.280.250.300.350.400.450.500.350.400.450.500.550.600 5 10 15 20 25 30 35 400 5 10 15 20 25 30 35 400 5 10 15 20 25 30 35 40(a) SR336 (UT)(b) SA04-13 (UT)(c) ST05-03 (UT)raw averageself-correctedPL-correctedTemora-2-corrected91500-correctedablation time (s)206Pb238UFigure 2 .9 . Diagrams of ablation time (in seconds) vs. 206Pb/238U showing time-resolved ratios for the analysis of untreated (UT) in-house zircon grains corrected using the downhole fractionation fit parameters of Plešovice (PL, green lines), Temora-2 (red lines), and 91500 (blue lines). (a) SR336 (UT), (b) SA04-13 (UT), (c) ST05-03 (UT). Thinner lines represent means of the LA-ICP-MS analyses and thicker lines indicate exponential fits (for raw average) or corrected exponential fits.56Chapter 2of pre-treatment applied to samples with variable Pb/U extending from the Mesoproterozoic back to the Neoarchean. Both annealing and chemical abrasion techniques impact the rate at which zircon ablates when compared with untreated varieties of each sample (Fig. 2.7), however, these effects are not consistent across all populations of zircon. Each of the three in-house zircon samples that were treated as unknowns (Laramie, Bushveld, Stillwater) were corrected using untreated varieties of the three zircon reference materials (Plešovice, Temora-2, 91500). The results of using different reference materials to correct and calibrate the three in-house zircon samples in this study are shown as concordia diagrams and presented in different perspectives in Figures 2.10-2.15. The results are displayed for all three unknowns as reduced using one of the three reference materials (Fig 2.10, Plešovice; Fig. 2.11, Temora-2; Fig. 2.12, 91500) and for each of the unknowns as reduced using each of the three reference materials (Fig. 2.13, SR336; Fig. 2.14, SA04-13; Fig. 2.15, ST05-03). Based on the relative effectiveness of the downhole correction that was applied (i.e., similarity of the downhole fit between the reference and the unknown), the resulting 206Pb/238U, 207Pb/235U, 207Pb/206Pb dates of the samples vary significantly with respect to each other and when compared to the published accepted ID-TIMS or CA-ID-TIMS ages (Table 2.5, Fig. 2.16). For Laramie zircon using Plešovice as a reference standard, the downhole fractionation corrections yield dates that are close to the ID-TIMS age (SR336, Fig. 2.13). For the Bushveld zircon (SA04-13, Fig. 2.14), the 206Pb/238U dates are all significantly below the CA-ID-TIMS age, with Plešovice as the reference providing the closest dates, followed by 91500. Using Temora-2 did not produce satisfying downhole corrections for either SR336 or ST05-03, and the resultant U-Pb dates show larger deviations from the accepted ID-TIMS ages compared with the other two reference materials (Fig 2.11).Stillwater AN2 zircon has been proposed as a U-Pb reference material for LA-ICP-MS dating of Archean zircon (Wall et al., 2016). In Wall et al. (2016), untreated 91500 grains were used as the reference and 58 analyses from 19 grains yielded overlapping 207Pb/206Pb dates from 2680 to 2770 Ma, a weighted mean 207Pb/206Pb date of 2715 ± 9 Ma and a U-Pb concordia age of 2710.3 ± 5.0 Ma. The ages determined by this study broadly agree with these LA-ICP-MS and TIMS dates (Fig. 2.15). Using 91500 as a reference reproduces the reported age of the sample for all three treatment protocols, whereas Temora-2 yields significant biases compared 57Chapter 22600270028002600270028002600270028000.220.230.240.250.280.270.260.320.340.360.380.400.460.480.500.520.580.560.542.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 4.00.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.8511 1312 14 15 1611 1312 14 15 16 11 1312 14 15 16(a) SR336 (UT) (b) SR336 (AN) (c) SR336 (CA)(d) SA04-13 (UT) (e) SA04-13 (AN) (f) SA04-13 (CA)(g) ST05-03 (UT) (h) ST05-03 (AN) (i) ST05-03 (CA)206 Pb/238 U207Pb/235UUntreatedPlešoviceAnnealed Chemical Abrasion135014501550135014501550135014501550185019502050215018501950205021501850195020502150206Pb/238U = 1432 ± 11 MaMSWD = 0.98n = 20206Pb/238U = 1409 ± 11 MaMSWD = 0.61n = 16206Pb/238U = 1425 ± 15 MaMSWD = 1.4n = 15206Pb/238U = 2025 ± 14 MaMSWD = 0.46n = 13206Pb/238U = 2006 ± 19 MaMSWD = 1.8n = 16206Pb/238U = 1998 ± 13 MaMSWD = 0.73n = 16206Pb/238U = 2776 ± 16 MaMSWD = 0.75n = 16206Pb/238U = 2710 ± 19 MaMSWD = 1.4n = 18206Pb/238U = 2688 ± 15 MaMSWD = 0.73n = 16PlešovicePlešoviceFigure 2 .10 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the three in-house samples as reduced in Iolite 2.5 using Plešovice as the reference zircon. The panels are arranged to show the results for the different samples (SR336, upper row; SA04-13, middle row; ST05-03, lower row) with different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion.58Chapter 22600270028002600270028000.220.230.240.250.280.270.260.320.340.360.380.400.460.480.500.520.580.560.542.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 4.00.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.8511 1312 14 15 1611 1312 14 15 16 11 1312 14 15 16206 Pb/238 U207Pb/235U(a) SR336 (UT) (b) SR336 (AN) (c) SR336 (CA)(d) SA04-13 (UT) (e) SA04-13 (AN) (f) SA04-13 (CA)(g) ST05-03 (UT) (h) ST05-03 (AN) (i) ST05-03 (CA)135014501550135014501550135014501550185019502050215018501950205021501850195020502150260027002800206Pb/238U = 1427 ± 14 MaMSWD = 2.1n = 20206Pb/238U = 1403.4 ± 9.3 MaMSWD = 1.1n = 16206Pb/238U = 1405 ± 15 MaMSWD = 2.7n = 15206Pb/238U = 1993.5 ± 9.5 MaMSWD = 0.87n = 13206Pb/238U = 2009 ± 17 MaMSWD = 3.5n = 16206Pb/238U = 2014 ± 12 MaMSWD = 1.5n = 16206Pb/238U =2685 ± 18 MaMSWD = 2.4n = 16206Pb/238U = 2652 ± 19 MaMSWD = 4.0n = 18206Pb/238U = 2668 ± 14 MaMSWD = 2.1n = 16Temora-2Temora-2Temora-2Untreated Annealed Chemical AbrasionFigure 2 .11 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the three in-house samples as reduced in Iolite 2.5 using Temora-2 as the reference zircon. The panels are arranged to show the results for the different samples (SR336, upper row; SA04-13, middle row; ST05-03, lower row) with different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion.59Chapter 22600270028002600270028002600270028000.220.230.240.250.280.270.260.320.340.360.380.400.460.480.500.520.580.560.542.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 4.00.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.8511 1312 14 15 1611 1312 14 15 16 11 1312 14 15 16206 Pb/238 U207Pb/235U(a) SR336 (UT) (b) SR336 (AN) (c) SR336 (CA)(d) SA04-13 (UT) (e) SA04-13 (AN) (f) SA04-13 (CA)(g) ST05-03 (UT) (h) ST05-03 (AN) (i) ST05-03 (CA)135014501550135014501550135014501550185019502050215018501950205021501850195020502150206Pb/238U = 1453 ± 11 MaMSWD = 1.4n = 20206Pb/238U = 1425.3 ± 9.5 MaMSWD = 1.1n = 16206Pb/238U = 1436 ± 15 MaMSWD = 2.7n = 15206Pb/238U = 2006.2 ± 9.2 MaMSWD = 0.85n = 13206Pb/238U = 2004 ± 18 MaMSWD = 3.7n = 16206Pb/238U = 1994 ± 11 MaMSWD = 1.2n = 16206Pb/238U = 2740 ± 15 MaMSWD = 1.7n = 16206Pb/238U = 2706 ± 18 MaMSWD = 3.5n = 18206Pb/238U = 2691 ± 15 MaMSWD = 2.5n = 16915009150091500Untreated Annealed Chemical AbrasionFigure 2 .12 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the three in-house samples as reduced in Iolite 2.5 using 91500 as the reference zircon. The panels are arranged to show the results for the different samples (SR336, upper row; SA04-13, middle row; ST05-03, lower row) with different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion.60Chapter 21350145015501350145015501350145015501350145015501350145015501350145015501350145015501350145015501350145015502.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 2.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 4.00.220.230.240.250.280.270.260.220.230.240.250.280.270.260.220.230.240.250.280.270.26 PlešoviceUntreated Annealed Chemical AbrasionTemora-291500206 Pb/238 U(a) (b) (c) (d) (e) (f) (g) (h) (i) 207Pb/235U206Pb/238U = 1432 ± 11 MaMSWD = 0.98n = 20206Pb/238U = 1409 ± 11 MaMSWD = 0.61n = 16206Pb/238U = 1425 ± 15 MaMSWD = 1.4n = 15206Pb/238U = 1427 ± 14 MaMSWD = 2.1n = 20206Pb/238U = 1403.4 ± 9.3 MaMSWD = 1.1n = 16206Pb/238U = 1405 ± 15 MaMSWD = 2.7n = 15206Pb/238U = 1453 ± 11 MaMSWD = 1.4n = 20206Pb/238U = 1425.3 ± 9.5 MaMSWD = 1.1n = 16206Pb/238U = 1436 ± 15 MaMSWD = 2.7n = 15Figure 2 .13 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the Mesoproterozoic sample SR336 (Laramie) for untreated and treated grains as reduced in Iolite 2.5 using each of the three reference zircon materials. The panels are arranged to show the results using corrections based on Plešovice (upper row), Temora-2 (middle row), and 91500 (lower row) using different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel.61Chapter 21850195020502150185019502050215018501950205021500.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.850.320.340.360.380.400.320.340.360.380.400.320.340.360.380.40206 Pb/238 U207Pb/235UPlešoviceUntreated Annealed Chemical AbrasionTemora-291500(a) (b) (c) (d) (e) (f) (g) (h) (i) 185019502050215018501950205021501850195020502150185019502050215018501950205021501850195020502150206Pb/238U = 2025 ± 14 MaMSWD = 0.46n = 13206Pb/238U = 2006 ± 19 MaMSWD = 1.8n = 16206Pb/238U = 1998 ± 13 MaMSWD = 0.73n = 16206Pb/238U = 1993.5 ± 9.5 MaMSWD = 0.87n = 13206Pb/238U = 2009 ± 17 MaMSWD = 3.5n = 16206Pb/238U = 2014 ± 12 MaMSWD = 1.5n = 16206Pb/238U = 2006.2 ± 9.2 MaMSWD = 0.85n = 13206Pb/238U = 2004 ± 18 MaMSWD = 3.7n = 16206Pb/238U = 1994 ± 11 MaMSWD = 1.2n = 16Figure 2 .14 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the Paleoproterozoic sample SA04-13 (Bushveld) for untreated and treated grains as reduced in Iolite 2.5 using each of the three reference zircon materials. The panels are arranged to show the results using corrections based on Plešovice (upper row), Temora-2 (middle row), and 91500 (lower row) using different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the CA-ID-TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel.62Chapter 226002700280026002700280026002700280026002700280026002700280011 1312 14 15 1611 1312 14 15 1611 1312 14 15 160.460.480.500.520.580.560.540.460.480.500.520.580.560.540.460.480.500.520.580.560.54260027002800206 Pb/238 U207Pb/235UPlešoviceUntreated Annealed Chemical AbrasionTemora-291500(a) (b) (c) (d) (e) (f) (g) (h) (i) 260027002800260027002800260027002800206Pb/238U = 2776 ± 16 MaMSWD = 0.75n = 16206Pb/238U = 2710 ± 19 MaMSWD = 1.4n = 18206Pb/238U = 2688 ± 15 MaMSWD = 0.73n = 16206Pb/238U =2685 ± 18 MaMSWD = 2.4n = 16206Pb/238U = 2652 ± 19 MaMSWD = 4.0n = 18206Pb/238U = 2668 ± 14 MaMSWD = 2.1n = 16206Pb/238U = 2740 ± 15 MaMSWD = 1.7n = 16206Pb/238U = 2706 ± 18 MaMSWD = 3.5n = 18206Pb/238U = 2691 ± 15 MaMSWD = 2.5n = 16Figure 2 .15 . Concordia diagrams for the U-Pb geochronological results determined by LA-ICP-MS of zircon from the Neoarchean sample ST05-03 (Stillwater) for untreated and treated grains as reduced in Iolite 2.5 using each of the three reference zircon materials. The panels are arranged to show the results using corrections based on Plešovice (upper row), Temora-2 (middle row), and 91500 (lower row) using different pre-treatment protocols (untreated, left column; annealed, middle column; chemical abrasion, right column). The concordia curve (grey line) is indicated with ages in millions of years (Ma). Each ellipse represents the results of a single LA-ICP-MS ablation with propagated uncertainties reported as 2σ. The white star indicates the CA-ID-TIMS age determined for each sample (see Table 2.1). For reference, the 206Pb/238U dates are indicated in the boxes in the lower right of each panel.63Chapter 2Table 2 .5 . Summary of ages of zircon from the in-house samples based on different pre-treatment protocols206Pb/238U Weighted Mean (Ma)1 207Pb/235U Weighted Mean (Ma) 207Pb/206Pb Weighted Mean (Ma)Reference Zircon Plešovice Temora-2 91500 Plešovice Temora-2 91500 Plešovice Temora-2 91500Sample Age (Ma) Treatment2SR336Larmie 1435.63UT 1432 ± 11 1427 ± 14 1453 ± 11 1416 ± 13 1480 ± 15 1440 ± 15 1403 ± 26 1523 ± 26 1406 ± 26AN 1409 ± 11 1403.4 ± 9.3 1425.3 ± 9.5 1405 ± 15 1452 ± 17 1417 ± 18 1383 ± 33 1489 ± 33 1384 ± 33CA 1425 ± 15 1405 ± 15 1436 ± 15 1411 ± 15 1447 ± 17 1415 ± 18 1379 ± 31 1477 ± 30 1382 ± 31SA04-13Bushveld 2057.044UT 2025 ± 14 1993.5 ± 9.3 2006.2 ± 9.2 2026 ± 16 2059 ± 19 2029 ± 19 2027 ± 22 2109 ± 21 2033 ± 22AN 2006 ± 19 2009 ± 17 2004 ± 18 2037 ± 14 2065 ± 17 2041 ± 17 2093 ± 15 2169 ± 15 2099 ± 15CA 1998 ± 13 2014 ± 12 1994 ± 11 2014 ± 14 2039 ± 17 2019 ± 17 2039 ± 17 2107 ± 17 2048 ± 17ST05-03Stillwater 2710.445UT 2776 ± 16 2685 ± 18 2740 ± 15 2716 ± 12 2732 ± 16 2716 ± 16 2686.4 ± 9.0 2740.8 ± 8.9 2696.0 ± 9.0AN 2710 ± 19 2652 ± 19 2706 ± 18 2714 ± 12 2724 ± 15 2714 ± 16 2699.1 ± 7.8 2746.8 ± 7.8 2709.8 ± 8CA 2688 ± 15 2668 ± 14 2691 ± 15 2704 ± 12 2723 ± 15 2718 ± 16 2700.7 ± 8.7 2742.6 ± 8.7 2712.8 ± 8.71. All uncertainties are 2σ2. Abbreviations: UT, untreated; AN, annealed; CA, chemical abrasion3. Scoates and Chamberlain (2003)4. Scoates and Wall (2015)5. Wall et al. (2016)64Chapter 2136013801400142014401460148015001520154013601380140014201440146014801500152015401960198020002020204020602080264026602680270027202740276027802800200020402080212021602200PL Tem-2 91500 PL Tem-2 91500 PL Tem-2 91500PL Tem-2 91500 PL Tem-2 91500 PL 91500Weighted Mean Age (Ma)Reference Zircon Used206Pb/238U Date (Ma) 207Pb/235U Date (Ma) 207Pb/206Pb Date (Ma)(a) SR336 (b)  SR336 (c) SR336(d) SA04-13 (e) SA04-13 (f) SA04-13 (g) ST05-03 (h) ST05-03  (i) ST05-03  19802000202020402060264026602680270027202740276027802800untreatedannealedchemical abrasionSR336SA04-13ST05-03Figure 2 .16 . Summary figure showing the effect of using the three reference zircon materials (Plešovice, Temora-2, 91500) for downhole fractionation correction on the weighted mean 206Pb/238U, 207Pb/235U, and 207Pb/206Pb ages for the untreated and treated zircon grains from three samples (SR336, SA04-13, ST05-03). The ID-TIMS age for each sample is noted by a solid- line (see Table 2.1). Age scales are constant across each sample with the exception of diagram (f) due to the larger uncertainties and variation present in the sample. Abbreviations: PL, Plešovice; Tem-2, Temora-2. Uncertainties shown represent 2σ propagated error on each weighted mean.65Chapter 2to either 91500 or Plešovice, especially for the 206Pb/238U dates of the untreated grains. When comparing downhole fractionation corrections of ST05-03 using the three zircon references (Fig. 2.9c), neither 91500 nor Plešovice result in ideal (flat) corrections, however, the very different downhole fit resulting from Temora-2 produces a constant 206Pb/238U in the corrected Stillwater AN2 zircon that yields inaccurate dates (Fig. 2.16).2 .6 .2 . Impact on LA-ICP-MS methodologiesDuring data reduction following LA-ICP-MS analysis of an unknown zircon, it is common to trim time sections from the record of a full ablation due to integration of inclusions, zoning, or ablating through small or thin zircon grains into the epoxy. When only a partial ablation can be utilized, it is important that application of the downhole fractionation function properly corrects the data at each time point (i.e., depth) during the analysis. We observed that various correction factors tended to over-correct or under-correct the analytical data throughout the course of a 40 second ablation and that the corrected ratios gradually changed with time (Figs. 2.8, 2.9). For example, if an ablation passed through Stillwater AN2 zircon 15 seconds into the analysis, the resulting downhole correction would be significantly under-corrected using Temora-2 as the reference standard, whereas using 91500 as the reference standard would produce a relatively flat correction (Fig 2.9c). These results confirm that an optimal correction requires that unknown zircon grains be matrix-matched to their reference materials so that they behave similarly throughout the ablation. The experiments conducted in this study were designed to assess the accuracy of specific downhole corrections on both untreated reference materials and treated zircon from the three mafic intrusions. The absolute ages determined for the treated grains in this study relied on matrix matching and may have yielded different results if they had instead been corrected to reference zircon that had been pre-treated in the same manner. Most published U-Pb zircon analyses by LA-ICP-MS are obtained using untreated reference materials to calibrate their unknowns, therefore this study focused solely on reducing treated unknowns with untreated reference materials. Further study will be required to reduce pre-treated reference materials with treated unknowns to fully determine the effect of the treatment. Consistent with Allen and Campbell (2012), we find that the analysis of annealed zircon showed improvement in the 66Chapter 2consistency of the ablation rate and minimized downhole fractionation differences between samples. Results from the chemically abraded zircon grains in this study, however, did not typically exhibit improvements in their downhole fractionation patterns when compared with treatments by thermal annealing alone. The significant improvements to U-Pb zircon geochronology by LA-ICP-MS reported in Crowley et al. (2014) were not observed in this study beyond the effects of annealing, suggesting that the additional time and cost associated with chemical leaching may not make the chemical abrasion step a practical addition to LA-ICP-MS lab protocols. However, as none of the analyzed unknown zircon grains showed evidence for significant Pb loss, we recommend that the impact of the application of chemical abrasion to radiation-damaged zircon continue to be actively investigated. The three zircon samples analyzed here were from mafic intrusions with relatively low U contents, and as a result, their intact crystal structure did not require pre-treatments in comparison to zircon from other settings.2 .7 . ConclusionsThree zircon samples from Proterozoic to Archean mafic layered intrusions were investigated to determine how representative zircon reference materials (Plešovice, Temora-2, 91500) correct for variable downhole fractionation by LA-ICP-MS. All samples analyzed by LA-ICP-MS produce distinct downhole fractionation behaviours and require application of an exponential downhole correction model. It is important that appropriate reference materials are available to accurately calibrate unknowns and that matrix-related biases are minimized. We found that the most robust correction method was to characterize downhole fractionation in different reference materials and then match the corrections to the unknowns that behaved similarly to the reference material during ablation. Different pre-treatment protocols were applied to the reference and in-house zircon to assess the relative effects of pre-treatment on ablation characteristics. In most cases, annealing zircon grains prior to LA-ICP-MS analysis lessened the magnitude of U-Pb mass fractionation during laser ablation by 0.1-3.5%, although some samples showed negligible effects or even an increase in fractionation downhole. Chemical leaching of the annealed grains appeared to have little effect on the ablation behaviour of the analyzed low-U zircon (7-334 ppm) beyond the effects of annealing. This study highlights the importance of developing a comprehensive understanding of the physical ablation characteristics of zircon 67Chapter 2reference materials and unknowns analyzed by LA-ICP-MS to adequately assess and correct for downhole fractionation in U-Pb geochronology, especially for Proterozoic to Archean samples.68Chapter 3Chapter 3Chapter 3Trace Element Systematics of Zircon and Rutile from the Bushveld Complex, South Africa69Chapter 33 .1 . IntroductionLayered intrusions are sill-like plutons that typically crystallize from mafic-ultramafic magmas in the continental crust and provide ideal natural laboratories for studying magmatic evolution and differentiation in time and space (Wager and Brown, 1968; Cawthorn, 1996; Irvine et al., 1998; Maier et al., 2001; Charlier et al., 2015). The study of layered intrusions has typically focused on the textural setting and major element chemistry of the primary cumulus mineral assemblage formed at high temperature (i.e., liquidus minerals: olivine, pyroxene, spinel, plagioclase), however, recent research is revealing that there is much to be learned from examining the final stages of crystallization of cumulates near the solidus (Holness et al., 2011; Scoates and Wall, 2015; Zeh et al., 2015). These late-stage processes, which can include textural maturity (Holness et al., 2007; Holness and Vernon, 2015), accessory mineral crystallization (Scoates and Chamberlain, 1995; Scoates and Wall, 2015), isotopic mineral disequilibrium (Tepley and Davidson, 2003; Chutas et al., 2012), and even liquid immiscibility (VanTongeren and Mathez, 2012; Veksler and Charlier, 2015), provide critical insight into the magmatic history of these remarkable intrusions. The mineral zircon (ZrSiO4) is now recognized as a relatively common accessory mineral in mafic and ultramafic rocks of layered intrusions (Scoates and Chamberlain, 1995; Scoates and Friedman, 2008; Wotzlaw et al., 2012; Scoates and Wall, 2015; Zeh et al., 2015). Zircon is widely used in U-Th-Pb geochronology (e.g., Silver and Deutsch, 1963; Schoene, 2013; Barboni and Schoene, 2014), and increasingly used in Hf isotope geochemistry (e.g., Griffin et al., 2002; Belousova et al., 2006, 2010) and O isotope geochemistry (e.g., Valley, 2003; Hawkesworth and Kemp, 2006). A wide range of incompatible trace elements are readily incorporated into the zircon crystal structure, leading to its emergence as a powerful tool for identifying and fingerprinting magmatic sources and processes (e.g., Belousova et al., 2002a; Grimes et al., 2009, 2015; Claiborne et al., 2010). Rare earth element concentrations and ratios in zircon can be used to monitor crystallization processes and magmatic conditions (e.g., Belousova et al., 2006; Trail et al., 2012; Burnham and Berry, 2014). In addition, the temperature-dependent substitution of Ti4+ in its structure allows zircon to serve as a robust thermometer (Ti-in-zircon thermometry) under a range of geologic conditions when in equilibrium with quartz (SiO2) and rutile (TiO2) (Watson and Harrison, 2005; Ferry and Watson, 2007). Other accessory minerals reported from 70Chapter 3mafic layered intrusions with applications to U-Pb geochronology and trace element-isotopic geochemistry include baddeleyite (ZrO2), apatite (Ca5(PO4)3(F, Cl, OH)), rutile (TiO2), and titanite (CaTiSiO5) (Scoates and Wall, 2015).In this study, the trace element geochemistry of accessory zircon and rutile were investigated from samples that span nearly the entire 8 km-thick stratigraphic sequence of the Paleoproterozoic Bushveld Complex, South Africa, including the overlying granites and granophyres. The textural setting of zircon and rutile was established by combined petrography-scanning electron microscopy (SEM), the internal structure and zoning of individual grains were imaged by SEM- cathodoluminescence (SEM-CL), and their trace element concentrations were determined in situ by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS; n = 247 analyses). The trace element variations were then used to constrain the late-stage crystallization history of fractionated interstitial melt in the cumulates and granites and they allow for evaluation of petrologic relationships, including thermometry (e.g., Ti-in-zircon, Zr-in-rutile), between the major zones of the intrusion and between the uppermost mafic rocks and the roof granites. A forward geochemical model is then developed for proposed Bushveld parental magmas to track the evolution of late-stage fractionated melt down to temperatures approaching the solidus with implications for the consolidation history of mafic layered intrusions in general.3 .2 . Geologic setting of the Bushveld ComplexThe Bushveld Complex in South Africa is the world’s largest mafic-ultramafic layered intrusion and was emplaced into the Kaapvaal Craton at ca. 2.06 Ga (Fig. 3.1) (Eales et al., 1993; Eales and Cawthorn, 1996; Cawthorn et al., 2009; Scoates and Wall, 2015; Zeh et al., 2015). Covering more than 95,000 km2 (Finn et al., 2015), the Bushveld Complex is associated with a number of satellite intrusions (e.g., Uitkomst, Losberg, Moloto, Rhenosterhoekspruit) and overlying volcanic sequences within the Bushveld Magmatic Province. The Bushveld Complex includes the Rustenburg Layered Suite, an up to 8 km thick sequence of stratified mafic and ultramafic cumulates that hosts world-class deposits of chromium, platinum group elements (PGE), and vanadium (Eales and Cawthorn, 1996; Maier, 2005; Cawthorn et al., 2009; Maier et al., 2013) (Fig. 3.2). In the Eastern Limb, the Upper Zone is in direct contact with contemporaneous volcanic rocks of the Rooiberg Group, the Stavoren Granophyre of the 71Chapter 3100 km26°E 27°E 28°E 29°E26°S25°S24°S28°E 29°E 30°ENTMLAlkaline IntrusionsRashoop Granophyre SuiteRustenburg Layered SuiteRooiberg GroupTransvaal SupergroupLebowa Granite SuitefaultskimberlitesPretoriaJohannesburgRustenburgPietersburgLydenburgBushveldComplexFigure 3 .1 . Generalized geologic map of the Bushveld Complex in South Africa locations of the analyzed samples containing zircon and rutile) in this study noted by orange stars. The location of the PGE-rich Merensky Reef is indicated by the white dashed line and divides the Rustenburg Layered Suite into two units with the purple unit representing the Marginal Zone, Lower Zone, and Critical Zone, and the green unit representing the stratigraphically higher Main Zone and Upper Zone. Felsic roof granites of the Rashoop Granophyre Suite and Lebowa Granite Suite are shown in pink and red, respectively. Map modified from Kinnaird et al. (2005) with additional features from Webb et al. (2004) and Vorster (2003). Major faults and fault segments related to the transpressional Thabazimbi-Murchison Lineament (TML) are also indicated (Good and de Wit, 1997). 72Chapter 3Bastard ReefTennis Ball MarkerMerensky ReefBoulder BedUpper GroupChromititesMiddle GroupChromititesLower GroupChromitites1234534212176DT28-912B00-1-6B4LZ10-02TW477661.15TW477SA04-06439.15TW477206.14DT2 882.82B90-7(0)SA04-08SA04-13MPD24D225.8B90-12000-28003100-2200520-10002300-4300780-800820-1390Upper ZoneFelsicRoof RocksMain ZoneCritical ZoneMarginal ZoneLower ZoneUpperLowerMERENSKY REEFPyroxenite MarkerMMLM21MMMMMMB10-056B10-054B07-051B07-040B07-020B90-1B06-060DT28-912B00-1-6LZ10-02TW477-439.15TW477 206.14SA04-06TW477-661.15MPD24D2 25.8DT2 882.82B90-7(0)SA04-08SA04-13B4B3B2B1UUMZFigure 3 .2 . Schematic stratigraphic sections of the Bushveld Complex showing samples examined in this study. Sample locations are indicated by stars with pink stars representing samples that yielded zircon for study and yellow stars indicating samples that did not contain zircon. The left column shows a complete section of the Rustenburg Layered Suite and roof rocks with maximum unit thickness in meters in the format (Western Limb-Eastern Limb) taken from Cawthorn et al. (2009). The PGE-rich Merensky Reef in the Upper Critical Zone is shown as the white dashed line and the magnetitite layers in the Upper Zone are indicated with black dashed lines. B1, B2, and B3 refer to marginal rocks from Barnes et al. (2010). UUMZ = Upper and Upper Main Zone from VanTongeren (2010). The right column shows a detailed section of the Lower Zone and Critical Zone where most of the samples are located with major chromitites, PGE reefs, and other horizons indicated. Stratigraphic column modified from Scoates and Friedman (2008). Abbreviations: M=Magnetitite layer, MML=Main Magnetitite Layer, M21=Magnetitite layer 21.73Chapter 3Rashoop Granophyre Suite, and the Nebo Granite of the Lebowa Granite Suite, all of which show complex field and petrogenetic relationships with the Rustenburg Layered Suite (Twist and French, 1983; Walraven, 1985; VanTongeren et al., 2010; Mathez et al., 2013; VanTongeren and Mathez, 2015) (Fig. 3.3). The Bushveld Complex outcrops in five major limbs – Eastern, Western, Far Western, Northern, Southern – stretching nearly 400 km from east-to-west with the limbs dipping gently inward to form a bowl-shaped intrusion (Cawthorn and Webb, 2001; Webb et al., 2011). The limbs appear to be interconnected at depth based on geophysical evidence, stratigraphic relations, and xenolith studies (Hall, 1932; Cawthorn and Walraven, 1998; Webb et al., 2011). The Eastern Limb of the Bushveld Complex, which has been mapped in the most detail (von Gruenewaldt, 1973; Cameron, 1978; Sharpe, 1981; Harmer and Sharpe, 1985; Molyneaux, 2008) (Fig. 3.3), provides the best surficial exposures of the intrusion due to relatively rugged topography and lack of vegetation compared to the Western and Northern limbs. One of the best studied localities in the Eastern Limb is Cameron’s Section, an exposure of the Lower Zone and Critical Zone in the Olifants River Trough that has been the subject of extensive study over the past several decades (Cameron, 1978, 1979, 1980; Willmore et al., 2000) and a number of samples examined in detail in this study are from Cameron’s section.3 .2 .1 . Geology of the Rustenburg Layered SuiteRocks of the Rustenburg Layered Suite are divided from base-to-top into the Marginal, Lower, Critical, Main, and Upper zones with most contacts based on changes in primocryst mineralogy and significant marker horizons such as the PGE-rich Merensky Reef (Kruger et al., 1987; Eales and Cawthorn, 1996; Cawthorn et al., 2009). Parental magmas to the Bushveld Complex have been proposed for the four major zones based on the chemistry of marginal rocks and sills found in contact with the Rustenburg Layered Suite (Fig. 3.2) (Sharpe, 1981, 1985; Barnes et al., 2010). The Marginal Zone, which typically contains fine-grained norites to gabbronorites, is up to a few hundred meters thick when present and may be found in contact with the Lower Zone, the Critical Zone, and the Main Zone in the Eastern Limb (Sharpe, 1981; Maier et al., 2013) (Fig. 3.3). Xenoliths of the floor, including dolomite and quartzite, are common in the Marginal Zone. The magmas that produced the Marginal Zone may represent 74Chapter 329°15’E 29°30’E 29°45’E 30°00’E 30°15’E 30°30’E29°15’E 29°30’E 29°45’E 30°00’E 30°15’E 30°30’E25°45’S25°30’S25°15’S25°00’S24°45’S24°30’S24°15’S25°45’S25°30’S25°15’S25°00’S24°45’S24°30’S24°15’S0 5 10 15 20KilometersNEastern Bushveld ComplexSteelport RiverSteelport FaultWonderkop FaultOlifants RiverDwars RiverSpekboom RiverOlifants RiverLoksop DamR37R25R33R555R540R555R104R579R37N11N4BurgersfortSteelpoortStoffbergBelfastGroblersdalB90-1(0)B90-7MP-24D2SA04-08B00-1-6DT28-912TW477-661LZ10-02B07-051B07-040B10-056B10-054HornfelsNot MappedDolomite / DiabaseQuartziteMarginal ZoneDullstroom volcanic rocksLower ZoneCritical ZoneMain ZoneUpper ZoneMagnetite SeamStavoren GranophyreLeptiteRoadSample (underground)Sample (surface)FaultMerensky Reef (trace)Rooiberg FelsiteAlkaline IntrusionsNebo GraniteRustenberg Layered SuiteBushveld ComplexRiverLegendSymbolsFigure 3 .3 . Geologic map of the Eastern Limb of the Bushveld Complex modified from Molyneaux (2008). Locations for samples that yielded zircon for this study are indicated by white filled circles (drill core/underground) or squares (surface). Note the discontinuous nature of the Marginal Zone, the restricted area of the Critical Zone, and the major trough structure in the Burgersfort area dominated by rocks of the Lower Zone.75Chapter 3residual melts derived from crystallization of the main Bushveld magmas based on intrusive contacts with the Critical Zone rocks and on the presence of rare anorthosite xenoliths (Sharpe, 1981; Eales and Cawthorn, 1996). Some of the marginal rocks and sills to the Marginal Zone are considered to represent parental melts to the Bushveld Complex based on trace element concentrations, platinum group element ratios, and modelled crystallization sequences (Barnes et al., 2010).The Lower Zone has a maximum thickness of 1.4 km in the Eastern Limb and is composed primarily of adcumulate dunites and harzburgites at the base and top of the unit with lesser volumes of orthopyroxenite in the middle (Cameron, 1978; Maier et al., 2013; Wilson, 2015). The lower contact with the Marginal Zone is mostly present in the Burgersfort area of the Eastern Limb (Fig. 3.3) where the marginal rocks are relatively Mg-rich tholeiites (Mg# = 77) referred to as B1 (Sharpe, 1981, 1982; Barnes et al., 2010). Chromite is rare throughout the zone and the upper contact with the Critical Zone is generally defined by an increase in the abundance of cumulus plagioclase (>8 vol.%).The Critical Zone is characterized by abundant orthopyroxenites and numerous cyclic units with geochemical reversals on the scale of millimeters to hundreds of meters (Eales et al., 1990). It is host to world-class chromium and PGE deposits found within laterally continuous horizons of chromitites and sulphide-rich “reefs”  (Cameron, 1980; Naldrett et al., 1986, 2012; Eales et al., 1990; Mondal and Mathez, 2006). The Critical Zone is subdivided into the Lower Critical Zones and Upper Critical Zones, separated by a 1-3 m thick anorthosite layer that is continuous across both limbs of the complex. The Lower Critical Zone is up to 800 m thick in the Eastern Limb and is host to a number of significant chromitite horizons, including all of the Lower Group chromitites (LG1-7) and two of the Middle Group chromitites (MG1-2); the remaining Middle Group chromitites (MG3-4) and the Upper Group chromitites (UG1-3) are found in the Upper Critical Zone (Cameron, 1980; Eales et al., 1990). Marginal rocks in contact with the Lower Critical Zone are comparable in composition to the Mg-rich B1 compositions of the Lower Zone.Above the anorthosite unit, the Upper Critical Zone is up to 1000 m thick and consists predominantly of orthopyroxenite cumulates along with lesser amounts of norite and anorthosite 76Chapter 3(Naldrett et al., 1986; Teigler and Eales, 1996; Maier et al., 2013). Notably, the world-class PGE deposits of the Bushveld Complex are found in the Upper Critical Zone within the Upper Group Chromitite 2 (UG2) layer, the Merensky Reef in the Eastern and Western limbs of the complex, and the Platreef horizon in the Northern Lobe (Campbell et al., 1983; Naldrett et al., 1986, 2008; Mathez, 1995; Kinnaird et al., 2005; Mondal and Mathez, 2006). These horizons are typically coarse-grained pegmatites with abundant interstitial plagioclase that vary from 10 cm to 3 m (average 0.9 m) in thickness. Marginal rocks to the Upper Critical Zone consist of a less-magnesian tholeiitic basalt (Mg# = 55), referred to as B2, compared with the B1 type of marginal rocks (Sharpe, 1981; Barnes et al., 2010).The >2 km thick Main Zone of the Bushveld Complex is recognized by the presence of primocrystic (cumulus) plagioclase and also includes mafic rocks of noritic to gabbronoritic composition. It is relatively homogeneous and devoid of economic deposits, and stretches from the top of the Bastard Reef, which sits stratigraphically above the Merensky Reef, to the Pyroxenite Marker, a major compositional reversal from massive noritic rocks to layered orthopyroxenites (von Gruenewaldt, 1973; Sharpe, 1985). Based on associated marginal rocks, the parental magma for the Main Zone is considered to be the B3 composition, which is similar to the B2 tholeiite, but with higher Mg# (62) (Sharpe, 1981; Barnes et al., 2010).From the top of the Pyroxenite Marker to the roof of the Rustenburg Layered Suite, the <2 km thick Upper Zone consists of gabbronorites and diorites that contain layers (up to 21) of massive to semi-massive magnetite, the most significant being the Main Magnetite Layer (MML) (VanTongeren et al., 2010; Cawthorn, 2013a). The top of the Pyroxenite Marker was not historically considered to represent the base of the Upper Zone and instead the contact was defined by the first presence of cumulus magnetite. Variations in whole rock initial Sr isotope composition (87Sr/86Sri), however, indicate a significant shift towards a more crustal signature at the Pyroxenite Marker (Sharpe, 1985). The Upper Zone is interpreted to represent the crystallization of the final pulse of magmatism in the Bushveld Complex as represented by the mafic proposed UUMZ parental magma (UUMZ = Upper Zone Upper Main Zone) (VanTongeren et al., 2010). In the southeastern section of the Bushveld Complex, above the Upper Zone and beneath the Rooiberg Group, lies a sequence of quartz hornblende monzonites referred to as the “Residual Zone” (Cawthorn, 2013b).77Chapter 33 .2 .2 . Geology of the felsic roof rocksThe roof rocks of the Bushveld Complex overlie the Rustenburg Layered Suite and are composed of a series of felsic igneous rocks dominated by granites and granophyres with a total thickness ranging from 2 to over 4 km (Cawthorn et al., 2009; Mathez et al., 2013). In the Eastern Bushveld Complex, the Upper Zone is immediately overlain by the Rashoop Granophyre Suite, and includes the Stavoren Granophyre, which is defined by micrographic intergrowths of quartz and alkali feldspar, and has been interpreted as a felsic differentiate from Upper Zone magmas (Walraven, 1985). Sheets of the Stavoren Granophyre are found in direct contact with the underlying Rustenburg Layered Suite and between the Nebo Granite of the Lebowa Granite Suite and the overlying volcanic rocks of the Rooiberg Group (Cawthorn et al., 2009). The Lebowa Granite Suite overlies much of the eastern Bushveld Complex and is typically present as a course-grained Bushveld differentiate (Eales and Cawthorn, 1996; Mathez et al., 2013). The >5 km thick Rooiberg Group consists of thick volcanic sequences (up to 400 m each) (Harmer and Von Gruenewaldt, 1991) that range from basaltic to granitic in composition and are mostly stratigraphically above the Rustenburg Layered Suite, although the basaltic-dacitic Dullstroom Formation sits below the Rustenburg Layered Suite in the Eastern Bushveld (Twist and French, 1983; Buchanan et al., 1999). The Lebowa Granite Suite, Rashoop Granophyre Suite, and Rooiberg Formation are all considered to be contemporaneous with mafic-ultramafic magmatism of the Bushveld Complex based on field observations and radiometric dating results, however, their precise relationships continue to be a topic of significant discussion and debate (Mathez et al., 2013; VanTongeren and Mathez, 2015). 3 .2 .3 . Previous work on zircon and rutile in the Bushveld ComplexZircon was observed in rocks of the Critical Zone by Cameron (1979). It was recovered from a pegmatitic orthopyroxenite of the Merensky Reef in the Western Limb by Scoates and Friedman (2008), who recognized the interstitial textural setting of this U-Th-Pb-bearing accessory mineral and published the first high-precision U-Pb date from the Bushveld Complex using the chemical abrasion-ID-TIMS technique (weighted mean 207Pb/206Pb date = 2054.4 ± 1.3 Ma). Scoates and Wall (2015) re-analyzed zircon from this sample and reported a revised age for this sample of 2057.04 ± 0.55 Ma and a 2056.88 ± 0.41 Ma date for zircon from 78Chapter 3the Merensky Reef in the Eastern Limb. The trace element geochemistry of the zircon from Bushveld cumulates has previously been examined by Yudovskaya et al. (2013) and Zeh et al. (2015). Yudovskaya et al. (2013) analyzed zircon from chromitites of the Critical Zone in the Eastern, Western, and Northern lobes for trace elements by LA-ICP-MS. They identified anomalously high Th/U = 1-4 in zircon from the Merensky Reef and documented a range in Ti-in-zircon temperatures for zircon from the chromitites of 930-760°C. They also recognized zonation features between zircon cores and rims that appeared to reflect the influx of new primitive magmas during the crystallization of zircon. Zeh et al. (2015) observed similar trace element variations in zircon from zircon samples covering most of the Rustenburg Layered Suite, reporting a maximum Th/U = 18 in a sample from the UG2 chromitite and Ti-in-zircon temperatures for the entire sample suite from 940-670°C. The presence of rutile in the Bushveld Complex has long been recognized (Cameron and Emerson, 1959). Cameron (1979) described rutile in samples from the Critical Zone and recognized up to seven distinct settings and morphologies including associations with chromite (either as rims or as inclusions) and as independent crystals within interstitial minerals (plagioclase, biotite). Vukmanovic et al. (2013) studied microstructures in chromite grains from the Merensky Reef and observed rutile that they interpreted as an exsolution product from chromite with morphologies similar to those described by Cameron (1979). The exsolved rutile was present both as fine, needle-like lamellae in chromite and as globular exsolved grains. Rutile has been observed in other layered intrusions, including the Fiskanaesset Complex, Greenland (Ghisler, 1970) and the Muskox Intrusion, Canada (Irvine, 1975), and warrants further investigation.3 .3 . Samples and analytical techniquesAll samples examined in this study are from the Eastern Limb of the Bushveld Complex, with the exception of SA04-13, which was collected from the West Mine (Townlands shaft) near Rustenburg in the Western Limb (Table 3.1). A total of 20 samples, including surficial, underground, and drill-core samples were processed through mineral separation, of which 13 yielded zircon and six contained rutile. Sample descriptions and thin section scans are found in Appendix D. The sample set includes one each from the Lower Zone (LZ10-02) and Lower 79Chapter 3Table 3 .1 . Summary of samples examined from the Bushveld Complex for zircon and rutile trace element geochemistrySample Stratgraphic Position Subunit Locality Rock Type Latitude Longitude ReferenceB10-056 Roof Rocks Lebowa (Nebo) GraniteMesekete River Section Granite 29°50.636'E 25°00.256'S Mathez et al. (2013)B10-054 Roof RocksRashoop (Stavoren) GranophyreMesekete River Section Granophyre 29°50.634'E 25°00.214'S Mathez et al. (2013)B07-051 Roof Rocks Rashoop Droogehoek River Section Granodiorite 29°54.287'E 24°51.669'SVanTongeren et al. (2016)B07-040 Upper Zone Droogehoek River Section Diorite 29°54.465'E 24°51.794'S VanTongeren (2010)B90-1 Main Zone Tennis Ball Marker NE of Stoffberg Norite 29°59.935'E 24°17.767'SVermaak and von Gruenewaldt (1981)MP24D21 Upper Critical Zone Bastard Reef Atok Mine Pyroxenite 29°51'50.90"E 24°17'46.05"S Mathez et al. (1997)B90-7(0)1 Upper Critical Zone Merensky Reef Atok Mine Pyroxenite 29°51'50.90"E 24°17'46.05"S Mathez (1995)SA04-132 Upper Critical Zone Merensky ReefWest Mine (Western Limb) Pyroxenite 27°15’31.9”E 25°37’29.1”SScoates and Friedman (2008)SA04-08 Upper Critical Zone Merensky Reef Farm Driekop Pyroxenite 30°05’11.4”E 24°31’11”SScoates and Wall (2015)B00-1-62 Upper Critical Zone UG2 Middelpunt Mine Pyroxenite Middlepunt MineMathez and Mey (2004)DT28-9121  Upper Critical Zone UG2 Diamand 422 KS Pyroxenite 29°49'22.63"E 24°17'08.16"SMondal and Mathez (2007)SA04-06 Upper Critical Zone MG3 Surface Chromitite 29°53.293E 24°16.215'S This studyTW477 661.151 Lower Critical ZoneCameron's SectionTwickenham 114 KT Pyroxenite 30°00'46.65"E 24°23'40.08"SCameron (1980), Mondal and Mathez (2007)LZ10-02 Lower Zone Burgersfort Harzburgite 30°11.114'E 24°38.260'S Zirakparvar (2015)All samples collected from ouctrop, except (1) drill core sample and (2) underground sample. 80Chapter 3Critical Zone (TW477-661) with the majority of samples concentrated in the Upper Critical Zone, including two samples from the UG2 chromitite horizon (DT28-912, B00-1-6), three samples from the PGE-rich Merensky Reef (B90-7, SA04-08, SA04-13), and one sample from the uneconomic Bastard Reef (MP24D2). Rocks from the Main Zone and Upper Zone proved to be relatively poor targets for zircon recovery and only one sample from the base of the Main Zone (B90-1, Tennis Ball Marker) and one sample from near the top of the Upper Zone (B07-040) yielded zircon. The felsic roof rocks of the Bushveld Complex are represented by a “leptite” (B07-051), a granophyre with graphic intergrowths of quartz, plagioclase, and alkali feldspar (Iannello, 1971), and a sample each of the Stavoren granophyre (B10-054) and Nebo granite (B10-056) (Mathez et al., 2013; VanTongeren and Mathez, 2015).All samples were crushed and separated using standard heavy liquid and magnetic separation techniques at the Pacific Centre for Isotopic and Geochemical Research at the University of British Columbia (UBC). Zircon grains were concentrated into the N2 and N2/M5 magnetic splits and selected under a binocular microscope on the basis of clarity, size, external morphology, and lack of visible inclusions or discoloration. Rutile was most commonly found in the N2/M5 magnetic split with some grains sourced from the N2 split. Grains of each mineral were selected and mounted in epoxy set in 2.5 cm diameter pucks, then ground and polished to their approximate mid-sections. Mounted grains of zircon and rutile were imaged for internal structure at the Electron Microbeam/X-Ray Diffraction Facility (EMXDF) at UBC, Vancouver, using a Philips Xl-30 scanning electron microscope (SEM). Zircon grains were imaged using a Robinson cathodoluminescence (CL) detector, and rutile grains along with a subset of zircon grains from the roof rock samples were analyzed by backscattered electron imaging (BSE) using a Bruker Quanta 200 energy-dispersion X-ray microanalysis system with XFlash 6010 SDD detector at a voltage of 15 kv. Energy dispersion X-ray spectroscopy (EDS) was used to identify inclusions (e.g., apatite, albite) in zircon within the felsic roof rocks.To verify the stoichiometry of zircon for use as an internal standard during analysis by LA-ICP-MS, a random sampling of three to five grains per sample (total analyses = 64) were analyzed by electron probe micro-analysis (EPMA) at the EMXDF; full results are provided in Appendix E. Analyses were carried out using a fully automated CAMECA SX-50 instrument operating in wavelength-dispersion mode with an excitation voltage of 15kV and a beam current 81Chapter 3of 20 nA. Concentrations of Si, Zr, and Hf were measured using spot diameters of 5 μm and peak count times of 20 seconds, 10 seconds, and 100 seconds, respectively. The following standards, X-ray lines, and crystals were used for the elements considered: zircon, SiKα, TAP; zircon, ZrLα, PET; Hf element, HfLα, LIF; diopside, CaKα, PET. Spots were mostly placed in the centers of grains; fractures or slopes on the grain surfaces were avoided. Both Zr and Si are stoichiometric with an average value of 48.6 wt. % and 14.9 wt. %, respectively; Hf contents are more variable (0.93-1.41 wt. %).Trace element concentrations were determined in zircon and rutile by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at UBC using a Resonetics (now ASI) RESOlution M-50-LR Class I laser ablation system coupled to an Agilent 7700x quadrupole ICP-MS (Table 3.2). Ablations were carried out using a beam energy of 100 mJ and a pit diameter of 34 μm with a pulse rate of 5 Hz for a duration of 40 seconds followed by 20 seconds of gas blank. Spots were chosen based on grain-scale variations observed in CL images and grain size with typically two analyses per grain. For zircon, measurements were conducted on the masses 7Li, 29Si, 43Ca, 45Sc, 49Ti, 85Rb, 88Sr, 89Y, 90Zr, 93Nb, 139La, 140Ce, 141Pr, 146Nd, 147Sm, 153Eu, 157Gd, 159Tb, 163Dy, 165Ho, 166Er, 169Tm, 172Yb, 175Lu, 177Hf, 188Ta, 202Hg (as a monitor for Pb), Pb (204Pb, 206Pb, 207Pb, 208Pb), 232Th, and U (235U and 238U); these masses were chosen based on high relative abundances and the absence of interferences. For rutile, 53Cr, 57Fe, and 182W were also analyzed. Sample-standard bracketing was carried out with spot analyses of synthetic glasses NIST 612 and NIST 610 between zircon and rutile analyses. The natural zircon reference materials 91500, Plešovice, and FC-1 were also analyzed; analytical results from the reference materials are found in Appendix F.Data were reduced using Iolite 2.5 software running within the Igor Pro environment  using the Trace_Elements_IS data reduction scheme (Paton et al., 2011). For zircon, NIST 612 was used as the standard and the average Zr concentrations (by sample) determined by EPMA were employed as an internal standard value for the unknowns. For rutile, the same reduction scheme was initially employed with a stoichiometric value of 59.5 wt.% Ti as the internal standard. This method resulted in trace element concentrations in the NIST 610 reference material that were ~30% below values reported in Pearce et al. (1997), likely due to the refractory nature of Ti and the physical and compositional differences between NIST 612 and 82Chapter 3Table 3 .2 . Procedure for LA-ICP-MS analysis of zircon and rutileParameter ValueZircon RutileResonetics RESOlution M-50 LR Class I LaserWavelength 193 nmEnergy density 5 J cm-2Repetition rate 5 HzSpot diameter 34 μmHelium flow 0.75 L min-1High-purity N2 gas flow 0.002 L min-1Ablation time / gas blank time 40 s / 20 sAgilent 7700x  Quadrupole ICP-MSArgon carrier gas flow 0.53 L min-1  0.53 L min-1Masses measured 34 37Mass sweep time 705 ms 606 msThO+/Th+ (NIST612) <0.4 wt %U238/Th232 sensitivity (NIST612) 102-120%Standardization and ReductionTrace element standard NIST612Standards and reference materialsNIST610, 91500, Plešovice, FC-1 NIST 610Data reduction Iolite 2.5 extension1 for Igor Pro, Trace_Elements_IS reduction schemeInternal standard Zr ~ 49.5 wt. % (EPMA) Ti = 59.5 wt. % (stoichiometric)1. See Patton et al. (2011)83Chapter 3NIST610.  Using a semi-quantitative reduction scheme (no internal standard) yielded precise and accurate trace element concentrations in the NIST 610 reference material. The trace element concentrations and uncertainties for the rutile analyses were nearly identical using the two reduction methods, therefore, results from the semi-quantitative reduction method are utilized for this study. All concentrations are reported in ppm with uncertainties of 2σ.3 .4 . Results3 .4 .1 . Textural setting and internal structure of zircon and rutile in the Bushveld ComplexZircon occurs as a relatively common accessory mineral in ultramafic-mafic cumulates of the Bushveld Complex and is associated with interstitial pockets containing quartz, plagioclase, and locally alkali feldspar, which are commonly observed as granophyric and myrmekitic intergrowths (Figs. 3.4, 3.5). This textural setting is consistent with crystallization from fractionated pockets of interstitial melt (e.g., Scoates and Wall, 2015; Zeh et al., 2015; Wall and Scoates, 2016) (Fig. 3.6). Complete results from SEM-CL imaging of zircon are found in Appendix G. In the mafic-ultramafic cumulates of the Rustenburg Layered Suite, zircon grain sizes generally range from 100-250 μm in their longest dimension compared with zircon from the felsic roof rocks that are typically smaller than 100 μm. Zircon from the Lower Zone (LZ10-02) is irregular and shows complex sector zoning (Fig. 3.6a); some grains appear featureless in CL imaging. Zircon from the Critical Zone is highly variable both between samples and within grains from a single sample (Fig. 3.6b-g). Most grains are distinguished by sector zoning and some grains reveal convolute zoning with internal oscillatory bands (e.g., Fig. 3.6c). In the Critical Zone, zircon from the UG2 chromitite and Merensky Reef displays a range of features dominated by irregular (anhedral), sector-zoned grains that commonly contain fine oscillatory zoning within sectors (Fig. 3.6b-f). Zircon from the Main Zone (B90-1) is characterized by poor CL response and few zoning features, with many grains appearing flat in CL or displaying minor CL gradients or banding (Fig. 3.6h). In the Upper Zone sample, zircon is larger with more euhedral crystal shapes compared with zircon from the Main Zone, Critical Zone, and Lower Zone. Zircon from the Upper Zone shows a brighter CL response and commonly displays micron-scale oscillatory zoning within growth sectors (Fig. 3.6i). Zircon from the three different 84Chapter 3rutilerutilechropxplagopxopxchrplagrutileopxopxbiotiteqtzqtzzirconzirconzirconcpxopxkspplagqtzapatiteolplagcpxplag+sericitezircon qtzbiotitechrqtzrutilecpxopxchropx btplagrutilezirconchrrutilezirconplagcpxzirconbiotiteopxquartzcpx qtz opxkspkspplag + qtz+ sulphideapatiteplagqtzbiotiteopx(a) (b) (c)(d) (e) (f)(g) (h) (i)(j) (k) (l)85Chapter 3Figure 3 .4 . Photomicrographs showing the textural setting of accessory minerals in rocks from the Rustenburg Layered Suite of the Bushveld Complex (all scale bars are 200 μm). (a) Euhedral needle of rutile in contact with chromite in interstitial plagioclase (TW477-661, XPL). (b) Anhedral zircon grain in small interstitial pocket consisting of clinopyroxene, quartz, and biotite (TW477-661, XPL). (c) Interstitial pocket showing complex intergrowths of alkali feldspar, plagioclase, quartz, and minor sulphide along the contact of a larger quartz grain with cumulus orthopyroxene (DT28-912, BSE-SEM). (d) Two different petrologic settings of rutile, including a euhedral needle within interstitial plagioclase and a larger anhedral rutile grain on the rim of chromite, sharing a grain boundary with cumulus orthopyroxene (B00-1-6, PPL). (e) Two small zircon grains in small interstitial pockets associated with quartz and biotite (SA04-08, XPL). (f) Large interstitial pocket with a cluster of euhedral apatite grains intergrown with quartz, biotite, and plagioclase (SA04-13, BSE-SEM). (g) Zircon and rutile intergrown in the core of a chromite crystal that is hosted within an interstitial pocket of dominantly plagioclase with biotite rimming chromite (SA04-13, XPL). (h) Zircon and rutile in the core of a large chromite grain within interstitial plagioclase and clinopyroxene (SA04-13, XPL). (i) Interstitial quartz containing a rutile needle (MPD24D2, XPL). (j) Irregular grains of zircon rimming a chromite grain bordered by plagioclase with strong sericite alteration. The chromite grain in the lower left is in contact with biotite and quartz (B90-1, XPL). (k) Large euhedral zircon grains within gabbro (plagioclase, clinopyroxene, orthopyoxene) with some associated quartz and feldspar in small interstitial pockets (B07-040, XPL). (l) Euhedral apatite grains found along grain boundaries of gabbro (B07-040, XPL). Abbreviations: PPL, plane-polarized light; XPL, cross-polarized light; BSE-SEM, backscattered electron-scanning electron microscopy; opx, orthopyroxene; plag, plagioclase; chr, chromite; cpx, clinopyroxene; ksp, alkali feldspar; qtz, quartz; bt, biotite; ol, olivine.86Chapter 3plaggranobtopxopxchrqtzqtzzropxbtchrchrbtqtzgranoopxchrchrqtzqtzopxopxbtplaggranoopxopxcpxplagapchrzrrtplagbtopxopx(a)(b)b(c)(e) (f) (g)cge(d)dfFigure 3 .5 . Thin section scan and photomicrographs showing the distribution, shape, and mineralogy of interstitial pockets in sample TW477-661 from the Lower Critical Zone. (a) Thin section scan (4 x 2.5 cm) in transmitted light showing cumlus orthopyroxene (grey) with abundant interstitial material (white – quartz, Na-plagioclase), biotite (brown), and chromite (black). Black outlined boxes indicate areas shown in detail in the panel below. (b-g) Photomicrographs showing the mineralogy and textures of individual interstitial pockets. Scale bars are 500 microns in all panels. Abbreviations: opx, orthopyroxene; plag, plagioclase; chr, chromite; bt, biotite; grano, granophyre; zr, zircon; qtz, quartz; cpx, clinopyroxene.87Chapter 3Hf = 8353 ± 45  U = 172 ± 1.4 Th/U = 1.2831°C 829°C Hf = 8101 ± 49U = 138 ± 1.5Th/U = 1.1 60 μmLZ10-02 z7 70 μmTW477-661 z3Hf = 10781 ± 68U = 35 ± 1Th/U = 3.9 773°C 762°C Hf = 11391 ± 69U = 59 ± 1Th/U = 2.4 40 μmDT28-912 z19Hf = 11830 ± 170U = 45 ± 1Th/U = 8.0 Hf = 12070 ± 170U = 69 ± 3Th/U = 10.3789°C 760°C 80 μmB00-1-6 z5Hf = 9200 ± 200U = 3.3 ± 0.2Th/U = 32.2821°C 807°C Hf = 8950 ± 130U = 2.3 ± 0.1Th/U = 28.450 μmB90-7 z5Hf = 9447 ± 73U = 15.9 ± 0.4Th/U = 10.4 Hf = 9385 ± 76U = 21.8 ± 0.3Th/U = 8.5831°C 845°C 60 μmSA04-08 z14Hf = 7138 ± 93U = 100 ± 1.6Th/U = 0.80 802°C 824°C Hf = 7059 ± 79U = 104 ± 1.2Th/U = 0.8260 μmMP24D2-26 z14Hf = 11420 ± 100U = 45 ± 0.6Th/U = 8.5 796°C 811°C 813°C Hf = 10839 ± 97U = 61 ± 1.4Th/U = 11.9Hf = 10836 ± 88U = 53 ± 2.6Th/U = 11.440 μmB90-1 z3Hf = 9180 ± 200U = 220 ± 4Th/U = 1.0 883°C 884°C Hf = 9290 ± 100U = 193 ± 3Th/U = 1.170 μmB07-040 z1Hf = 8660 ± 130U = 108 ± 1Th/U = 0.39Hf = 8940 ± 150U = 88 ± 3Th/U = 0.37Hf = 9700 ± 110U = 118 ± 3Th/U = 0.36727°C 720°C 761°C 30 μmB07-051 z12Hf = 6728 ± 85U = 169 ± 4Th/U = 0.59756°C 30 μmB10-054 z2Hf = 7690 ± 100U = 169.1 ± 4.2Th/U = 0.62842°C 40 μmB10-056 z08Hf = 7360 ± 110U = 182.4 ± 4.7Th/U = 0.58 Hf = 8080 ± 110U = 160.1 ± 2.8Th/U = 0.44 777°C 775°C (a) (b) (c)(g) (h) (i)(d) (e) (f )(j) (k) (l)Figure 3 .6 . Representative scanning electron microscope-cathodoluminescence images of zircon from the Bushveld Complex. Yellow circles indicate locations of spot analyses by LA-ICP-MS (circle diameter is 34 μm) with measured values for Hf, U and Th/U shown. Temperatures are Ti-in-zircon temperatures calculated using aSiO2 = 1 and aTiO2 = 1 (Ferry and Watson, 2007), except for samples from the Upper Zone and roof granites where aTiO2 = 0.7. (a) LZ10-02, Lower Zone; (b) TW477-661, Lower Critical Zone; (c) DT28-912, UG2; (d) B00-1-6, UG2; (e) B90-7, Merensky Reef (Eastern Limb); (f) SA04-08, Merensky Reef (Eastern Limb) (g) MP24D2-26, Bastard Reef; (h) B90-1, base of Main Zone – Tennis Ball Marker; (i) B07-040, Upper Zone; (j) B07-051, Rashoop granophyre; (k) B10-054, Stavoren Granophyre (Rashoop); (l) B10-056, Nebo Granite (Lebowa). Scales as indicated by the white bars on each panel.88Chapter 3felsic roof units contrasts sharply with zircon from the mafic-ultramafic cumulates. The grains are typically euhedral and small, ranging from 50-150 microns in length, and oscillatory zoning is present in nearly all grains with more complex zoning locally present in some grains (Fig. 3.6j-l). Small inclusions observed in BSE images of the roof rock zircon are identified as apatite, sodic plagioclase, potassium feldspar, and pure calcium oxide.Rutile, which occurs in the Lower Zone and Main Zone samples and in all samples from the Critical Zone, is typically small and ranges from 60-250 μm in length, with typical grains being ~150×100 μm in size. Most rutile is found as acicular crystals within interstitial pockets containing quartz, plagioclase, alkali feldspar, biotite, and zircon (Fig. 3.4a, d, i). In the Critical Zone, subequant to rounded rutile is also found intimately associated with chromite either on the rims or in the cores of chromite grains (Fig. 3.4d, g, h; Fig. 3.5f). In some samples (e.g., B00-1-6 from UG2), both morphologies are present within millimetres of each other and highlight the contrast between the two habits (Fig. 3.4d). In BSE images, there is minimal internal structure revealed in rutile (Fig. 3.7); a catalogue of BSE images of rutile is found in Appendix H. Some grains display fine sharp bright lines in BSE that represent exsolution lamellae of ilmenite (Fig. 3.7c-d). 3 .5 . Trace element geochemistry of zirconTable 3.3 contains a summary of trace element concentrations in zircon, and the complete LA-ICP-MS results are found in Appendix I. Chondrite-normalized patterns showing the results for each analysis are shown in Appendix J. In the following section, the Hf-Ti, U-Th, and REE geochemical variations of zircon from the Bushveld Complex are addressed.3 .5 .1 . Hafnium and titaniumThe Hf concentrations of zircon from the Bushveld mafic-ultramafic cumulates span a relatively wide range from 6903-13,350 ppm with zircon from the felsic roof rocks showing less variation (6768-9690 ppm) (Fig. 3.8). Titanium (4-61 ppm) is negatively correlated with Hf in all analyzed samples and three distinct Ti-Hf trends distinguish zircon from the Bushveld Complex (Fig. 3.8d). Zircon from the Lower Zone and Main Zone is characterized by moderate Ti variations (10.1-52 ppm) over a wide range of Hf (7900-12,860 ppm). Zircon from the Critical 89Chapter 360 ȝmSA04-13 r7Hf = 10Nb = 50Ta = 2.6 Hf = 9.9Nb = 53Ta = 3.6 603°C 598°C 60 ȝmSA04-13 r21Hf = 44Nb = 512Ta = 26 Hf = 30Nb = 438Ta = 14 764°C 729°C 50 ȝmTW477-661 r10Hf = 108Nb = 4840Ta = 246 Hf = 94Nb = 4250Ta = 220 863°C 878°C 30 ȝmTW477-661 r4Hf = 6.22Nb = 92.2Ta = 1.82 582°C 50 ȝmDT28-912 r11Hf = 214Nb = 10470Ta = 840 Hf = 212Nb = 10640Ta = 941 961°C 959°C 60 ȝmDT28-912 r22Hf = 140Nb = 10450Ta = 786 Hf = 141Nb = 10550Ta = 777 Hf = 141Nb = 10830Ta = 777 908°C 904°C 908°C 60 ȝmSA04-08 r1Hf = 147Nb = 10870Ta = 715 Hf = 164Nb = 12620Ta = 787 906°C 945°C 50 ȝmSA04-08 r2Hf = 19.6Nb = 285Ta = 7.3 655°C 20 ȝmMPD24D2 r3Hf = 105Nb = 27400Ta = 1760 962°C (a) (b) (c)(d) (e) (f)(g) (h) (i)Figure 3 .7 . Backscattered electron (BSE) images of representative rutile grains from the Critical Zone of the Bushveld Complex. Circles indicate locations of spot analyses by LA-ICP-MS (circle diameter is 34 μm) with measured concentrations of Hf, Nb, and Ta shown. Temperatures are Zr-in-rutile temperatures calculated assuming aSiO2 = 1 for primary magmatic rutile (yellow circles: b, c, d, e, i) and aSiO2 = 0.5 for grains exsolved from chromite (white circles: a, f, g, h) (Ferry and Watson, 2007). (a-b) TW477-661 (Lower Critical Zone) rutile characterized by fractured subhedral grains with no obvious zonation in BSE. (c) DT28-912 (UG2 – Upper Critical Zone) rutile grain with euhedral prismatic habit. (d) DT28-912 (UG2 – Upper Critical Zone) rutile with anhedral habit and exsolved ilmenite (bright lines). Small inclusions and fractures are present. (e-f). SA04-08 (Merensky Reef – Upper Critical Zone) rutile grains are small and anhedral with show no significant BSE variation. (g) SA04-13 (Merensky Reef – Upper Critical Zone, Western Limb) rutile with angular subhedral morphology and minimal BSE variation. (h) SA04-13 (Merensky Reef – Upper Critical Zone, Western Limb) rutile with prismatic appearance, no major BSE variation, and minor fracturing. (i) MP24D2 (Bastard Reef – Upper Critical Zone) rutile grain that is very small (<50 μm). Scales as indicated by the white bars on each panel.90Chapter 3Table 3 .3 . Summary of ranges of trace element concentrations of zircon from the Bushveld ComplexElement Li Sc Ti Rb Sr Y Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U Th/U Tzrc (°C)LZ10-02 - Lower Zone (n = 19)Q1 0.50 411 21 0.10 0.23 377 3.28 0.03 14.9 0.16 2.10 2.61 0.76 10.86 3.08 36.4 12.2 51 9.38 75 15 8340 0.81 230 184 170 1.0 821Median 1.05 419 23 0.13 0.26 499 3.51 0.04 16.3 0.21 3.08 4.33 1.29 16.80 4.59 49.6 16.3 66 11.94 94 19 8493 1.17 280 220 207 1.1 830Q3 2.81 431 25 0.15 0.30 589 4.58 0.07 16.9 0.42 5.07 5.19 1.44 19.71 5.38 58.2 19.0 79 14.28 116 23 8848 1.36 375 310 288 1.1 840TW477-661 - Lower Critical Zone (n = 18)Q1 0.79 362 13 0.10 0.27 451 2.73 0.00 11.4 0.06 1.27 2.64 0.60 13.37 3.94 42.8 14.5 59 10.80 85 17 9659 0.55 82 69 59 1.0 773Median 1.89 375 15 0.13 0.32 697 3.15 0.02 12.7 0.17 2.65 4.45 1.09 17.49 5.08 59.1 21.5 96 18.29 147 29 10855 0.80 191 149 82 3.0 786Q3 3.42 397 27 0.28 0.45 1420 4.10 0.05 23.8 0.37 5.00 7.09 1.73 36.33 11 131 45.8 195 36.01 290 56 11284 1.28 539 446 122 4.3 849DT28-912 -  Upper Critical Zone, UG2 (n = 24)Q1 1.34 270 18 0.06 0.21 380 0.90 0.00 3.4 0.05 1.01 2.31 0.36 11.43 3.24 34.7 11.7 50 9.45 78 15 10048 0.33 130 131 5 12.8 806Median 2.45 281 26 0.09 0.25 647 1.13 0.00 3.8 0.17 2.87 4.29 0.79 18.48 5.40 58.8 20.1 87 15.62 125 24 10360 0.40 192 205 7 20.0 842Q3 3.85 287 29 0.14 0.28 771 1.62 0.01 5.5 0.25 4.61 7.07 0.97 26.20 6.77 72.8 23.9 101 18.47 141 27 10878 0.84 243 255 19 30.2 858B00-1-6 - Upper Critical Zone, UG2 (n = 31)Q1 1.08 232 14 0.07 0.18 322 0.73 0.00 3.2 0.04 0.82 1.87 0.33 8.70 2.73 29.6 9.8 43 8.22 69 13 9125 0.26 118 101 4 8.0 779Median 1.49 240 21 0.09 0.20 505 0.86 0.00 3.8 0.07 1.70 4.36 0.58 15.60 4.36 48.8 15.9 63 11.90 96 18 9550 0.34 152 135 4 25.0 818Q3 3.98 246 23 0.14 0.23 654 1.47 0.00 5.9 0.18 3.12 6.04 0.83 21.69 5.91 63.3 20.3 83 15.45 124 24 10110 0.71 219 195 25 32.8 830B90-7 - Upper Critical Zone, Merensky Reef (n = 20)Q1 0.25 389 22 0.10 0.30 358 2.23 0.00 2.8 0.03 0.74 1.60 0.29 7.64 2.48 31.0 11.2 52 10.62 92 19 9988 0.29 266 155 10 10.3 828Median 0.38 395 24 0.13 0.34 620 2.35 0.00 3.2 0.14 2.39 4.32 0.54 17.53 5.17 58.7 19.8 83 15.54 128 25 10510 0.38 332 199 13 11.3 835Q3 0.69 410 26 0.16 0.37 724 2.57 0.01 3.8 0.25 3.98 5.60 0.75 22.31 6.11 68.2 23.2 98 18.24 150 29 11270 0.47 518 252 19 18.8 846SA04-08 Upper Critical Zone, Merensky Reef (n = 25)Q1 0.41 239 18 0.04 0.15 229 1.16 0.00 3.2 0.02 0.45 0.84 0.19 5.32 1.60 20.6 7.4 34 6.34 53 11 7212 0.38 106 99 101 0.8 802Median 0.63 249 20 0.07 0.18 272 1.34 0.00 3.9 0.03 0.65 1.16 0.26 6.08 1.89 23.4 8.7 39 7.67 65 13 7455 0.48 186 149 114 1.0 817Q3 0.98 256 22 0.09 0.21 448 1.58 0.03 4.8 0.14 2.21 2.83 0.46 12.85 3.53 42.1 14.7 62 11.54 93 18 7853 0.69 243 187 155 1.3 825SA04-13 Upper Critical Zone, Merensky Reef (n = 22)Q1 0.17 227 17 0.06 0.17 329 1.14 0.00 3.7 0.03 0.53 1.52 0.23 8.02 2.51 30.9 10.5 44 8.05 65 12 8752 0.54 90 77 30 2.0 801Median 0.27 233 21 0.09 0.20 406 1.38 0.00 5.9 0.06 1.01 2.19 0.34 10.70 3.25 37.7 12.8 53 9.96 82 15 8995 0.64 149 142 44 2.8 820Q3 0.72 237 25 0.13 0.23 626 1.69 0.01 6.6 0.11 1.44 3.90 0.58 19.26 5.64 63.3 20.2 82 14.71 115 21 9741 0.77 195 168 57 3.7 839All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace elements reduction scheme with Zr concentration determined by EPMA as internal standard. Q1 = quartile 1, Q3 = quartile 3. Q1-Q3 represents the range of the middle 75% of analyses for each sample. Tzrc (°C) is the Ti-in-zircon temperature calculated using the method of Ferry and Watson (2007).91Chapter 3Table 3 .3 (cont) . Summary of ranges of trace element concentrations of zircon from the Bushveld ComplexElement Li Sc Ti Rb Sr Y Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U Th/UTzrc (°C)MPD24D2 - Upper Critical Zone, Bastard Reef (n = 15)Q1 0.45 281 23 0.04 0.20 314 1.36 0.00 5.4 0.08 1.26 2.26 0.50 11.25 3.01 32.4 10.5 41 7.74 58 11 8950 0.50 423 105 27 3.1 830Median 1.11 290 34 0.07 0.21 348 1.69 0.01 7.2 0.13 2.30 3.12 0.65 12.59 3.32 36.0 11.2 45 8.14 65 12 9565 0.86 1507 147 45 3.6 875Q3 1.56 295 47 0.12 0.27 530 2.62 0.01 7.8 0.23 3.57 4.73 0.96 19.10 5.09 54.2 17.2 68 12.27 94 18 10088 0.90 3158 155 48 6.9 915B90-1 - Main Zone, Tennis Ball Marker (n = 20)Q1 1.05 333 25 0.22 0.44 981 2.78 0.09 21.3 0.36 4.38 6.00 0.71 24.98 7.76 90.6 31.6 142 27.93 236 46 9195 0.72 369 170 190 0.8 839Median 2.73 346 29 0.32 0.57 1400 3.08 0.21 24.2 0.72 8.75 8.10 0.99 35.25 10.8 133 46.0 201 39.65 332 62 9611 1.11 622 227 263 1.0 856Q3 30.45 351 35 0.40 11 1725 4.61 1.89 39.5 1.38 10.5 12.4 1.72 48.95 13.7 165 56.5 247 45.92 369 71 10418 1.62 935 475 643 1.1 879B07-040 - Upper Zone (n = 32)Q1 0.60 235 6 0.11 0.22 470 0.39 0.00 2.6 0.02 0.37 1.14 0.22 7.40 2.74 37.5 15.1 75 15.95 140 27 8835 0.17 137 57 132 0.4 698Median 1.58 239 7 0.16 0.25 767 0.43 0.00 3.1 0.05 1.17 2.82 0.54 16.20 5.17 66.6 24.8 118 23.55 200 39 9375 0.19 164 79 163 0.5 713Q3 2.69 242 8 0.19 0.29 1089 0.51 0.01 3.3 0.10 2.13 4.50 0.86 25.10 7.68 97.0 36.2 165 32.82 273 51 9644 0.22 225 105 189 0.6 730B07-051 - Felsic roof rock, Microgranite (n = 15)Q1 1.07 169 8 0.20 0.28 890 2.09 0.08 7.1 0.25 2.58 4.65 0.83 22.40 6.87 83.5 30.0 136 26.75 227 43 6835 0.81 90 88 159 0.6 723Median 2.29 170 9 0.24 0.39 1140 2.29 0.39 10.4 0.38 5.33 7.13 1.14 30.20 9.25 111 37.0 161 31.40 257 49 6954 0.88 101 96 165 0.6 731Q3 3.58 171 11 0.35 1.17 1572 3.09 7.45 26.5 2.55 13.6 8.78 1.26 37.10 11.3 138 48.4 214 40.20 330 62 7560 1.11 112 101 179 0.6 751B10-054 - Stavoren Granophyre (n = 16)Q1 0.64 192 10 0.25 0.28 1130 2.41 0.06 7.3 0.21 3.22 5.32 0.91 25.70 8.47 107 38.2 174 33.53 284 54 7646 1.01 80 84 153 0.5 749Median 1.16 194 11 0.28 0.33 1274 2.48 0.59 9.5 0.43 5.70 6.69 1.02 33.00 9.74 120 42.6 190 36.60 302 58 7750 1.04 98 93 165 0.6 754Q3 2.57 195 11 0.33 0.55 1479 2.86 3.68 19.0 1.43 8.88 9.45 1.26 40.30 12.3 145 50.0 216 40.70 336 64 7811 1.13 133 109 185 0.6 758B10-056 - Nebo Granite (n = 20)Q1 0.54 169 7 0.21 0.38 728 2.16 0.22 8.6 0.41 4.58 4.64 0.78 15.52 5.25 67.7 25.1 117 23.35 199 38 7305 0.88 79 74 156 0.4 714Median 0.90 169 8 0.32 0.78 980 2.88 2.50 13.9 1.02 7.05 8.01 1.15 36.90 9.84 100 32.4 137 26.52 224 43 7510 0.98 89 78 170 0.5 723Q3 1.93 170 11 0.67 2.27 1595 3.53 23.4 71.3 7.78 38.8 14.1 3.27 41.93 12.2 141 49.5 219 41.68 341 64 8158 1.29 111 104 188 0.6 757All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace elements reduction scheme with Zr concentration obtained by EPMA as internal standard. Q1 = quartile 1, Q3 = quartile 3. Q1-Q3 represents the range of the middle 75% of analyses for each sample. Tzrc (°C) is the Ti-in-zircon temperature calculated using the method of Ferry and Watson (2007).92Chapter 3Ti (ppm)Hf (ppm)6000 8000 10000 12000 14000Hf (ppm)6000 8000 10000 12000 14000900˚C800˚C700˚C600˚C900˚C800˚C700˚C600˚C0.11101000 100 200 300 400 500U (ppm)0 100 200 300 400 500U (ppm)02004006008001000Th (ppm)Th / U02040600204060Ti (ppm)Th/U = 0.5 Th/U = 1 Th/U = 2 Th/U = 4 Th/U = 10 (a) (b)(c) (d)avg 2σavg 2σavg 2σavg 2σNeboStavorenGranophyreUZMZUCZUCZ-MRLCZLZFigure 3 .8 . Trace element variations of select high field strength elements and actinides in zircon from the Bushveld Complex. (a) Th vs. U with lines of constant Th/U indicated. Three populations are defined: Upper Zone and roof rocks with Th/U ~0.5, Lower Zone and Main Zone rocks with Th/U ~1, and highly variable Th/U of Critical Zone samples (2 to >40). (b) Th/U vs. Hf showing large variation in Th/U of the Critical Zone samples and variable Hf contents. Note logarithmic y-axis. (c) Ti vs. U. (d) Ti vs. Hf showing negative trends of decreasing Ti with increasing Hf concentration. Horizontal dashed lines in panels c and d are Ti-in-zircon temperatures calculated using aSiO2 = 1 and aTiO2 = 1 (Ferry and Watson, 2007), except for samples from the Upper Zone and roof granites where aTiO2 = 0.7. Average 2σ uncertainty is indicated in each panel. Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations in legend: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ-MR, Upper Critical Zone-Merensky Reef; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone.93Chapter 3Zone has the highest and most variable Ti concentrations (4-61 ppm). Zircon from the Upper Zone has low Ti concentrations (Ti = 4.0-9.8 ppm) and overlaps with samples from the felsic roof rocks (Ti = 6.4-23.7 ppm). 3 .5 .2 . Thorium and uraniumThere are three distinct populations of zircon from the Bushveld Complex based on Th-U concentrations (Fig. 3.8a-b). Zircon from the Lower Zone and Main Zone contain comparable Th (98-1092 ppm) and U (104-1580 ppm) with Th/U = 0.15-1.5. Zircon from the Upper Zone and felsic roof rock samples contain lower Th (28-201 ppm) and U (U = 80-351 ppm) concentrations and have relatively consistent Th/U (0.35-0.74). Zircon from the Critical Zone, including the UG2 and Merensky Reef horizons, is characterized by comparable Th (280-1002 ppm) to zircon from the other samples, but is characterized by anomalously low U concentrations (2.3-457 ppm) yielding elevated and highly variable Th/U (0.60-77) (Fig. 3.8a), with the exception of zircon from sample SA04-08 (Merensky Reef, Western Limb). The Hf concentrations of the high-Th/U zircon in the Critical Zone are nominally higher than in the other samples, however, there is no apparent correlation between increasing Hf and higher Th/U in the dataset (Fig. 3.8b). 3 .5 .3 . Rare earth elementsChondrite-normalized rare earth element (REE) patterns of zircon from the Bushveld Complex display typical igneous zircon patterns with relatively depleted light REE (LREE) and relatively enriched heavy REE (HREE), sharp positive Ce anomalies, and prominent negative Eu anomalies (Fig. 3.9). In the mafic-ultramafic cumulates, patterns in zircon from the Lower Zone and Critical Zone are broadly subparallel and display similar ranges within each sample (Fig. 3.9a-d). In zircon from the Main Zone, the LREE are elevated by 1-2 orders of magnitude when compared to zircon from the Lower Zone, Critical Zone, and Upper Zone, while displaying similar Ce and Eu anomalies (Fig. 3.9e). Patterns from Upper Zone zircon are typical of igneous zircon and are comparable to the Critical Zone samples (Fig. 3.9e). Zircon from the granites and granophyres of the roof rocks display strong enrichment in the LREE with La values ranging over five orders of magnitude (0.03-1000 times chondritic values) in the Nebo Granite sample (Fig. 3.9f). This LREE-enrichment is characteristic of all three roof rock samples and, as a result, 94Chapter 3LZ10-02 [LZ](a) Lower Zonezircon/chondriteLa Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb(b) Critical Zonezircon/chondrite TW477 661 [LCZ]MP24D2 [Bastard Reef - UCZ]La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb(c) UG2 - Upper Critical Zonezircon/chondriteB00-1-6DT28-912DT28-912B00-1-6La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb(d) Merensky Reef - Upper Critical Zonezircon/chondriteSA04-13SA04-08B90-7 (0)B90-7(0)SA04-13SA04-08B07-040 [UZ]B90-1 [MZ](e) Main Zone + Upper Zonezircon/chondriteLa Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm YbB10-056 [Nebo Granite]B10-054 [Stavoren Granophyre]B07-051 [Granophyre](f) Roof Graniteszircon/chondriteLa Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er LuTm Yb10-310-210-110010110210310410-310-210-110010110210310410-310-210-110010110210310410-310-210-110010110210310410-310-210-110010110210310410-310-210-1100101102103104Figure 3 .9 . Chondrite-normalized rare earth element patterns of zircon from the Bushveld Complex. Lines and symbols represent median values and shaded areas indicate the range of all analyses within a sample. All panels are at the same scale. (a) Lower Zone; (b) Lower Critical Zone and Bastard Reef (Upper Critical Zone); (c) UG2 (Upper Critical Zone); (d) Merensky Reef (Upper Critical Zone); (e) Main Zone and Upper Zone; (f) Felsic roof rocks. Normalization values from McDonough and Sun (1995). Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone.95Chapter 3many REE patterns are nearly flat. Some analyses from zircon from each of the three felsic roof rocks samples show more typical zircon REE patterns with no significant LREE enrichment.Anomalies in the chondrite-normalized REE patterns and ratios of the rare earth elements distinguish zircon from the different zones and rock packages for the Bushveld Complex. The europium anomalies in the sample set are mostly below 0.5 (Eu/Eu* = 0.12-0.92) and show negative trends with Hf concentrations for analyses from a single sample (Fig. 3.10a). In contrast, cerium anomalies are more variable (Ce/Ce* = 0.4-12.6) and show no apparent trends (Fig. 3.10c). The ratio of Yb/Dy in zircon defines the slope of the HREE and Lu/Hf defines the partitioning of the REE (e.g., Lu) relative to high field strength elements (e.g., Hf) (e.g., Samperton et al., 2015). In Bushveld zircon, Yb/Dy ranges from 1.6-4.2, with the lower and less variable values generally associated with samples from the Lower Zone and Critical Zone (Fig. 3.10b, d). In zircon from the Main Zone and Upper Zone, along with the felsic roof rocks, Lu/Hf is significantly higher and shows a greater range (Lu/Hf = 21-114 × 104) compared with most zircon from the Lower Zone and Critical Zone (Lu/Hf <40 × 104) (Fig. 3.9b). 3 .5 .4 . Trace element geochemistry of rutileA summary of rutile trace element chemistry is provided in Table 3.4 and the all analytical results by LA-ICP-MS are found in Appendix K. Variations of Pb and U are assessed in Appendix L. Rutile readily accepts substitution of the high field strength elements including Ti, Zr, Hf, Nb, and Ta up to wt. % concentrations (e.g., Zack et al., 2004; Zack and Luvizottow, 2006; Luvizotto et al., 2009). Hafnium and Zr concentrations in rutile span a wide range from 2-303 ppm and from 43-8,230 ppm, respectively (Fig. 3.11a). The relationship between Nb and Ta distinguishes two distinct geochemical groups, a population of rutile typified by high HFSE (1000-20,000 ppm Nb, 100-1760 ppm Ta) and high Cr (5000-14,000 ppm) and Sc (8-17 ppm), and an anomalous population characterized by exceptionally low HFSE (<1000 ppm Nb, <100 ppm Ta) and low Cr (2000-4000 ppm) and Sc (3-15) (Fig. 3.11c). 3 .6 . DiscussionThe trace element chemistry of zircon and rutile from the Bushveld Complex reflects variations in the crystallization path of fractionated interstitial melt in their host cumulates. 96Chapter 300.20.40.60.10.30.5200406080100120Eu/Eu*Ce/Ce*Sc/Th6000 8000 10000 12000 14000 1 2 3 4 5Hf (ppm) Yb/Dy1 2 3 4 5Yb/DyLu/Hf (x 10000)6000 8000 10000 12000 14000Hf (ppm)42068101214543210678910(a) (b)(c) (d)avg 2σavg 2σavg 2σavg 2σNeboStavorenGranophyreUZMZUCZUCZ-MRLCZLZFigure 3 .10 . Trace element ratio variations in zircon from the Bushveld Complex. (a) Europium anomaly (Eu/Eu*) vs. Hf showing a general negative relationship of increasingly negative Eu anomaly with increasing Hf concentration for zircon. (b) Lu/Hf vs. Yb/Dy showing two distinct populations. Zircon from the Main Zone, Upper Zone and roof rock samples defines a steeper negative trend over a large range of Lu/Hf, whereas zircon from the Lower Zone and Critical Zone samples has shallower negative trend with a smaller range of Lu/Hf. (c) Cerium anomaly (Ce/Ce*) vs. Hf showing highly variable Ce anomalies over the range of Hf concentrations. (d) Sc/Th vs. Yb/Dy showing a weak positive correlation based on the entire dataset. Average 2σ uncertainty is indicated in each panel. Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone.97Chapter 3Table 3 .4 .  Summary of ranges of trace element concentrations of rutile from the Bushveld ComplexElement Si Sc Cr Fe Y Zr Nb Hf Ta W Pb Th U T (°C)TW477-661 - Lower Critical Zone (n = 14 (5))Q1 840 5.44 3850 40 0.014 499 72.2 11.4 0.958 17.1 12.0 0.038 5.73 685Median 980 8.68 6020 292 0.014 2445 5595 90.6 326 315 16.0 0.057 8.63 851Q3 1090 10.0 8100 419 0.014 3052 9670 112.6 566 456 43.0 0.12 24.4 878DT28-912 - Upper Critical Zone, UG2 (n = 27 (15))Q1 898 11.3 5555 13.4 0.137 3770 9065 138.8 649 491 2.99 0.040 1.75 906Median 1045 12.2 7510 800 0.174 4220 10640 149.1 806 566 5.14 0.063 2.44 921Q3 1185 13.5 7850 2565 0.194 5025 12375 204.2 928 584 6.47 0.13 3.03 945SA04-06 - Upper Critical Zone, Merensky Reef (n = 16 (16))Q1 855 5.89 2630 3.15 0.027 319 89.4 25.8 4.58 59.8 1.73 0.041 0.319 648Median 1060 8.36 2875 23.6 0.033 475 232 27.1 8.99 137 4.19 0.081 0.935 682Q3 1180 10.7 3160 72.8 0.074 1016 424 42.3 16.8 235 7.13 0.099 3.75 751SA04-08 - Upper Critical Zone, Merensky Reef (n = 24 (12))Q1 725 7.69 5050 16.9 0.01325 2587 6348 91.6 262 267 49.3 0.025 27.5 857Median 1080 11.4 6610 34.8 0.0155 3309 8200 112.4 466 397 66.5 0.033 35.1 888Q3 1340 13.4 7875 58.9 0.0565 4400 10728 155 705 481 88.6 0.056 46.8 927SA04-13 - Upper Critical Zone, Merensky Reef (n = 30 (18))Q1 800 6.02 2418 11.5 0 173 31.3 7.75 0.999 0.108 0.260 0.035 0.121 601Median 900 6.59 2510 15.8 0 220 45.4 9.65 2.61 0.440 0.720 0.035 0.370 619Q3 1100 7.42 2653 20.3 0 359 91.5 14.5 5.88 3.65 1.10 0.035 0.666 658MPD24D2 - Upper Critical Zone, Bastard Reef (n = 4 (0))Q1 1990 9.78NA81.8 0.44 3568 9360 132.1 778 445 4.89 0.49 2.55 898Median 1990 10.3 93.0 0.58 4490 10625 165.0 824 451 8.56 0.73 4.27 928Q3 1990 12.9 575 0.72 5385 15640 207.2 1072 607 16.7 0.97 8.86 955All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace element reduction scheme with stoichiometric Ti of 59.5% used as internal standard. Q1 = quartile 1, Q3 = quartile 3. Q1-Q3 represents the range of the middle 75% of analyses for each sample. Rare earth element (La-Lu) concentrations were collected but values were all below detection limits and are not included. Numbers in secondary parentheses indicate number of analyses with measured Cr concentrations. T (°C) is the Zr-in-rutile temperature calculated using the method of Ferry and Watson (2007). NA = not collected98Chapter 3avg 2σavg 2σavg 2σ0 100 200 300 400Hf (ppm)0200040006000800010000Zr (ppm)0 4000 8000 12000 16000Cr (ppm)0200040006000800010000Zr (ppm)1 10 100 103 104 105Nb (ppm)Ta (ppm)10.10.0110100103104Cr (ppm)0 4000 8000 12000 1600005101520Sc (ppm)SA04-08 [MR]SA04-13 [MR]SA04-06 [MR]DT28-912 [UG2]MPD24D2 [BR]TW477-661 [LCZ]Nb avg 2σ = 6.7%Ta avg 2σ = 8.6%(a) (b)(c) (d)primary igneous rutilerutile exsolved from chromiteFigure 3 .11 . Trace element variations of rutile from the Bushveld Complex. (a) Zr vs. Hf. (b) Zr vs. Cr. (c) Ta vs. Nb, note the logarithmic axes. (d) Sc vs. Cr. Two distinct types of rutile are revealed based on trace element geochemistry. The orange field highlights rutile that is interpreted to represent primary magmatic grains that crystallized from fractionated interstitial melt with elevated Zr, Hf, Ta, Nb, Cr, and Sc. The grey field outlines rutile that is interpreted to have exsolved from chromite and is characterized by low Zr and Hf, very low Ta and Nb, and anomalously low Cr. Average 2σ uncertainty is indicated in each panel. Abbreviations: LCZ, Lower Critical Zone; MR, Merensky Reef; BR, Bastard Reef.99Chapter 3Below, the significance of trace element concentrations and ratios (e.g., Th/U) with respect to the processes that are recorded into their respective mineral systems are considered. Using Ti-in-zircon and Zr-in-rutile thermometry, in conjunction with forward geochemical modelling of zircon saturation from proposed parental magmas, the crystallization pathways are constrained and their impact on the late, near-solidus processes of the Bushveld Complex is assessed. These results also allow for evaluation of relationships between the Upper Zone magmas and felsic magmas that crystallized to produce the variety of granitic rocks that typify the roof of the Bushveld Complex.3 .6 .1 . Mapping the solidus of cumulates and granites from the Bushveld Complex using Ti-in-zircon thermometryIn the Bushveld Complex, zircon occurs in mafic-ultramafic rocks that are characterized either by heterogeneous textures such as coarse grain sizes and the irregular distribution of minerals (e.g., UG2 pyroxenite, Merensky Reef, Bastard Reef), or by the presence of interstitial minerals, typically poikilitic plagioclase, as well as evidence of minerals that crystallized from highly fractionated melts (e.g., quartz, K-feldspar, biotite). The minimum temperature (Tzrc) at which zircon crystallized in the Bushveld cumulates and felsic roof rocks can be calculated following the method of Ferry and Watson (2007):log (ppm Ti-in-zircon) = (5.711 ± 0.072) – (4800 ± 86) / Tzrc (K)– log aSiO2 + log aTiO2Interstitial quartz is present in all mafic-ultramafic cumulates from the Bushveld Complex and thus aSiO2 = 1 for all calculations. Rutile occurs in all samples from Lower Zone, Critical Zone, and Main Zones, which fixes aTiO2 = 1; for the rutile-free Upper Zone and felsic roof rock samples, a value of aTiO2 = 0.7 was used (e.g., Hayden and Watson, 2007; Grimes et al., 2009). The Ferry and Watson (2007) thermometer was calibrated for a pressure of 1 GPa (10 kbars) and they estimated a pressure dependence of -5°C/kbar for pressures below 10 kbars, which would lower the calculated temperatures for the Bushveld Complex (pressure of emplacement ~3 kbars) zircon by ~35°C. In the discussion below, the uncorrected Tzrc values are utilized to compare with published Ti-in-zircon results (Yudovskaya et al., 2013; Zeh et al., 2015) and to compare directly to the Zr-in-rutile thermometry results (Ferry and Watson, 2007; Tomkins et al., 2007).100Chapter 3In the Bushveld Complex, application of Ti-in-zircon thermometry yields temperatures that range from ~950°C down to 690°C (Figs. 3.12, 3.13), comparable to those reported in Yudovskaya et al. (2013; 930-760°C) and Zeh et al. (2015; 940-670°C). The highest temperature for each sample marks the onset of zircon saturation in the fractionated interstitial melt and the lowest temperatures determined for each sample are assumed to represent solidus or near-solidus temperatures. In the ultramafic rocks of the Lower Zone and Critical Zone, higher Ti concentrations in zircon (up to 61 ppm) yield higher temperatures and a range of Tzrc from ~950-730°C with the highest values recorded in the Bastard Reef sample (MP24D2) from the top of the Upper Critical Zone. Temperatures from zircon in the Main Zone sample span a comparable range to those determined from the Critical Zone (Tzrc ~930-750°C). In contrast, zircon from the more evolved Upper Zone diorite and overlying felsic roof rocks are characterized by notably lower temperatures (Tzrc ~875-690°C) (Fig. 3.12j-m). Estimated temperature ranges for individual samples are 182°C (LZ10-02, Lower Zone) to 83°C (B07-040, Upper Zone).Most of the samples analyzed from the Bushveld Complex show prominent negative Ti-Hf relationships that reflect crystallization of zircon from progressively fractionated interstitial melt (i.e., increasing Hf) as temperature decreased (i.e., decreasing Ti) (Fig. 3.12) (e.g., Grimes et al., 2009). The relative range in temperature and composition exhibited by each sample likely reflects the connectivity of interstitial melt pockets within a given cumulate during cooling, compaction, and relative accessory mineral saturation (Meurer and Meurer, 2006; Holness et al., 2011; Cawthorn, 2013a). Zircon in the Upper Zone sample and the three felsic roof rocks record relatively limited Ti-Hf variation indicating that crystallization of zircon was near the eutectic temperature for these rocks.3 .6 .2 . Forward modelling of zircon saturation in fractionated interstitial melts during crystallization of the Bushveld ComplexForward geochemical modelling was carried out using rhyolite-MELTS v1.02 (Gualda et al., 2012) to investigate both the conditions required for zircon saturation in the mafic-ultramafic rocks of the Bushveld Complex and the predicted mineral assemblage at zircon saturation for comparison with the minerals observed in the late-crystallized interstitial pockets and with the thermometry results. The parental magma compositions used include the B1, 101Chapter 3900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°900°800°700°14000100006000 14000100006000 6000 1000010000600014000100006000 1400010000600014000100006000 1400010000600014000100006000 14000100006000 140001000060001400010000600014000100006000020406002040600204060020406002040600204060020406002040600204060020406002040600204060(a) (b) (c)(d) (e) (f)(g) (h) (i)(j) (k) (l) (m)LZ10-02LZTW477-661LCZDT28-912UCZ - UG2B00-1-6UCZ - UG2B90-7(0)UCZ - MRSA04-08UCZ - MRSA04-13UCZ - MRMP24D2UCZ - BRB90-1MZB07-040UZB07-051Roof - GranophyreB10-054RoofStavorenB10-056RoofNeboTi (ppm)Hf (ppm)av 2σNeboStavorenGranophyreUZMZUCZUCZ-MRLCZLZFigure 3 .12 . Ti vs. Hf diagrams for zircon from all samples analyzed from the Bushveld Complex. The horizontal dashed lines indicate Ti-in-zircon temperatures calculated using αSiO2 = 1 and aTiO2 = 1 for all samples, except for the Upper Zone and roof granite samples where aTiO2 = 0.7 (Ferry and Watson, 2007). All plots are shown at the same scale. (a) LZ10-02. (b) TW477-661. (c) DT28-912. (d) B00-1-6. (e) B90-7(0). (f) SA04-08. (g) SA04-13. (h) MP24D2. (i) B90-1. (j) B07-040. (k) B07-051. (l) B10-054. (m) B10-056. Most samples show distinct trends of decreasing Ti (and temperature) with increasing Hf that tracks the progressive crystallization of zircon from fractionated interstitial melt down to temperatures approaching the solidus for the mafic-ultramafic rocks (750-800°C). The roof granites show more restricted variation suggesting crystallization at or near the eutectic. Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone; MR, Merensky Reef; BR, Bastard Reef.102Chapter 36000 8000 10000 12000 14000Ti-in-Zircon Temperature (ºC)Frequency (n)7507006508008509009501000Ti-in-Zircon Temperature (ºC) (a)(b)650 700 750 800 850 900 950 10005010152025303540Hf (ppm)avg 2σNeboStavorenGranophyreUZMZUCZUCZ-MRLCZLZFigure 3 .13 . Summary of thermometry results for zircon from the Bushveld Complex. (a) Ti-in-zircon temperature vs. Hf showing distinct negative trends within the dataset. Ti-in-zircon temperatures calculated using aSiO2 = 1 and aTiO2 = 1 for all samples, except for the Upper Zone and roof granite samples where aTiO2 = 0.7 for UZ (Ferry and Watson, 2007). (b) Histogram showing the distribution of calculated Ti-in-zircon temperatures ranging from ~950°C down to 690°C. Average 2σ uncertainty in temperature is based on uncertainty in Ti concentration only. Uncertainty including error reported in the Ti-in-zircon thermometry equation is shown as grey band behind uncertainty. Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ-MR, Upper Critical Zone-Merensky Reef; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone.103Chapter 3B2, and B3 magmas from Barnes et al. (2010) and a 60:40 mixed composition of B1 and B2 magmas as a potential parent to the Upper Critical Zone (Barnes et al., 2010). The MELTS runs were carried out at 3 kilobars pressure in both equilibrium and fractional crystallization mode at 10°C temperature increments starting from just above the liquidus for each composition down to 690°C, or until no melt remained. To reproduce the predominantly orthopyroxenitic cumulates present in the Critical Zone, clinopyroxene was suppressed from crystallization. The initial starting water contents were varied from 0.25-1.0 wt.% H2O and a value of 1.0 wt. % H2O yielded phases that were most consistent with the observed late-stage mineral assemblages of quartz, biotite, and apatite. Amphibole was also suppressed during crystallization due to its absence in the mafic-ultramafic cumulates of the Bushveld Complex. Partition coefficients for Zr into the mineral phases present in the modelled Bushveld crystallization sequences were from Bédard (2006, 2007). Bulk zircon saturation was calculated following the experimentally determined relationship of Watson (1979) with revised coefficients by Boehnke et al. (2013) that relates zircon saturation in silicate magmas to melt composition and temperature:ln DZr = (10108 ± 32)/T(K) – 3(1.16 ± 0.15)(M – 1) – (1.48 ± 0.09)where DZr = distribution coefficient, T(K) = temperature in Kelvin, and M = (Na + K + 2Ca)/(Al ∙ Si) with each component representing the normalized molar ratio; calculation of Zrmelt requires division of DZr by the abundance of Zr in zircon (~500,000 ppm: Watson, 1979). The results of the MELTS modelling and zircon saturation are shown in Figures 3.14 and 3.15, and complete output tables and additional diagrams are provided in Appendix M.The MELTS modeling results confirm that zircon saturation can be reached using all four of the proposed parental melts as starting compositions (Fig. 3.14). The concentration of Zr, an incompatible element, in the melt increases during crystallization of the major cumulus minerals (i.e., Zr-free minerals) and the onset of saturation occurs with less than ~20% remaining melt and even under 10% melt (e.g., B2 and B3 magmas, Fig. 3.14c-d) at temperatures ranging from 800°C to 740°C. These temperatures are directly comparable to those determined by Ti-in-zircon thermometry (Fig. 3.13) and the predicted remaining melt volumes correspond to the observed rock textures (e.g., 5-20 vol.% interstitial material). The modelling results also reproduce the observed mineralogy in the mafic-ultramafic cumulates, forming predominantly orthopyroxenites 104Chapter 301002003004005006007008009001000700 750 800 850 900 950 100010% melt20% melt30% melt01002003004005006007008009001000700 750 800 850 900 950 100010% melt20% melt30% melt01002003004005006007008009001000700 750 800 850 900 950 100010% melt20% melt01002003004005006007008009001000700 750 800 850 900 950 100010% melt20% meltB1 B2B1:B2 60:40 Mix B3Tsat = [Zr]melt = M = SiO2 = Zri = 850 ºC300 ppm 1.03 67 wt. %77 ppmTsat = [Zr]melt = M = SiO2 = Zri = 800 ºC230 ppm 1.1865 wt. %68 ppmTsat = [Zr]melt = M = SiO2 = Zri = 790 ºC520 ppm 1.9162 wt. %54 ppmTsat = [Zr]melt = M =  SiO2 = Zri = 760 ºC220 ppm 1.5259 wt. %23 ppmTemperature (ºC)Zr (ppm)[Zr] in melt[Zr] for sat Figure 3 .14 . Zr vs. temperature (°C) plots summarizing zircon saturation modelling using rhyolite-MELTS of four proposed parental Bushveld magmas. (a) B1 magma. (b) 60:40 mix of B1 and B2 magmas. (c) B2 magma. (d) B3 magma. Estimated parental magma compositions from Barnes et al. (2010) based on the whole rock chemistry of marginal sills – see the relative locations on the stratigraphic column in Figure 2. The red lines track the evolution of the Zr concentration in the melt with fractionation (decreasing temperature) and the blue lines indicate the calculated Zr concentration for zircon saturation in the melt (Watson and Harrison, 1983; Boehnke et al., 2013). Zircon saturation occurs where the lines intersect and is denoted with a red star. The saturation temperature and the Zr concentration, SiO2 content, and M-value (M = [Na + K + 2Ca]/[Al ∙ Si]) in the melt at zircon saturation, and initial Zr content of the magma, are indicated for each composition – see text for additional details and MELTS parameters. Note that all plots are at the same scale for comparison. Vertical dashed lines indicate percent melt remaining based on MELTS calculations.105Chapter 301020304050607080901000102030405060708090100700 800 900 1000 1100 1200 1300meltopxplagoxide mtilmB1:B2 60:40 Mix0510152025012345678910700 720 740 760 780 800meltmeltoxideoxidequartz biotiteZr-sattitaniteksp H2O% Melt Remaining% Melt Remaining% MineralTemperature (˚C)Temperature (˚C)% Mineralequilibrium crystallizationfractional crystallizationequilibrium crystallizationfractional crystallizationFigure 3 .15 . Predicted temperature vs. mineral abundance for equilibrium crystallization (solid lines) and fractional crystallization (dashed lines) as modeled with rhyolite-MELTS for Bushveld parental magma B1:B2 (60:40 mix). (a) Complete temperature range from 1300°C (liquidus) to 700°C (solidus) showing similar minerals and abundances for both models. (b) Detailed view of the final 20% of crystallization from 800-700°C showing the differences between the models with biotite, quartz, and titanite crystallization in the equilibrium model and magnetite, alkali feldspar, and quartz crystallization in the fractional model. The secondary y-axis shows the % melt remaining (thick black lines, solid and dashed). The red star indicates the point of bulk zircon saturation at ~13% remaining melt. Clinopyroxene crystallization was suppressed in all models. Abbreviations: opx, orthopyroxene; plag, plagioclase; mt, magnetite; ilm, ilmenite; ksp, alkali feldspar.106Chapter 3followed by plagioclase and a late assemblage of minor and accessory minerals. At zircon saturation, the composition of the remaining liquid is felsic-intermediate (59-67 wt. % SiO2) and the predicted stable phases include biotite, quartz, and alkali feldspar, with titanite appearing in equilibrium models at <800°C (Fig. 3.14, 3.15), all of which occur in the samples themselves (e.g., Fig. 3.4a, b, e; Fig. 3.5). Zircon will be a stable liquidus phase in fractionated melts within mafic-ultramafic cumulates of layered intrusions provided that sufficient interstitial melt remains trapped within the matrix of the growing cumulus crystals to allow for crystallization of a Si-H2O-rich near-eutectic mineral assemblage (e.g., quartz, Na-plagioclase, K-feldspar, biotite), including zircon, at temperatures approaching the solidus.3 .6 .3 . High-Th/U zircon in the Critical Zone: a signal of late-stage fluid saturationIn Bushveld zircon, Th/U varies from typical magmatic values of ~0.5 to 1-2 (e.g., Belousova et al., 2002; Xiang et al., 2011; Kirkland et al., 2014) for most zircon to anomalously high values (2-77) from orthopyroxenites from the Upper Critical Zone (Fig. 3.8a). The high-Th/U analyses appear to be related to a depletion in U relative to Th as the majority of the Th concentrations in these zircon grains are similar to those analyzed from zircon in samples from the Rustenburg Layered Suite and felsic roof rocks. Similar to the high Th/U zircon documented in the Stillwater Complex (Wall, 2016), three distinct processes can be evaluated to account for the high-Th/U zircon from the Bushveld Complex: (1) co-crystallization of zircon with other U-rich phases, (2) a fractionation effect of zircon alone, and (3) late-stage oxidation and fluid saturation. The occurrence of co-crystallizing phases (e.g., uraninite, zirconolite, baddeleyite) with a greater affinity for U than Th would lead to high Th/U in the fractionating interstitial melt and would also result in high-Th/U zircon that crystallized from this melt. Baddeleyite is extremely rare in the Bushveld Complex (Wall, 2016), and there are no other U-rich phases in the examined mineral separates, thus the significant increase in Th/U required in the melt to produce high-Th/U Bushveld zircon cannot be explained by co-crystallization of other U-rich phases with zircon. Kirkland et al. (2014) demonstrated that Rayleigh fractionation of zircon with decreasing temperature will result in lower Th/U in zircon, opposite to what is observed here, due to the depletion in U (relative to Th) in cooler, fractionated melts being as U is extracted from the melt. This is supported by the lack of significant Th/U zoning within the analyzed grains from the 107Chapter 3Bushveld Complex or systematic trends of increasing Hf and decreasing Ti within individual grains (Appendix N).Highly variable Th/U (up to 10) in zircon from the UG2 chromitite was observed by Zeh et al. (2015) in their study of zircon chemistry from the Upper Critical Zone and lower Main Zone of the Bushveld Complex. When considered with the Ti-in-zircon results (940-670°C), Zeh et al. (2015) proposed that the Th/U variations in zircon reflected magmatic fractionation of zircon with coexisting minerals, including apatite and rutile, to increase Th/U in zircon, and potentially late thorite to drive Th/U back down to normal magmatic values, all within a single sample. They concluded that the high and variable Th/U could be attributed to simple Raleigh fractionation where the zircon-melt partitioning coefficients for U (DU) were much higher than that for Th (DTh) such that coefficient ratio DTh/DU decreased during cooling following the partition coefficient experiments of Rubatto and Hermann (2007). The results of  Kirkland et al. (2014) previously discussed, however, indicate that the fractionation effect of DTh/DU is unlikely to produce the required increases in Th/U in zircon during crystallization and thus an alternative mechanism is required to explain the high-Th/U zircon in the Bushveld Complex.A local change in the oxidation state of the fractionated interstitial melt may result in high-Th/U zircon that is characteristic of the orthopyroxenites of the Upper Critical Zone due to partitioning of U6+ in a Cl-rich fluid phase (Keppler and Wyllie, 1991; Bacon et al., 2007). Apatite has been used as a monitor of relative halogen variations of interstitial melts in mafic layered intrusions (Boudreau et al., 1986; Boudreau and McCallum, 1989) and it is a common interstitial mineral in the Bushveld Complex. Apatite and biotite from rocks below the Main Zone of the Bushveld Complex are characterized by high ratios of Cl/F (i.e., chlorapatite) (Boudreau and McCallum, 1989; Willmore et al., 2000). To produce the high-Th/U zircon in the orthopyroxenites from the Upper Critical Zone, it is proposed that zircon crystallized and grew from fractionated interstitial melt during and following exsolution of Cl-rich fluids. These fluids preferentially partitioned U6+ resulting in high Th/U in the remaining melt. This process must have begun at relatively high temperatures (~950°C) based on the Ti-in-zircon thermometry results (Fig. 3.13). This possibility is also consistent with evidence from the halogen geochemistry of apatite for fluid saturation in Critical Zone melt at temperatures >1000°C (Boudreau, 1999; Willmore et al., 2000). Zircon from individual samples has variable Th/U, 108Chapter 3reflecting the degree to which the interstitial melt pockets were interconnected and equilibrated with Cl-rich fluids.3 .6 .4 . Origin of LREE-enriched signature of zircon from the roof of the Bushveld ComplexThe LREE-enrichment (i.e., anomalously low (Sm/La)N) of zircon from the three felsic roof rocks and from the Main Zone sample is distinct from the normal magmatic REE patterns of zircon found in the mafic-ultramafic cumulates in the Bushveld Complex (Fig. 3.9). Relative enrichment of the LREE in zircon may result from hydrothermal alteration leading to solid-state partial recrystallization or re-equilibration with fluids during local dissolution-reprecipitation and formation of micro-inclusions (e.g., xenotime YPO4, monazite CePO4, apatite Ca5(PO4)3(F,Cl,OH)) (Hoskin and Schaltegger, 2003; Hoskin, 2005; Geisler et al., 2007; Grimes et al., 2009). Although relatively large inclusions of apatite, alkali feldspar, and albite may be found in some zircon in the roof granites (Fig. 3.16d-g), the analyzed grains were devoid of these types of inclusions (Appendix G). To test the effect of ablating zircon with micro-inclusions (i.e., not resolvable by SEM), mixing calculations were carried out using an analysis from B10-056 (Nebo granite) with the lowest La concentration (highest (Sm/La)N) as the starting composition and the most LREE-enriched analysis in the sample as the “contaminated” end-member (Fig. 3.16a-c). The effect of ablating micro-inclusions was simulated by using the average REE concentrations of apatite from the top of the Upper Zone (VanTongeren and Mathez, 2012) and monazite and xenotime compositions from Borai et al. (2002). The calculations demonstrate that addition of apatite could reproduce the LREE enrichment and overall shape of the REE patterns, although this requires mixing in an unrealistic amount of apatite (up to 35 wt.%). Due to the positive slope of the REE pattern for xenotime, mixing with zircon at any quantity yields increased concentrations, but does not flatten the LREE as observed in the zircon patterns from the top of the Bushveld Complex. In contrast, mixing with as little as 0.01 wt. % monazite could produce both the observed patterns and slopes and significant LREE enrichment occurs with incorporation of only 0.001 wt. % of monazite. With the exception of Y, which is significantly more abundant in zircon with the LREE-enriched compositions (Table 3.3) suggesting that some proportion of the micro-inclusions may be xenotime, incorporation of such small amounts of monazite (±xenotime) is unlikely to have a noticeable effect on the remaining trace element 109Chapter 3La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu10-210-1100101102103104Bushveld UZ ApatiteVanTongeren and Matthez (2010)0.1%1%10%50%10-210-1100101102103104105106107La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb LuMonaziteBorai et al. (2002)0.1%0.001%0.01%0.05%La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu10-210-1100101102103104105106XenotimeBorai et al. (2002)0.1%10%1%5%Sample / Chondriteapatiteapatitealbiteapatiteksparkspar(a)(b)(c)(d)(e)(f)(g)Figure 3 .16 . REE geochemistry and the effect of ablating inclusions in the felsic roof rocks. Modeling results for the Upper Zone sample (B10-056) show the effect of integrating accessory mineral inclusions on rare earth element (REE) concentration during ablation of zircon. (a-c) Chondrite-normalized REE patterns showing the effect of incorporating inclusions of apatite (a), xenotime (b), and monazite (c) during analysis of zircon. Yellow lines indicate zircon with a typical magmatic pattern from B10-056 (lower line) and an analysis with flat light REE (upper line). The Bushveld apatite pattern is from VanTongeren and Mathez (2010), and the xenotime and monazite compositions are from Borai et al. (2002). Mixing proportions are in wt. %. Addition of apatite reproduces the elevated light REE and does not affect the HREE. (d) BSE image of alkali feldspar inclusions within a strongly fractured zircon from sample B07-051, roof granophyre. (e) BSE image of a small apatite inclusion within a euhedral zircon from sample B10-054, Stavoren granophyre. (f) BSE image of large apatite inclusions and a small albite inclusion within a fractured euhedral zircon from sample B10-056, Nebo Granite. (g) BSE image of apatite and alkali feldspar inclusions in a zircon from sample B10-056, Upper Zone. Scales as indicated on panels d-g.110Chapter 3budget in zircon from the Bushveld Complex.3 .6 .5 . Zircon trace element constraints on the relationship between the Upper Zone magmas and felsic magmas in the roof of the Bushveld ComplexThe roofs of mafic layered intrusions play an important role in modulating their thermal evolution, yet remarkably, the floor and roof are only exposed in six layered intrusions worldwide: Skaergaard, Kiglapait, Muskox, Sept Iles, Dufek, and the Bushveld Complex (VanTongeren and Mathez, 2015). The petrogenetic relationship between the roof units of the Bushveld Complex, including the Lebowa Granite Suite, the Rashoop Granophyre Suite, and the volcanic rocks of the Rooiberg Group, has been the subject of vigorous debate for decades (Twist and French, 1983; Eales and Cawthorn, 1996; Schweitzer et al., 1997; Cawthorn, 2013b; Mathez et al., 2013). Mass balance calculations (e.g., Cr, Zr, K) indicate that the volume of magmas required to produce the rocks of the Rustenburg Layered Suite likely exceeded 1,000,000 km3, significantly greater than the 370,000-600,000 km3 of rock present today (Cawthorn and Walraven, 1998). Based on modeling of the estimated bulk composition of the Bushveld Upper Zone and Upper Main Zone (UUMZ), VanTongeren et al. (2010) concluded that 15-25% of the original magma volume was expelled and that it is manifest either as part of the upper volcanic sequence of the Rooiberg Group or as the Rashoop Granophyre. Mathez et al. (2013) proposed that the Rashoop Granophyre Suite formed by fractional crystallization of Bushveld magmas based on field relationships (e.g., Twist and French, 1983), isotopic systematics (e.g., Buchanan et al., 2002; Fourie and Harris, 2011), and major element chemistry and modelling (e.g., VanTongeren et al., 2010; VanTongeren and Mathez, 2012). Below, we evaluate the link between the Upper Zone of the Rustenburg Layered Suite and the overlying felsic roof rocks from the trace element perspective of zircon.The trace element systematics of zircon from the Upper Zone sample (B07-040) and from the three felsic roof rocks (B07-051, Rashoop granodiorite or “leptite”; B10-54, Rashoop [Stavoren] granophyre; B10-056 = Lebowa [Nebo] granite) are strikingly similar, and distinct from zircon at lower stratigraphic levels in the Rustenburg Layered Suite (Figs. 3.17, 3.18). Zircon from all four of these samples shares a common Th/U (~0.5) (Fig. 3.8a) and defines a continuous Ti-Hf co-variation (Fig. 3.8d) corresponding to Tzrc temperatures (875-690 °C) that 111Chapter 30 500 15001000 2000∑REE0 0.005 0.010 0.015Lu/HfTi (ppm)0 20 40 60900°C800°C700°C600°C0.1 1 10 1000 500 15001000 20000 0.005 0.010 0.0150 20 40 60 0.1 1 10 100Th/U(a) (b) (c) (d)BRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOFFigure 3 .17 . Box-and-whisker diagrams showing trace element variations in zircon vs. stratigraphic height in the Bushveld Complex. (a) Ti. (b) Th/U, note logarithmic scale. (c) Lu/Hf. (d) ∑REE = sum of the concentrations of the rare earth elements (La-Lu). Each box represents the lower 25% to upper 75% of values for each sample and the whiskers extend to minimum and maximum values. The line in each box shows the median value. Average 2σ uncertainty is indicated in each panel. The thick dashed red line indicates the location of the Merensky Reef for reference. Abbreviations in stratigraphic column: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone. Units indicated on left side of column: LG, Lower Group chromitites; MG, Middle Group chromitites; UG, Upper Group chromitites; BB, Boulder Bed; MR, Merensky Reef; BR, Bastard Reef; Main Magnetite Layer; M21, Magnetite layer 21.112Chapter 30 5 10Sc/YbBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOFYb/Dy0 2 4 6Eu/Eu*0.1 0.5 1U/Yb0.01 0.1 1 100 5 10 0 2 4 6 0.1 0.5 1 0.01 0.1 1 10Figure 3 .18 . Box-and-whisker diagrams showing trace element ratio variations in zircon vs. stratigraphic height in the Bushveld Complex. (a) Sc/Yb. (b) Yb/Dy. (c) Eu/Eu*, note logarithmic scale. (d) U/Yb, note logarithmic scale. Each box represents the lower 25% to upper 75% of values for each sample and the whiskers extend to minimum and maximum values. The line in each box shows the median value. Average 2σ uncertainty is indicated in each panel. The thick dashed red line indicates the location of the Merensky Reef for reference. Abbreviations in stratigraphic column: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone. Units indicated on left side of column: LG, Lower Group chromitites; MG, Middle Group chromitites; UG, Upper Group chromitites; BB, Boulder Bed; MR, Merensky Reef; BR, Bastard Reef; Main Magnetite Layer; M21, Magnetite layer 21.113Chapter 3are notably cooler than those from the mostly ultramafic cumulates. Zircon from the Upper Zone sample records the lowest temperatures, which would be consistent with crystallization of zircon from fractionated interstitial melt between the major cumulus phases (e.g., plagioclase, olivine, clinopyroxene) at the top of a thermally insulated pile of cumulates compared to the relatively rapid cooling that the higher level granitic intrusions likely experienced. Additional trace element commonalities between these samples include (1) the LREE-enriched patterns and geochemical evidence for incorporation of monazite/xenotime micro-inclusions (Fig. 3.9), and (2) trace element ratios (e.g., Lu/Hf, Sc/Yb, U/Yb; Fig. 3.18) that are relatively insensitive to changes in zircon/melt partitioning (e.g., Grimes et al., 2015; Samperton et al., 2015), and which can vary by an order of magnitude over several hundred degrees (e.g., Sano et al., 2002; Thomas et al., 2002; Hanchar and van Westrenen, 2007; Rubatto and Hermann, 2007). VanTongeren and Mathez (2015) argue that the microgranites (“leptites”), which form a distinctive, 100- to 300-m-thick rock layer mixed with hornfels that represent the immediate roof of the intrusion in the Eastern Limb, do not have the appropriate REE concentration to be the residual liquid from the Bushveld mafic magma and instead represent the product of partial melting at extreme temperatures (pyroxene-hornfels facies) of volcanic rocks of the Dullstroom or Damwal formation in the Rooiberg Group. Intriguingly, based on the trace element geochemistry of zircon from this study, it is permissible that all of these units in the uppermost part of the Bushveld Complex share a common petrogenetic link, whether as a direct lineage between the Upper Zone and Rashoop (Stavoren) granophyres (e.g., VanTongeren et al., 2010; Mathez et al., 2013; VanTongeren and Mathez, 2015) as ferroan granites (Lebowa, Nebo) that may have originated by fractional crystallization from Rustenburg Layered Suites magmas (Mathez et al., 2013), or perhaps as a result of melting of volcanic rocks that were contemporaneous with or immediately preceded by emplacement of the large volume of mafic-ultramafic magmas that crystallized to produce the Rustenburg Layered Suite (Buchanan et al., 2002, 2004).3 .6 .6 . Rutile as a petrogenetic indicator in the Bushveld Complex and other mafic layered intrusionsRutile, the most common naturally occurring titanium dioxide polymorph, is found in a wide range of rocks as an accessory mineral, including granitoids, metamorphic rocks, mantle 114Chapter 3rocks, and meteorites (Meinhold, 2010). Based on its chemical variability (e.g., major host of Nb, Ta and other HFSE such as Zr, appreciable U contents), rutile can be used as a key petrogenetic indicator mineral to monitor a variety of geochemical and geochronological processes (e.g., Rudnick, 2000; Zack et al., 2004a, 2004b; Schmidt et al., 2009; Meinhold, 2010; Scoates and Wall, 2015). In igneous rocks, rutile is most commonly found in granites and associated quartz veins, pegmatites, carbonatites, kimberlites, and metallic ore deposits (Meinhold, 2010), and its presence is now increasingly recognized in mafic-ultramafic plutonic rocks, including layered intrusions such as the Bushveld Complex (Cameron, 1979; Scoates and Friedman, 2008; Vukmanovic et al., 2013; Yudovskaya et al., 2013; Scoates and Wall, 2015) and the Great Dyke (Oberthür et al., 2002), as well as in anorthosite-hosted Fe-Ti oxide ore deposits (Morisset et al., 2010, 2013).The textural setting and geochemistry of rutile in rocks of the Critical Zone from the Bushveld Complex reveal two distinct paths for its formation in the mafic-ultramafic cumulates. Magmatic rutile that is inferred to have crystallized directly from interstitial melt is present as small euhedral to subhedral needles and is associated with biotite or finely dispersed within quartz (e.g., Fig. 3.4d). It is readily identifiable by high HFSE concentrations typical of igneous rutile from other settings (Meinhold, 2010) and by notably high Sc and Cr contents (Fig. 3.11d). The strong temperature dependence on the partitioning of zirconium into rutile coexisting with zircon or other Zr-rich phases allows for calibration of the Zr-in-rutile thermometer (Zack et al., 2004b; Watson et al., 2006; Ferry and Watson, 2007; Tomkins et al., 2007). The thermometer of Ferry and Watson (2007) expresses temperature as:log (ppm Zr-in-rutile) = (7.420 ± 0.105) – (4530 ± 111)/T(K) – log aSiO2Zr-in-rutile thermometry results for interstitial rutile yield a range of temperatures (~1000-800°C) that are interpreted as crystallization temperatures and that broadly overlap the Ti-in-zircon temperatures from the same rocks (Fig. 3.19). In contrast, rutile that forms rims or subequant grains on chromite is interpreted as an exsolution product of chromite (e.g., Ghisler, 1970; Ghosh and Konar, 2011; Vukmanovic et al., 2013). This rutile is depleted in the HFSE compared to the magmatic rutile, very highly depleted in Ta and Nb, and contains significantly less Cr than the interstitial grains (Fig. 3.11b-d). The exsolved rutile inherits the chemical signal 115Chapter 360050040070080090010001100Nb (ppm)magmaticrutilerutile exsolved from chromiteZr-in-Rutile Temperature (ºC)500 600 700 800 900 1000 110002468101214MPD24D2SA04-13SA04-08SA04-06DT28-912TW477-661(a) (b)1 10 100 103 104 105Figure 3 .19 . Summary of thermometry results for rutile from the Bushveld Complex. Temperatures are Zr-in-rutile temperatures calculated assuming aSiO2 = 1 for the primary magmatic rutile grains and aSiO2 = 0.5 for the rutile exsolved from chromite (Ferry and Watson, 2007). (a) Zr-in-rutile temperature vs. Nb concentration showing the high temperatures characteristic of magmatic rutile that crystallized from interstitial melt in the cumulates of the Upper Critical Zone and the anomalously low estimated temperatures for rutile that exsolved from chromite. Note the logarithmic scale for Nb. (b) Histogram showing the distribution of calculated Zr-in-rutile temperatures with a clear distinction between the two types of rutile. 116Chapter 3of its original chromite host, which contains very low abundances of the HFSE in general (Pagé et al., 2012) and which contains Cr as an essential structural constituent. Application of the Zr-in-rutile thermometer to the exsolved rutile requires an assessment of silica activity and a value of aSiO2 = 0.5 is assumed (e.g., Hayden and Watson, 2007). The estimated temperatures (800-480°C) are significantly lower than those determined for the coexisting magmatic rutile (Fig. 3.19b) and are consistent with exsolution of the TiO2 component of chromian spinel at subsolidus conditions during cooling of the Bushveld Complex. Some samples contain only magmatic rutile (e.g., DT28-912, MP24D2), others are dominated by exsolved rutile (e.g., SA04-13, SA04-06), and still others have mixed populations of the two different types of rutile (e.g., SA04-08, TW477-661). A combination of careful petrography/imaging and trace element geochemistry can successfully resolve which type of rutile is present in any given sample.The discovery of accessory rutile in rocks of the Bushveld Complex opens up new possibilities for examining geochemical pathways during late-stage consolidation of mafic-ultramafic cumulates and the timescales of cooling and uplift in layered intrusions. As this study demonstrates, the distinctive trace element chemistry of rutile allows for discriminating between different types of rutile even within individual samples. Isotopic fingerprinting of rutile (Hf-O isotopes) from layered intrusions holds promise to complement existing whole rock and mineral isotopic studies (e.g., Rb-Sr, Sm-Nd, Lu-Hf, Pb-Pb) that reveal both source constraints and processes involved in their crystallization and consolidation (DePaolo and Wasserburg, 1979 [Stillwater]; Stewart and DePaolo, 1990 [Skaergaard]; Chutas et al., 2012 [Bushveld]; VanTongeren et al., 2016 [Bushveld]). Rutile can also be exploited as a mineral chronometer in layered intrusions using combined U-Th-Pb geochronology and (U–Th)/He thermochronology to establish complete cooling histories for mafic layered intrusions. U-Pb dating of rutile, where the closure temperature for Pb diffusion is in the range of 400-600°C (Cherniak, 2000; Schmitz and Bowring, 2003) from the Bushveld Complex yields dates (ca. 2053 Ma) that are ~4 million years younger than the U-Pb zircon dates (ca. 2057 Ma) from the same rocks and allow for construction of a cooling history for this major layered intrusion (Scoates and Wall, 2015). For (U-Th)/He thermochronology, the closure temperature of He diffusion in rutile is much lower (~100-200°C) depending on grain size and cooling rate (Stockli et al., 2007; Cherniak and Watson, 2011), and this low-temperature chronometer can be applied to determine 117Chapter 3rates of exhumation and erosion of layered intrusions, a research area that has not yet been investigated. Based on the results of this study, we predict that rutile is undoubtedly present in other major layered intrusions, and target rocks should include those that contain chromite and especially those that contain crystallized pockets of interstitial minerals that represent the final crystallization products of fractionated interstitial melt (e.g., quartz, K-feldspar, biotite, apatite, zircon).3 .7 . ConclusionsThe trace element geochemistry of zircon and rutile determined by LA-ICP-MS from a suite of samples spanning nearly the entire stratigraphy of the Bushveld Complex establishes a temperature-composition framework for crystallization of fractionated interstitial melt in mafic-ultramafic cumulates and associated granitic magmas. Three broad groups are defined based primarily on similarities in Ti-Hf, Th/U, and REE variations in zircon, including (1) the Lower Zone and Main Zone, (2) the Critical Zone, and (3) the Upper Zone and felsic roof rocks (e.g., Rashoop, Lebowa). Ti-in-zircon thermometry yields near-solidus temperatures (950-730°C) for the mafic-ultramafic cumulates of the Lower Zone, Critical Zone, and Main Zone, and notably cooler temperatures (875-690°C) for an Upper Zone diorite and the overlying felsic rocks. Forward modelling using rhyolite-MELTS of the crystallization of proposed parental magmas for the Bushveld Complex produces zircon saturation (800-740°C) from highly fractionated melts (~5-20% remaining melt) with late-stage, near-solidus mineral assemblages that are identical to those observed in the rocks (e.g., quartz, Na-plagioclase, K-feldspar, biotite). High-Th/U zircon from the Critical Zone reflects U loss from the interstitial melt during exsolution of an oxidized Cl-rich fluid. Strikingly similar zircon chemistry between a diorite from the uppermost Upper Zone and the overlying felsic roof rocks supports proposals that these granites and granophyres formed from expelled residual magmas produced during fractional crystallization of Bushveld magmas and crystallization of the 8 km-thick stack of mafic-ultramafic cumulates. Identification of two distinct morphological and geochemical types of rutile in the Bushveld Complex, needle-like magmatic rutile with typical high HFSE that crystallized from fractionated interstitial melt (Zr-in-rutile thermometry = 1000-800°C) along with zircon and rutile exsolved from chromite (800-480°C) with anomalously low HFSE, provides a new tool for evaluating the 118Chapter 3consolidation of mafic-ultramafic cumulates and the timescales of cooling and uplift in layered intrusions. Exploring the near-solidus evolution of mafic layered intrusions like the Bushveld Complex using the trace element chemistry of accessory minerals provides a novel approach to constraining the late stages of crystallization from highly fractionated interstitial melt in these petrologically important intrusions.119Chapter 4Chapter 4Chapter 4Conclusions120Chapter 44 .1 . Summary of the thesis and key findingsThis chapter concludes the study of in situ zircon analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) where two distinct, yet complementary, approaches were used: (1) an analytical study that aimed to improve the precision and accuracy of U-Pb dating of zircon by addressing downhole fractionation in common zircon reference materials and samples, and (2) a practical application on the trace element geochemistry of zircon and rutile in the Bushveld Complex, a giant mafic-ultramafic intrusion in South Africa, to evaluate near-solidus processes and the fate of fractionated interstitial melt in layered intrusions. Below, the key findings of both studies are summarized and their significance to research is assessed and compared with established literature. Finally, suggestions for future research are made to further the impact of both of these studies, including recommendations for enhanced LA-ICP-MS methodologies for U-Pb zircon dating and approaches to the study of mafic magmatism in the Earth’s crust through the trace element chemistry of accessory minerals.4 .2 . Correcting for downhole fractionation in U-Pb zircon geochronology by LA-ICP-MSU-Th-Pb zircon geochronology remains a core application of LA-ICP-MS with advancements continually being made to enhance both precision and accuracy. While major innovations have dramatically improved both instrumentation and data reduction (Günther and Heinrich, 1999; Paton et al., 2010, 2011; Sylvester and Jackson, 2016), the ability to properly calibrate analyses with suitable reference materials, especially for downhole fractionation effects, still limits the overall precision and accuracy of U-Pb zircon dating by LA-ICP-MS. For dating very old samples (>1000 Ma), few zircon reference materials are available (Wall et al., 2016), which makes matrix-matching of unknown samples with reference materials challenging. A significant issue in obtaining accurate U-Pb zircon dates is assessing the effect of downhole fractionation, the time-dependent evolution of Pb-U ratios as an ablation pit deepens, which must be characterized and corrected for (Paton et al., 2010).This study aimed to improve the method by which LA-ICP-MS data for U-Th-Pb zircon geochronology are calibrated and reduced by assessing variations in the effectiveness of 121Chapter 4downhole fractionation corrections when applied to Precambrian samples. Through analysis of three well-characterized zircon reference materials (Plešovice, Temora-2, 91500) and three in-house zircon samples from mafic intrusions treated as unknowns (Laramie, Bushveld, Stillwater), the variability in downhole fractionation was measured between the six zircon samples as well as the effect on the final calculated ages. Downhole fractionation showed significant differences between the mafic intrusion zircon and reference materials (Fig. 4.1), demonstrating that it is essential to match the downhole fractionation of a chosen reference material with the observed behaviour of an unknown zircon to adequately correct Pb/U as the ablation progresses. One proposed method to effectively standardize the downhole behaviour between standards and unknowns is through pre-treatment protocols designed to recrystallize the zircon structure and heal any zones that have been affected by Pb loss (Crowley et al., 2014; Solari et al., 2015; Marillo-Sialer et al., 2016). In this study, both annealing and annealing + leaching (chemical abrasion) (Mattinson, 2005) typically lessened the degree of Pb/U fractionation over the course of an ablation in most samples. Age calculations for both the treated and untreated zircon populations using the untreated reference materials (Plešovice, Temora-2, 91500), the technique employed in the vast majority of studies, produced significant shifts in the final calculated ages that were a function of the effectiveness of the applied downhole fractionation correction (i.e., similarity of downhole fractionation pattern between reference material and unknown). Optimal U-Pb ages were determined when downhole fractionation in both the reference material and unknown zircon was most similar (Fig. 4.1).4 .3 . Implications of trace element systematics in zircon in layered intrusionsConstraints on the petrogenesis of mafic layered intrusions are derived based principally from high-temperature processes related to the sequence of crystallization of the major cumulus minerals (i.e., olivine, pyroxenes, plagioclase) (Bowen, 1928; Wager and Brown, 1968; Parsons, 1987; Eales and Cawthorn, 1996). The presence of zircon associated with late-crystallized minerals (e.g., quartz, Na-plagioclase, K-feldspar, biotite) within late-stage interstitial pockets presents a new approach for the study of crystallization processes and geochemical evolution of these intrusions from a lower temperature perspective (e.g., Scoates and Wall, 2015). Based on the analysis of zircon from 13 samples spanning the stratigraphy of the 122Chapter 418501950205021500.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.850.320.340.360.380.40207Pb/235U207Pb/235U weighted mean = 2026 ± 16207Pb/206Pb weighted mean= 2025 ± 32206 Pb/238 Uconcordiaage of sample 2057.04 ± 0.55(CA-ID-TIMS) LA-ICP-MS analysis with 2σ propagated error elipse(b) SA04-13 (n=13)206 Pb/238 U weighted mean = 2025 ± 14∆t≈35 Ma0.220.230.240.250.280.270.262.2 2.62.4 2.8 3.0 3.2 3.4 3.6 3.8 4.0207Pb/235U207Pb/235U weighted mean = 1416 ± 13206 Pb/238 Uconcordiaage of sample 1435.6 ± 2.5(ID-TIMS) LA-ICP-MS analysis with 2σ propagated error elipse(a) SR336 (n=20)207 Pb/235 U weighted mean = 1432 ± 11207Pb/206Pb weighted mean= 1403 ± 33135013001450150014001550Figure 4 .1 . Summary concordia diagrams showing the U-Pb LA-ICP-MS zircon results and age interpretations for Precambrian zircon. The high-precision ID-TIMS or CA-ID-TIMS 207Pb/206Pb accepted ages of the samples are indicated with a red star in each panel and the grey bands indicate the weighted mean 206Pb/238U, 207Pb/235U, and 207Pb/206Pb dates by LA-ICP-MS including 2σ propagated uncertainty; each ellipse indicates the results of a single ablation and the concordia curve is marked in millions of years (Ma). (a) SR336, Sybille monzonite from the Mesoproterozoic Laramie anorthosite complex, Wyoming. The U-Pb results are consistent between the accepted ID-TIMS date (Scoates and Chamberlain, 2003) and the in situ LA-ICP-MS weighted mean dates (e.g., 207Pb/235U, 206Pb/238U, 207Pb/206Pb). The LA-ICP-MS analyses are corrected using zircon reference material 91500. (b) SA04-13, Merensky Reef from the Paleoproterozoic Bushveld Complex, South Africa. The U-Pb LA-ICP-MS dates are all significantly younger (~35 Ma) than the CA-ID-TIMS dates (Scoates and Wall, 2015). The LA-ICP-MS analyses are corrected using zircon reference material 91500.123Chapter 4Bushveld Complex, combined with rutile from the Critical Zone, this study used the textural setting and trace element geochemistry of these accessory minerals to provide a framework to constrain the crystallization paths of fractionated interstitial melt in mafic layered intrusions. Based on the Ti-Hf, Th/U, and REE variations, distinct compositional trends discriminate between samples from the Lower Zone and Main Zone, from the Critical Zone, and from the Upper Zone and felsic roof rocks. Application of Ti-in-zircon thermometry (Ferry and Watson, 2007) yields temperatures of 950-730°C for the mafic-ultramafic cumulates and lower temperatures of 875-690°C in the Upper Zone and overlying felsic rocks. Forward modelling of zircon saturation using rhyolite-Melts of proposed parental magma compositions of the Bushveld Complex (Barnes et al., 2010) predicts zircon saturation at temperatures that correspond to the Ti-in-zircon thermometry results with an estimated 5-20% remaining melt and produces late-stage minerals (e.g., quartz, biotite, apatite, titanite) identical to what is observed in the rocks.4 .3 .1 . Comparison to the Stillwater ComplexThe ca. 2.71 Stillwater Complex (Wall and Scoates, 2016; Wall et al., 2016) is a large mafic-ultramafic layered intrusion in southwestern Montana (USA) that contains many analogous features to the Bushveld Complex, including compositions, textures, types of layering sequences, and mineralized horizons that are present in their respective stratigraphic sections (e.g., McCallum, 1996; Boudreau, 2016). Based on the results of this study, there are also remarkable similarities between the trace element geochemistry zircon from the Bushveld Complex and zircon from samples spanning the complete stratigraphy of the Stillwater Complex (Wall, 2016). Both intrusions contain a distinctive population of zircon with high and variable Th/U that is restricted primarily to orthopyroxenites in the Critical Zone in the Bushveld Complex and ultramafic rocks of the Peridotite Zone and Bronzitite Zone in the Stillwater Complex (Fig. 4.2). These anomalously high-Th/U compositions of zircon appear to signal U loss to an oxidized Cl-rich fluid that exsolved from interstitial melt – a feature that may be typical of orthopyroxenite-dominated sequences in large open-system mafic layered intrusions. In addition, the ranges of Ti-in-zircon temperatures determined for zircon from each intrusion are similar (950-690°C, Bushveld Complex; 1000-720°C, Stillwater Complex) (Fig. 4.3). The similarities in the chemistry of zircon from the Bushveld Complex and Stillwater Complex, two of the 124Chapter 4Th/U = 0.5 Th/U = 1 Th/U = 2 Th/U = 4 Th/U = 10 020040060080010000 200 400 600 800 1000Th/U = 0.5 Th/U = 1 Th/U = 2 Th/U = 4 Th/U = 10 020040060080010000 200 400 600 800 1000U (ppm)Th (ppm)U (ppm)Th (ppm)(a) Bushveld Complex(b) Stillwater ComplexFigure 4 .2 . Comparison of Th vs. U concentrations for zircon from mafic layered intrusions. Both panels are set to the same scale for comparison. a) Bushveld Complex (n = 278, 13 samples), this study. Circles represent samples from the Lower Zone, Lower Critical Zone, Main Zone, Upper Zone, and felsic roof rocks and the diamonds indicate samples from the Upper Critical Zone, most of which show anomalously high Th/U. b) Stillwater Complex (n= 357, 17 samples), data from Wall (2016). Circles represent samples from the Basal Series and Banded Series and the diamonds indicate samples from the Peridotite Zone and Bronzitite Zone of the Ultramafic Series, most of which show anomalously high Th/U. The Th-U systematics in zircon from these two major layered intrusions are strikingly similar, especially with respect to the range of Th/U and the presence of a significant population of high Th/U-zircon; zircon from the Bushveld Complex has notably lower U concentrations than zircon from the Stillwater Complex.125Chapter 40510152025051015202530Ti-in-Zircon Temperature (ºC)Ti-in-Zircon Temperature (ºC)650 700 750 800 850 900 950 1000650 700 750 800 850 900 950 1000(a) Bushveld Complex(b) Stillwater ComplexFigure 4 .3 . Comparison of the distribution of Ti-in-zircon temperatures determined from mafic layered intrusions Ti-in-zircon calculations made following the formulation of Ferry and Watson (2007). a) Bushveld Complex (n = 278, 13 samples), this study. The majority of samples from the Rustenburg Layered Suite contain both rutile and quartz and an aSiO2 = 1 and aTiO2 = 1 was used; the Upper Zone sample and the three felsic roof rock samples did not contain rutile and an aTiO2 = 0.7 was used. b) Stillwater Complex (n = 357, 17 samples), data from Wall (2016). The Stillwater samples do not contain primary rutile, thus a αTiO2 = 0.7 was used for all calculations (Wall et al., 2016). The results indicate similar temperatures (Bushveld = 950-700°C; Stillwater = 1000-725°C) and ranges (deltaT ~250°C) for crystallization of zircon from fractionated interstitial melt down to temperatures that correspond to the solidus in these two major layered intrusions. 126Chapter 4most influential layered intrusions in petrology, indicates that the processes that lead to zircon saturation in fractionated interstitial melt were likely comparable.4 .3 .2 . Tectono-magmatic implications of zircon chemistryThe trace element geochemistry of zircon is strongly controlled by the composition of the parental magma from which it crystallizes and can be used as a tool for fingerprinting magmatic processes and sources related to specific tectonic environments (Belousova et al., 2002; Grimes et al., 2009, 2015). Based on global zircon classification diagrams from Belousova et al. (2002) (662 zircon analyses by LA-ICP-MS), zircon from the Bushveld Complex broadly displays a granitic-syenitic signature, with the exception of samples that have been affected by U loss in the Critical Zone (Fig. 4.4a-b). Using the recent discrimination diagrams from Grimes et al. (2015) (>5300 zircon analyses by SHRIMP-RG), zircon from the Bushveld Complex plots either within the field defined by continental zircon or outside this field due to high Sc contents compared to zircon from the global database (Fig. 4.4c-d). The compositions of zircon from the Bushveld Complex and Stillwater Complex are remarkably similar and both intrusions are characterized by zircon with high Sc/Yb relative to the the fields determined by Grimes et al. (2015) (Fig. 4.5), that are derived from the analysis of zircon from modern or young tectonic environments (e.g., various mid-ocean ridges, Cascadian and New Zealand continental arcs, Hawaiian ocean island). Although the relatively high Sc-zircon from these two major layered intrusions may be an analytical artifact (Grimes et al., 2015), this may represent a signature of zircon from ancient cratonic plutons that crystallized from highly fractionated melts without a modern equivalent. 4 .4 . Directions for future research4 .4 .1 . Pre-treatment of zircon for LA-ICP-MS analysisThis study assessed the effect of using untreated reference materials to reduce U-Pb analytical data from unknowns that were both untreated or had been annealed or annealed and leached (chemical abrasion). This approach was chosen to isolate the effects of the pre-treatment protocols on the unknowns while the reference material was kept constant. For U-Pb geochronology, most LA-ICP-MS laboratories currently use untreated zircon reference materials with untreated unknowns (Yuan et al., 2008; Nemchin et al., 2013; Schaltegger et al., 2015). 127Chapter 4KimberliteGranitoidKovdorCarbonatiteNorwegianSyeniteDoleriteLarvikiteLamproiteSyenite-4 -3 -2 -1 0log(Nb/Yb)-2 -1 0 1 2 3 4 5log (U)-1 0 1 2 3 4 5log (Th)-2.5-2-1.5-1-0.500.51log (U/Yb)0126543log (Y)0126543log (Y)-4 -3 -2 -1 0log(Nb/Yb)-2-1.5-1-0.500.511.5log (Sc/Yb)zrn0.5%ttn21% ap5%ttn110%ilm10%amph10%OIMORBCONTU-lossKimberliteGranitoidKovdorCarbonatiteNorwegianSyeniteOIMORBCONT(a) (b)(c) (d)NeboStavorenFelsiteUZMZUCZUCZ-MRLCZLZFigure 4 .4 . Trace element distribution diagrams for zircon from the Bushveld Complex compared to classification schemes from global zircon datasets. (a-b) Logarithmic plots of Y vs. U and Y vs. Th compared to fields and rock types from Belousava et al. (2002). The composition of the Bushveld zircon is consistent with zircon from dolerites and other mafic rocks. The trend to low-U zircon defined mainly by samples from the Upper Critical Zone reflects U loss from interstitial melt during crystallization. (c-d) Logarithmic plots of U/Yb vs. Nb/Yb and Sc/Yb vs. Nb/Yb compared to fields established for various tectono-magmatic settings from Grimes et al. (2015). The majority of the samples unaffected by U loss plot within the continental zircon field (green-shaded field); the other fields include analyses of zircon from mid-ocean ridge gabbros (MOR-type) and ocean islands (OI-type). The vectors indicate the effect of crystallization of zircon (zrn), apatite (ap), titanite (ttn), ilmenite (ilm), and amphibole (amph). Mean 2σ analytical uncertainties for each calculated ratio are smaller than the symbol size. Symbols: square = lherzolite/norite, diamond = orthopyroxenite, triangle = diorite, circle = granite/granophyre. Abbreviations: LZ, Lower Zone; LCZ, Lower Critical Zone; UCZ-MR, Upper Critical Zone-Merensky Reef; UCZ, Upper Critical Zone; MZ, Main Zone; UZ, Upper Zone.128Chapter 4zrn0.5%ttn21% ap5%ttn110%ilm10%amph10%BushveldStillwaterlog(Nb/Yb)log(Sc/Yb)Cont. ArcOIMORBCont. ArcOIMORBMantle Array-2.5-2.0-1.5-1.0-0.500.51.0log(Nb/Yb)log(U/Yb)-4 -3 -2 -1 0-4 -3 -2 -1 0-2.0-1.50.51.0-0.5-1.001.5a)b)Figure 4 .5 . Trace element discrimination diagrams comparing zircon chemistry from the Bushveld Complex and the Stillwater Complex. Discrimination fields from Grimes et al. (2005) based on 5300 analyses of zircon by SHRIMP-RG. a) log(Sc/Yb) vs. log(Nb/Yb). The results from both intrusions overlap and are both characterized by high Sc/Yb values relative to the global classification fields (based primarily on Cenozoic samples) and plot above the continental arc field. Minerals: zrn, zircon; ap, apatite; ilm, ilmenite; amph, amphibole; ttn, titanite. b) log(U/Yb) vs. log(Nb/Yb. The majority of analyses from both intrusions plot within the continental arc field. The high-Th/U zircon from both intrusions (U loss during volatile saturation in fractionated interstitial melt) yields anomalously low U/Yb that cannot be used to reliably interpret tectono-magmatic setting. Abbreviations: MORB, mid-ocean ridge basalt; OI, ocean island basalt; Cont. arc, continental arc.129Chapter 4The observation that both annealing and chemical abrasion of zircon can produce significant shifts in calculated U-Pb ages due of the effects on downhole fractionation (Allen and Campbell, 2012; Solari et al., 2015, this study) highlights the need for additional studies to assess the effect of using pre-treated reference materials in U-Pb data reduction of unknown zircon that has undergone the same treatment. This study also focused on relatively low-U, homogeneous zircon from Precambrian mafic layered intrusions to minimize any effects of zoning or radiation damage since crystallization. To fully assess the effectiveness of these pre-treatment protocols, which were primarily designed for dating zircon grains affected by Pb loss, future research should be carried out to evaluate the effect of pre-treatment on metamict or damaged zircon and the resultant U-Pb systematics.4 .4 .2 . Recommendations for improving methodologyBased on the results of this study, an LA-ICP-MS dating protocol is recommended that involves a preliminary assessment of the downhole fractionation behaviours of unknowns prior to analysis, and matrix-matching with reference materials that produce ablation characteristics. Properly correcting for downhole fractionation is one of the largest factors in the accuracy in U-Pb dating of zircon by LA-ICP-MS (Paton et al., 2010; Allen and Campbell, 2012; Schaltegger et al., 2015). Currently, the Iolite software does not display data related to the downhole behaviour of unknowns or monitors that are run concurrently with the chosen reference material and the calculations assume that downhole behaviour is equivalent amongst all analyzed samples (Paton et al., 2010, 2011). A visualization of the downhole behaviour of all samples would provide a useful tool for geochronologists to ensure that this assumption is valid.4 .4 .3 . Future of accessory mineral trace element studies in mafic-ultramafic plutonic rocksMafic magmatism and the formation of layered intrusions has been an integral part of the development of the Earth’s crust (e.g., Scoates and Wall, 2015). Recognition of the interstitial setting and temperature-composition conditions for zircon saturation in mafic cumulates opens a new avenue of research for the study of mafic-ultramafic plutonic rocks worldwide. Using the techniques and interpretations presented here, the trace element systematics of large open-system layered intrusions (e.g., Bushveld, Stillwater, Great Dyke, Dufek) can be compared 130Chapter 4with those of smaller, single-stage or closed-system intrusions (e.g., Skaergaard, Kiglapait) to address similarities and differences during late-stage crystallization at near-solidus temperatures. Results from layered intrusions in turn can be compared to results emerging from the study of zircon found in gabbros of the oceanic crust (Grimes et al., 2008, 2009; Rioux et al., 2016). 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Summary of ranges of trace element concentrations in untreated, annealed, and leached zircon reference materials and unknownsElement Ti Y Ce Nd Sm Eu Gd Dy Ho Er Yb Lu Hf Pb Th UPlešovice, n = 85Untreatedmin 51.3 202.6 1.29 0.58 1.19 0.346 5.17 21.78 6.14 22.5 29.5 3.73 10570 4.91 28.0 360Q1 66.3 280.0 2.02 0.99 2.04 0.479 7.78 30.96 8.5 32.51 47.4 6.34 11390 7.79 47.2 522median 82.7 576.5 2.48 2.36 4.03 1.04 15.02 64.6 17.6 65.2 81.2 10.0 11590 11.04 66.8 669Q3 96.6 640.7 2.76 2.94 4.99 1.26 18.01 73.8 19.8 70.9 90.7 11.8 11890 12.62 77.1 746max 126 830.9 4.69 6.45 8.64 1.89 24.8 94.3 25.7 95.7 118.3 15.5 12530 25 152 1109Annealed min 28.8 237.5 1.74 0.77 1.59 0.389 6.38 25.82 7.22 26.29 33.90 4.33 11190 6.60 33.9 372Q1 43.8 274.1 2.35 1.36 2 0.543 7.93 31.29 8.37 29.92 37.06 4.61 11275 9.45 62.4 612.5median 86.3 482.8 2.71 2.09 3.43 0.925 13.6 54.55 14.7 53.35 66.05 8.61 11415 13.5 80.8 714.5Q3 100 657.6 5.12 4.55 5.63 1.56 21.2 78.65 20.5 70.8 82.08 10.4 11788 24.3 137 862max 119 743.9 15.2 21.1 13.47 3.58 30.6 95.3 23.5 81.6 95.5 12.4 12170 31.8 196 1641Chemical Abrasionmin 53.9 244.9 1.44 0.550 1.1 0.28 5.49 26.24 7.3 28.26 36.52 4.62 11230 4.66 30.4 421Q1 72.6 287.0 1.60 0.828 1.54 0.390 6.45 29.76 8.40 31.71 41.15 5.44 11728 6.81 41.2 489.3median 84.1 425.1 1.92 1.42 2.42 0.678 10.3 46.8 12.58 47.3 58.35 7.74 12015 8.16 50 541.5Q3 90.9 585.8 2.39 2.55 4.25 1.07 16.2 67.03 17.65 62.75 69.03 9.02 12120 13.13 80.8 718.5max 104 634.9 3.6 5.58 7.74 1.64 23.4 79.4 19.34 67 81.6 10.7 12340 22.7 137 871Temora-2, n = 84Untreatedmin 4.1 461.8 2.77 0.41 1.31 0.314 7.3 39.2 15.41 76 168 30.7 7330 5.92 28.2 88.4Q1 8.4 795.0 3.47 1.07 2.42 0.509 12.8 64.6 25.2 133.1 310 53.7 8150 10.25 46 151median 10 1077 3.79 1.93 3.8 0.843 19.8 92.7 34.6 173 386 69.1 8540 16.9 76.1 173.3Q3 12 1301 4.43 3.24 5.55 1.16 26.8 117.9 44.5 207.3 422 77.1 9260 20.9 100.8 244max 15 1715 6.73 3.76 7.34 1.62 37.9 160.5 57.4 263.3 536 98 10360 40.1 178.7 409Annealed min 8.0 472.4 2.36 0.63 1.47 0.24 8.48 39.91 15.31 75.1 157.6 30.2 8170 5.27 27.6 71.1Q1 8.8 945.3 3.22 1.23 3.26 0.663 18.7 86.4 31.88 148.8 277.8 50.7 8798 9.01 46.3 119median 10.8 1272 3.68 2.29 4.02 0.912 22.0 107 42.70 201.1 379.3 70.3 9210 13.1 65.4 144Q3 12.5 1458 4.01 3.33 5.72 1.14 29.0 130.7 49.03 237.3 452.2 83.3 9570 19.0 96.8 191max 14.2 1791 8.07 3.7 6.21 1.45 34.9 154.6 58.48 283.3 573 116 10255 40.0 199 473Chemical Abrasionmin 6.20 427.6 2.44 0.48 1.17 0.277 7.66 36.55 14.08 69 140.3 26.7 7960 4.33 22.71 66.1Q1 8.83 651.9 2.71 0.81 1.76 0.377 11.1 52.33 20.44 107.8 241.7 48.1 8509 5.65 29.41 108.1median 10.6 747.6 3.57 0.91 2.20 0.460 12.4 60.3 23.75 123.0 265.2 52.4 9076 11.8 60.18 149.5Q3 12.0 1114 4.69 1.99 3.99 0.898 21.3 92.75 35.63 169.7 343.8 65.6 10305 22.9 123.3 251.0max 16.9 1547 7.49 3.48 6.13 1.21 31.2 131.5 50.1 244 485 95.6 10700 47.8 235.8 405.3All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace elements reduction scheme with Zr = 49.5 wt. % as internal standard. Abbreviations: min = minimum, Q1 = quartile 1, Q3 = quartile 3, max = maximum.151Appendix ATable A.1. (continued) Summary of ranges of trace element concentrations in untreated, annealed, and leached zircon reference materials and unknownsElement Ti Y Ce Nd Sm Eu Gd Dy Ho Er Yb Lu Hf Pb Th U91500, n = 85Untreatedmin 3.3 130.4 2.42 0.03 0.19 0.143 1.8 10.33 4.28 23.9 63.2 12.3 5119 14.2 28.1 75.0Q1 4.6 134.6 2.57 0.079 0.3 0.184 1.95 10.87 4.43 24.61 64.8 12.7 5236 14.77 29.6 79.5median 5.4 136.7 2.62 0.111 0.32 0.202 2.08 11.19 4.55 25.08 66 12.9 5282 15.01 30.0 80.1Q3 6.0 140.9 2.67 0.142 0.37 0.214 2.22 11.39 4.67 25.78 67.1 13.3 5434 15.17 30.4 80.7max 8.3 144.6 2.81 0.249 0.47 0.24 2.59 12.04 4.88 26.95 70.4 13.7 5617 16.95 33.3 86.0Annealed min 4.0 136.5 2.46 0.078 0.25 0.178 1.8 11.29 4.45 24.9 65.9 13.18 5545 74.1 26.86 13.20Q1 4.8 140.5 2.54 0.101 0.324 0.202 1.99 11.49 4.64 25.60 67.43 13.43 5593 75.08 27.74 13.57median 5.4 141.6 2.61 0.121 0.338 0.205 2.13 11.69 4.67 25.84 68.65 13.65 5652 75.6 28.03 13.95Q3 5.8 142.5 2.67 0.139 0.383 0.225 2.23 11.88 4.71 26.07 69.23 13.79 5674 76.33 28.42 14.40max 6.3 143.5 2.77 0.159 0.46 0.254 2.5 12.24 4.82 26.92 70.5 13.86 5726 76.7 28.7 14.81Chemical Abrasionmin 3.7 142.7 2.66 0.071 0.285 0.176 1.99 11.63 4.74 26.37 69.3 13.64 5625 14.53 29.39 77.2Q1 4.6 145.0 2.69 0.105 0.369 0.222 2.16 12.03 4.82 26.70 70.55 13.82 5648 15.40 30.69 79.9median 5.0 147.3 2.77 0.127 0.395 0.236 2.24 12.24 4.93 27.29 71.55 14.00 5664 15.82 31.95 82.0Q3 5.9 148.5 2.81 0.147 0.468 0.244 2.35 12.33 5.04 27.54 72.7 14.10 5687 16.43 32.22 83.5max 6.5 150.4 2.89 0.233 0.61 0.258 2.71 12.70 5.13 28.02 73.4 14.30 5723 16.92 32.77 85.0SR336, Laramie anorthosite complex,  n = 51Untreatedmin 16.3 223.2 1.76 0.51 1.13 0.138 6.00 22.8 7.61 34.92 69.6 12.66 7700 6.00 9.05 26.07Q1 21.5 287.3 2.14 0.755 1.50 0.202 7.49 28.93 10.33 44.6 86.3 15.88 8200 10.0 14.26 39.13median 25.7 349.7 3.27 0.92 1.69 0.245 9.08 33.8 12.34 55.1 105.2 19.10 8625 18.3 25.23 61.3Q3 31.0 651.1 3.60 2.92 5.63 0.675 22.8 73.13 23.51 98.525 164.0 28.66 9325 25.0 35.07 68.23max 36.3 1113 6.50 10.62 12.43 1.53 43.1 126.4 40.6 166.8 267 46.4 9570 62.8 90.5 146.4Annealed min 16.7 236.2 1.86 0.430 1.08 0.130 5.35 23.28 8.38 36.99 70.9 13.05 7930 6.01 8.99 26.24Q1 18.1 271.5 1.95 0.593 1.31 0.189 6.87 27.51 9.45 42.71 79.25 15.06 8158 7.71 12.04 32.75median 23.4 350.4 2.43 0.885 1.73 0.259 9.33 35.22 12.26 55.95 100.6 18.95 8425 11.56 17.92 44.6Q3 27.6 411.1 2.91 1.08 2.23 0.286 11.1 39.61 14.17 64.5 114.7 20.87 8700 15.37 23.41 57.3max 30.7 516.0 3.75 2.02 3.63 0.384 15.8 54.9 18.3 81 139.3 25.04 9482 23.1 34.68 77.8Chemical Abrasionmin 13.5 231.6 1.89 0.361 1.08 0.146 5.61 22.71 7.85 37.8 69.4 13.02 7800 6.89 10.94 29.04Q1 16.6 276.0 2.08 0.615 1.16 0.171 6.64 27.1 9.65 44.3 81.25 15.2 8109 9.2 13.68 33.54median 22.0 328.6 2.84 0.74 1.50 0.207 8.47 33.09 11.25 51.8 95.7 18.23 8280 11.47 17.36 41.98Q3 24.6 460.5 3.93 1.65 2.75 0.356 12.7 46.95 16.11 72.8 125.8 23.54 9045 20.66 29.51 65.55max 31.5 1400 6.58 7.99 11.49 1.42 49.6 151.4 50.2 208 309 54.9 9850 67.9 97.9 167.3All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace elements reduction scheme with Zr = 49.5 wt. % as internal standard. Abbreviations: min = minimum, Q1 = quartile 1, Q3 = quartile 3, max = maximum.152Appendix ATable A.1. (continued) Summary of ranges of trace element concentrations in untreated, annealed, and leached zircon reference materials and unknownsElement Ti Y Ce Nd Sm Eu Gd Dy Ho Er Yb Lu Hf Pb Th USA04-13, Bushveld Complex, Merensky Reef, n = 48Untreatedmin 18.1 144.8 2.01 0.131 0.5 0.083 3.26 13.32 4.55 19.77 34.54 6.21 9456 52.8 55.9 17.86Q1 21.0 359.7 3.55 0.675 1.82 0.277 9.67 33.54 11.3 48.45 76.33 13.90 10849 92.9 96.2 28.1median 23 514.4 4.51 1.32 2.64 0.387 12.8 47.5 16.1 70.5 112.6 21.18 10957 133 136.8 45.8Q3 30.4 731.1 6.38 3.5 5.78 0.737 23.3 73.7 23.6 98.75 142.8 25.85 11277 205.8 217 80.8max 42.3 990.2 8.61 5.86 8.34 1.03 30.9 96.3 31.34 138.2 202.2 37.75 11930 329.1 337.3 110.7Annealed min 8.6 325.4 3.27 0.52 1.63 0.25 8.66 30.65 10.21 44.5 69 12.46 10230 73.4 74 14.83Q1 13.7 543.3 4.97 0.765 2.21 0.347 13.0 54.2 17.54 71.4 104.1 18.67 11278 125.2 131.5 30.93median 17.4 736.0 6.48 0.915 2.69 0.441 17.5 70.25 23.79 102.1 160.6 29.24 12555 225.9 234.7 46.6Q3 27.3 853.9 8.97 1.70 3.03 0.576 19.2 75.55 27.15 116.6 179.9 32.45 13153 300.8 307.5 79.63max 38.3 902.1 27.0 9.74 6.87 2.61 26.1 82.5 28.71 124.5 187.7 35.04 14660 530 543 314Chemical Abrasionmin 7.5 237 3.66 0.3 0.78 0.116 5.4 21.3 7.65 33.6 54.87 9.99 10091 53.4 52.4 20.82Q1 15.4 409 4.23 0.698 2.17 0.299 11.8 40.32 13.06 54.22 80.33 14.60 10558 93.28 91.0 28.55median 23.2 479 5.36 0.98 2.48 0.349 12.1 44.05 15.10 66 103.6 19.30 11603 136.1 136 33.25Q3 26.5 763 7.80 3.20 6.11 0.706 25.6 73.78 24.79 103.8 152.8 27.95 12367 202.4 201 79.55max 36.5 1409 16.5 5.62 9.16 1.22 38.5 128.8 44.38 194.2 291.5 54.26 14098 669 646 200.7ST05-03, Stillwater Complex AN2, n = 50Untreatedmin 10 349 1.66 0.082 0.46 0.0111 4.09 24.57 10.78 57.9 135.1 27.95 7377 43.4 30.01 74.30Q1 14.8 811 1.97 0.447 1.62 0.069 11.6 64.88 26.16 125.3 245.3 47.8 8173 107.0 76.2 104.4median 17.1 1314 2.98 1.38 3.74 0.162 23.7 110 42.83 208.9 415.3 80.6 9165 137.5 97.8 156.0Q3 19.0 1693 3.14 1.96 4.85 0.211 29.3 142 55.55 273.0 545 104.6 10693 171.1 119.6 191.5max 20.9 1882 4.26 3.04 5.87 0.324 35.1 160 62.54 306.1 613 119.2 11780 184.7 132.8 205.9Annealed min 9.00 761 2.45 0.23 1.1 0.027 9.84 58.3 24.14 126.7 285.2 57.55 8950 104.7 76.7 135.9Q1 10.3 975 2.85 0.545 1.62 0.0673 13.4 76.7 31.53 158.0 344.6 69.79 9508 138.3 99.6 166.9median 12.7 1536 3.12 0.775 2.87 0.105 24.9 127 50.63 254.7 529.4 104.4 9890 146.8 103.9 176.6Q3 15.5 1714 3.31 1.283 3.95 0.158 27.2 142 56.48 281.1 600 114.9 11050 198.1 139.7 207.5max 22.7 2008 3.5 2.46 5.12 0.267 33.5 168 66.2 319.1 628 124.8 13720 246.0 182.3 297.0Chemical Abrasionmin 8.6 389 1.79 0.065 0.45 0.0085 4.2 28.1 12.27 63.3 152.6 30.28 9100 62.9 41.6 98.7Q1 12.1 826 2.11 0.251 1.14 0.0328 10.853 63.7 26.44 133.3 294.5 59.64 9608 87 65.73 117.4median 13.3 957 2.64 0.535 1.67 0.0625 13.41 75.9 30.94 156.6 352.4 70.15 10140 99.5 70.20 132.9Q3 14.5 1235 3.15 0.898 2.90 0.103 21.408 103 40.98 198.7 422.3 83.53 10815 123.9 90.83 162.7max 16.2 1725 3.97 1.76 4.20 0.127 29.42 146 57.1 277.1 564.8 108.5 12699 171.2 121.0 185.1All concentrations reported in parts per million (ppm). Raw LA-ICP-MS data reduced using Iolite 2.5 trace elements reduction scheme with Zr = 49.5 wt. % as internal standard. Abbreviations: min = minimum, Q1 = quartile 1, Q3 = quartile 3, max = maximum.153Appendix A10-210-110010110210310410-210-110010110210310410-210-110010110210310410-210-110010110210310410-210-110010110210310410-210-1100101102103104La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm YbLa Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm YbLa Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm YbLa Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm YbLa Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm YbLa Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er LuTm Yb(a) Plešovice (n=88)(b) Temora-2(n=84)(c) 91500(n=85)(f) ST05-03 (Stillwater)(n=50)(e) SA04-13 (Bushveld)(n=51)(d) SR336 (Laramie)(n=51)Figure A.1. Chondrite-normalized rare earth element patterns for the reference materials and in-house zircon samples analyzed by LA-ICP-MS for Chapter 2. Coloured lines and points represent individual analyses and the thicker black line indicates the median value. Only representative rare earth elements were analyzed during the same ablations where the Pb/U ratios were determined. All panels are at the same scale. (a) Plešovice. (b)  Temora-2. (c) 91500. (d) SR336, Laramie anorthosite complex. (e) SA04-13, Bushveld Complex. (f) ST05-03 Stillwater Complex. Normalization values from McDonough and Sun (1995). 154Appendix ATh/U = 2 Th/U = 1Th/U = 0.5Th/U = 0.11000°C900°C800°C700°C4000 6000 8000 10000 12000 14000 160000204060801001201400 200 400 600 800 1000 1200 1400 1600 18000100200300400500600700800Ti (ppm)Th (ppm)Hf (ppm)(a)U (ppm)(b)PlešoviceTemora-291500SA04-13SR336ST05-03Figure A.2. Trace element variations of the zircon reference materials and in-house samples analyzed by LA-ICP-MS for Chapter 2. (a) Ti vs. Hf with dashed lines indicating Ti-in-zircon thermometry temperatures corresponding to αSiO2 = 1 and αTiO2 = 1 (Ferry and Watson, 2007). Note the large variation in concentrations, most notably 91500, which is characterized by very low Ti (3-8 ppm) and low Hf (mean = 5450 ppm) with limited variation, and Plešovice, which contains higher Hf (mean = 11660 ppm) and displays a very large range in Ti (30-126 ppm). (b) Th vs. U with lines of constant Th/U indicated. The samples span a very wide range in Th and U concentrations with relatively uniform Th/U within each sample. Plešovice zircon contains relatively low Th contents for high U concentrations (mean Th/U = 0.1). Zircon from the Bushveld Complex (SA04-13) has the highest Th/U and Th contents (mean Th/U = 3.3, max Th = 692 ppm), whereas analyses from 91500 show limited variation in both Th (28-35 ppm) and U (81-100 ppm).155Appendix BAppendix BMATLAB code for processing downhole fractionation dataNotes:Integrations of each analysis were taken from the raw Agilent data using Iolite 2.5 in Igor Pro. The data were background subtracted and counts per second  waves of Pb, Th, and U isotopes were exported with individual time-resolved files for each integration. This data was manipulated and analyzed in MATLAB using the following code. Correction factors come from exponential fits calculated in Iolite. 156Appendix B  1 clear, clc, clf  2 ProgFolder = cd;  3 FilesFold = uigetdir(pwd, 'Select a folder');  4   5 %User selects folder with all time-based integrations in .txt format. All   6 %text files must contain exported TimeSeries from Iolite in which the   7 %column order is:   8 %1. ElapsedTime 2. Pb204_CPS 3. Pb206_CPS 4. Pb207_CPS 5.  9 %Pb208_CPS 6. Th232_CPS 7. U235_CPS 8. U238_CPS 10  11 files = dir(fullfile(FilesFold, '*.txt')); 12 CurrentSample=getfield(files(1),'name'); 13 CurrentSample=CurrentSample(1:length(CurrentSample)-4); 14 cd(FilesFold); 15  16 % reads all integration .txt files within the selected folder to determine 17 % the length of each ablation. The longest value will be used later 18  19 for i = 1:length(files) 20      21     integration=getfield(files(i), 'name'); 22     n=dlmread(integration, '\t', 1, 0); 23      24     nsize(i)=size(n,1); 25      26 end 27  28 %makes blank matrices for each isotope in which each column will contain 29 %one ablation analysis. n=length of longest ablation. i=ablation # of 30 %longest ablation 31  32 [n,i]=max(nsize); 33 Pb204 = NaN(n,length(files)); 34 Pb206 = NaN(n,length(files)); 35 Pb207 = NaN(n,length(files)); 36 Pb208 = NaN(n,length(files)); 37 Th232 = NaN(n,length(files)); 38 U235 = NaN(n,length(files)); 39 U238 = NaN(n,length(files)); 40  41 %creates time variable "t" from the longest ablation (i) which will be used  42 %as the master time variable to align each ablation (t in seconds) 43  44 integration=getfield(files(i), 'name'); 45     n=dlmread(integration, '\t', 1, 0); 46 t=n(:,1);  47  48 %choose whether to use U235_CPS or to calculate U235 based on U238 counts. 49 %1=use, 0=don't use 50 Use_235= 0;  51  52 %puts CPS values for each ablation into corresponding column for each 53 %isotope 54 for i = 1:length(files) 55      56     integration=getfield(files(i), 'name'); 57     n=dlmread(integration, '\t', 1, 0); 58     nlen =size(n,1); 59      60     Pb204(1:nlen(1), i) = n(:,2); 61     Pb206(1:nlen(1), i) = n(:,3); 62     Pb207(1:nlen(1), i) = n(:,4); 63     Pb208(1:nlen(1), i) = n(:,5); 64     Th232(1:nlen(1), i) = n(:,6); 65     157Appendix B 66     if Use_235==1 67         U235(1:nlen(1), i) = n(:,7); 68          69     else 70     end 71      72     U238(1:nlen(1), i) = n(:,8); 73          74 end 75  76 %calculates U235 CPS based on U238_CPS values if not using U235_CPS 77 if Use_235==0 78 U235=U238/137.88; 79 end  80  81 %cleans up, returns to parent folder 82 cd(ProgFolder) 83 clear a CurrentSample FilsFold i integration n nlen nsize 84  85 %creates raw isotopic ratios for Pb206/U238, Pb207/U235, and Pb208/Th232 and  86 %cleans variables of NaN values 87 r68 = Pb206./U238; 88 r75 = Pb207./U235; 89 r82 = Pb208./Th232; 90  91 r68(isnan(r68))==0; 92 r75(isnan(r75))==0; 93 r82(isnan(r82))==0; 94  95 %creates time-integrated means for each ratio 96 r68av = mean(r68'); 97 r75av = mean(r75','omitnan'); 98 r82av = mean(r82'); 99 100 %asks user for exponential fit coefficients to use from 'factors.txt' text101 %file in the parent directory. This table should contain variable names in102 %column 1 followed by a/b/c coefficients for 206/238 fractionation in103 %columns 2:4, 207/235 in columns 5:7, and 208/232 in columns 8:10104 factors = dlmread('factors.txt', '\t',0,1);105 factor_n = readtable('factors.txt','Delimiter','\t','ReadVariableNames',false);106 FactNames = factor_n{:,1};107 %User must pick the number of the sample that was chosen initially from the108 %list109 FactNames110 j=input('Sample Number');111 fact68=factors(:,1:3);112 fact75=factors(:,4:6);113 fact82=factors(:,7:9);114 115 %creates lines of average exponential fit to each ratio using the116 %coeffients following the equation: f(x)=a+b*e^(-ct)117 avFit68=fact68(j,1)+fact68(j,2)*exp(-fact68(j,3)*t);118 avFit75=fact75(j,1)+fact75(j,2)*exp(-fact75(j,3)*t);119 avFit82=fact82(j,1)+fact82(j,2)*exp(-fact82(j,3)*t);120 121 122 123 %plots raw ratios vs time for all samples with mean ratio and exponential124 %fit lines superimposed125 figure(1)126 hold on127 plot(t,r68)128 plot(t,r68av,'k','LineWidth',2)129 plot(t,avFit68,'r','LineWidth',2)130 title('206Pb/238U')158Appendix B131 figure(2)132 hold on133 plot(t,r75)134 plot(t,r75av,'k','LineWidth',2)135 plot(t,avFit75,'r','LineWidth',2)136 title('207Pb/235U')137 figure(3)138 hold on139 plot(t,r82)140 plot(t,r82av,'k','LineWidth',2)141 plot(t,avFit82,'r','LineWidth',2)142 title('208Pb/232Th')143 144 145 %applies downhole corrections to each time slice of the raw ratios for the 146 %untreated (UT), annealed (AN), and chemically abraded (CA) versions of the sample. For 147 %this to work, the selected sample must be untreated, and the following two 148 %samples in the factors.txt file must be the AN and CA version of the149 %sample sample, respectively.150 for i=1:size(r68,2)151     152 DC68_UT(:,i) = r68(:,i)./(1+((fact68(j,2)/fact68(j,1)).*exp(-fact68(j,3).*t)));%UT153 DC68_AN(:,i) = r68(:,i)./(1+((fact68(j+1,2)/fact68(j+1,1)).*exp(-fact68(j+1,3).*t))); %AN154 DC68_CA(:,i) = r68(:,i)./(1+((fact68(j+2,2)/fact68(j+2,1)).*exp(-fact68(j+2,3).*t))); %CA155 156 end157 158 %takes time-integrated mean of downhole corrected ratios159 DCav68(:,1) = mean(DC68_UT');160 DCav68(:,2) = mean(DC68_AN');161 DCav68(:,3) = mean(DC68_CA');162 163 %corrects the time-integrated exponential fits of 206/238. This should164 %produce a flat line for the chosen sample (UT). AN and CA fits are placed165 %in the 2nd and 3rd column of the variable, respectively.166 DCfit68(:,1) = avFit68./(1+((fact68(j,2)/fact68(j,1)).*exp(-fact68(j,3).*t))); %UT167 DCfit68(:,2) = avFit68./(1+((fact68(j+1,2)/fact68(j+1,1)).*exp(-fact68(j+1,3).*t))); %AN168 DCfit68(:,3) = avFit68./(1+((fact68(j+2,2)/fact68(j+2,1)).*exp(-fact68(j+2,3).*t))); %CA169 170 171 %plots the corrected and uncorrected average 206/238 ratios vs time the172 %corrected and uncorrected downhole exponential fits173 figure(4)174 hold on175 plot(t,r68av)176 plot(t,avFit68,'LineWidth',2)177 plot(t,DCav68)178 plot(t,DCfit68,'LineWidth',2)179 180 181 avFit68_AN=fact68(j+1,1)+fact68(j+1,2)*exp(-fact68(j+1,3)*t);182 avFit68_CA=fact68(j+2,1)+fact68(j+2,2)*exp(-fact68(j+2,3)*t);183 184 figure(5)185 hold on186 plot(t,avFit68)187 plot(t,avFit68_AN)188 plot(t,avFit68_CA)189 190 191 159Appendix CAppendix CCathodoluminescence (CL) images of untreated and treated zircon reference materials and in-house zirconNotes:Samples are organized by page. Images in left, center, and right columns contain untreated, annealed, and annealed and chemically abraded grains, respectively. All scale bars are 50 μm.160Appendix CPlešoviceAnnealedUntreated Chemical AbrasionPlešovice UT 1 Plešovice UT 1Plešovice AN 1Plešovice UT 3 Plešovice CA 1Plešovice AN 2Plešovice UT 4 Plešovice CA 3Plešovice AN 3Plešovice UT 5 Plešovice CA 4Plešovice AN 4Plešovice UT 6 Plešovice CA 5Plešovice AN 5  all scale bars 50 μm161Appendix CPlešoviceAnnealedUntreated Chemical AbrasionPlešovice UT 8 Plešovice CA 7Plešovice AN 7Plešovice UT 9 Plešovice CA 8Plešovice AN 8Plešovice UT 10 Plešovice CA 9Plešovice AN 9Plešovice CA 10Plešovice AN 10Plešovice UT 7 Plešovice UT 6Plešovice AN 6 all scale bars 50 μm162Appendix CTemora-2AnnealedUntreatedTemora-2 UT 1 Temora-2 CA 1Temora-2 AN 1Temora-2 UT 2 Temora-2 CA 2Temora-2 AN 2Temora-2 UT 3 Temora-2 CA 3Temora-2 AN 3Temora-2 UT 4 Temora-2 CA 4Temora-2 AN 4Temora-2 UT 5 Temora-2 CA 5Temora-2 AN 5  all scale bars 50 μm163Appendix CTemora-2AnnealedUntreated Chemical AbrasionTemora-2 UT 6 Temora-2 CA 6Temora-2 AN 6Temora-2 UT 7 Temora-2 CA 7Temora-2 AN 7Temora-2 UT 8 Temora-2 CA 8Temora-2 AN 8Temora-2 UT 9 Temora-2 CA 9Temora-2 AN 9Temora-2 UT 10 Temora-2 CA 10Temora-2 AN 10  all scale bars 50 μm164Appendix C91500AnnealedUntreated Chemical Abrasion91500 UT 1 91500 CA 191500 AN 191500 UT 2 91500 CA 191500 AN 291500 UT 3 91500 AN 3  all scale bars 50 μm165Appendix CSR336 (Laramie)AnnealedUntreated Chemical AbrasionSR336 UT 1 SR336 CA 1SR336 AN 1SR336 UT 2 SR336 CA 2SR336 AN 2SR336 UT 3 SR336 CA 3SR336 AN 3SR336 UT 4 SR336 CA 4SR336 AN 4SR336 UT 5 SR336 CA 5SR336 AN 5  all scale bars 50 μm166Appendix CSR336 (Laramie)AnnealedUntreated Chemical AbrasionSR336 UT 6 SR336 CA 6SR336 AN 6SR336 UT 7 SR336 CA 7SR336 AN 7SR336 UT 8 SR336 CA 8SR336 AN 8SR336 UT 9 SR336 CA 9SR336 AN 9SR336 UT 10 SR336 CA 10SR336 AN 10  all scale bars 50 μm167Appendix CSA04-13 (Bushveld)AnnealedUntreated Chemical AbrasionSA04-13 UT 1 SA04-13 CA 1SA04-13 AN 1SA04-13 UT 2 SA04-13 CA 2SA04-13 AN 2SA04-13 UT 3 SA04-13 CA 3SA04-13 AN 3SA04-13 UT 4 SA04-13 CA 4SA04-13 AN 4SA04-13 UT 5 SA04-13 CA 5SA04-13 AN 5  all scale bars 50 μm168Appendix CSA04-13 (Bushveld)AnnealedUntreated Chemical AbrasionSA04-13 UT 6 SA04-13 CA 6SA04-13 AN 6SA04-13 UT 7 SA04-13 CA 7SA04-13 AN 7SA04-13 UT 8 SA04-13 CA 8SA04-13 AN 8SA04-13 UT 9 SA04-13 CA 9SA04-13 AN 9SA04-13 UT 10 SA04-13 CA 10SA04-13 AN 10  all scale bars 50 μm169Appendix CST05-03 (Stillwater)AnnealedUntreated Chemical AbrasionST05-03 UT 1 ST05-03 CA 1ST05-03 AN 1ST05-03 UT 2 ST05-03 CA 2ST05-03 AN 2ST05-03 UT 3 ST05-03 CA 3ST05-03 AN 3SA04-13 UT 4 SA04-13 CA 4SA04-13 AN 4ST05-03 UT 5 ST05-03 CA 5ST05-03 AN 5  all scale bars 50 μm170Appendix CST05-03 (Stillwater)AnnealedUntreated Chemical AbrasionST05-03 UT 6 ST05-03 CA 6ST05-03 AN 6ST05-03 UT 7 ST05-03 CA 7ST05-03 AN 7ST05-03 UT 8 SST05-03 CA 8ST05-03 AN 8ST05-03 UT 9 ST05-03 CA 9ST05-03 AN 9ST05-03 UT 10 ST05-03 CA 10ST05-03 AN 10all scale bars 50 μm171Appendix DAppendix D Thin section scans and petrographic descriptions of samples from the Bushveld Complex172Appendix DBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: XXXXXXUnit: Upper Critical Zone Subunit: Merensky ReefLat: Latitude Long: LongitudeRock type: based on primocryst mineralogyPrimocryst Mineralogy: rock-forming minerals in decreasing order of abundanceInterstitial Mineralogy:minerals found in interstitial pockets between primocrystsAccessory Minerals:accessory minerals including zircon, rutile, apatite, titanite, etc.Scan of petrographic thin section in transmitted light (TL)0.5 cmScan of petrographic thin section in cross-polarized light (XPL)0.5 cmstratigraphic location of sample (pink star)Index Page: samples described in this appendix follow the format belowregional map with with sample location (pink star)173Appendix DSample: LZ10-02 Unit: Lower ZoneLat: 30°11.114'E Long: 24°38.260'SRock type: harzburgitePrimocryst Mineralogy: orthopyroxeneolivineInterstitial Mineralogy:plagioclase, alkali feldspar, quartzAccessory Minerals:zircon, rutileTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmEastern Limb174Appendix DTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: TW477-661  Unit: Lower Critical ZoneSubunit: Cameron’s SectionLat: 30°00'46.65"E Long: 24°23'40.08"SRock type: Feldspathic orthopyroxenitePrimocryst Mineralogy: orthopyroxenechromiteInterstitial Mineralogy:plagioclase, alkali feldspar, biotite, quartzAccessory Minerals:zircon, rutile, apatiteEastern Limb175Appendix DTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: DT28-912 Unit: Upper Critical Zone Subunit: UG2Lat: 29°49'22.63"E Long: 24°17'08.16"SRock type: orthopyroxenitePrimocryst Mineralogy:  orthopyroxene, clinopyroxene Interstitial Mineralogy: plagioclase, quartz, biotiteAccessory Minerals:zircon, rutileEastern Limb176Appendix DTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: B00-1-6Unit: Upper Critical Zone Subunit: UG2Lat: 29°49'22.63"E Long: 24°17'08.16"SRock type: orthopyroxenitePrimocryst Mineralogy: orthopyroxene, chromiteInterstitial Mineralogy:plagioclase, quartzAccessory Minerals:zircon, rutileEastern Limb177Appendix DTL XPLSample: B90-7(0) Unit: Upper Critical Zone Subunit: Merensky ReefLat: 29°51'50.90"E Long: 24°17'46.05"SRock type: feldspathic orthopyroxenitePrimocryst Mineralogy:orthopyroxene, clinopyroxene Interstitial Mineralogy:plagioclase, alkali feldspar, quartz, biotiteAccessory Minerals:zircon, rutile, chromiteBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmEastern Limb178Appendix DSample: SA04-08BUnit: Upper Critical Zone Subunit: Merensky ReefLat: 30°05’11.4”E Long: 24°31’11”SRock type: Feldspathic orthopyroxenitePrimocryst Mineralogy: orthopyroxene, clinopyroxene, Interstitial Mineralogy:plagioclase, alkali feldspar, quartzAccessory Minerals:zircon, rutile, apatiteTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmEastern Limb179Appendix DSample: SA04-13Unit: Upper Critical Zone Subunit: Merensky ReefLat: 27°15’31.9”E Long: 25°37’29.1”SRock type: feldspathic orthopyroxenitePrimocryst Mineralogy: orthopyroxene, chromiteInterstitial Mineralogy:plagioclase, alkali feldspar, quartz, biotite, sulphideAccessory Minerals:zircon, rutile, apatiteTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF100 kmWestern Limb180Appendix DSample: MP24D2Unit: Upper Critical Zone Subunit: Bastard ReefLat: 29°51'50.90"E Long: 24°17'46.05"SRock type: orthoyroxenitePrimocryst Mineralogy: orthopyroxene, clinopyroxeneInterstitial Mineralogy:plagioclase, clinopyroxene, alkali feldspar, biotite, quartzAccessory Minerals:zircon, rutile, apatiteTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmEastern Limb181Appendix DTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: B90-1 Unit: Main ZoneSubunit: Tennis Ball MarkerLat: 29°59.935'E Long: 24°17.767'SRock type: noritePrimocryst Mineralogy: orthopyroxene, clinopyroxene, plagioclaseInterstitial Mineralogy:plagioclase, clinopyroxene, biotite, quartzAccessory Minerals:zircon, rutile, apatiteEastern Limb182Appendix DTL XPLBRMRBBMGLGUGMMLM21LZLCZUCZUZMZROOF20 kmSample: B07-040 Unit: Upper ZoneLat: 29°54.465'E Long: 24°51.794'SRock type: olivine-bearing amphibole dioritePrimocryst Mineralogy: plagioclase, clinopyroxene, olivineInterstitial Mineralogy:plagioclase, alkali feldspar, amphibole, quartz, biotiteAccessory Minerals:zircon, apatite, titaniteEastern Limb183Appendix EAppendix E Major and minor element oxides of zircon in the Bushveld Complex determined by EPMA184Appendix ETable E.1. Major and minor element oxides in zircon from the Bushveld ComplexSample Grain SiO2 ZrO2 HfO2 TotalOxide (wt. %) wt. %LZ10-02 Lower Zone1 32.34 66.82 1.10 100.255 32.37 67.13 1.02 100.536 32.48 67.62 1.19 101.297 32.55 66.61 1.21 100.36TW477-661Lower Critical Zone1 32.72 66.15 1.30 100.172 32.47 66.88 1.51 100.863 32.74 66.83 1.45 101.014 32.75 66.63 1.45 100.835 32.37 65.97 1.37 99.71DT28-912Upper Critical Zone UG21 31.99 66.58 1.57 100.142 32.34 66.83 1.41 100.583 32.72 67.47 1.44 101.634 32.56 66.87 1.57 100.995 32.49 67.03 1.58 101.10B00-1-6 Upper Critical Zone UG21 32.51 66.94 1.37 100.812A 32.40 66.53 1.45 100.372B 32.44 66.61 1.68 100.733 32.50 66.99 1.34 100.834 32.20 67.24 1.44 100.885 32.50 66.79 1.39 100.68B90-7Upper Critical Zone Merensky Reef1 32.37 66.96 1.53 100.862 32.42 66.03 1.35 99.803 32.28 66.82 1.52 100.614 32.33 67.22 1.57 101.125 32.37 67.04 1.31 100.72SA04-08Upper Critical Zone Merensky Reef1 32.46 66.46 1.29 100.212 32.66 66.77 1.24 100.673 0.22 0.00 0.04 0.264 32.18 67.04 1.21 100.435 32.15 66.72 1.17 100.04Oxides determined using zircon standard NMNH 117288-3185Appendix ETable E.1. (continued) Major and minor element oxides in zircon from the Bushveld ComplexSample Grain SiO2 ZrO2 HfO2 TotalOxide (wt. %) wt. %SA04-13Upper Critical Zone Merensky Reef1 32.55 66.76 1.53 100.842 32.37 66.56 1.60 100.533 32.49 66.84 1.42 100.754 32.50 66.25 1.45 100.205 32.94 65.99 1.67 100.60MP24D2Upper Critical Zone Bastard Reef1 32.37 67.09 1.29 100.742 32.54 66.72 1.22 100.483 32.84 66.17 1.32 100.334 32.46 66.81 1.48 100.765 32.35 66.76 1.43 100.55B90-1Main Zone         Tennis Ball Marker1 32.24 67.14 1.31 100.682 32.46 66.83 1.15 100.443 32.39 65.95 1.10 99.444 32.48 66.82 1.32 100.625 32.39 67.70 1.29 101.38B07-040Upper Zone1 32.14 67.36 1.30 100.812 32.44 65.70 1.30 99.443 32.45 66.46 1.52 100.434A 32.18 66.65 1.38 100.214B 32.44 67.06 1.36 100.865 32.53 66.80 1.27 100.60B07-051Roof Granophyre1 32.50 66.98 1.08 100.562 32.27 66.47 1.05 99.793 32.73 67.02 1.10 100.854 32.24 66.83 1.10 100.175 32.25 66.73 1.06 100.04B10-054Rashoop             Stavoren Granophyre1 32.10 67.20 1.05 100.362 32.44 67.24 1.08 100.753 32.64 66.60 1.04 100.27B10-056Lebowa               Nebo Granite1 31.88 66.01 1.18 99.072 32.69 66.88 1.20 100.763 32.33 66.80 1.37 100.514 32.66 67.57 1.25 101.485 32.73 66.53 1.20 100.46Oxides determined using zircon standard NMNH 117288-3186Appendix E3040506070656667686965666768690.9 1.1 1.3 1.5 1.7 1.9 0.9 1.1 1.3 1.5 1.7 1.90.9 1.1 1.3 1.5 1.7 1.9 31 32 33 3431323334HfO2 (wt. %)HfO2 (wt. %) HfO2 (wt. %)SiO2 (wt. %)ZrO2 (wt. %)ZrO2 (wt. %)Zr / HfSiO2 (wt. %)NeboStavorenGranophyreUZMZUCZUCZ-MRLCZLZ(a) (b)(c) (d)Figure E.1. Major and minor element oxide variations in zircon from the Bushveld Complex measured by EPMA. (a) Zr/Hf vs. HfO2 showing that all analyses define an expected decreasing trend in Zr/Hf with increasing Hf content. (b) SiO2 vs. HfO2 showing minimal variation in SiO2 contents of zircon over the entire range of HfO2. (c) ZrO2 vs. HfO2 showing minimal variation in ZrO2 over the entire range of HfO2. (d) ZrO2 vs. SiO2 showing tight clustering of stoichiometric Zr and Si in the analyzed zircon grains from the Bushveld Complex. Analytical uncertainties are smaller than point sizes.187Appendix FAppendix F LA-ICP-MS results for reference materials determined during analysis of zircon and rutile from the Bushveld Complex188Appendix F0.60.70.80.91.01.11.21.31.4Li Si Ca Sc Ti Rb Sr Y Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Th U(a) NIST610 during zircon analyses(b) NIST610 during rutile analysesall analysesmean valueuncertainty in referenceall analysesmean valueuncertainty in referenceanalysis / reference valueanalysis / reference valueSi Ca Sc Ti Cr Fe Y Zr Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho ER Tm Yb Lu Hf Ta W Th UTi +30%0.60.50.70.80.91.01.11.21.31.41.5semi-quantitative (NIST612)Zr-internal standard (NIST612)Figure F.1. Compilation of trace element results for reference material NIST610 analyzed by LA-ICP-MS. Data were reduced using NIST612 as a standard. Measured trace element concentrations in NIST610 are normalized to values reported in Pierce et al. (2006). The uncertainty of the reference values is shown as a grey error envelope behind the results. (a) NIST610 values determined during four analytical sessions of zircon (n=40) and reduced using 90Zr as the internal standard. Mean values for all elements are within the internal error of analyses of the reference material, with the exception of Ti. (b) NIST610 values determined during three analytical sessions of rutile (n=23) and reduced semi-quantitatively. Initially, 49Ti was used as an internal standard, however, this resulted is NIST610 values that were ~30% lower than reported concentrations due to systematically high Ti measurements in NIST610. Semi-quantitative reduction results in accurate reference values and has no significant effect on rutile concentrations or uncertainties.  189Appendix F0.000010.00010.0010.010.11101001000La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Luall analysesmean valuerange in 91500 zircon0.0010.010.1110100100010000La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Luall analysesmean valuerange in Plešovice zirconrange in actinide-rich Plešovice zircon(a) 91500 Zircon (n=118)(b) Plešovice Zircon (n=41)analysis / chondriteanalysis / chondriteFigure F.2. Chondrite-normalized rare earth element patterns in the 91500 and Plešovice zircon reference materials analyzed by LA-ICP-MS during eight analytical sessions. Mean values are shown with red lines. Error envelopes for the reference materials are shown in grey. (a) 91500: values are from Wiedenbeck et al. (2004). Note that most La concentrations are below detection limits. (b) Plešovice: values are from Sláma et al. (2008). Note that Plešovice zircon has been reported to contain actinide-rich zones characterized by elevated light REE (i.e., flatter patterns); these LREE-rich patterns are shown in the lighter grey shading. Chondrite-normalizing values from McDonough and Sun (1995).190Appendix FLa Ce Pr Nd SmPm Eu Gd Tb Dy Ho Er Tm Yb Lu0.00010.0010.010.1110100100010000La Ce Pr Nd SmPm Eu Gd Tb Dy Ho Er Tm Yb Lu0.00010.0010.010.1110100100010000all analysesmean value(a) FC-1 Zircon (n=58)(b) ST05-03 Zircon (n=51)analysis / chondriteanalysis / chondriteall analysesmean valuerange in ST05-03 zirconFigure F.3. Chondrite-normalized rare earth element patterns in the FC-1 and ST05-03 (Stillwater AN2) zircon reference materials analyzed by LA-ICP-MS during eight analytical sessions. Mean values are shown with red lines. (a) FC-1. (b) ST05-03, values from Wall et al. (2016). Chondrite-normalizing values from McDonough and Sun (1995).191Appendix GAppendix G Cathodoluminescence images of zircon grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicatedNotes:Yellow circles indicate the locations of 34 μm spots for LA-ICP-MS analyses. Spots were selected based on zircon size and appearance in CL. Multiple spots were chosen in some grains to characterize grain-scale geochemical variations. Not all of the imaged grains were analyzed. Spot numbers correspond to analyses in Table I.1, Appendix I. All scales as indicated. 192Appendix GSample: LZ10-02Unit: Lower ZoneRock Type: Harzburgite47A7B8 9112A2B 311A11B1112B12A40 μm30 μm 40 μm 40 μm40 μm 30 μm193Appendix GSample: LZ10-02Unit: Lower ZoneRock Type: Harzburgite1350 ȝmLZ10-02 z1515C15A15B1618194Appendix GSample: TW477-661Unit: Lower Critical ZoneRock Type: Feldspathic orthopyroxenite3A3B156A6B6C4B4A7A7B8195Appendix GSample: TW477-661Unit: Lower Critical ZoneRock Type: Feldspathic orthopyroxenite1110A10B141513196Appendix GSample: DT28-912Unit: Upper Critical Zone – UG2Rock Type: Orthoyroxenite7A7B1A1B47A 7B7A7B7B7A97A7B11 1213A13B197Appendix GSample: DT28-912Unit: Upper Critical Zone – UG2Rock Type: Orthoyroxenite1617 19A 19B2114198Appendix GSample: B00-1-6Unit: Upper Critical Zone – UG2Rock Type: Orthopyroxenite13A13B60 umB00-1-6 Z11B1A2A2B3A 3B480 ȝmB00-1-6 z57A7B67A 7B89B9A10A199Appendix GSample: B00-1-6Unit: Upper Critical Zone – UG2Rock Type: Orthoyroxenite1415A15B16A16B17B17A19B19A 20B20A200Appendix GSample: B90-7(0)Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxenite7B7C7A891011A1B235A5B6A6B201Appendix GSample: B90-7(0)Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxenite12131619 2223202Appendix GSample: SA04-08Unit: Upper Critical Zone – Merensky Reef (Western Limb)Rock Type: Feldspathic orthopyroxenite1B1A23A3B4A4B5A5B5C791011A11B12203Appendix GSample: SA04-08Unit: Upper Critical Zone – Merensky Reef (Western Limb)Rock Type: Feldspathic orthopyroxenite1718B18A19212324B24A14A14B16B16A204Appendix GSample: SA04-13Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxenite12A2B3A3B3C4A4B5A5B710A10C10B11205Appendix GSample: SA04-13Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxenite15A15B17A17B17C1821206Appendix GSample: MP24D2Unit: Upper Critical Zone – Bastard ReefRock Type: Orthopyroxenite6A 6B9B9A9C2A2B 2C207Appendix GSample: MP24D2Unit: Upper Critical Zone – Bastard ReefRock Type: Orthopyroxenite1814A14B14C16208Appendix GSample: B90-1Unit: Main Zone – Tennis Ball MarkerRock Type: Norite1 3B3A4A4B5678A8B910209Appendix GSample: B90-1Unit: Main Zone – Tennis Ball MarkerRock Type: Norite1516 181920121314210Appendix GSample: B07-040Unit: Upper Zone – Near roof contactRock Type: Olivine-bearing amphibole diorite12B12A1A1B1C2A2B4A4B5A5B6A6B6C7A7B8A 8C8B8D911B11A211Appendix GSample: B07-040Unit: Upper Zone – Near roof contactRock Type: Olivine-bearing amphibole diorite16B16A18A18B1913B13A 1415A15B212Appendix GSample: B07-051Unit: Roof Rocks - GranophyreRock Type: Granophyre891012123A3B45A5B6213Appendix GSample: B07-051Unit: Roof Rocks - GranophyreRock Type: Granophyre141516214Appendix GSample: B10-054Unit: Roof Rocks – Stavoren Granophyre (Rashoop)Rock Type: Granophyre7 89101213123A3B4 5215Appendix GSample: B10-054Unit: Roof Rocks – Stavoren Granophyre (Rashoop)Rock Type: Granophyre15161718 20216Appendix GSample: B10-056Unit: Roof Rocks – Nebo Granite (Lebowa)Rock Type: Granite6A6B78B8A910B10A111B1A2A2B4B4A5217Appendix GSample: B10-056Unit: Roof Rocks – Nebo Granite (Lebowa)Rock Type: Granite131617218Appendix HAppendix H Backscattered electron images of rutile grains analyzed by LA-ICP-MS from the Bushveld Complex with laser spots indicatedNotes:Yellow circles indicate the locations of 34 μm spots for LA-ICP-MS analyses. Small grain sizes typically only allowed for one spot per gain. Not all of the imaged grains were analyzed. Spot numbers correspond to analyses in Table K.1, Appendix K. All scales as indicated. 219Appendix HSample: TW477-661Unit: Lower Critical ZoneRock Type: Feldspathic orthopyroxenite12 348813 14109756A6B220Appendix HSample: DT28-912Unit: Upper Critical Zone – UG2Rock Type: Orthopyroxenite1317181920 2122A22C22B23A23B24A24BDT28-912 R13 DT28-912 R14 DT28-912 R15DT28-912 R16 DT28-912 R17 DT28-912 R18DT28-912 R19 DT28-912 R20 DT28-912 R21DT28-912 R22 DT28-912 R23 DT28-912 R24221Appendix HSample: DT28-912Unit: Upper Critical Zone – UG2Rock Type: Orthopyroxenite2 34 67101211A 11B98DT28-912 R1 DT28-912 R2 DT28-912 R3DT28-912 R4 DT28-912 R5 DT28-912 R6DT28-912 R7 DT28-912 R8 DT28-912 R9DT28-912 R10 DT28-912 R11 DT28-912 R12222Appendix HSample: SA04-08Unit: Upper Critical Zone – Merensky Reef (Western Limb)Rock Type: Feldpspathic orthopyroxenite1A2 345678910111B223Appendix HSample: SA04-13Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxeniteSA04-13 R2 SA04-13 R3 SA04-13 R4SA04-13 R5 SA04-13 R6 SA04-13 R7SA04-13 R8 SA04-13 R9 SA04-13 R10SA04-13 R11 SA04-13 R12 SA04-13 R132 3 4567A7B8A8B 9101113224Appendix HSample: SA04-13Unit: Upper Critical Zone – Merensky ReefRock Type: Feldspathic orthopyroxeniteSA04-13 R14 SA04-13 R15 SA04-13 R16SA04-13 R17 SA04-13 R18 SA04-13 R19SA04-13 R20 SA04-13 R211415161718A18B1920A21A21B225Appendix HSample: MPD24D2Unit: Upper Critical Zone – Bastard ReefRock Type: Orthopyroxenite1 2 345226Appendix IAppendix I Complete trace element analyses of zircon from the Bushveld Complex determined by LA-ICP-MS227Appendix ITable I.1. Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: LZ10-02, Lower ZoneSpot #11 16.5 1.9 201700 7800 2030 410 461.9 8.3 16.7 3.4 0.67 0.15 15.8 2.5 1740 150 11.2 1.2 0.610 0.170 37.9 3.5 0.71 0.10 8.21 0.99 8.77 0.842A 3.68 0.85 191800 5100 - - 413.8 3.6 39.8 7.9 4.7 1.2 0.81 0.17 277.4 2.6 4.96 0.30 0.207 0.062 16.15 0.40 0.195 0.042 2.13 0.29 2.18 0.252B 1.45 0.31 178400 3400 - - 418.6 4.9 25.2 2.9 0.051 0.024 0.235 0.047 298.9 4.7 4.72 0.23 0.038 0.014 17.76 0.50 0.174 0.031 2.04 0.27 2.44 0.343 4.40 0.61 183200 3700 - - 428.4 4.3 21.4 2.4 0.114 0.037 0.299 0.056 360.4 8.6 4.65 0.23 0.0132 0.0093 16.73 0.46 0.152 0.027 1.84 0.30 2.41 0.354 1.97 0.35 187500 4000 - - 433.1 4.9 10.1 1.9 0.111 0.035 0.308 0.055 431 17 5.58 0.25 0.047 0.022 17.02 0.43 0.142 0.031 1.44 0.28 2.12 0.337A 0.31 0.12 180200 3500 - - 432.7 4.1 23.1 2.6 0.097 0.031 0.230 0.050 535.8 4.5 2.97 0.16 0.0201 0.0092 16.30 0.33 0.352 0.044 4.87 0.37 5.52 0.427B 0.40 0.13 179500 3400 - - 408.0 4.2 22.7 2.3 0.087 0.037 0.205 0.040 394.0 5.8 3.27 0.19 0.0077 0.0059 13.98 0.30 0.204 0.034 3.44 0.32 3.75 0.458 1.96 0.47 169300 4200 - - 419.1 4.9 20.4 3.2 0.146 0.056 0.335 0.063 499.0 4.8 3.63 0.27 0.062 0.027 14.94 0.45 0.230 0.044 3.08 0.48 4.33 0.639A 2.56 0.38 181600 4100 - - 446.6 5.0 21.9 3.5 0.147 0.048 0.257 0.064 624.5 6.6 3.29 0.18 0.151 0.038 17.41 0.53 0.424 0.070 5.54 0.45 5.02 0.4110 0.37 0.15 181800 3200 - - 423.8 4.2 28.0 2.6 0.134 0.041 0.252 0.055 563.2 3.9 2.72 0.17 0.044 0.017 16.33 0.33 0.481 0.050 5.52 0.40 5.89 0.5111A 0.34 0.13 182800 3400 - - 435.5 3.7 22.9 2.6 0.133 0.040 0.266 0.051 651.1 4.3 3.15 0.18 0.064 0.017 16.50 0.31 0.420 0.049 4.75 0.38 5.00 0.4011B 7.0 1.2 183400 3900 - - 406.0 3.9 52 23 0.154 0.051 0.246 0.070 416 12 4.51 0.35 0.044 0.019 13.09 0.39 0.196 0.042 2.42 0.30 2.88 0.3712 0.59 0.18 180400 3200 - - 424.5 4.0 21.9 2.8 0.105 0.034 0.202 0.042 507.0 5.6 2.86 0.18 0.037 0.015 16.24 0.38 0.415 0.048 5.23 0.44 5.68 0.5113 0.70 0.20 185700 3800 - - 413.0 4.4 25.1 3.4 0.070 0.034 0.214 0.048 346 10 3.37 0.18 0.063 0.019 12.02 0.30 0.141 0.028 2.06 0.27 2.77 0.3315A 0.91 0.22 184900 4000 - - 409.6 3.8 19.5 2.7 0.114 0.037 0.242 0.057 553.8 3.1 3.51 0.18 0.0141 0.0074 16.77 0.38 0.145 0.030 2.81 0.29 4.60 0.4315B 0.87 0.29 180500 3800 - - 379.2 4.9 23.7 2.6 0.065 0.034 0.194 0.050 278 11 3.94 0.21 0.0055 0.0061 12.35 0.33 0.055 0.016 0.79 0.17 1.91 0.3115C 0.29 0.14 182000 3500 - - 417.0 4.1 20.7 2.4 0.135 0.042 0.288 0.056 472.4 4.1 3.35 0.15 0.031 0.012 14.80 0.29 0.214 0.036 3.01 0.31 4.26 0.4516 1.05 0.21 183900 3500 - - 419.3 4.3 26.1 3.0 0.160 0.048 0.266 0.061 614.6 5.2 3.45 0.18 0.076 0.019 15.74 0.34 0.421 0.045 5.11 0.36 5.23 0.4818 3.05 0.44 192500 4800 140 130 403.4 5.7 23.1 3.7 0.176 0.060 0.344 0.082 652 12 3.98 0.21 0.294 0.071 18.63 0.43 0.540 0.066 5.02 0.50 5.15 0.45Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G228Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: LZ10-02, Lower ZoneSpot #11 2.50 0.31 43.1 3.9 13.2 1.2 158 14 55.7 4.8 237 19 43 3 336 25 65.2 4.9 9540 120 3.77 0.35 1930 120 2300 240 1580 1302A 0.74 0.10 8.74 0.49 2.39 0.12 26.87 0.73 8.67 0.21 37.11 0.97 7.06 0.19 57.3 1.2 11.27 0.27 8331 48 1.171 0.085 229 17 177.8 5.4 180.8 3.42B 0.855 0.084 10.37 0.56 2.78 0.13 29.9 1.1 9.79 0.28 39.8 1.0 7.45 0.23 60.1 1.6 11.72 0.33 8393 51 1.165 0.089 280 21 205.9 6.2 200.0 5.13 0.736 0.098 10.64 0.86 3.02 0.14 35.0 1.3 11.42 0.37 48.9 1.5 9.24 0.32 75.3 2.5 14.68 0.45 9591 93 1.204 0.086 467 18 319.5 8.1 299.1 5.94 0.505 0.068 9.88 0.78 3.14 0.18 37.7 2.0 13.27 0.65 59.3 2.7 11.36 0.49 94.1 3.8 19.91 0.61 9761 59 2.138 0.092 472 36 367 14 449.1 8.37A 1.51 0.11 19.30 0.82 5.33 0.15 56.7 1.3 17.81 0.37 71.3 1.3 12.77 0.26 101.6 1.5 19.19 0.33 8353 45 0.666 0.058 264 13 207.8 1.7 171.6 1.47B 1.14 0.11 14.41 0.74 3.78 0.15 39.7 1.2 12.97 0.28 52.4 1.2 9.51 0.23 75.3 2.0 14.72 0.33 8101 49 0.832 0.059 198 8 154.7 1.7 139.3 1.58 1.29 0.13 16.77 0.80 4.59 0.19 49.6 1.4 16.26 0.37 67.7 1.2 12.60 0.37 98.1 2.2 19.26 0.46 8646 75 0.817 0.065 298 20 226.1 2.3 214.3 3.39A 1.34 0.14 19.6 1.0 5.49 0.24 60.5 1.3 19.51 0.41 84.4 1.6 15.26 0.38 123.4 2.5 24.28 0.52 8678 79 1.290 0.100 321 32 299.9 2.6 277.8 3.910 1.53 0.12 19.42 0.66 5.42 0.16 58.0 1.0 18.66 0.37 74.6 1.1 13.30 0.26 107.8 2.0 20.98 0.40 7902 47 0.798 0.064 242 10 192.1 1.2 173.2 1.711A 1.39 0.13 20.23 0.89 5.61 0.20 61.3 1.2 21.19 0.39 89.9 1.2 16.75 0.29 135 2.0 27.38 0.41 9140 48 1.261 0.079 427 17 331.8 2.5 317.5 2.011B 0.772 0.087 11.79 0.74 3.31 0.19 38.7 1.6 13.14 0.50 56.4 1.9 10.84 0.38 90.1 2.6 18.06 0.51 9017 62 1.438 0.087 243 27 219.8 5.5 254.3 3.912 1.50 0.14 19.99 0.84 5.00 0.18 52.5 1.3 16.56 0.36 66.4 1.1 11.94 0.27 93.3 1.7 18.08 0.30 8169 36 0.607 0.048 230 13 183.3 2.2 152.7 0.913 0.698 0.085 11.07 0.74 2.91 0.13 33.3 1.1 10.98 0.37 47.0 1.8 8.72 0.34 69.3 2.6 13.78 0.47 8506 91 0.992 0.080 151 9 123.9 3.1 139.2 3.915A 1.35 0.12 19.30 0.78 5.17 0.17 54.9 1.2 18.11 0.29 72.4 1.2 13.08 0.26 104.9 1.6 20.13 0.35 8526 53 0.757 0.048 301 13 240.5 2.1 207.0 1.915B 0.476 0.079 7.93 0.68 2.37 0.17 26.4 1.3 8.71 0.40 36.2 1.7 6.72 0.31 55.7 2.0 10.83 0.38 8349 53 1.098 0.078 175 13 130.0 3.0 139.4 1.615C 1.23 0.12 16.80 0.75 4.29 0.16 47.4 1.1 15.18 0.35 61.1 1.1 11.37 0.30 89.8 1.9 17.33 0.31 8493 56 0.769 0.063 230 16 185.5 1.5 168.3 1.416 1.48 0.11 19.87 0.81 5.42 0.18 59.4 1.2 19.41 0.38 83.5 1.4 15.3 0.29 125.8 2.2 25.20 0.44 8066 62 2.06 0.13 338 18 257.2 1.7 251.1 1.818 1.33 0.15 19.81 0.85 5.34 0.18 58.3 1.5 20.41 0.49 89.4 2.0 16.41 0.46 131.1 2.6 26.89 0.49 8455 85 2.15 0.11 411 30 359.3 8.8 457.7 7.1Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G229Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: TW477-661.15, Lower Critical ZoneSpot #11 0.32 0.16 181600 2900 - - 357.4 3.9 27.7 3.3 0.140 0.044 0.284 0.058 568 11 2.75 0.18 - - 11.25 0.33 0.054 0.017 1.37 0.23 2.96 0.323A 0.53 0.20 182700 2900 - - 400.1 4.1 13.3 1.9 0.100 0.037 0.295 0.055 643 20 3.06 0.19 - - 12.55 0.32 0.049 0.016 1.18 0.19 2.82 0.393B 1.69 0.33 181800 2800 - - 411.4 4.8 11.8 1.9 0.129 0.044 0.353 0.056 750 17 3.24 0.17 - - 12.93 0.30 0.049 0.015 1.31 0.20 2.94 0.364A 1.22 0.20 183600 3200 - - 388.7 4.5 11.7 2.0 0.258 0.060 0.477 0.077 1214 10 3.42 0.19 0.081 0.029 20.04 0.43 0.375 0.062 5.04 0.52 6.83 0.624B 1.91 0.30 183900 3300 - - 381.6 3.5 12.4 2.0 0.385 0.081 0.510 0.080 1547 22 3.84 0.20 0.056 0.019 23.09 0.43 0.511 0.057 7.60 0.47 10.45 0.615A 4.06 0.80 167300 3900 - - 372.2 9.0 9.1 3.0 0.170 0.075 0.440 0.140 639.1 5.1 4.75 0.31 0.006 0.008 18.02 0.54 0.090 0.035 1.25 0.37 2.44 0.406A 9.30 1.60 177700 4000 - - 405.7 8.1 16.3 2.7 0.332 0.081 0.452 0.085 1570 130 4.38 0.27 0.085 0.025 26.9 1.2 0.368 0.060 4.89 0.72 7.17 0.996B 3.49 0.71 179700 3200 - - 414.6 6.0 15.4 2.2 0.242 0.064 0.367 0.070 1015 24 3.39 0.25 0.011 0.008 25.0 1.3 0.220 0.040 4.30 0.51 6.43 0.666C 4.27 0.84 179000 3300 - - 438.0 11.0 16.1 2.4 0.289 0.079 0.449 0.070 1489 97 4.18 0.44 0.034 0.014 29.5 2.5 0.423 0.061 5.80 0.54 8.92 0.687A 2.32 0.29 179200 2800 - - 369.5 4.2 34.4 4.0 0.113 0.044 0.281 0.051 548 10 2.81 0.18 0.029 0.012 11.45 0.35 0.280 0.037 3.95 0.31 5.07 0.487B 1.87 0.31 176300 2100 - - 361.7 4.5 32.0 3.6 0.095 0.041 0.237 0.057 418.7 7.8 2.70 0.19 0.056 0.024 11.27 0.41 0.250 0.050 2.81 0.38 3.82 0.548 0.14 0.13 176900 2100 - - 366.7 5.1 14.9 2.6 0.101 0.040 0.264 0.058 774 48 2.14 0.17 0.00 0.00 11.76 0.84 0.113 0.032 2.48 0.44 5.50 0.7910A 3.21 0.48 180100 2700 - - 382.6 4.9 13.4 2.3 0.570 0.100 0.573 0.081 2392 90 4.93 0.28 0.051 0.018 27.47 0.95 0.593 0.084 9.30 0.58 12.81 0.8010B 3.87 0.47 182000 2300 - - 377.7 4.0 14.9 2.4 0.289 0.061 0.533 0.089 2062 21 4.55 0.23 0.043 0.016 24.07 0.53 0.562 0.054 8.45 0.63 10.99 0.7611 0.47 0.17 178500 2200 - - 347.9 3.5 36.7 3.5 0.045 0.030 0.265 0.060 320.4 7.7 2.95 0.17 - - 11.37 0.30 0.055 0.018 1.05 0.21 1.96 0.2913 2.02 0.32 178500 2600 100 90 343.3 3.7 25.9 3.3 0.098 0.043 0.218 0.050 371.9 6.2 2.50 0.15 0.016 0.010 9.00 0.22 0.096 0.023 1.09 0.18 2.01 0.3214 1.03 0.23 179100 2400 - - 351.3 3.8 30.6 3.1 0.027 0.025 0.237 0.049 317.1 5.9 2.72 0.18 0.031 0.013 11.41 0.37 0.105 0.024 1.61 0.24 2.58 0.3015 0.71 0.18 179500 2300 - - 364.8 3.4 14.9 2.4 0.061 0.036 0.285 0.054 341.3 2.6 2.07 0.14 - - 6.76 0.23 0.018 0.010 0.72 0.15 1.39 0.26Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G230Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: TW477-661.15, Lower Critical ZoneSpot #11 0.775 0.083 15.99 0.75 4.58 0.23 52.5 1.8 17.24 0.48 71.2 1.7 12.41 0.34 99.0 2.0 19.13 0.43 9651 46 0.463 0.047 100.6 3.2 75.1 1.6 78.4 1.23A 0.615 0.086 13.24 0.64 4.35 0.18 50.4 1.5 18.40 0.65 84.0 3.2 16.01 0.64 133.3 5.4 27.5 1.3 10781 68 0.531 0.053 173.3 8.5 133.2 2.1 34.53 0.933B 0.649 0.080 15.39 0.75 4.91 0.20 60.4 1.9 22.14 0.57 97.6 2.1 18.58 0.47 158.2 4.2 31.37 0.86 11391 69 0.974 0.065 185.3 6.2 142.1 2.1 58.91 0.644A 1.55 0.13 30.7 1.0 9.10 0.23 103.5 1.8 36.62 0.60 157.9 2.3 29.45 0.58 236.5 3.3 44.93 0.60 11863 72 0.978 0.070 451 21 345.0 5.6 123.1 2.54B 1.97 0.13 43.2 1.1 12.25 0.29 143.2 2.0 51.38 0.88 222.7 3.7 41.17 0.74 327.2 6.3 63.8 1.4 11322 83 1.149 0.087 692 22 548.0 11.0 158.0 1.75A 0.420 0.094 14.61 0.78 4.54 0.30 57.8 1.9 20.78 0.49 93.5 2.3 18.28 0.57 149.8 3.5 30.40 0.62 12760 130 2.07 0.13 343 11 215.1 2.3 167.3 2.76A 2.06 0.26 38.5 4.0 12.4 1.2 145.0 14.0 51.50 4.60 221 19 40.20 3.30 320.0 26.0 61.1 5.1 10850 100 1.30 0.13 663 86 495.0 55.0 117.0 6.36B 1.24 0.14 28.7 1.3 8.27 0.31 95.0 2.8 33.14 0.95 143.7 4.3 26.75 0.85 221.9 6.0 44.1 1.3 10990 73 1.28 0.11 401 20 310.0 16.0 96.8 6.06C 1.79 0.17 38.2 2.3 12.14 0.75 139.8 8.3 48.9 3.1 207 13 38.20 2.40 308.0 19.0 59.5 3.4 10912 72 1.35 0.14 568 51 479.0 53.0 108.5 8.87A 1.23 0.12 18.98 0.90 5.25 0.20 56.4 1.5 18.11 0.44 72.7 1.9 13.29 0.33 105.2 2.4 20.06 0.48 8390 51 0.595 0.064 100.5 2.8 81.8 2.3 85.1 1.67B 0.95 0.14 13.75 0.88 3.80 0.19 40.3 1.4 13.60 0.40 54.4 1.6 10.26 0.36 80.4 2.4 15.08 0.35 8645 58 0.611 0.066 75.6 5.1 67.3 2.3 71.9 1.88 1.22 0.17 23.7 2.1 6.70 0.55 74.7 5.5 24.2 1.6 98.1 5.9 18.30 1.10 144.6 8.5 27.0 1.5 11168 71 0.287 0.048 197 23 155.0 13.0 26.1 4.310A 2.62 0.21 54.3 2.6 16.46 0.85 201.2 9.4 73.8 2.9 321 11 59.1 1.9 466.0 14.0 90.7 2.3 10723 48 1.282 0.089 1195 43 1002.0 32.0 171.3 5.210B 2.20 0.17 45.9 1.5 13.77 0.31 169.1 2.7 63.28 0.80 285.8 3.4 53.62 0.76 430.2 5.2 84.6 1.1 10859 58 1.472 0.099 999 53 830.0 10.0 189.2 3.511 0.456 0.071 9.45 0.59 2.88 0.16 32.1 1.4 10.59 0.41 44.9 1.4 8.24 0.30 67.4 1.9 13.15 0.36 9297 68 0.635 0.062 73.9 2.7 61.6 1.3 73.4 1.413 0.526 0.076 10.79 0.64 3.08 0.13 36.2 1.1 12.19 0.30 52.0 1.3 9.57 0.27 78.3 1.8 15.02 0.33 9683 58 0.404 0.049 63.4 2.3 50.93 0.93 60.62 0.7614 0.592 0.074 10.32 0.57 2.97 0.13 32.2 1.2 10.52 0.33 43.6 1.0 8.11 0.24 65.8 1.5 12.78 0.32 9055 65 0.595 0.052 59.8 4.0 48.2 1.4 57.78 0.8215 0.295 0.063 7.29 0.56 2.46 0.11 29.33 0.97 10.63 0.28 47.2 1.0 9.14 0.28 78.4 1.7 16.12 0.26 11627 53 0.195 0.035 67.6 3.7 57.64 0.67 10.82 0.29Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G231Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: DT28-912, Upper Critical Zone, UG2Spot #11A 2.54 0.61 167700 7300 840 330 282.5 7.1 33.0 5.2 13.6 3.8 0.41 0.10 437 55 0.88 0.13 0.03 0.02 3.73 0.28 0.153 0.047 1.47 0.44 2.45 0.631B 4.50 1.00 158800 5600 - - 290.0 4.2 22.6 3.8 0.128 0.062 0.279 0.068 770.3 8.2 0.92 0.10 - - 3.57 0.18 0.202 0.041 4.11 0.52 5.97 0.582A 0.83 0.24 165200 5600 75 67 258.3 5.5 25.9 3.2 0.048 0.043 0.137 0.048 293 15 0.89 0.12 - - 2.49 0.18 0.022 0.013 0.72 0.20 1.64 0.422B 1.43 0.38 164800 6800 166 94 246.7 5.5 46.0 10.0 4.4 2.4 0.82 0.30 220 11 0.99 0.13 0.06 0.03 2.41 0.19 0.130 0.066 0.71 0.25 0.99 0.193A 1.21 0.23 160700 6200 550 260 273.2 4.3 25.3 2.9 0.050 0.045 0.246 0.069 359.4 4.2 1.44 0.16 - - 4.27 0.25 0.044 0.020 1.02 0.25 2.61 0.353B 1.18 0.29 162700 4800 68 60 260.5 4.3 27.0 3.4 0.018 0.043 0.255 0.072 293.4 6.3 1.08 0.14 - - 3.53 0.28 0.022 0.014 0.73 0.20 1.44 0.294 2.27 0.44 162900 6100 64 61 280.3 4.8 11.3 2.9 0.178 0.066 0.283 0.074 880 12 1.63 0.16 - - 11.82 0.72 0.143 0.036 3.53 0.48 7.10 0.747A 3.95 0.52 162600 6200 - - 287.0 4.4 29.2 3.9 0.047 0.039 0.223 0.069 775.9 8.6 0.85 0.12 - - 2.96 0.19 0.233 0.048 5.35 0.53 7.63 0.797B 3.89 0.58 161200 5600 114 85 288.7 4.2 17.1 3.3 0.073 0.046 0.182 0.061 789.0 6.0 0.692 0.098 - - 3.90 0.27 0.247 0.042 5.94 0.54 7.77 0.718A 0.25 0.13 158200 5900 - - 279.8 4.7 37.2 4.6 0.085 0.051 0.221 0.052 829.3 7.7 1.62 0.15 - - 5.44 0.28 0.350 0.054 5.33 0.51 7.67 0.718B 0.30 0.13 161700 5200 72 62 283.0 5.0 45.1 4.9 0.119 0.050 0.182 0.047 771.7 8.2 1.83 0.16 0.010 0.008 5.48 0.23 0.317 0.050 5.58 0.67 7.32 0.569 2.28 0.40 161400 5500 67 58 265.8 3.9 8.6 1.9 0.144 0.063 0.203 0.053 621 18 1.96 0.15 - - 14.56 0.64 0.031 0.015 0.89 0.21 2.00 0.4210A 2.51 0.44 159400 6600 98 77 268.3 4.1 28.9 4.4 0.058 0.046 0.207 0.073 374.1 3.4 1.20 0.13 0.025 0.013 3.77 0.23 0.203 0.042 2.60 0.41 2.39 0.3510B 1.38 0.27 162100 6000 260 130 271.8 6.6 28.1 3.3 0.88 0.22 0.67 0.17 364.5 6.4 1.18 0.13 0.014 0.014 3.66 0.18 0.035 0.017 0.97 0.20 2.08 0.3411 3.55 0.60 159000 6000 - - 281.1 4.2 41.4 4.3 0.088 0.056 0.262 0.064 705 26 1.52 0.14 0.036 0.019 5.49 0.23 0.353 0.049 5.15 0.61 6.96 0.6912 3.83 0.46 157500 6100 83 73 288.2 4.7 22.2 3.3 0.075 0.042 0.270 0.069 728.5 7.4 0.559 0.075 - - 2.84 0.19 0.253 0.050 4.43 0.40 6.94 0.5213A 3.39 0.40 161000 5800 76 67 282.5 4.0 22.5 3.4 0.164 0.072 0.271 0.061 769 30 0.92 0.11 - - 3.81 0.18 0.279 0.054 4.33 0.44 7.06 0.7013B 2.38 0.33 158300 5500 94 79 280.7 5.0 29.3 3.5 0.091 0.045 0.210 0.064 673.9 7.7 0.81 0.10 - - 3.51 0.22 0.234 0.039 3.81 0.49 6.40 0.5713C 3.27 0.39 160600 5500 - - 270.1 5.5 16.7 2.7 0.058 0.038 0.238 0.064 470.9 5.7 2.39 0.15 - - 9.63 0.48 0.058 0.019 1.74 0.29 2.74 0.3416 4.99 0.49 161800 6300 - - 290.1 4.1 18.7 3.1 0.090 0.056 0.267 0.060 766 15 1.47 0.15 - - 5.44 0.25 0.189 0.048 3.13 0.43 5.07 0.5017 0.85 0.23 156800 6400 85 63 270.0 4.8 20.3 2.7 0.018 0.034 0.59 0.23 381.4 8.7 0.90 0.11 - - 3.21 0.21 0.034 0.018 0.90 0.19 1.88 0.3119A 4.36 0.44 162500 5800 77 61 289.4 5.3 11.7 2.2 0.071 0.050 0.207 0.048 592 13 2.08 0.18 0.052 0.024 11.42 0.40 0.137 0.031 2.38 0.40 3.50 0.4819B 4.05 0.73 162700 4700 - - 288.9 4.9 15.5 2.7 0.136 0.063 0.287 0.072 953 55 2.23 0.20 0.016 0.012 15.33 0.77 0.377 0.057 5.37 0.72 7.40 0.8821 2.15 0.45 159400 6500 - - 277.1 6.3 26.9 4.0 0.015 0.031 0.200 0.051 421.9 8.8 1.02 0.12 - - 2.90 0.17 0.063 0.022 1.48 0.30 3.04 0.46Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G232Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: DT28-912, Upper Critical Zone, UG2Spot #11A 0.357 0.096 11.5 2.1 3.31 0.51 39.3 5.1 13.4 1.6 58.7 7.4 11.5 1.3 92.1 9.9 18.2 1.9 10900 170 0.368 0.050 130 27 110 17 6.39 0.861B 0.92 0.15 22.04 0.91 6.36 0.27 70.1 1.5 23.83 0.54 102.0 1.8 19.29 0.43 152.1 3.0 30.24 0.55 10410 120 0.334 0.043 234.2 7.0 239.5 3.0 5.62 0.202A 0.231 0.066 7.94 0.96 2.26 0.20 26.5 2.0 8.95 0.52 38.2 2.1 7.37 0.41 61.4 3.1 11.90 0.56 10270 130 0.222 0.034 86.6 5.0 86.9 2.9 4.14 0.132B 0.197 0.067 5.65 0.49 1.66 0.12 19.1 1.3 6.59 0.40 29.8 1.5 5.59 0.31 47.5 2.6 9.45 0.47 10570 120 0.332 0.045 73.3 7.4 65.0 5.2 3.41 0.213A 0.302 0.059 11.21 0.67 2.92 0.17 33.9 1.2 11.32 0.36 45.8 0.9 8.95 0.28 70.4 2.1 13.41 0.32 10380 120 0.330 0.048 152.5 3.6 143.9 2.0 4.78 0.233B 0.229 0.048 7.56 0.66 2.29 0.15 27.1 1.2 9.11 0.35 38.1 1.3 7.42 0.28 60.9 1.9 11.86 0.41 10590 140 0.413 0.070 99.1 3.3 99.3 3.0 7.40 2.004 0.815 0.097 31.1 1.2 8.43 0.22 88.5 2.1 28.39 0.57 115.1 2.2 20.36 0.47 156.7 3.0 29.47 0.65 11450 150 0.893 0.094 414 38 368 21 43.30 4.707A 0.98 0.12 27.0 1.3 7.16 0.23 74.7 1.6 24.29 0.56 100.7 2.1 18.36 0.37 141.3 2.5 27.53 0.61 9896 98 0.389 0.054 221 11 233.3 3.6 6.57 0.167B 1.16 0.14 28.4 1.4 7.46 0.19 78.1 1.8 24.99 0.45 102.4 1.7 18.90 0.41 144.6 2.7 28.15 0.49 10214 76 0.354 0.040 225.4 7.6 250.0 3.0 9.79 0.758A 1.18 0.14 26.3 1.2 7.49 0.21 80.6 1.8 26.13 0.57 105.9 1.8 18.81 0.47 141.7 2.5 26.17 0.55 9290 110 0.856 0.070 210 10 232.9 3.8 16.71 0.368B 1.21 0.12 26.16 0.97 7.07 0.23 78.2 1.8 24.83 0.50 97.7 1.8 17.27 0.35 130.3 2.0 24.84 0.42 9400 89 0.841 0.086 176.7 8.4 200.2 2.2 14.21 0.269 0.299 0.073 12.30 0.81 4.07 0.27 53.3 2.1 19.05 0.67 84.9 2.7 16.49 0.54 130.1 3.9 25.41 0.75 13350 240 1.298 0.094 386 35 420 20 87.20 5.8010A 0.760 0.110 12.34 0.80 3.37 0.15 34.9 1.2 11.44 0.42 47.8 1.1 9.01 0.25 72.1 1.7 14.49 0.36 10040 140 0.377 0.047 110.9 5.5 111.5 2.0 4.79 0.1510B 0.465 0.080 11.05 0.70 3.02 0.17 33.7 1.1 11.48 0.37 48.0 1.3 8.78 0.27 72.1 2.2 14.31 0.49 10340 150 0.334 0.041 137.4 5.2 136.9 2.9 5.17 0.1511 1.14 0.15 23.6 1.2 6.56 0.32 69.0 2.9 22.35 0.77 90.5 3.2 15.69 0.61 119.1 4.6 22.63 0.85 9420 120 0.741 0.084 194.9 6.0 186 10 15.38 0.9912 0.94 0.12 26.7 1.1 6.67 0.24 69.3 1.8 22.76 0.50 94.7 1.5 17.27 0.35 133.8 2.4 26.33 0.47 10040 130 0.388 0.038 225 11 210.3 3.4 6.46 0.1813A 1.11 0.10 24.2 1.2 6.58 0.25 72.1 2.1 23.71 0.88 98.9 4.1 17.85 0.83 138.3 6.2 26.8 1.2 10050 110 0.467 0.059 353 24 219 16 7.16 0.5913B 0.82 0.10 23.2 1.1 6.33 0.24 64.3 1.5 21.15 0.46 88.2 1.5 15.54 0.33 123.9 2.6 23.25 0.51 10070 120 0.455 0.066 365 25 179.9 3.7 5.90 0.2213C 0.358 0.070 13.08 0.90 3.77 0.16 43.7 1.2 14.81 0.41 62.9 1.5 11.79 0.38 95.5 1.9 18.28 0.41 11480 190 1.070 0.110 693 82 271.8 7.5 34.20 2.4016 0.90 0.13 21.2 1.1 6.00 0.21 69.5 2.2 23.71 0.65 103.2 2.9 19.22 0.56 159.3 3.6 31.60 0.85 10870 120 0.681 0.062 128.3 4.1 325 10 24.92 0.6417 0.353 0.056 9.69 0.58 2.87 0.15 34.0 1.4 11.81 0.37 50.3 1.3 9.60 0.29 79.3 2.3 15.36 0.32 10510 110 0.250 0.044 106.9 4.5 114.2 3.4 5.41 0.2219A 0.530 0.098 15.75 0.81 4.79 0.20 53.1 1.9 18.82 0.62 81.1 2.1 15.19 0.41 126.2 2.8 26.09 0.68 11830 170 1.81 0.12 188.9 6.3 360 11 45.25 0.8919B 0.97 0.15 28.8 2.5 8.09 0.57 87.4 5.8 30.1 2.1 127.5 7.7 23.1 1.4 187 10 35.8 1.8 12070 170 1.70 0.14 165.3 6.0 708 55 68.9 3.321 0.427 0.087 13.01 0.86 3.63 0.18 39.4 1.5 13.01 0.36 54.0 1.2 10.13 0.37 82.8 2.0 15.85 0.44 10290 180 0.258 0.044 271 16 139.5 2.5 4.20 0.17Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G233Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: B00-1-6, Upper Critical Zone, UG2Spot #11A 3.12 0.34 107500 8300 - - 240.4 6.2 25.1 3.3 0.067 0.044 0.200 0.052 671.6 6 0.823 0.093 - - 4.13 0.20 0.307 0.047 4.19 0.48 6.31 0.571B 5.61 0.81 109500 8800 - - 245.1 5.8 23.3 3.0 0.033 0.043 0.181 0.038 499 11 0.932 0.092 - - 3.82 0.18 0.187 0.032 2.90 0.39 4.55 0.542A 1.05 0.26 101600 7800 - - 237.0 5.3 20.9 2.9 0.051 0.034 0.192 0.049 505.2 5.4 0.725 0.079 - - 3.61 0.18 0.148 0.025 2.77 0.30 4.99 0.522B 1.61 0.39 105900 8400 - - 224.4 5.5 20.5 2.7 0.050 0.038 0.203 0.053 299 16 0.86 0.11 - - 2.80 0.15 0.040 0.015 0.76 0.19 1.72 0.313A 5.21 0.96 108400 8000 - - 255.7 5.1 24.6 2.8 0.094 0.046 0.191 0.041 615.9 5.9 0.731 0.096 - - 4.20 0.16 0.236 0.038 4.68 0.44 7.22 0.603B 1.57 0.27 112800 8800 - - 255.8 5.5 26.3 3.7 0.198 0.078 0.186 0.045 609.5 8.5 0.854 0.087 - - 4.07 0.20 0.308 0.053 4.55 0.35 6.79 0.524 1.00 0.19 111700 8300 67 56 234.1 5.2 19.5 2.5 0.067 0.041 0.164 0.046 300 15 1.02 0.12 - - 3.44 0.26 0.039 0.016 0.92 0.18 2.12 0.385A 1.33 0.27 108900 7800 - - 235.0 4.5 21.1 2.2 0.171 0.076 0.215 0.054 461 36 0.643 0.079 - - 3.19 0.21 0.134 0.034 2.54 0.56 4.50 0.795B 0.28 0.12 102200 7500 - - 233.0 4.7 18.6 2.9 0.026 0.038 0.182 0.043 281 11 0.809 0.084 - - 2.44 0.17 0.021 0.012 0.83 0.18 1.62 0.226 0.63 0.16 114400 8500 - - 243.6 4.7 28.9 3.2 0.119 0.057 0.223 0.059 636 17 0.96 0.10 - - 3.86 0.16 0.142 0.024 2.93 0.31 4.96 0.457A 4.87 0.43 107600 7900 69 61 214.5 3.9 22.6 2.9 0.121 0.052 0.172 0.055 205.9 4.2 1.00 0.11 0.020 0.011 3.16 0.21 0.045 0.017 0.81 0.16 1.03 0.197B 4.26 0.46 106300 7900 - - 221.8 4.6 16.6 2.5 0.056 0.043 0.184 0.045 245.6 6.7 0.717 0.097 - - 3.02 0.19 0.019 0.011 0.46 0.13 1.23 0.258 6.50 1.40 111400 8300 - - 227.9 4.2 16.0 2.6 0.110 0.061 0.155 0.043 344 19 1.36 0.14 - - 4.41 0.27 0.012 0.008 0.76 0.17 2.02 0.299A 0.78 0.21 105000 7600 - - 199.7 3.1 11.1 2.1 0.046 0.041 0.209 0.049 247 36 0.665 0.069 - - 3.79 0.18 0.013 0.010 0.27 0.11 1.05 0.329B 6.09 0.50 108000 8100 - - 231.2 3.1 21.1 3.0 0.127 0.048 0.261 0.054 687 15 0.503 0.077 - - 3.30 0.18 0.146 0.030 3.25 0.46 6.08 0.6010 1.03 0.21 114600 8200 - - 253.8 4.2 11.4 2.5 0.146 0.065 0.274 0.057 584 44 1.56 0.11 - - 6.41 0.35 0.087 0.033 1.93 0.53 3.43 0.7111A 1.22 0.37 108800 8100 57 48 232.8 4.3 11.2 2.2 0.116 0.053 0.242 0.059 773.7 5.1 1.50 0.14 - - 8.35 0.24 0.062 0.018 1.54 0.24 4.36 0.5111B 1.49 0.26 110900 8000 - - 232.4 3.6 11.5 1.9 0.081 0.039 0.166 0.042 429.5 2.7 2.24 0.13 - - 6.86 0.26 0.044 0.018 0.59 0.14 1.71 0.2213A 1.21 0.25 121600 9000 - - 241.2 3.2 15.4 1.6 0.145 0.059 0.261 0.055 672 62 1.65 0.12 - - 7.28 0.53 0.175 0.050 2.53 0.58 5.00 0.8813B 1.10 0.20 108000 7900 - - 258.0 4.2 14.1 2.1 0.149 0.046 0.224 0.054 558 11 1.65 0.12 0.0083 0.0064 6.18 0.19 0.043 0.015 1.08 0.24 2.39 0.3414 2.02 0.35 114800 8300 - - 244.0 3.6 11.8 2.1 0.196 0.063 0.262 0.050 917.9 5.0 1.73 0.14 0.0101 0.0072 7.36 0.25 0.303 0.038 4.77 0.40 7.84 0.5415A 3.17 0.62 106800 7200 230 130 222.7 3.8 9.9 2.1 1.590 0.730 2.6 1.1 286 12 1.53 0.13 0.029 0.019 5.00 0.28 0.026 0.013 0.48 0.13 0.99 0.2115B 0.72 0.18 107700 7700 - - 240.5 3.9 12.2 2.1 0.144 0.053 0.282 0.056 790.1 5.3 1.44 0.11 - - 7.74 0.27 0.135 0.031 2.99 0.28 6.00 0.5416A 7.89 0.92 114800 8400 - - 245.9 4.7 21.3 2.9 0.072 0.043 0.196 0.056 623.3 9.6 0.684 0.068 - - 3.57 0.17 0.201 0.034 3.30 0.35 6.10 0.4016B 3.70 0.64 116000 10000 - - 249.7 4.6 22.8 3.3 0.075 0.041 0.170 0.047 388 19 0.766 0.087 - - 2.62 0.18 0.065 0.021 1.19 0.23 2.40 0.3817A 4.60 1.80 115900 9400 - - 247.1 5.4 16.0 2.1 0.149 0.047 0.224 0.047 860 25 1.29 0.12 0.0090 0.0071 5.66 0.20 0.237 0.039 3.79 0.50 6.08 0.5217B 1.36 0.26 102700 7500 - - 240.5 4.3 14.2 2.9 0.091 0.050 0.223 0.067 436.9 3.6 1.70 0.15 - - 6.74 0.25 0.063 0.022 1.37 0.21 2.59 0.3419A 1.46 0.34 106900 7900 - - 246.0 4.2 23.1 2.5 0.133 0.056 0.187 0.046 614.2 4.7 0.649 0.081 - - 3.31 0.18 0.060 0.020 1.70 0.29 4.37 0.4119B 0.56 0.18 112100 8100 - - 235.0 4.3 22.1 3.0 0.083 0.046 0.158 0.044 355 29 0.801 0.078 - - 3.19 0.18 0.048 0.019 1.04 0.25 2.12 0.3920A 2.17 0.31 100500 7200 - - 259.8 5.1 24.6 3.4 0.093 0.049 0.236 0.062 766.2 8.8 0.499 0.077 - - 3.72 0.16 0.226 0.038 4.26 0.52 6.30 0.4820B 1.19 0.24 105300 8200 - - 231.3 4.7 23.5 3.4 0.093 0.049 0.181 0.049 272.3 4.8 0.833 0.091 - - 2.93 0.18 0.028 0.016 0.69 0.15 1.55 0.20Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G234Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: B00-1-6, Upper Critical Zone, UG2Spot #1A 1.00 0.11 21.2 1.2 5.86 0.18 62.5 1.8 20.86 0.37 86.0 1.4 15.74 0.40 126.2 2.6 23.75 0.55 8830 180 0.391 0.045 230 11 196.6 4.1 6.74 0.161B 0.81 0.10 16.02 0.96 4.36 0.19 47.9 1.8 15.59 0.41 63.1 1.4 11.90 0.37 95.8 2.4 17.83 0.49 8830 170 0.447 0.040 152.6 7.7 127.3 3.5 6.12 0.172A 0.719 0.089 17.99 0.98 4.90 0.19 51.63 0.95 15.94 0.40 62.8 1.1 11.40 0.31 93.0 2.1 16.86 0.41 8990 180 0.254 0.029 126.0 5.1 109.5 2.6 3.51 0.122B 0.364 0.072 8.70 1.10 2.44 0.23 27.4 1.8 9.22 0.61 37.8 2.0 7.34 0.41 60.6 3.1 11.47 0.50 9040 170 0.331 0.036 82.6 2.3 72.7 3.6 3.12 0.163A 1.04 0.10 22.44 0.94 6.14 0.19 64.3 1.5 19.80 0.31 77.9 1.1 14.24 0.33 112.1 2.0 20.32 0.51 9090 160 0.287 0.041 146.0 7.2 128.1 2.2 4.48 0.143B 1.011 0.083 23.45 0.92 6.02 0.19 63.0 1.6 18.92 0.33 76.3 1.1 14.03 0.29 109.7 2.3 20.24 0.53 9020 200 0.300 0.037 145.7 6.0 123.0 2.7 4.41 0.174 0.302 0.060 8.19 0.88 2.63 0.20 28.0 1.8 8.93 0.51 39.2 2.1 7.46 0.45 60.5 2.9 11.51 0.49 9280 150 0.288 0.034 103.2 5.2 91.4 5.4 3.65 0.245A 0.63 0.11 15.6 2.0 4.30 0.45 44.9 3.9 14.5 1.1 58.0 4.5 10.80 0.74 85.7 6.2 15.90 0.98 9200 120 0.228 0.030 127 14 104.7 9.7 3.25 0.175B 0.296 0.059 7.61 0.69 2.23 0.15 25.6 1.3 8.66 0.44 36.4 1.6 7.06 0.36 58.4 2.3 11.17 0.36 8950 130 0.266 0.034 76.7 6.2 64.4 3.5 2.27 0.106 0.80 0.10 20.41 0.95 5.64 0.28 63.5 2.2 19.74 0.61 80.7 2.4 14.53 0.48 118.3 3.7 22.01 0.68 9160 130 0.341 0.033 199 14 192.9 6.6 5.02 0.157A 0.380 0.081 4.71 0.38 1.53 0.10 18.33 0.66 6.27 0.25 26.94 0.81 5.09 0.19 44.3 1.4 8.51 0.26 8953 98 0.373 0.049 59.7 1.1 51.7 1.9 3.627 0.0857B 0.218 0.046 6.12 0.48 1.89 0.10 21.49 0.86 7.57 0.31 32.4 1.2 6.49 0.26 53.2 1.6 10.21 0.37 9830 130 0.210 0.029 89.4 1.5 78.4 3.4 3.42 0.268 0.247 0.054 8.69 0.87 2.82 0.20 31.1 2.2 10.37 0.61 46.3 2.7 8.72 0.52 72.8 4.1 13.97 0.69 9780 140 0.623 0.067 140 11 122.3 6.5 9.44 0.979A 0.121 0.047 5.3 1.1 1.75 0.35 21.0 3.6 7.1 1.1 32.7 4.5 6.23 0.70 52.6 5.5 11.0 1.0 11670 110 0.344 0.044 147.7 6.6 135 11 3.59 0.129B 0.784 0.097 22.3 1.1 5.94 0.20 63.9 1.8 21.43 0.57 88.5 2.7 16.89 0.47 134.5 4.0 26.41 0.99 10430 160 0.365 0.043 264.1 9.6 235.9 3.1 3.05 0.1410 0.52 0.11 15.4 2.0 4.52 0.49 52.8 5.0 18.2 1.5 78.2 5.7 15.16 0.94 121.0 6.1 23.6 1.2 10420 130 0.841 0.065 223 16 206 23 26.19 0.9611A 0.74 0.10 22.17 0.96 6.75 0.18 74.1 1.4 24.34 0.44 98.9 1.4 18.37 0.31 140.3 2.2 26.32 0.50 10730 100 0.696 0.057 321.1 9.6 281.5 4.0 35.0 1.111B 0.277 0.050 9.66 0.62 3.19 0.14 37.92 0.97 13.15 0.26 58.0 1.1 11.07 0.21 90.7 1.4 17.18 0.34 10580 100 0.977 0.064 191.9 4.6 164.9 2.7 29.1 1.113A 0.580 0.093 19.7 2.4 5.66 0.58 62.5 6.1 21.6 2.0 90.3 8.8 17.1 1.5 137.0 11.0 26.4 2.0 9810 130 0.916 0.059 300 25 277 33 35.2 3.413B 0.419 0.060 12.21 0.68 4.05 0.18 48.8 1.3 17.29 0.51 76.8 1.7 15.03 0.41 122.6 2.4 24.39 0.54 10313 86 0.836 0.056 215.9 4.5 184.9 5.5 29.04 0.4414 0.956 0.086 26.53 0.78 7.63 0.19 83.1 1.2 28.45 0.46 125.3 1.3 23.95 0.33 191.7 2.5 38.18 0.52 9850 100 1.42 0.10 467 16 396.7 4.5 59.13 0.5615A 0.155 0.036 5.68 0.54 1.91 0.12 23.6 1.2 8.86 0.46 40.3 1.9 7.84 0.39 67.6 3.1 13.13 0.60 10920 180 0.820 0.073 98.4 7.7 80.7 4.4 22.30 1.8015B 0.817 0.091 24.98 0.95 6.94 0.18 79.0 1.3 24.86 0.50 101.5 1.5 18.73 0.30 148.0 2.5 27.30 0.50 10170 140 0.715 0.061 304 13 264.1 4.0 34.47 0.6916A 0.94 0.12 21.20 0.91 5.88 0.20 62.6 1.4 19.29 0.46 77.4 1.6 14.17 0.34 114.4 3.0 20.64 0.53 9280 130 0.238 0.031 185.0 3.3 161.1 4.5 3.86 0.1216B 0.435 0.074 10.60 0.99 3.30 0.23 36.3 2.2 11.91 0.68 50.0 2.6 9.30 0.44 77.4 3.5 14.65 0.56 9290 180 0.295 0.037 108 11 89.2 6.9 2.87 0.1617A 0.94 0.12 23.1 1.2 6.49 0.23 76.9 2.6 27.21 0.83 115.9 2.7 21.72 0.68 173.7 4.9 33.77 0.96 9320 150 0.732 0.054 359 18 324.1 9.3 23.08 0.7617B 0.365 0.051 11.80 0.71 3.61 0.12 41.39 0.88 13.78 0.34 59.7 1.2 11.10 0.25 91.6 1.8 17.32 0.33 10050 130 0.668 0.049 215.0 6.0 192.3 3.4 29.4 1.519A 0.86 0.11 19.66 0.94 5.63 0.17 61.2 1.2 19.42 0.33 77.6 1.3 14.18 0.34 112.7 2.2 20.95 0.41 9550 130 0.196 0.033 151.8 5.1 138.8 2.0 3.98 0.1019B 0.454 0.087 10.8 1.4 3.04 0.31 34.2 3.1 11.03 0.98 45.9 3.7 8.59 0.64 70.0 5.3 12.78 0.88 9591 82 0.218 0.027 132.3 2.4 118.7 3.9 3.562 0.09820A 0.838 0.091 23.27 0.96 6.45 0.18 71.9 1.7 23.64 0.39 101.2 1.8 18.96 0.43 149.1 3.4 28.77 0.57 9330 150 0.218 0.034 205.9 8.0 183.9 2.9 4.939 0.09520B 0.274 0.042 7.59 0.56 2.23 0.09 24.23 0.88 8.29 0.26 35.2 0.8 6.70 0.23 57.0 1.7 10.72 0.32 9780 120 0.211 0.033 110.0 4.5 98.0 1.5 2.715 0.086Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G235Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: B90-7(0), Upper Critical Zone, Merensky ReefSpot #11A 0.32 0.12 190800 4100 - - 434.2 3.7 23.8 2.4 0.107 0.027 0.331 0.045 359.0 3.3 2.58 0.14 - - 2.44 0.10 0.029 0.010 0.547 0.091 1.16 0.261B 0.28 0.09 189900 4200 - - 428.8 4.0 26.7 2.0 0.094 0.023 0.326 0.045 353.0 4.4 2.67 0.14 - - 2.45 0.12 0.012 0.006 0.490 0.100 1.10 0.162 0.23 0.10 196600 6200 - - 435.4 3.9 37.3 2.7 0.134 0.038 0.339 0.047 722 26 2.57 0.14 0.0118 0.0059 4.35 0.14 0.291 0.032 4.03 0.37 5.54 0.373 0.72 0.17 195400 5200 - - 404.4 3.1 24.5 2.3 0.107 0.032 0.339 0.052 339.3 6.7 3.20 0.15 - - 2.92 0.13 0.044 0.014 0.810 0.160 1.74 0.245A 2.06 0.25 205000 8400 - - 396.0 4.0 26.3 2.7 0.061 0.028 0.259 0.045 272.0 8.5 2.61 0.13 - - 2.81 0.13 0.033 0.016 0.440 0.140 1.17 0.235B 1.25 0.19 191700 4200 - - 383.9 4.1 23.0 2.1 0.067 0.026 0.244 0.040 243.2 7.1 2.30 0.12 - - 2.73 0.11 0.010 0.006 0.293 0.067 0.74 0.156A 200400 4100 95 79 404.4 4.2 29.6 3.5 0.148 0.044 0.370 0.064 662.6 6.3 2.57 0.18 - - 4.05 0.17 0.272 0.045 3.97 0.43 5.57 0.516B 0.26 0.13 191700 4400 79 70 387.1 5.6 21.6 2.0 0.50 0.24 0.367 0.065 417 39 2.31 0.14 - - 2.82 0.16 0.063 0.021 0.980 0.240 2.06 0.397A 0.46 0.21 193100 4800 147 75 423.7 4.1 24.2 2.2 0.246 0.044 0.372 0.055 869 12 2.16 0.11 0.0051 0.0042 3.41 0.13 0.189 0.030 3.320 0.330 5.68 0.387B 1.37 0.25 190400 4200 - - 410.3 3.9 22.4 2.1 0.120 0.032 0.393 0.066 485 32 2.44 0.17 - - 3.09 0.12 0.070 0.015 1.44 0.22 2.78 0.307C 0.05 0.11 195000 4200 85 77 409.3 3.3 25.9 2.7 0.273 0.067 0.466 0.079 1164 11 2.68 0.15 - - 3.32 0.16 0.186 0.040 3.27 0.30 5.31 0.518 0.44 0.21 202800 5600 91 78 377.9 4.4 20.5 2.9 0.098 0.044 0.293 0.050 559 19 2.04 0.15 - - 2.65 0.20 0.022 0.011 1.06 0.20 2.40 0.349 0.27 0.16 208900 7500 - - 394.4 4.6 22.5 2.4 0.204 0.055 0.414 0.063 1079 26 2.25 0.11 0.0145 0.0094 4.36 0.14 0.257 0.032 4.15 0.36 6.75 0.4810 193800 4900 85 65 402.8 3.6 30.1 2.6 0.156 0.042 0.305 0.046 676.8 8.0 2.41 0.12 0.0122 0.0065 3.96 0.13 0.299 0.030 3.99 0.26 5.73 0.4012 0.20 0.13 194200 4600 - - 393.3 3.1 28.2 2.4 0.164 0.044 0.319 0.046 730 11 2.38 0.13 0.0108 0.0064 3.63 0.15 0.273 0.031 4.16 0.32 6.23 0.4013 0.68 0.17 194900 5700 - - 347.2 3.5 23.2 2.4 0.058 0.027 0.206 0.039 162.2 2.0 2.12 0.10 - - 1.901 0.081 0.007 0.005 0.202 0.061 0.43 0.1116 1.39 0.45 186300 4200 - - 394.5 4.1 21.0 2.8 0.161 0.068 0.397 0.077 895 25 2.23 0.21 0.0220 0.0130 4.10 0.27 0.234 0.064 4.21 0.54 5.84 0.5619 0.62 0.23 189200 5100 - - 390.0 4.3 24.5 2.4 0.142 0.044 0.361 0.061 682 14 2.19 0.14 - - 3.57 0.13 0.173 0.027 2.91 0.34 5.12 0.3822 0.65 0.20 186000 5500 - - 385.5 4.5 20.3 2.0 0.108 0.037 0.297 0.059 578 55 2.23 0.12 - - 3.03 0.36 0.112 0.030 1.86 0.43 3.51 0.6723 0.28 0.13 188500 4900 - - 389.0 3.4 23.4 2.7 0.123 0.043 0.352 0.041 696.8 4.0 2.28 0.15 0.0105 0.0073 3.77 0.18 0.244 0.028 3.82 0.38 5.57 0.43Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G236Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: B90-7(0), Upper Critical Zone, Merensky ReefSpot #11A 0.219 0.036 6.43 0.36 2.292 0.094 30.7 0.8 11.22 0.23 51.84 0.78 10.68 0.19 92.6 1.6 19.11 0.36 11274 92 0.488 0.041 200.3 8.0 103.5 3.0 10.17 0.151B 0.235 0.036 6.51 0.37 2.305 0.090 30.05 0.69 11.03 0.24 50.67 0.77 10.42 0.23 91.3 1.5 18.83 0.36 11280 110 0.470 0.036 205.7 8.1 102.5 3.5 10.22 0.132 0.766 0.080 19.86 0.72 5.82 0.14 67.1 1.9 23.23 0.90 101.7 4.2 19.61 0.90 161.8 6.8 32.4 1.6 10010 82 0.608 0.060 436 40 197.3 3.6 18.33 0.993 0.308 0.047 8.01 0.43 2.54 0.13 31.1 1.1 10.79 0.31 48.4 1.0 9.62 0.23 79.7 1.6 15.93 0.31 10370 100 0.561 0.047 275 18 125.1 1.9 11.62 0.365A 0.217 0.042 6.13 0.66 1.84 0.13 23.6 1.3 8.56 0.44 40.7 1.8 8.02 0.31 71.0 2.3 14.44 0.48 9447 73 0.269 0.032 346 26 164.5 5.6 15.89 0.375B 0.148 0.028 4.72 0.39 1.603 0.088 20.66 0.78 7.66 0.28 35.4 1.1 7.32 0.22 65.2 1.9 13.12 0.38 9385 76 0.272 0.028 317 23 185.7 3.9 21.80 0.336A 0.808 0.096 21.78 0.95 6.09 0.23 67.6 1.5 21.80 0.45 89.8 1.6 16.28 0.39 133.1 2.4 25.58 0.44 10380 110 0.430 0.053 283 13 197.1 2.3 16.76 0.676B 0.341 0.067 10.6 1.4 3.24 0.41 38.6 4.3 13.6 1.3 57.5 5.1 11.20 0.97 93.6 7.0 18.1 1.4 11230 110 0.294 0.034 220 32 121 13 10.17 0.567A 0.716 0.060 23.23 0.76 6.82 0.19 78.8 1.5 27.93 0.43 122.7 2.2 24.18 0.56 200.0 5.2 41.1 1.3 11280 140 0.452 0.048 563 36 322.1 2.7 9.32 0.187B 0.342 0.050 12.9 1.1 3.91 0.28 46.4 3.5 15.7 1.1 65.1 4.4 12.89 0.82 104.6 6.3 20.2 1.2 11720 130 0.300 0.037 503 39 279.5 3.1 7.18 0.157C 0.750 0.092 24.28 0.98 7.21 0.21 93.0 2.1 36.23 0.46 169.3 2.5 32.60 0.63 272.8 4.5 55.54 0.99 10640 110 0.644 0.055 624 31 419.6 3.3 13.63 0.268 0.358 0.068 15.2 1.2 4.52 0.28 52.9 2.8 17.99 0.69 75.8 2.8 13.97 0.51 116.3 3.5 22.28 0.49 10890 110 0.269 0.042 237.5 7.1 176.2 5.5 9.78 0.449 0.735 0.084 27.36 0.78 7.94 0.24 94.1 2.4 34.0 1.0 146.6 4.0 27.17 0.83 221.1 5.8 43.4 1.3 11269 95 0.275 0.034 799 92 555 17 22.85 0.6910 0.750 0.072 21.23 0.74 6.00 0.16 66.5 1.2 21.66 0.38 90.8 1.7 16.66 0.35 135.5 2.5 26.22 0.49 10127 65 0.494 0.045 303 19 204.7 4.3 18.81 0.7612 0.774 0.075 22.88 0.86 6.17 0.17 69.8 1.2 23.24 0.42 97.0 1.7 17.78 0.38 145.8 2.6 27.99 0.54 9923 57 0.422 0.045 318 13 223.8 5.5 21.95 0.7613 0.091 0.024 2.98 0.26 0.948 0.051 12.55 0.47 4.90 0.14 23.2 0.5 4.93 0.13 43.48 0.99 9.19 0.21 8320 74 0.272 0.029 106.7 7.3 55.9 0.5 8.90 0.1216 1.18 0.24 24.0 1.2 7.05 0.32 81.7 2.3 28.21 0.89 123.4 3.5 23.30 0.70 193.6 5.2 38.4 1.0 10857 99 0.354 0.037 880 80 416 15 26.30 3.4019 0.665 0.073 21.2 1.0 5.87 0.22 65.8 2.0 21.67 0.51 90.8 2.3 16.59 0.39 135.9 2.9 26.11 0.57 10343 82 0.377 0.041 456 40 222.9 4.7 13.36 0.4022 0.411 0.089 14.9 1.9 4.37 0.50 51.0 5.2 17.6 1.8 77.0 6.9 14.8 1.4 122.5 9.8 24.1 1.7 11590 160 0.382 0.064 569 98 243 32 11.5 1.723 0.800 0.083 22.12 0.73 5.98 0.18 64.4 1.1 21.82 0.30 92.4 1.2 17.03 0.30 135.7 2.2 26.37 0.40 9849 61 0.363 0.044 422 27 201.4 1.0 18.74 0.26Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G237Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: SA04-08, Upper Critical Zone, Merensky Reef (Eastern Limb)Spot #11A 0.41 0.13 153900 8200 - - 252.0 5.8 13.3 2.3 0.035 0.044 0.179 0.042 165.6 3.1 0.704 0.078 - - 2.53 0.14 0.005 0.008 0.18 0.08 0.46 0.131B 0.39 0.13 151600 8500 - - 253.0 5.8 14.8 2.4 0.016 0.040 0.201 0.066 246 35 0.737 0.072 - - 2.94 0.34 0.044 0.023 0.80 0.31 1.13 0.392 0.21 0.09 157500 7500 - - 276.7 6.8 20.6 3.4 0.107 0.057 0.184 0.046 535.7 8.4 1.34 0.14 0.031 0.012 5.50 0.25 0.193 0.034 3.08 0.32 4.04 0.373A 0.95 0.21 159500 6800 - - 261.6 6.4 20.9 3.0 0.043 0.052 0.149 0.035 342 19 1.22 0.13 - - 4.71 0.20 0.065 0.022 1.03 0.24 1.81 0.313B 0.63 0.14 149900 7900 - - 253.2 4.1 20.4 2.6 0.038 0.040 0.197 0.045 271.6 2.3 1.159 0.080 - - 4.28 0.17 0.032 0.016 0.65 0.15 0.98 0.195A 0.71 0.14 151100 8600 - - 263.5 4.8 20.6 2.6 0.054 0.043 0.146 0.037 277.3 6.5 1.34 0.11 0.034 0.026 3.17 0.19 0.026 0.013 0.65 0.17 1.27 0.264B 0.54 0.17 147500 8300 - - 258.1 5.5 19.7 2.4 0.033 0.039 0.162 0.034 244.7 2.4 1.58 0.13 - - 3.78 0.20 0.016 0.010 0.61 0.14 0.99 0.175C 1.29 0.45 147600 8700 - - 251.2 6.0 15.0 2.5 0.072 0.043 0.213 0.052 239.6 3.0 1.21 0.10 - - 3.86 0.18 0.017 0.012 0.45 0.13 0.82 0.197 0.47 0.14 141900 8600 - - 255.0 4.5 16.8 2.9 0.077 0.048 0.200 0.048 286.9 3.6 1.05 0.12 - - 4.06 0.16 0.021 0.012 0.64 0.17 1.31 0.239 0.59 0.18 148000 8600 - - 226.4 3.2 12.8 2.2 0.059 0.049 0.163 0.032 181.6 2.8 0.98 0.12 - - 3.30 0.17 0.003 0.007 0.202 0.081 0.43 0.1310 1.12 0.46 153500 9800 - - 226.7 3.3 25.7 9.2 5.5 4.5 0.85 0.44 150.6 4.7 1.48 0.17 - - 2.49 0.14 0.018 0.012 0.183 0.089 0.51 0.1211A 0.35 0.12 145700 8700 - - 233.4 3.7 21.9 2.6 0.048 0.036 0.213 0.056 186.5 4.0 2.19 0.17 - - 3.77 0.18 0.018 0.012 0.35 0.12 0.61 0.1611B 0.37 0.11 141800 8300 - - 225.2 2.9 19.2 2.4 0.019 0.032 0.147 0.034 143.9 3.6 1.34 0.11 - - 2.69 0.12 0.000 0.004 0.26 0.10 0.46 0.1212 0.88 0.18 150100 8100 - - 266.1 3.7 25.7 2.6 0.087 0.046 0.135 0.041 448.4 9.8 1.49 0.14 0.053 0.019 5.00 0.17 0.309 0.044 3.25 0.37 3.73 0.4314A 0.49 0.15 139600 8500 - - 243.9 4.1 21.7 2.5 0.064 0.036 0.150 0.048 228.6 2.0 1.70 0.15 - - 3.14 0.16 0.028 0.016 0.46 0.12 1.13 0.2014B 0.45 0.13 146800 7800 - - 236.8 3.6 17.7 2.3 0.040 0.034 0.168 0.041 205.1 2.8 1.74 0.15 - - 3.05 0.18 0.009 0.007 0.39 0.09 0.84 0.1716A 1.31 0.21 149300 8000 - - 248.9 4.7 22.9 2.8 0.103 0.039 0.190 0.049 463.0 13.0 1.53 0.13 0.047 0.016 4.83 0.19 0.191 0.038 2.72 0.36 2.83 0.2716B 0.25 0.12 154900 7000 - - 255.6 5.0 23.6 2.3 0.098 0.051 0.134 0.046 476.3 9.1 1.24 0.11 0.035 0.015 4.99 0.28 0.175 0.035 2.90 0.36 3.61 0.3617 0.70 0.17 143500 8300 - - 247.7 3.6 21.6 3.1 0.093 0.044 0.226 0.053 275.3 5.3 1.172 0.096 0.086 0.020 3.86 0.16 0.044 0.016 0.65 0.16 1.16 0.1518A 2.56 0.37 142500 8700 960 360 236.3 5.0 24.8 3.3 0.077 0.036 1.86 0.63 465 53 1.67 0.15 0.093 0.022 4.85 0.33 0.263 0.048 3.18 0.49 3.62 0.5318B 1.89 0.25 146300 9000 - - 245.3 4.2 28.7 3.2 0.184 0.064 0.243 0.056 736.1 6.5 2.16 0.13 0.051 0.017 5.13 0.22 0.278 0.041 3.27 0.35 3.48 0.3419 0.34 0.15 136100 8700 - - 258.3 3.7 11.3 1.9 0.127 0.059 0.242 0.049 601 20 1.67 0.16 0.0237 0.0099 7.31 0.27 0.141 0.028 2.21 0.29 2.94 0.3323 1.43 0.24 132300 8800 - - 248.9 4.0 18.6 2.5 0.077 0.037 0.169 0.046 432.7 4.3 1.09 0.11 - - 4.02 0.20 0.093 0.022 1.48 0.21 2.69 0.2924A 0.77 0.18 142600 9300 - - 241.7 6.4 19.1 2.7 0.052 0.037 0.213 0.049 241.0 3.2 1.21 0.11 - - 3.36 0.16 0.006 0.005 0.62 0.11 1.10 0.2124B 0.98 0.19 140900 8300 - - 239.4 4.9 18.0 2.4 0.070 0.045 0.140 0.040 242.3 2.7 1.16 0.11 - - 3.46 0.18 0.031 0.013 0.55 0.12 1.30 0.19Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G238Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: SA04-08, Upper Critical Zone, Merensky Reef (Eastern Limb)Spot #11A 0.111 0.038 2.56 0.34 0.997 0.078 13.15 0.50 5.20 0.20 25.29 0.71 5.41 0.20 49.1 1.4 10.42 0.33 8410 150 0.245 0.035 74.8 3.3 59.6 1.6 83.1 1.71B 0.30 0.11 5.5 1.3 1.71 0.33 21.70 3.40 7.90 1.10 37.4 4.7 7.38 0.89 65.5 7.4 13.4 1.5 8270 160 0.229 0.029 104 12 99.0 16.0 109 112 0.69 0.10 15.27 0.86 4.53 0.18 50.00 1.30 17.65 0.35 76.1 1.4 14.43 0.29 116.8 2.8 22.53 0.55 7290 150 0.475 0.048 248 11 200.0 5.1 193.1 4.13A 0.276 0.059 7.64 0.65 2.54 0.20 29.20 2.00 10.89 0.67 49.4 3.1 9.46 0.58 81.4 4.5 16.23 0.97 7840 140 0.384 0.040 264 17 206.4 6.8 149.9 4.03B 0.226 0.050 6.23 0.47 2.05 0.12 24.02 0.71 8.74 0.22 40.22 0.93 7.67 0.21 64.7 1.5 13.13 0.28 7970 120 0.390 0.047 218.7 8.6 173.8 2.8 132.2 1.65A 0.268 0.051 5.97 0.55 1.82 0.12 23.43 0.78 8.83 0.26 41.3 1.3 8.34 0.36 78.0 3.5 16.94 0.99 7240 130 0.606 0.063 160.6 8.7 120.9 3.0 127.1 6.24B 0.263 0.047 5.32 0.40 1.73 0.10 21.92 0.71 7.91 0.23 35.66 0.84 7.14 0.21 60.7 1.5 12.37 0.29 7640 140 0.461 0.045 201.7 7.7 158.1 3.3 111.7 2.05C 0.183 0.041 4.56 0.43 1.600 0.085 20.62 0.78 7.61 0.17 36.4 1.1 7.08 0.24 65.0 1.7 12.83 0.34 8710 200 0.361 0.044 260 18 197.3 4.8 129.6 4.47 0.212 0.056 5.91 0.43 2.031 0.094 25.51 0.75 9.06 0.22 41.4 1.0 8.05 0.22 67.9 1.7 13.69 0.34 8060 140 0.282 0.042 220 14 183.9 3.3 91.3 1.89 0.111 0.029 3.01 0.35 1.056 0.074 14.55 0.55 5.71 0.19 26.83 0.97 5.28 0.20 46.7 1.2 9.50 0.24 7853 85 0.298 0.043 126.7 3.1 106.0 2.5 66.9 1.210 0.133 0.045 2.62 0.33 0.974 0.078 12.57 0.66 4.83 0.22 22.89 0.89 4.32 0.19 39.8 1.5 8.16 0.35 7558 84 0.507 0.055 76.7 4.4 55.3 2.1 84.1 1.411A 0.148 0.043 4.05 0.45 1.250 0.079 16.29 0.62 5.95 0.21 26.83 0.86 5.42 0.20 46.4 1.1 9.20 0.28 7410 110 0.786 0.057 93.5 2.7 77.0 1.8 118.5 2.111B 0.085 0.033 2.98 0.41 0.963 0.069 12.15 0.60 4.57 0.20 21.68 0.76 4.20 0.16 36.7 1.2 7.80 0.26 7627 85 0.503 0.047 61.4 2.8 50.74 0.77 87.13 0.9912 0.686 0.081 14.19 0.76 4.24 0.16 43.30 1.50 14.70 0.51 62.1 2.0 11.54 0.37 92.2 2.8 18.05 0.51 7017 83 0.792 0.075 185.7 8.7 149.4 2.2 155.0 2.314A 0.208 0.042 5.70 0.47 1.688 0.072 20.99 0.85 7.39 0.21 33.64 0.71 6.34 0.15 53.3 1.1 10.74 0.26 7059 79 0.631 0.048 106.2 4.4 86.3 1.1 104.9 1.214B 0.188 0.041 5.40 0.45 1.498 0.071 18.05 0.64 6.58 0.20 30.16 0.76 5.99 0.18 49.4 1.4 9.80 0.26 7138 93 0.602 0.046 98.4 3.2 79.5 1.3 99.9 1.616A 0.615 0.092 13.00 0.72 3.71 0.17 42.10 1.50 14.93 0.59 65.9 2.9 12.41 0.53 101.9 4.0 19.91 0.75 7212 76 0.762 0.071 241 12 188.0 8.1 206.7 8.416B 0.554 0.086 13.88 0.91 3.96 0.22 43.90 1.10 15.42 0.48 67.9 1.8 12.98 0.49 103.8 3.0 20.61 0.61 7370 100 0.691 0.074 225.7 8.5 187.4 4.5 198.0 10.017 0.271 0.046 6.78 0.43 2.02 0.12 24.99 0.73 8.76 0.27 39.3 1.1 7.72 0.22 64.3 1.7 12.73 0.29 8160 61 0.409 0.049 173.8 6.0 128.9 2.5 101.1 1.918A 1.96 0.24 11.8 1.2 3.43 0.33 42.30 4.40 15.20 1.80 66.2 7.8 12.4 1.4 99 11 19.3 2.2 7071 97 0.86 0.10 274 51 183 30 209.0 28.018B 0.583 0.084 14.14 0.82 4.57 0.14 59.40 1.30 23.76 0.39 109.4 2.0 20.73 0.50 168.3 2.7 33.88 0.67 6903 97 1.91 0.10 467 18 385.8 5.4 457.3 7.619 0.460 0.068 14.60 0.82 4.51 0.25 54.40 2.10 19.34 0.86 87.4 3.0 16.78 0.62 140.2 4.5 27.93 0.86 7791 84 0.874 0.071 372 16 311 13 235.7 6.223 0.457 0.057 12.85 0.74 3.53 0.14 41.00 1.10 14.26 0.32 60.4 1.0 11.13 0.26 93.3 1.6 17.98 0.40 7455 85 0.423 0.043 185.6 5.2 156.8 2.1 113.5 1.824A 0.203 0.049 6.08 0.47 1.89 0.12 21.88 0.77 7.70 0.24 34.06 0.94 6.60 0.19 56.5 1.5 11.31 0.29 7110 140 0.362 0.038 129.1 7.5 102.6 2.7 106.7 1.824B 0.208 0.045 6.26 0.45 1.88 0.10 22.13 0.71 7.93 0.21 34.20 0.73 6.78 0.16 58.1 1.2 11.50 0.30 7230 100 0.394 0.045 131.6 7.7 105.9 2.3 107.1 1.5Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G239Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: SA04-13, Upper Critical Zone, Merensky Reef (Western Limb)Spot #11 0.16 0.07 136800 9500 - - 241.2 4.5 18.4 2.7 0.110 0.045 0.207 0.043 420.4 5.5 1.24 0.10 - - 5.33 0.21 0.066 0.020 1.07 0.19 2.12 0.352A 0.93 0.18 127700 9100 - - 234.7 3.2 17.2 2.3 0.106 0.054 0.199 0.055 465.2 5.6 0.97 0.12 - - 6.02 0.24 0.061 0.018 1.36 0.16 2.76 0.392B 0.84 0.18 137300 9000 - - 236.9 4.6 16.0 2.8 0.044 0.032 0.194 0.050 476.7 8.8 0.98 0.11 - - 6.14 0.24 0.086 0.024 1.31 0.25 2.62 0.363A 0.83 0.19 129800 9000 - - 232.9 3.4 18.7 2.6 0.139 0.062 0.227 0.049 762 12 1.35 0.11 0.028 0.012 6.80 0.25 0.201 0.033 4.03 0.51 6.56 0.463B 0.80 0.18 134500 9500 - - 239.0 4.5 21.0 2.5 0.158 0.063 0.220 0.046 781.0 7.1 1.26 0.11 0.0156 0.0099 6.74 0.24 0.330 0.045 4.86 0.47 7.07 0.523C 0.20 0.09 135000 8700 - - 236.8 3.4 21.1 2.9 0.204 0.075 0.265 0.048 836.7 7.3 1.47 0.13 0.017 0.011 6.95 0.31 0.326 0.052 4.62 0.44 7.08 0.564A 0.28 0.12 118500 8200 - - 243.3 4.3 23.3 3.3 0.159 0.067 0.330 0.110 723.0 6.0 1.17 0.11 - - 6.39 0.25 0.174 0.031 2.88 0.37 6.29 0.554B 0.17 0.11 127400 5400 - - 259.3 9.7 25.3 4.1 0.230 0.084 0.222 0.076 746 16 1.13 0.14 - - 6.62 0.47 0.229 0.045 4.53 0.75 6.79 0.875A 0.63 0.17 122200 8500 1050 450 234.0 4.8 15.8 2.5 0.068 0.035 1.27 0.46 402.9 4.8 1.54 0.11 0.018 0.013 6.06 0.25 0.061 0.021 1.02 0.22 2.26 0.375B 1.00 0.20 98500 7400 290 120 233.2 3.5 13.1 2.8 0.028 0.048 0.60 0.19 408.4 6.0 1.47 0.15 - - 6.13 0.28 0.029 0.014 0.85 0.18 1.56 0.337 0.40 0.13 123200 8800 - - 218.5 3.8 23.0 3.0 0.065 0.039 0.112 0.036 244 10 1.88 0.14 - - 3.72 0.18 0.030 0.013 0.45 0.12 1.04 0.2110A 0.24 0.12 116200 8400 - - 216.3 3.1 27.1 3.0 0.056 0.033 0.168 0.042 233.8 6.2 1.38 0.14 - - 3.32 0.17 0.024 0.011 0.48 0.14 1.23 0.1910B 0.75 0.17 121500 8500 - - 239.3 3.5 13.2 1.7 0.130 0.060 0.235 0.047 448.7 5.3 1.81 0.14 - - 8.11 0.37 0.058 0.018 1.00 0.21 2.38 0.3110C 0.21 0.11 126600 8700 - - 227.6 2.9 20.6 2.9 0.113 0.053 0.183 0.051 346.8 5.3 2.04 0.17 - - 5.87 0.27 0.042 0.016 0.64 0.18 1.72 0.2411 0.51 0.12 128500 9200 - - 232.1 3.5 25.0 2.9 0.127 0.051 0.200 0.051 675.7 4.2 1.38 0.14 - - 5.63 0.26 0.035 0.014 1.33 0.21 4.22 0.3715A 0.13 0.08 122000 9500 - - 230.7 5.9 18.7 2.7 0.100 0.043 0.158 0.051 348.2 5.6 2.04 0.17 - - 3.67 0.20 0.021 0.011 0.50 0.15 1.76 0.2615B 0.17 0.09 120000 8900 - - 227.8 5.4 17.7 2.2 0.050 0.031 0.159 0.041 327.3 5.7 1.70 0.14 - - 3.42 0.17 0.029 0.013 0.44 0.13 1.66 0.2417A 0.25 0.11 116200 8800 - - 201.1 5.3 24.7 2.7 0.061 0.034 0.174 0.044 136.3 2.5 1.061 0.097 0.148 0.034 3.31 0.17 0.075 0.021 0.61 0.17 0.56 0.1817B 0.41 0.13 118000 8600 - - 206.4 4.8 30.6 3.5 0.047 0.030 0.097 0.034 183.2 2.4 1.10 0.10 - - 3.12 0.17 0.006 0.005 0.46 0.10 0.67 0.1417C 0.10 0.07 113900 8200 - - 202.4 4.4 27.7 2.9 0.059 0.035 0.158 0.041 142.8 1.4 0.994 0.094 - - 2.83 0.16 0.025 0.012 0.32 0.11 0.60 0.1519 0.18 0.09 128000 9400 54 42 226.8 6.2 17.3 2.5 0.056 0.034 0.195 0.049 365.8 4.8 1.64 0.12 - - 7.28 0.30 0.017 0.010 0.65 0.14 1.51 0.2621 0.07 0.06 120500 9400 - - 236.5 5.4 34.1 3.5 0.074 0.039 0.167 0.045 334.1 3.7 1.96 0.15 - - 5.07 0.22 0.118 0.029 1.46 0.18 2.92 0.35Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G240Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: SA04-13, Upper Critical Zone, Merensky Reef (Western Limb)Spot #11 0.325 0.061 10.74 0.69 3.25 0.16 40.73 0.99 13.61 0.31 56.13 0.92 10.50 0.26 87.3 1.8 16.52 0.39 9940 140 0.643 0.051 193.0 6.1 161.0 2.8 37.44 0.952A 0.385 0.054 12.91 0.76 3.67 0.16 44.2 1.4 15.17 0.37 62.1 1.6 11.94 0.32 97.1 2.5 18.32 0.48 10000 110 0.317 0.031 256 12 214.3 3.3 47.59 0.762B 0.386 0.051 13.18 0.57 3.84 0.21 45.6 1.5 15.30 0.45 63.2 1.6 11.86 0.35 96.9 2.3 18.63 0.48 10050 140 0.346 0.036 271 14 217.0 3.5 48.98 0.913A 0.92 0.11 25.8 1.1 7.08 0.21 77.3 1.9 24.65 0.60 97.0 2.1 17.34 0.49 136.1 3.7 25.08 0.73 9030 120 0.718 0.063 224.0 5.5 190.7 4.4 62.0 1.73B 0.831 0.097 26.0 1.1 7.20 0.19 77.2 1.5 25.15 0.54 104.4 1.9 18.58 0.46 151.3 2.9 29.25 0.57 8820 130 0.974 0.066 254.8 6.2 207.6 3.4 85.0 1.73C 0.854 0.095 27.5 1.1 7.35 0.21 82.3 1.8 27.08 0.44 109.3 1.7 19.53 0.36 156.1 3.0 29.20 0.55 8786 86 0.794 0.052 273.5 7.9 225.5 3.1 77.3 1.84A 0.83 0.11 27.46 0.90 7.18 0.20 75.2 1.7 23.59 0.36 92.3 1.6 16.38 0.34 125.4 2.7 23.19 0.60 8740 130 0.531 0.051 169 12 148.8 2.3 52.92 0.774B 0.91 0.14 27.5 1.7 7.49 0.36 80.0 4.0 23.5 1.1 96.0 3.5 17.7 1.0 139.8 8.8 23.86 0.78 8950 410 0.61 0.11 104 26 158.3 7.5 57.7 2.45A 0.293 0.054 10.33 0.62 3.20 0.15 37.2 1.0 12.76 0.31 52.1 1.1 10.05 0.25 82.0 1.6 15.33 0.34 9930 130 0.732 0.053 181.6 3.9 155.1 2.8 40.1 1.25B 0.363 0.077 10.66 0.65 3.25 0.16 38.1 1.2 12.77 0.35 53.8 1.3 9.86 0.22 82.5 1.7 15.16 0.39 9804 81 0.638 0.060 141 11 157.0 4.1 40.4 1.57 0.150 0.040 4.96 0.51 1.77 0.14 21.2 1.3 7.60 0.37 33.7 1.4 6.64 0.34 53.6 2.2 10.82 0.38 8282 86 0.960 0.066 89.5 4.8 74.9 2.0 39.01 0.6810A 0.177 0.046 6.02 0.51 1.81 0.13 21.93 0.96 7.48 0.27 31.5 1.1 6.01 0.21 49.8 1.4 9.89 0.29 8960 110 0.618 0.047 50.7 3.0 43.1 1.5 21.22 0.3110B 0.260 0.063 11.46 0.65 3.52 0.13 41.5 1.1 14.15 0.29 61.6 1.2 11.29 0.24 94.0 1.8 17.60 0.43 9882 99 0.782 0.064 195.4 4.2 170.1 3.3 81.6 2.510C 0.233 0.049 9.57 0.60 2.83 0.13 33.50 0.78 11.06 0.31 46.0 1.2 8.51 0.24 70.7 1.7 13.34 0.35 9309 87 0.748 0.061 114.9 3.3 102.5 1.9 48.9 1.111 0.622 0.075 21.29 0.95 6.24 0.19 69.2 1.6 21.81 0.34 88.9 1.2 15.63 0.28 120.8 2.0 22.30 0.34 9034 69 0.562 0.046 158.7 6.9 136.0 1.3 49.07 0.5715A 0.239 0.052 9.46 0.58 2.70 0.14 32.4 1.1 11.00 0.31 46.26 0.89 8.56 0.24 71.4 2.2 13.47 0.43 8960 210 0.874 0.068 95.5 5.1 85.0 2.5 27.83 0.6715B 0.212 0.049 7.86 0.66 2.44 0.14 30.42 0.99 10.43 0.35 43.5 1.0 8.20 0.25 68.2 1.8 13.43 0.39 9050 230 0.875 0.073 85.0 7.1 71.8 3.3 25.92 0.6417A 0.441 0.080 3.08 0.33 0.976 0.077 11.33 0.51 4.13 0.15 19.23 0.61 3.84 0.16 31.1 1.0 6.15 0.19 8410 160 0.477 0.048 41.8 3.2 28.35 0.84 26.37 0.5417B 0.153 0.036 4.09 0.37 1.355 0.081 16.36 0.58 5.78 0.20 25.80 0.53 4.82 0.15 41.2 1.1 7.78 0.23 8150 180 0.528 0.048 49.3 1.2 45.5 1.6 37.50 0.8317C 0.105 0.038 3.12 0.33 1.024 0.060 12.90 0.52 4.54 0.16 20.24 0.56 3.89 0.16 34.0 1.0 6.69 0.23 8350 160 0.403 0.047 33.4 1.6 30.26 0.66 25.27 0.3619 0.243 0.052 8.49 0.57 2.95 0.15 34.52 0.80 11.79 0.25 50.27 0.95 9.57 0.24 77.9 1.8 14.91 0.38 9550 210 0.670 0.054 149.3 6.2 130.6 2.9 64.7 1.021 0.385 0.053 11.55 0.66 3.27 0.13 34.3 1.0 10.80 0.25 43.6 1.2 8.00 0.21 64.1 1.5 11.50 0.34 7790 200 0.605 0.057 118.7 4.5 105.3 2.5 26.97 0.47Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G241Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: MP24D2 26.3, Upper Critical Zone, Bastard ReefSpot #12A 1.38 0.33 160700 4200 - - 261.8 4.8 22.5 3.2 0.035 0.029 0.228 0.066 182.8 3.1 1.06 0.13 0.014 0.011 3.71 0.28 0.025 0.016 0.46 0.16 0.66 0.172B 1.11 0.21 162400 4600 - - 259.6 3.8 29.4 3.1 0.074 0.043 0.200 0.058 234.1 4.7 1.18 0.11 - - 3.75 0.20 0.077 0.027 1.10 0.22 1.80 0.272C 0.62 0.20 167900 5400 - - 298.9 4.8 33.8 4.0 0.119 0.048 0.212 0.075 562.9 5.2 1.70 0.14 - - 6.26 0.32 0.295 0.042 4.96 0.42 5.95 0.506A 0.43 0.41 159400 4900 - - 290.0 10.0 46.4 7.4 0.22 0.10 311 45 1.47 0.32 - - 5.34 0.64 0.129 0.072 2.26 0.66 2.64 0.886B 0.21 0.15 172700 4400 - - 312.6 4.1 54.9 4.8 0.048 0.030 0.188 0.041 648.1 5.5 1.52 0.13 0.039 0.017 7.18 0.25 0.405 0.055 5.86 0.56 6.80 0.609A 0.46 0.27 177600 4200 190 140 298.6 5.9 61 10 0.128 0.089 0.30 0.12 348.2 3.5 2.50 0.30 - - 7.43 0.47 0.148 0.057 2.30 0.46 3.50 0.789B 1.43 0.41 159200 3500 181 89 301.2 6.4 59.0 5.9 0.106 0.052 0.373 0.090 346.2 3.4 2.79 0.24 0.037 0.019 7.90 0.33 0.160 0.034 2.50 0.35 3.03 0.419C 1.25 0.38 167500 4800 - - 292.1 5.1 45.9 3.9 0.063 0.040 0.199 0.064 347.6 3.2 2.91 0.19 - - 7.63 0.30 0.196 0.042 2.56 0.47 3.40 0.459D 0.27 0.16 167400 4500 - - 289.3 5.7 47.1 4.4 0.044 0.034 0.147 0.047 347.6 3.6 3.01 0.20 - - 7.55 0.29 0.130 0.033 2.30 0.31 3.12 0.4710 0.73 0.18 167400 6500 - - 279.6 3.4 42.4 4.4 0.026 0.032 0.161 0.052 317.8 2.7 2.73 0.19 - - 6.22 0.36 0.080 0.028 1.42 0.25 2.13 0.3014A 2.23 0.37 169300 5400 - - 285.1 4.1 16.6 2.3 0.042 0.031 0.266 0.080 437.9 4.2 1.84 0.15 - - 9.63 0.30 0.065 0.021 0.99 0.24 2.38 0.4514B 1.68 0.44 168200 4800 - - 292.0 4.0 19.3 2.6 0.119 0.056 0.278 0.069 1175 27 1.63 0.15 0.0106 0.0098 10.22 0.36 0.334 0.060 5.37 0.59 8.01 0.7414C 1.68 0.30 168100 4900 - - 292.1 5.4 19.6 3.0 0.325 0.094 0.213 0.051 1060 52 1.69 0.17 0.028 0.017 9.72 0.35 0.270 0.051 4.57 0.47 6.92 0.6716 0.37 0.17 164800 5900 - - 282.4 4.5 23.2 3.9 0.099 0.043 0.209 0.054 497 19 1.25 0.14 - - 5.03 0.28 0.100 0.030 1.81 0.29 3.45 0.5718 3.19 0.86 174400 8400 360 170 255.0 5.1 29.5 4.8 0.22 0.11 0.40 0.12 213.7 7.1 1.11 0.17 - - 5.43 0.41 0.024 0.017 0.81 0.26 0.98 0.35Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G242Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: MP24D2 26.3, Upper Critical Zone, Bastard ReefSpot #12A 0.209 0.061 3.67 0.47 1.171 0.077 14.56 0.66 5.50 0.21 24.9 0.9 5.04 0.23 40.7 1.5 8.41 0.29 10200 110 0.383 0.058 121.0 3.3 72.1 4.3 13.4 1.72B 0.272 0.063 6.93 0.54 1.87 0.12 21.76 0.92 7.45 0.26 30.5 0.8 5.80 0.21 47.3 1.6 9.16 0.27 9565 87 0.482 0.055 1530 60 59.3 1.0 17.17 0.482C 1.22 0.14 23.2 1.0 5.83 0.19 59.5 1.4 18.46 0.32 71.3 1.5 12.70 0.29 95.4 1.8 17.77 0.35 9065 76 0.737 0.066 3240 130 149.6 1.5 29.29 0.416A 0.85 0.26 10.9 2.7 2.98 0.56 31.8 6.3 10.7 1.5 41.4 5.6 7.8 1.1 56.3 6.5 10.7 1.4 9700 210 0.52 0.13 96 10 77 10 23.8 2.36B 1.34 0.13 24.7 1.2 6.50 0.22 67.4 1.4 21.18 0.42 84.7 1.4 14.85 0.27 114.4 2.3 21.12 0.39 8907 77 0.864 0.067 433 18 155.8 1.5 40.57 0.439A 0.62 0.14 13.7 1.1 3.14 0.23 36.1 2.0 11.09 0.47 44.7 1.5 8.14 0.41 65.0 2.5 11.65 0.48 8950 80 0.885 0.099 165.9 3.7 140.1 1.7 47.65 0.779B 0.67 0.11 12.16 0.92 3.35 0.18 35.4 1.1 10.87 0.30 45.1 1.3 7.93 0.25 62.7 1.7 11.90 0.28 8790 110 0.902 0.079 419 22 142.0 1.7 47.25 0.529C 0.679 0.093 12.59 0.97 3.32 0.15 36.0 1.2 11.49 0.38 45.7 1.1 8.29 0.23 65.3 2.3 12.12 0.28 8910 100 0.889 0.085 2910 130 149.7 1.9 48.11 0.549D 0.59 0.10 12.66 0.87 3.13 0.16 35.9 1.2 11.21 0.26 44.7 1.3 8.05 0.28 63.8 1.6 12.05 0.31 8950 110 0.828 0.078 2490 130 147.2 2.0 46.68 0.7010 0.534 0.084 11.59 0.65 3.04 0.14 32.92 0.86 10.24 0.30 41.5 1.1 7.67 0.24 59.5 1.4 11.23 0.28 9312 70 0.860 0.074 5510 230 118.9 1.2 32.99 0.5514A 0.469 0.086 12.35 0.56 3.47 0.14 40.0 1.2 14.08 0.31 57.5 1.4 11.10 0.32 89.1 2.3 17.27 0.36 11420 100 0.923 0.078 9580 690 377.8 3.5 44.59 0.5814B 1.17 0.18 33.0 1.5 9.80 0.37 109.6 3.2 37.6 1.0 153.6 3.9 27.48 0.69 208.5 4.3 40.9 1.1 10839 97 1.033 0.078 7600 760 719 22 60.6 1.414C 1.06 0.13 31.7 1.8 9.09 0.47 102.4 4.9 33.3 1.6 137.5 6.2 24.1 1.2 184 10 34.9 1.7 10836 88 1.11 0.10 1483 69 600 37 52.7 2.616 0.65 0.11 15.0 1.1 4.35 0.28 48.8 2.5 15.85 0.71 65.3 2.7 11.84 0.48 93.2 3.4 17.66 0.73 9975 97 0.472 0.072 1062 46 153.6 4.3 13.71 0.3418 0.164 0.064 4.74 0.58 1.51 0.11 18.76 0.98 7.00 0.34 28.7 1.0 5.41 0.25 45.4 1.6 9.26 0.44 9620 160 0.392 0.059 281 22 91.5 9.1 51.8 5.4Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G243Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: B90-1, Main Zone, Tennis Ball MarkerSpot #11 2.5 1.7 201200 8100 - - 343.0 3.6 34.1 2.7 0.410 0.082 1.18 0.70 1799 38 2.83 0.17 0.30 0.15 23.6 1.2 0.729 0.086 9.45 0.75 12.74 0.683A 3.24 0.69 168500 5300 - - 354.3 6.1 36.2 5.1 0.290 0.075 0.62 0.17 1689 20 2.94 0.23 0.140 0.038 23.71 0.77 0.772 0.095 9.67 0.46 11.4 1.33B 2.89 0.45 181600 4400 210 210 365.0 3.9 36.4 3.9 0.423 0.066 0.476 0.094 1723 17 2.74 0.16 0.146 0.038 22.79 0.41 0.705 0.062 9.31 0.55 12.30 0.684A 36.5 6.3 184700 6900 1770 560 345.6 7.3 47.8 5.9 0.68 0.12 11.4 2.6 2710 250 5.35 0.73 2.49 0.46 41.4 3.3 1.51 0.20 12.8 1.3 12.6 1.34B 17.7 7.4 177200 5000 1170 930 339.8 8.8 37.9 4.3 0.56 0.11 15 11 3010 130 5.06 0.61 2.90 0.53 46.4 6.2 1.91 0.20 15.7 1.5 14.64 0.885 1.03 0.20 192100 6800 - - 363.7 3.2 33.6 3.2 0.297 0.063 0.423 0.060 1230 11 2.96 0.14 0.039 0.013 21.69 0.56 0.255 0.035 3.84 0.36 6.11 0.506 2.21 0.36 208900 6900 - - 368.9 4.2 33.6 3.1 0.319 0.060 0.527 0.082 1473 36 3.35 0.16 0.104 0.053 26.67 0.78 0.387 0.047 4.56 0.40 7.48 0.537 1.05 0.20 203900 6600 - - 365.1 4.1 28.9 2.8 0.197 0.050 0.351 0.062 985 19 3.27 0.17 0.0179 0.0086 16.60 0.32 0.180 0.031 2.99 0.31 5.37 0.388A 58 10 215100 6400 4130 830 327.9 3.7 24.5 2.4 0.227 0.061 28.3 5.4 959 97 4.73 0.43 3.54 0.47 38.9 2.7 1.37 0.15 9.22 0.75 5.30 0.698B 88.7 6.5 217900 7600 5020 640 321.0 4.0 23.6 3.1 0.363 0.079 31.8 2.3 1379 41 4.08 0.26 5.44 0.67 49.7 2.8 2.38 0.31 13.5 1.4 8.59 0.689 0.85 0.19 201100 5800 - - 349.3 3.6 26.3 2.6 0.241 0.054 0.401 0.073 984.3 5.2 2.96 0.16 0.03 0.01 20.09 0.37 0.205 0.030 3.29 0.25 6.01 0.4410 1.07 0.23 204400 7500 - - 346.1 3.6 39.0 3.9 0.198 0.051 0.374 0.064 934 15 2.79 0.15 0.0207 0.0093 18.28 0.46 0.215 0.033 3.34 0.31 5.53 0.5212 0.63 0.20 181800 5300 - - 341.4 6.2 24.7 3.0 0.380 0.082 0.477 0.088 1550 100 2.66 0.18 0.129 0.049 23.7 1.7 0.53 0.12 8.20 1.40 10.2 1.313 0.44 0.18 203600 6500 - - 335.3 4.2 26.4 3.2 0.336 0.062 0.442 0.063 1314 60 2.63 0.15 0.158 0.043 19.78 0.51 0.454 0.085 5.30 0.78 7.6 1.014 0.26 0.13 199500 5100 - - 321.3 3.1 30.8 3.1 0.196 0.049 0.368 0.054 972 38 2.52 0.15 0.256 0.080 14.84 0.65 0.287 0.053 3.48 0.54 5.98 0.4915 2.56 0.49 175200 4300 - - 346.3 3.5 27.3 3.7 0.393 0.058 0.51 0.10 1730 17 2.65 0.18 0.037 0.014 24.74 0.51 0.502 0.072 8.29 0.49 12.62 0.7316 30.6 3.2 196400 7700 1330 390 347.9 4.5 25.1 3.3 0.539 0.088 9.8 2.9 2540 160 4.85 0.36 1.35 0.17 37.6 1.2 1.42 0.12 13.55 0.95 13.79 0.7918 41.3 5.7 214000 10000 1780 220 347.6 3.2 24.3 3.6 0.321 0.063 10.7 1.0 1421 40 5.13 0.28 1.22 0.27 56.8 2.1 1.14 0.22 9.2 1.7 7.10 0.6119 30.1 5.2 214000 11000 880 250 301.7 3.4 13.7 3.0 0.163 0.056 5.4 1.6 636 57 4.57 0.36 1.69 0.36 34.7 4.0 0.81 0.17 5.4 1.1 2.73 0.5920 30.4 5.0 208500 7600 1730 350 314.5 3.9 190 43 0.148 0.048 11.9 1.9 650 44 3.19 0.18 6.02 0.95 49.1 4.9 5.93 0.89 39.9 6.0 11.3 1.8Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G244Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: B90-1, Main Zone, Tennis Ball MarkerSpot #11 0.11 49.4 1.6 14.24 0.34 169.8 3.4 58.5 1.4 253.5 6.0 44.87 0.98 356.7 8.9 67.0 1.7 9140 110 1.106 0.078 769 50 366 20 346 263A 1.08 0.10 46.0 2.0 13.27 0.40 159.6 3.2 54.9 1.0 247.0 3.8 45.9 1.1 376.3 8.6 71.0 1.9 9180 200 1.38 0.13 687 33 227.1 3.7 219.5 3.93B 0.93 0.12 48.8 1.1 13.50 0.29 163.8 2.7 56.14 0.69 246.6 3.3 46.78 0.81 383.3 6.7 72.6 1.0 9290 100 1.058 0.077 507 35 204.0 1.8 193.7 2.74A 1.88 0.28 70.8 8.0 20.7 2.0 251 24 83.7 6.7 359 27 65.6 5.2 515 38 90.8 5.8 8640 260 1.68 0.18 930 110 610 120 657 414B 1.89 0.23 75.8 3.1 23.1 1.1 285 13 96.0 5.2 409 21 73.3 3.3 574 25 101.7 5.2 8920 160 1.71 0.18 1940 290 1000 370 620 1105 0.581 0.063 28.5 1.0 9.73 0.27 115.2 2.1 40.39 0.46 177.8 2.1 35.52 0.56 303.8 5.1 59.15 0.85 9280 110 1.104 0.073 494 27 244.8 3.1 263.4 4.06 0.717 0.078 35.6 1.5 11.47 0.37 137.5 3.9 48.1 1.2 214.5 4.9 42.8 1.1 367.0 8.1 71.8 1.6 9200 100 1.287 0.088 673 83 373 20 340 127 0.497 0.063 25.19 0.98 8.02 0.25 94.6 1.8 32.25 0.65 141.0 2.3 28.10 0.53 239.7 3.9 47.20 0.81 9690 64 1.056 0.058 268 24 140.4 3.1 201.4 7.08A 1.00 0.10 22.2 2.4 7.19 0.79 84.8 9.3 30.3 3.2 134 13 27.4 2.7 231 22 41.6 3.5 11190 140 2.00 0.23 940 250 1010 170 1160 1608B 1.66 0.23 35.6 1.5 11.19 0.47 129.4 4.6 45.0 1.5 192.8 5.7 37.2 1.2 313.2 9.5 54.2 1.5 11270 150 1.60 0.11 1350 190 1092 55 1343 899 0.466 0.064 24.34 0.78 7.44 0.19 89.2 1.2 31.70 0.37 145.4 1.4 28.76 0.36 238.3 3.0 46.40 0.57 9542 67 0.625 0.050 310 24 168.2 1.2 172.1 1.510 0.507 0.066 24.1 1.2 7.24 0.26 86.0 1.5 30.48 0.73 138.3 2.5 26.59 0.64 224.5 4.8 43.95 0.83 8909 83 0.535 0.047 251 17 141.4 2.4 137.9 2.412 0.86 0.13 43.3 3.6 12.5 1.0 144 10 50.4 3.3 226 14 42.8 2.8 351 21 65.6 3.9 10020 150 0.678 0.068 500 70 209 18 187 1313 0.76 0.10 34.9 2.6 10.32 0.62 121.5 6.3 42.1 2.0 189.5 8.1 35.7 1.5 287 11 54.5 2.0 9900 150 0.579 0.051 374 34 171.7 9.9 167.0 8.014 0.690 0.084 27.6 1.9 7.87 0.43 91.1 4.0 31.4 1.4 142.6 5.3 27.4 1.1 224.6 7.7 43.0 1.4 9488 69 0.463 0.042 206 20 107.6 4.8 103.7 3.515 0.98 0.13 49.7 1.4 15.26 0.38 196.1 3.5 57.63 0.91 246.8 3.2 45.98 0.77 366.9 5.0 68.7 1.1 10320 130 0.729 0.071 622 27 248.5 5.6 212.0 6.816 2.31 0.21 72.5 3.7 21.6 1.3 276 15 81.8 5.0 334 21 60.2 3.9 463 28 85.0 4.8 9680 110 1.56 0.17 1220 150 806 58 645 4518 2.10 0.46 30.3 1.3 10.23 0.38 145.2 4.1 47.0 1.3 209.5 5.6 42.1 1.2 354.4 9.6 67.9 1.7 12860 170 2.16 0.15 946 73 576 26 833 2819 1.17 0.24 12.5 1.8 3.98 0.51 59.2 6.2 19.7 1.9 89.3 7.4 18.4 1.4 155 10 30.4 1.8 11530 300 2.64 0.22 363 34 222 19 640 4620 2.21 0.32 20.4 2.8 4.70 0.54 60.6 6.1 20.0 1.6 92.6 5.8 19.7 1.0 173.3 7.3 35.4 1.4 10710 260 0.987 0.092 268 75 97.7 4.3 621 52Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G245Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Li 2σ Si 2σ Ca 2σ Sc 2σ Ti 2σ Rb 2σ Sr 2σ Y 2σ Nb 2σ La 2σ Ce 2σ Pr 2σ Nd 2σ Sm 2σSample: B07-040, Upper ZoneSpot #11A 0.26 0.15 168800 7200 - - 240.3 5.2 8.2 2.2 0.154 0.060 0.206 0.061 373.9 5.0 0.513 0.091 - - 2.20 0.14 0.020 0.013 0.23 0.10 1.00 0.241B 0.20 0.12 168300 6200 239.4 6.4 5.3 1.8 0.034 0.029 0.135 0.039 341.8 9.9 0.520 0.084 - - 1.99 0.18 0.0096 0.0085 0.30 0.11 0.94 0.221C 0.22 0.14 164100 5500 60 59 238.6 4.3 5.7 1.9 0.139 0.064 0.245 0.070 376.8 6.1 0.434 0.087 - - 2.37 0.16 0.0135 0.0096 0.243 0.097 0.84 0.182A 0.42 0.16 165800 5500 - - 238.8 3.8 7.5 2.1 0.041 0.032 0.249 0.063 407 14 0.426 0.080 - - 2.42 0.17 0.0032 0.0042 0.28 0.10 0.77 0.202 0.61 0.24 165700 4800 - - 242.1 3.3 7.4 2.6 0.107 0.051 0.188 0.060 477.3 4.9 0.532 0.065 - - 2.75 0.18 0.0077 0.0064 0.37 0.16 0.92 0.224A 2.13 0.39 165900 5400 105 76 228.7 3.6 6.8 1.9 0.109 0.052 0.302 0.081 713 74 0.431 0.080 - - 2.58 0.22 0.018 0.011 0.45 0.17 1.60 0.354B 4.23 0.56 168300 5600 - - 248.8 4.7 4.4 1.8 0.210 0.056 0.375 0.078 1220 54 0.418 0.077 0.090 0.038 4.44 0.28 0.186 0.049 3.43 0.39 4.89 0.595A 1.33 0.29 162700 5200 - - 241.9 4.0 9.8 2.4 0.048 0.034 0.210 0.067 520.4 5.8 0.504 0.081 - - 2.24 0.17 0.031 0.016 0.48 0.17 1.36 0.235B 0.58 0.19 166200 5000 - - 237.6 5.6 9.3 1.9 0.164 0.066 0.271 0.067 780 130 0.509 0.076 - - 2.84 0.22 0.124 0.041 1.91 0.56 2.97 0.766A 0.47 0.17 165800 6300 - - 241.3 4.5 6.1 1.8 0.218 0.073 0.275 0.069 1143.1 7.4 0.360 0.087 - - 3.44 0.18 0.087 0.028 1.67 0.34 4.48 0.446B 0.57 0.17 166300 5700 - - 236.5 3.8 8.4 2.5 0.136 0.057 0.278 0.056 1088.9 9.4 0.46 0.10 - - 3.07 0.18 0.051 0.023 1.20 0.25 3.52 0.417A 0.83 0.20 164800 5900 - - 242.0 4.3 9.4 2.6 0.144 0.058 0.217 0.061 1077 12 0.355 0.070 - - 2.76 0.14 0.073 0.026 2.48 0.42 5.20 0.657B 1.38 0.26 165800 5100 - - 246.3 4.4 9.0 2.4 0.221 0.072 0.272 0.079 928 12 0.473 0.072 - - 2.84 0.17 0.171 0.039 2.26 0.37 3.72 0.557A 2.12 0.33 166100 5500 - - 233.0 5.1 7.8 1.8 0.056 0.030 0.169 0.049 305.7 8.4 0.405 0.062 - - 1.92 0.16 0.0011 0.0019 0.209 0.095 0.56 0.158B 2.94 0.38 166500 5800 57 52 237.9 4.8 5.1 1.7 0.190 0.066 0.297 0.067 1098 24 0.398 0.069 - - 3.30 0.19 0.051 0.019 1.57 0.26 3.98 0.508C 2.79 0.38 164700 4800 - - 239.7 5.4 7.0 1.8 0.188 0.071 0.284 0.072 1085.0 9.9 0.349 0.071 - - 3.07 0.19 0.074 0.027 1.41 0.29 3.77 0.478D 2.66 0.38 169300 5500 - - 238.2 5.6 5.9 1.4 0.163 0.065 0.281 0.073 1125 12 0.377 0.078 - - 3.74 0.21 0.057 0.021 1.27 0.28 3.41 0.399 1.35 0.32 167600 6000 - - 231.6 5.6 4.0 1.7 0.119 0.057 0.153 0.052 431 30 0.460 0.092 - - 2.52 0.22 0.0070 0.0057 0.23 0.12 0.73 0.2111A 3.40 0.52 163500 6200 133 79 228.3 4.5 9.3 2.2 0.060 0.039 0.200 0.053 418.9 5.8 0.57 0.10 - - 2.48 0.18 0.025 0.013 0.38 0.13 1.15 0.2711B 2.95 0.42 165700 6200 103 86 233.0 4.8 8.6 2.4 0.105 0.049 0.252 0.062 475.5 5.4 0.419 0.079 - - 3.32 0.20 0.026 0.015 0.28 0.11 1.09 0.2812A 2.67 0.36 167500 6000 108 84 233.2 4.9 5.5 1.9 0.114 0.058 0.257 0.072 470.2 4.4 0.511 0.091 - - 3.10 0.21 0.0060 0.0062 0.35 0.13 1.40 0.2812B 3.66 0.41 166000 5100 - - 239.2 4.4 4.5 1.7 0.175 0.070 0.200 0.066 753 59 0.469 0.080 0.068 0.028 3.04 0.19 0.053 0.023 1.14 0.34 2.67 0.6413A 1.78 0.31 167900 6000 121 80 235.9 4.8 6.3 2.3 0.750 0.190 0.321 0.058 813 52 0.445 0.070 0.037 0.021 2.96 0.19 0.035 0.018 0.71 0.25 2.20 0.4413B 2.48 0.39 166200 5300 124 77 231.9 4.4 6.2 2.1 0.192 0.069 0.293 0.075 984 29 0.416 0.081 0.037 0.020 3.44 0.21 0.084 0.033 1.74 0.49 3.24 0.6114 1.16 0.31 162900 5500 - - 233.8 3.9 6.9 2.0 0.068 0.035 0.232 0.061 470 15 0.531 0.078 - - 3.14 0.21 0.0159 0.0094 0.51 0.20 1.18 0.2515A 0.89 0.17 162900 6100 - - 245.3 5.7 6.2 1.7 0.197 0.063 0.359 0.078 1172 15 0.315 0.057 - - 3.63 0.18 0.120 0.026 2.55 0.34 5.66 0.5915B 0.51 0.21 163600 5600 - - 243.4 4.2 8.1 2.4 0.215 0.065 0.241 0.064 1117.6 9.7 0.420 0.084 - - 3.20 0.19 0.155 0.039 2.78 0.38 5.26 0.5916A 1.38 0.27 162500 6100 - - 239.9 3.9 5.9 1.8 0.094 0.043 0.242 0.074 553.5 5.0 0.479 0.078 - - 3.01 0.17 0.0159 0.0098 0.39 0.17 1.21 0.2316B 2.75 0.38 162900 5200 - - 246.1 5.0 6.4 2.1 0.163 0.062 0.222 0.066 974 41 0.362 0.065 - - 3.29 0.16 0.126 0.030 2.40 0.34 4.57 0.5918A 2.41 0.39 163300 5600 5400 3400 246.6 5.4 8.2 2.0 0.241 0.086 2.8 1.7 1089 45 0.380 0.078 19 12 38 23 5.2 3.3 24 14 8.2 2.518B 3.36 0.83 143100 8300 35000 28000 240.0 18.0 24 25 0.166 0.084 34 27 651 80 0.53 0.17 100 82 210 160 26 21 130 100 24 1719 2.45 0.34 165300 6700 177 85 239.5 4.4 8.4 2.4 0.170 0.054 0.279 0.065 1114 12 0.347 0.089 0.058 0.024 3.31 0.23 0.097 0.025 2.09 0.31 4.87 0.48Raw data were reduced using Iolite 2.5 using Zr = 48.6 wt. % as an internal standard as measured by EPMA.Dashed values indicate values below detection limit.1. Spot numbers correspond to CL images of zircon grains shown in Appendix G246Appendix ITable I.1. (continued) Trace element concentrations of zircon from the Bushveld Complex measured by laser ablation ICP-MSElement Eu 2σ Gd 2σ Tb 2σ Dy 2σ Ho 2σ Er 2σ Tm 2σ Yb 2σ Lu 2σ Hf 2σ Ta 2σ Pb 2σ Th 2σ U 2σSample: B07-040, Upper ZoneSpot #1A 0.219 0.060 5.71 0.52 2.17 0.13 30.89 0.94 11.96 0.35 59.3 1.3 12.42 0.37 110.7 2.3 21.43 0.46 8660 130 0.197 0.033 146.8 6.5 42.05 0.75 107.5 1.31B 0.161 0.047 5.17 0.63 2.01 0.14 28.1 1.3 10.86 0.39 54.4 1.7 11.85 0.41 102.4 3.0 20.39 0.68 8940 150 0.202 0.046 110.7 9.1 32.2 1.8 88.0 3.01C 0.127 0.044 5.45 0.60 1.99 0.13 29.4 1.1 12.13 0.33 60.5 1.5 13.76 0.45 120.5 2.7 23.89 0.57 9700 110 0.239 0.039 127.3 4.0 42.30 0.96 117.8 2.92A 0.145 0.049 5.64 0.50 2.10 0.15 30.6 1.5 12.96 0.58 65.4 2.5 14.17 0.63 128.9 4.5 26.0 1.0 9522 93 0.208 0.034 125 10 44.4 2.3 118.6 3.52 0.201 0.049 6.78 0.71 2.60 0.12 36.4 1.2 15.10 0.41 76.2 1.3 16.75 0.29 149.4 2.7 29.42 0.50 9642 93 0.249 0.036 117.2 4.9 57.11 0.63 141.8 1.84A 0.296 0.071 12.1 1.5 4.31 0.55 57.9 6.2 23.3 2.5 113 11 23.3 2.2 197 18 38.8 3.4 10040 110 0.198 0.033 148 12 78.6 7.7 180 114B 1.48 0.23 27.1 1.5 8.30 0.50 103.5 4.7 39.4 1.8 188.2 8.4 38.8 1.5 325 13 62.5 2.4 10000 120 0.229 0.033 321.7 9.4 168.0 6.7 329.1 9.65A 0.234 0.049 9.51 0.78 3.53 0.18 45.0 1.5 17.29 0.41 80.4 1.3 16.33 0.35 141.4 3.0 26.96 0.52 8180 65 0.216 0.035 94.9 4.6 47.86 0.88 95.9 1.05B 0.53 0.15 16.1 3.3 5.23 0.96 66 12 25.2 4.3 118 19 23.1 3.5 193 28 37.1 5.1 8577 93 0.196 0.034 160 24 74.1 9.1 147 116A 0.85 0.12 25.1 1.2 8.01 0.26 103.3 1.9 38.29 0.69 177.5 2.9 35.47 0.70 288.5 4.5 55.20 0.92 9460 110 0.200 0.030 237 11 121.2 2.2 211.8 4.16B 0.76 0.11 23.0 1.5 7.48 0.29 96.9 2.4 36.15 0.63 167.9 2.2 33.57 0.55 274.6 3.8 52.29 0.73 9510 130 0.166 0.030 216 10 109.3 1.7 194.3 2.37A 0.84 0.11 26.4 1.3 8.09 0.28 97.8 2.3 36.13 0.70 165.0 2.3 31.92 0.57 261.4 4.2 48.63 0.80 8594 68 0.172 0.033 163.8 5.4 84.9 1.5 146.2 2.37B 0.67 0.12 20.91 0.97 6.67 0.26 83.7 2.3 31.10 0.66 141.4 2.9 27.72 0.61 229.5 4.8 43.35 0.74 8253 84 0.216 0.039 149.0 7.5 76.3 1.1 135.9 1.57A 0.091 0.031 4.21 0.44 1.73 0.13 23.7 1.1 10.05 0.42 49.9 1.2 10.87 0.48 94.8 3.1 19.43 0.66 9200 130 0.171 0.030 57.8 2.0 28.06 0.78 80.2 1.98B 0.96 0.11 25.1 1.3 7.73 0.31 96.5 2.7 36.16 0.97 167.4 4.1 33.80 0.93 277.2 6.6 52.3 1.3 9650 150 0.178 0.031 260.2 6.2 121.3 2.7 215.0 4.38C 0.76 0.12 23.74 0.99 7.66 0.27 97.0 2.6 35.79 0.64 167.9 2.0 32.86 0.59 274.5 4.6 51.22 0.85 9400 140 0.153 0.028 237 12 103.6 1.7 181.7 2.08D 0.669 0.096 22.4 1.1 7.41 0.19 97.0 2.3 36.19 0.57 173.4 2.5 35.59 0.62 296.8 4.2 56.6 1.0 10160 160 0.191 0.034 312 12 139.5 2.3 266.2 3.19 0.171 0.065 6.76 0.76 2.46 0.24 34.8 3.0 13.8 1.1 69.7 4.9 14.80 0.88 132.2 7.4 25.5 1.3 9940 240 0.240 0.042 118.6 5.3 54.9 4.2 143.5 4.611A 0.198 0.058 7.17 0.71 2.52 0.11 34.06 0.95 13.64 0.40 65.0 1.2 14.09 0.40 120.7 2.7 24.05 0.54 8780 130 0.180 0.034 106.8 4.4 48.2 1.1 115.9 2.111B 0.223 0.058 7.48 0.56 2.80 0.13 37.8 1.2 15.03 0.37 75.7 1.5 16.34 0.46 142.6 3.0 28.20 0.74 9630 130 0.176 0.034 179.1 6.8 78.9 1.4 187.7 3.012A 0.228 0.060 8.17 0.62 2.83 0.15 38.4 1.1 15.44 0.36 74.0 1.3 15.72 0.37 138.8 2.7 27.03 0.54 9350 100 0.204 0.043 163.7 7.1 70.62 0.97 167.5 1.912B 0.55 0.12 16.3 2.1 5.10 0.55 66.1 6.4 24.4 2.0 117.4 8.6 23.8 1.6 202 13 39.0 2.4 9310 130 0.235 0.033 185.7 6.1 83.1 4.4 161.2 5.213A 0.46 0.10 13.7 1.4 4.90 0.41 67.0 4.3 26.3 1.7 128.3 8.2 25.8 1.7 222 13 41.9 2.6 9700 230 0.191 0.035 220 21 89.4 7.0 187 1613B 0.96 0.22 20.0 2.1 6.45 0.51 83.1 4.2 32.1 1.2 151.2 4.4 30.38 0.88 256.1 5.2 48.6 1.1 9790 220 0.167 0.029 253 15 103.4 3.6 209 1214 0.281 0.063 7.68 0.74 2.78 0.20 38.0 1.6 15.31 0.55 75.2 2.9 16.03 0.70 140.0 5.5 27.3 1.0 9490 120 0.164 0.031 181 17 75.5 4.9 176.1 8.215A 0.87 0.13 27.1 1.2 8.51 0.22 104.7 2.1 38.43 0.78 175.0 2.4 35.84 0.81 299.7 4.7 56.1 1.2 9520 170 0.167 0.028 296 19 127.1 3.9 221.5 6.915B 0.93 0.14 28.0 1.2 8.41 0.26 104.6 2.2 37.34 0.65 163.9 2.2 32.65 0.61 2