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Radiogenic isotopic systematics of layered intrusions : application to the Mesoproterozoic Kiglapait… Fourny, Anaïs 2018

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RADIOGENIC ISOTOPIC SYSTEMATICS OF LAYERED INTRUSIONS: APPLICATION TO THE MESOPROTEROZOIC KIGLAPAIT INTRUSION OF COASTAL LABRADOR, CANADA, AND TO MAFIC-ULTRAMAFIC ROCK REFERENCE MATERIALSbyAnaïs FournyM.Sc., Université Joseph Fourier, 2011A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES(Geological Sciences)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)July 2018© Anaïs Fourny, 2018iiThe following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled:Radiogenic isotopic systematics of layered intrusions: application to the Mesoproterozoic Kiglapait intrusion of coastal Labrador, Canada, and to mafic-ultramafic rock reference materialssubmitted by Anaïs Fourny in partial fulfilment of the requirements forthe degree of Doctor of Philosophyin Geological SciencesExamining Committee:James S. Scoates, Geological SciencesCo-supervisorDominique Weis, Geological SciencesCo-supervisor Marghaleray Amini, Geological SciencesSupervisory Committee MemberLeslie Lavkulich, Soil ScienceUniversity ExaminerGregory Dipple, Geological SciencesUniversity ExaminerAdditional Supervisory Committee Members:Supervisory Committee MemberSupervisory Committee MemberiiiABSTRACTMafic layered intrusions in the Earth’s crust are natural laboratories for evaluating differentiation processes of mantle-derived magma. The Mesoproterozoic Kiglapait intrusion (Labrador, Canada) represents a remarkable case study of how these intrusions form under closed-system crystallization of basaltic magma. The Kiglapait intrusion is the largest and youngest troctolitic intrusion contained within the vast Nain Plutonic Suite, one of the best-preserved examples of Proterozoic anorthosite massifs that distinguish magmatic activity in the Earth’s crust from ~1.8 to 0.9 billion years ago. The radiogenic isotope ratios of Pb-Sr-Nd-Hf are powerful geochemical tools for identifying magma sources, detecting contamination, and tracing mixing processes in igneous rocks. To measure accurate and precise isotopic ratios by MC-ICP-MS, the analysis of sample–matrix-matched reference materials is required. A new comprehensive isotope database of mafic to ultramafic reference materials is provided to assess the accuracy of Pb-Sr-Nd-Hf isotopes in Kiglapait samples and to be used as a reference dataset for the isotopic study of other terrestrial, and extraterrestrial, mafic-ultramafic rocks. Integration of Pb-Sr-Nd-Hf isotope and trace element geochemistry of whole rocks and mineral separates allows for definition of the Kiglapait source and parent magma composition. An event of post-crystallization addition of radiogenic Pb is distinguished, the effects of which are effectively leached from plagioclase during sample pre-treatment. An in situ LA-ICP-MS technique is also developed for measuring Pb isotope ratios at high spatial resolution in minerals with very low Pb concentrations, such as plagioclase and clinopyroxene. Combined, the solution-based Pb-Sr-Nd-Hf and in situ Pb isotopic results demonstrate that the primary Kiglapait magma was mantle-derived, with minor assimilation of lower crust during ponding and ascent, and that assimilation of local country rocks, as recorded primarily in Sr isotopic variations, was limited to the uppermost gabbros and ferrosyenites during the final stages of crystallization. This multi-isotopic and trace element geochemical framework developed for the Kiglapait intrusion, and at a larger ivABSTRACTscale for the entire Nain Plutonic Suite, can be adapted to layered intrusions and Proterozoic anorthosite plutonic suites worldwide to better constrain a wide range of geological issues from mantle heterogeneity to crustal differentiation to Proterozoic geodynamics.vLAY SUMMARYThe Earth’s crust is dominated by rocks that crystallized from basaltic magma (molten rock). Most magma does not erupt at the surface to form volcanoes, but instead stalls and crystallizes in the crust. Layered intrusions are fossil magma chambers that represent natural laboratories where we can study how magma solidifies. Most layered intrusions form as open systems by repeated injections of magma over time and only a few intrusions in the geological rock record appear to have crystallized as closed systems from single batches of magma. Analyzing the chemistry of samples from closed-system intrusions, like the remote and remarkably well-exposed Kiglapait layered intrusion of coastal Labrador in northern Canada, allows scientists the opportunity to reconstruct their entire crystallization history. These results can then be used as a template for examining other geologically more complex intrusions worldwide.viPREFACEThis dissertation encompasses three chapters (Chapters 2 to 4) that were prepared in manuscript format appropriate for submission to international scientific journals. I am the lead author of the three chapters and all are co-authored with my supervisors Drs. Dominique Weis and James Scoates, who provided substantial advice and edits on the entire dissertation. Dr. Marghaleray Amini, a member of my supervisory committee, is a coauthor of Chapter 4 as she provided essential expertise and training on the laser ablation technique as well as advice and edits on the chapters.All research, analytical work, including sample digestion, chemical analyses, and data reduction, and interpretation were carried out by me at UBC in the PCIGR facilities. I prepared all figures, data tables and drafts of each manuscript submitted for publication and for the chapters of this dissertation. For each chapter, the contributions of my supervisors and co-authors included the exchange of ideas, advice, insightful comments, careful reviewing and editing, as well as financial support. Specific contributions to each manuscript are described below. Chapter 2 Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials – a version of this chapter has been published in the journal Geochemistry, Geophysics, Geosystems Authors: Anaïs Fourny, Dominique Weis, James S. Scoates Fourny, A., D. Weis, and J. S. Scoates (2016), Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials, Geochemistry, Geophysics, Geosystems 17, 739–773, doi: 10.1002/2015GC006181.Drs. Andreas Stracke (Institut für Mineralogie, Universität Münster), Jasper Konter viiPREFACE(University of Hawaii Manoa) and an anonymous reviewer provided constructive reviews of the submitted manuscript for Geochemistry, Geophysics, Geosystems. Chapter 3 Isotopic and trace element constraints on magmatic processes and source of the Kiglapait layered intrusion – is intended for publicationAuthors: Anaïs Fourny, Dominique Weis, James S. Scoates  Dr. Stearns A. Morse provided samples from the Kiglapait intrusion accessed from the Kiglapait Collection of the University of Massachusetts Amherst.Chapter 4LA-ICP-MS Pb isotope geochemistry of plagioclase, clinopyroxene, and sulfide from the Kiglapait intrusion: in situ testing for isotopic differences between minerals in cumulates of layered intrusions – is intended for publication. Authors: Anaïs Fourny, Dominique Weis, James S. Scoates, Marghaleray AminiDr. Stearns A. Morse provided samples from the Kiglapait intrusion accessed from the Kiglapait Collection of the University of Massachusetts Amherst. Dr. Marghaleray Amini played a critical role in setting up the RESOlution laser ablation analytical capabilities at PCIGR. viiiTABLE OF CONTENTSABSTRACT  iiiLAY SUMMARY  vPREFACE  viTABLE OF CONTENTS  viiiLIST OF TABLES  xiiiLIST OF FIGURES  xviiLIST OF ABBREVIATIONS  xxiiiACKNOWLEDGEMENTS  xxviiDEDICATION  xxixCHAPTER 1. Introduction  11.1 Introduction and Scope of the Project  11.2 Mafic layered intrusions  41.2.1 Layered intrusions and their significance in the geological record  41.2.2 Isotopic studies of layered intrusions  61.2.3 Isotopic differences between minerals in layered intrusions  71.3 Isotope Geochemistry: Reference Materials and Mass Spectrometry  111.3.1 Isotopic analyses by MC-ICP-MS and TIMS  111.1.1.1 Overview of the techniques  111.1.1.2 The need for reference materials  131.3.2 In situ isotopic analyses by laser ablation-ICP-MS  161.4 The Kiglapait intrusion  181.4.1 Proterozoic anorthosite plutonic suites  181.4.2 The Nain Plutonic Suite  211.4.3 The Kiglapait intrusion  231.5 Overview of the Dissertation  26ixTABLE OF CONTENTS1.6 Research and training opportunities related to this project  301.6.1  Meetings/Conferences  301.6.2  MAGNET  321.6.3  Field Experiences   34CHAPTER 2. Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials  402.1 Introduction  402.2 Reference materials  432.2.1 Pyroxene-rich ultramafic reference material  432.2.2 Basaltic reference materials  452.2.3 Gabbroic reference materials  452.2.4 Plagioclase-rich reference materials  462.3 Analytical techniques  462.3.1 Laboratory environment and reagents  462.3.2 Sample preparation  472.3.3 Mass spectrometry  482.4 Results  532.4.1 Pyroxene-rich ultramafic reference material  572.4.2 Basaltic reference materials  572.4.3 Gabbroic reference materials  672.4.4 Plagioclase-rich reference materials  762.5 Discussion  792.5.1 Trace element concentrations and the effect of sample matrix  792.5.2 Variable effects of acid leaching of basaltic rocks  822.5.3 Reproducible Pb and Hf isotopic ratios: a challenge for plutonic rocks  852.5.4 Recommended reference materials for mafic-ultramafic rocks   872.6 Conclusions  87CHAPTER 3. Isotopic and trace element constraints on magmatic processes and source of xTABLE OF CONTENTSthe Kiglapait layered intrusion, Labrador  903.1 Introduction  903.2 Geologic setting  913.2.1 Nain Plutonic Suite and troctolitic intrusions  913.2.2 Kiglapait intrusion  933.3 Samples and mineralogy  973.4 Analytical techniques  993.4.1 Sample preparation  1013.4.2 Mass spectrometry  1023.4.3 Supplementary TIMS (ULB) analyses   1073.5 Results  1083.5.1 Trace elements  1143.5.1.1 Whole rocks  1143.5.1.2 Plagioclase  1143.5.1.3 Mafics and clinopyroxene  1173.5.2 Radiogenic isotopic compositions   1173.5.2.1 Nd and Hf isotopes  1173.5.2.2 Sr isotopes  1193.5.2.3 Pb isotopes  1213.6 Discussion  1273.6.1 Initial Pb isotopic differences between coexisting minerals in the Kiglapait intrusion  1303.6.2 Isotopic constraints on the composition of the Kiglapait parent magma  1343.6.2.1 Isotope constraints on assimilation of country rock during crystallization  1363.6.2.2 Comparison with other troctolitic intrusions in the Nain Plutonic Suite  1373.6.3 Trace element constraints on the Kiglapait parent magma  139xiTABLE OF CONTENTS3.6.4 Mantle and lower crustal components in the source of the Kiglapait parent magma  1463.7 Conclusion  150CHAPTER 4. LA-ICP-MS Pb isotope geochemistry of plagioclase, clinopyroxene, and sulfide from the Kiglapait intrusion: in situ testing for isotopic differences between minerals in cumulates of layered intrusions  1524.1 Introduction  1524.2 Kiglapait intrusion  1544.3 Kiglapait mineralogy  1564.4 Sample and analytical strategy  1604.5 Analytical techniques  1604.5.1 Analysis  1604.5.2 Data reduction  1634.5.3 Reference results  1674.5.4 Age correction  1694.6 Results  1694.6.1 Plagioclase  1754.6.2 Clinopyroxene  1754.6.3 Sulfides  1804.6.4 Other minerals  1804.6.5 Plagioclase from granitic dikes  1834.7 Discussion  1834.7.1 In situ Pb isotope variations in the Kiglapait intrusion  1834.7.2 Significance of in situ Pb isotope measurements by LA-ICP-MS in plutonic rocks  1854.8 Conclusion  187CHAPTER 5. Conclusions  1895.1 Summary and conclusions  189xiiTABLE OF CONTENTS5.2 Summary of the dissertation and key findings  1905.2.1 Trace element and isotope geochemistry of the Kiglapait intrusion and implications for origin of the Nain Plutonic Suite  1905.2.2 The global isotopic signature of mafic layered intrusions  1955.2.3 In situ Pb isotope measurements by LA-ICP-MS  2025.2.4 Characterization of mafic to ultramafic geological reference materials  2055.3 Suggestions for future research  2065.3.1 Effect of acid leaching on plagioclase and implications for isotopic analyses  2065.3.2 Significance of troctolitic magmatism in Proterozoic anorthosite plutonic suites  209BIBLIOGRAPHY  213APPENDIX A. Description, location, and photomicrographs of the Kiglapait samples investigated during this study    261            Supplementary Material A: Petrographic Descriptions of Analyzed Kiglapait Samples  262APPENDIX B. Supporting Information for Chapter 2: Comprehensive Pb-Sr-Nd-Hf isotopic, trace element, and mineralogical characterization of mafic to ultramafic rock reference materials    280APPENDIX C. Supporting Information for Chapter 3: Isotopic and trace element constraints on magmatic processes and source of the Kiglapait layered intrusion, Labrador  305            Supplementary Material C.1: Kiglapait Sampling Protocols   306            Supplementary Material C.2: Trace Elements and Isotope Measurements in Duplicates and Reference Materials  308APPENDIX D. Supporting Information for Chapter 4: LA-ICP-MS Pb isotope geochemistry of plagioclase, clinopyroxene, and sulfide from the Kiglapait intrusion: in situ testing for isotopic differences between minerals in cumulates of layered intrusions  347xiiiLIST OF TABLESTable 1.1. Summary of hypotheses for the origin of isotopic differences between minerals in layered intrusions  8Table 1.2. Compilation of in situ Pb isotopic measurement techniques  17Table 1.3. List of appendices in this dissertation  31Table 1.4. Description of MAGNET workshops (2013-2018)  35Table 2.1. Summary of major compositional characteristics and Pb, Sr, Nd and Hf elemental concentrations of mafic and ultramafic rock reference materials analyzed in this study  42Table 2.2. Mineralogical composition of mafic-ultramafic rock reference materials determined by Rietveld refinement of XRD results  44Table 2.3. Typical instrument settings for trace element and isotopic analyses of mafic-ultramafic rock reference materials at PCIGR  50Table 2.4. Trace element concentrations of the pyroxene-rich and plagioclase-rich rock reference materials measured by HR-ICP-MS  54Table 2.5. Trace element concentrations of the basaltic rock reference materials measured by HR-ICP-MS  55Table 2.6. Trace element concentrations of the gabbroic rock reference materials measured by HR-ICP-MS  56Table 2.7. Pb isotopic analyses of the mafic-ultramafic rock reference materials  61Table 2.8. Hf-Nd-Sr isotopic analyses of mafic-ultramafic rock reference materials.  64Table 2.9. Compilation of Pb isotopic compositions of mafic-ultramafic reference materials  77Table 2.10.  Compilation of Hf-Nd-Sr isotopic compositions of mafic-ultramafic rock reference materials  78Table 2.11. Recommended reference materials for mafic-ultramafic rocks  88Table 3.1. Description of the Kiglapait samples  98Table 3.2. Trace element concentrations in Kiglapait whole rocks by HR-ICP-MS  103Table 3.3. Trace element concentrations in Kiglapait plagioclase by HR-ICP-MS  104Table 3.4. Trace element concentrations in Kiglapait mafic separates by HR-ICP-MS  105xivLIST OF TABLESTable 3.5. Trace element concentrations in Kiglapait clinopyroxene separates by HR-ICP-MS  106Table 3.6. Measured and initial Nd isotopic compositions of the Kiglapait samples by MC-ICP-MS  109Table 3.7. Measured and initial Hf isotopic compositions of the Kiglapait samples by MC-ICP-MS  110Table 3.8. Measured and initial Sr isotopic compositions of the Kiglapait samples by TIMS  111Table 3.9. Measured and initial Pb isotopic compositions of the Kiglapait samples by MC-ICP-MS  112Table 3.10.  Summary of potential sources for the isotopic composition of the Kiglapait parent magma  149Table 4.1. Typical instrument settings for in situ Pb isotopic analyses at PCIGR  162Table 4.2. Summary of measured in situ Pb isotopic compositions of Kiglapait plagioclase  170Table 4.3. Summary of measured and initial in situ Pb isotopic compositions of Kiglapait pyroxene  171Table 4.4. Measured and initial in situ Pb isotopic compositions of Kiglapait sulfides  172Table 4.5. Measured and initial in situ Pb isotopic compositions of miscellaneous Kiglapait minerals  173Table 4.6. Measured and initial in situ Pb isotopic compositions of plagioclase from granitic dikes  174Table 5.1. References for the ages and Nd isotopic compositions of the NPS plutons used in Figure 5.1  192Table 5.2. References for ages and Pb-Sr-Nd isotopic compositions of layered intrusions in Figures 5.4-5.5 and 5.7  200Table B.1. Individual trace element analyses: NIM-P   292Table B.2. Individual trace element analyses: unleached BE-N and leached BE-N L  293Table B.3. Individual trace element analyses: DNC-1  294Table B.4. Individual trace element analyses: BIR-1a  295Table B.5. Individual trace element analyses: unleached GSR-3 and leached GSR-3 L  296Table B.6. Individual trace element analyses: NIM-N  297Table B.7. Individual trace element analyses: BHVO-2  298xvLIST OF TABLESTable B.8. Individual trace element analyses: W-2  299Table B.9. Individual trace element analyses: unleached JB-3 and leached JB-3 L  300Table B.10. Individual trace element analyses: ST05-03  301Table B.11. Individual trace element analyses: AN-G  302Table B.12. Pb isotopic analyses of reference material BCR-2  303Table B.13. Hf-Nd-Sr isotopic analyses of reference material BCR-2  304Table C.1. RSD and blank concentrations for the trace elements analyzed during this study  321Table C.2. Trace element concentrations of reference materials DNC-1 and BE-N duplicates  322Table C.3. Pb isotopic analyses of reference materials analyzed during this study  323Table C.4. Hf-Nd-Sr isotopic analyses of the reference materials analyzed during this study  324Table C.5. Description of TIMS (ULB) regional samples  325Table C.6. Measured and initial Pb isotopic compositions of Kiglapait samples by TIMS (ULB)  326Table C.7. Measured and initial Nd and Sr isotopic composition of KI samples by TIMS (ULB)  327Table C.8. Measured and initial Pb isotopic composition of NPS samples by TIMS (ULB)   328Table C.9. Measured and initial Nd and Sr isotopic compositions of Kiglapait samples from the literature  329Table C.10. References and descriptions of samples from the Nain Province  330Table C.11. Compilation of Sr-Nd-Pb isotopic compositions of samples from the Nain Province  332Table C.12. References and descriptions of samples of samples from the Churchill Province and other Proterozoic country rocks  335Table C.13. Compilation of Sr-Nd-Pb isotopic compositions of samples from the Churchill Province and other Proterozoic country rocks  337Table C.14. References and descriptions of samples from the Nain Plutonic Suite  339Table C.15. Compilation of Sr-Nd isotopic compositions of samples from the Nain Plutonic Suite  342Table C.16. Compilation of Pb isotopic compositions of samples from the Nain Plutonic Suite  345Table D.1. Measured in situ Pb isotopic compositions of USGS reference glass BCR-2G (89 μm) xviLIST OF TABLES 360Table D.2. Measured in situ Pb isotopic compositions of reference glass NIST SRM 612 (89 μm)  365Table D.3. Measured in situ Pb isotopic compositions of reference glass NIST SRM 612 after normalization to BCR-2G (89 μm)  369Table D.4. Measured in situ Pb isotopic compositions of MPI-DING reference glass KL2-G after normalization to BCR-2G (89 μm)  373Table D.5. Measured in situ Pb isotopic compositions of USGS reference glass BCR-2G (47 μm)  375Table D.6. Measured in situ Pb isotopic compositions of reference glass NIST SRM 612 (47 μm)  376Table D.7. Measured in situ Pb isotopic compositions of reference glass NIST SRM 612 after normalization to BCR-2G (47 μm)  377Table D.8. Measured in situ Pb isotopic compositions of USGS reference polymetal sulfide pellet MASS-1 after normalization to BCR-2G (47 μm)  378Table D.9. Measured and initial in situ Pb isotopic compositions of Kiglapait plagioclase cores  379Table D.10. Measured and initial in situ Pb isotopic compositions of Kiglapait plagioclase rims  383Table D.11. Measured and initial in situ Pb isotopic compositions of Kiglapait plagioclase boundaries  387Table D.12. Measured and initial in situ Pb isotopic compositions of Kiglapait pyroxene  388xviiLIST OF FIGURESFigure 1.1. Photographs and photomicrographs of igneous layering and textures in the Kiglapait intrusion, Labrador, Canada.   5Figure 1.2. Schematic diagrams showing processes by which isotopic differences between minerals may be generated in cumulates of layered intrusions.   10Figure 1.3. Photographs showing the clean room and instrumentation used during the course of this study at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia.   12Figure 1.4. Map showing the global distribution of Proterozoic massif-type anorthosite plutonic suites after the compilation of Ashwal (1993)  19Figure 1.5. Geological setting of the Kiglapait intrusion in the Nain Plutonic Suite of coastal Labrador, Canada.   22Figure 1.6. Isotopic ratios versus percent solidified (PCS) in the Kiglapait intrusion from existing studies.   25Figure 1.7. Age-corrected lead isotopic ratios versus percent solidified (PCS) in the Kiglapait intrusion measured by TIMS at ULB in the 1990s 27Figure 1.8. Photographs of the NSERC CREATE Multidisciplinary Applied Geochemistry Network (MAGNET) workshops between 2013 and 2016 33Figure 1.9. Photographs of layered intrusions visited during the course of this research.  37Figure 1.10. Photographs of representative field conditions and key features of the Kiglapait intrusion during the Kiglapait Field Conference in July-August 2013.   39Figure 2.1. Flow chart summarizing the sample processing and analytical steps leading to the measurement of trace element concentrations and Pb-Sr-Hf-Nd isotopic ratios of mafic-ultramafic rock reference materials.   49Figure 2.2. Multi-element %RSD of the analyzed mafic-ultramafic rock reference materials  52Figure 2.3. Multi-element concentrations of the mafic-ultramafic rock reference materials normalized to Primitive Mantle (McDonough & Sun, 1995) 58Figure 2.4. Measured 208Pb/204Pb for mafic-ultramafic rock reference materials.  69Figure 2.5. Measured 176Hf/177Hf for mafic-ultramafic rock reference materials 71xviiiLIST OF FIGURESFigure 2.6. Measured 143Nd/144Nd for mafic-ultramafic rock reference materials 73Figure 2.7. Measured 86Sr/87Sr for mafic-ultramafic rock reference materials 75Figure 2.8. Multi-element concentrations for basaltic reference materials BE-N (panel A), GSR-3 (panel B), and JB-3 (panel C), comparing leached and unleached values normalized to Primitive Mantle (McDonough & Sun, 1995).   80Figure 2.9. Comparison of the Pb isotopic variations in mafic-ultramafic rock reference materials.   83Figure 2.10. Comparison of the Sr-Nd-Hf isotopic variation in mafic-ultramafic rock reference materials.   84Figure 3.1. Simplified geological map of the Nain Plutonic Suite (after Scoates & Mitchell, 2000) 92Figure 3.2. Geology and stratigraphy of the Kiglapait intrusion, Labrador, Canada 94Figure 3.3. Photographs showing examples of layering and textures in cumulates of the Kiglapait intrusion.   96Figure 3.4. Representative photomicrographs of samples from the Kiglapait intrusion analyzed in this study.   100Figure 3.5. Chondrite-normalized rare earth element patterns for rocks and minerals in the Kiglapait intrusion.   115Figure 3.6. Primitive mantle-normalized trace element patterns for rocks and minerals in the Kiglapait intrusion.   116Figure 3.7. Age-corrected Nd-Hf isotopic ratios versus percent solidified (PCS) in the Kiglapait intrusion.   118Figure 3.8. Age-corrected Sr isotopic ratios versus percent solidified (PCS) in the Kiglapait intrusion.   120Figure 3.9. Age-corrected lead isotopic ratios versus percent solidified (PCS) in the Kiglapait intrusion 122Figure 3.10. Age-corrected lead isotopic ratios versus percent solidified (PCS) in the plagioclase separates and leaching experiments of samples from the Kiglapait intrusion  123Figure 3.11. Measured 207Pb/204Pb versus measured 206Pb/204Pb for rocks and minerals from the Kiglapait intrusion.   124Figure 3.12. Diagrams comparing age-corrected lead isotopic ratios for rocks and minerals in the Kiglapait intrusion.   125xixLIST OF FIGURESFigure 3.13. Comparison of lead isotopic ratios of plagioclase of the Kiglapait intrusion to those of mortar, pestle, and diverse sources of Pb added in North American gasoline prior to 1996.  128Figure 3.14. Schematic diagrams showing the proposed evolution of the Kiglapait intrusion  129Figure 3.15. Hydrothermal circulation model explaining the enigmatic presence of radiogenic Pb isotopic compositions in the Kiglapait intrusion and possible petrological evidence.   132Figure 3.16. Pb isotope contamination models for the Kiglapait mafic minerals.   135Figure 3.17. Assimilation models applied to 87Sr/86Sr1.307 Ga for the Kiglapait intrusion  138Figure 3.18. Comparison of lead isotopic ratios of leached plagioclase of the Kiglapait intrusion to other rocks from the Nain Plutonic Suite, Nain Province, Churchill Province, and other relevant country rocks  140Figure 3.19. Diagram of εNd1.307 Ga versus 87Sr/86Sr1.307 Ga for the Kiglapait intrusion and other rocks from the Nain Plutonic Suite, Nain and Churchill provinces, and other relevant country rocks with source models for the Kiglapait magma.   141Figure 3.20. Primitive mantle-normalized trace element patterns of the modeled parental Kiglapait magma.   144Figure 3.21. Primitive mantle-normalized trace element patterns of the modeled parental magma of the Kiglapait intrusion compared to regional magma compositions and potential source end-members.   145Figure 4.1. Simplified geological map of the Kiglapait intrusion (after Morse, 1979a).   155Figure 4.2. Magmatic stratigraphy of the Kiglapait intrusion in volume percent solidified (PCS) (Morse, 1979a) with locations and representative photomicrographs of the samples analyzed in this study (dark blue); additional samples examined in Chapter 3 are shown in light blue text  157Figure 4.3. Photomicrographs showing the studied samples from the Kiglapait intrusion and representative laser ablation spots for the determination of in situ Pb isotopic compositions  159Figure 4.4. 208Pb/206Pb of the glass references BCR-2G, NIST SRM 612 and KL2-G, and the polymetal sulfide pellet MASS-1 measured in this study 165Figure 4.5. 207Pb/206Pb of the glass references BCR-2G, NIST SRM 612 and KL2-G, and the polymetal sulfide pellet MASS-1 measured in this study  166Figure 4.6. Diagrams showing the concentrations of Pb measured in reference materials and in minerals from the Kiglapait intrusion compared to uncertainties on measured 208Pb/206Pb  168Figure 4.7. Diagram of in situ 208Pb/206Pb versus 207Pb/206Pb determined by LA-ICP-MS for minerals from the Kiglapait intrusion.   176xxLIST OF FIGURESFigure 4.8. Comparison of all in situ Pb isotopic compositions (208Pb/206Pb versus 207Pb/206Pb) determined by LA-ICP-MS for minerals from the Kiglapait intrusion  177Figure 4.9. Diagrams showing the in situ Pb isotopic compositions along profiles in minerals from the Kiglapait intrusion (all values are initial ratios)  179Figure 4.10. Diagrams of age-corrected lead isotopic ratios (LA-ICP-MS and MC-ICP-MS) versus volume percent solidified (PCS) in the Kiglapait intrusion.   181Figure 4.11. Diagrams comparing the Pb isotopic compositions of the Kiglapait minerals and granitic dikes determined in situ by LA-ICP-MS and in whole rocks and mineral separates by MC-ICP-MS and TIMS.   182Figure 4.12. Schematic diagrams showing several different scenarios for how the Pb isotope compositions of co-existing minerals in cumulates of mafic plutonic rocks may vary and be recorded by in situ LA-ICP-MS analyses.   186Figure 5.1. Age and isotopic evolution of the Nain Plutonic Suite through time.   192Figure 5.2. Schematic diagrams showing the emplacement of the Nain Plutonic Suite based on the age compilation of Myers et al. (2008).   195Figure 5.3. Summary of the distribution of representative mafic layered intrusions (MLI) and anorthosites occurrences through geologic time (after Wall, 2016).   196Figure 5.4. A global overview of the initial Nd and Sr isotopic composition of representative layered intrusions.   198Figure 5.5. A global overview of the Pb isotopic compositions of representative layered intrusions.  199Figure 5.6. Pb isotope constraints on the crystallization and post-crystallization history of Kiglapait cumulates.  203Figure 5.7. Simplified magmatic stratigraphy of six representative layered intrusions from the geological record arranged in order of decreasing age (Fiskenæsset to Skaergaard)  204Figure 5.8. Effect of acid leaching on plagioclase grains from the Kiglapait intrusion  208Figure 5.9. Nd and Hf isotopic compositions of Archean anorthosite, Proterozoic anorthosite plutonic suites, and layered intrusions with anorthosite based on the compilation of Ashwal & Bybee (2017).   211Figure B.1. XRD Rietveld refinement plot: NIM-P (Pyroxenite).   281Figure B.2. XRD Rietveld refinement plot: BE-N (Melilite-bearing Nephelinite).   282Figure B.3. XRD Rietveld refinement plot: DNC-1 (Dolerite).   283xxiLIST OF FIGURESFigure B.4. XRD Rietveld refinement plot: BIR-1a (Olivine Tholeiite).   284Figure B.5. XRD Rietveld refinement plot: GSR-3 (Olivine Basalt) 285Figure B.6. XRD Rietveld refinement plot: NIM-N (Norite).   286Figure B.7. XRD Rietveld refinement plot: BHVO-2 (Basalt).   287Figure B.8. XRD Rietveld refinement plot: W-2 (Diabase)  288Figure B.9. XRD Rietveld refinement plot: JB-3 (High-alumina Basalt).   289Figure B.10. XRD Rietveld refinement plot: ST05-03 (Leucogabbro)   290Figure B.11. XRD Rietveld refinement plot: AN-G (Anorthosite) 291Figure C.1. Feldspar compositional variation (An) throughout the stratigraphy of the Kiglapait intrusion 311Figure C.2. Stratigraphic changes in olivine composition (Fo) in the Kiglapait intrusion. Data are from Morse (2012).   312Figure C.3. Age-corrected 87Sr/86Sri versus percent solidified (PCS) in the Kiglapait intrusion. 313Figure C.4. Representative photographs of mafic grains from sample KI3267 (60 PCS) of the Kiglapait intrusion.   314Figure C.5. Representative photographs of clinopyroxene grains from sample KI3369 (89.3 PCS) of the Kiglapait intrusion.  315Figure C.6. Representative photographs of plagioclase grains from sample KI3646 (47.2 PCS) of the Kiglapait intrusion.  316Figure C.7. Measured lead isotopic ratios versus percent solidified (PCS) in the plagioclase separates and leaching experiments of samples from the Kiglapait intrusion.   317Figure C.8. Diagrams comparing age-corrected radiogenic isotopic ratios from the Kiglapait intrusion.   318Figure C.9. Age-corrected isotopic ratios versus percent solidified (PCS) in the whole rocks from the Kiglapait intrusion.   319Figure C.10. Assimilation models applied to Nd and Pb isotopes in the Kiglapait intrusion 320Figure D.1. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the troctolite KIG13-15 (5.1 PCS).  348Figure D.2. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the leucotroctolite KI3652 (26.7 PCS).   349xxiiLIST OF FIGURESFigure D.3. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the melatroctolite KI3267 (60 PCS)  350Figure D.4. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the troctolite KI3276 (68 PCS)  351Figure D.5. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the gabbro KI3369 (89.3 PCS)  352Figure D.6. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of sulfide grains in the troctolite KIG13-15 (5.1 PCS)  353Figure D.7. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of sulfide grains in the leucotroctolite KI3652 (26.7 PCS)  354Figure D.8. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of sulfide grains in the melatroctolite KI3267 (60 PCS)  355Figure D.9. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of sulfide grains in the melatroctolite KI3276 (68 PCS)  356Figure D.10. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of sulfide grains in the melatroctolite KI3369 (89.3 PCS)  357Figure D.11. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the granitic dike KIG13-20  358Figure D.12. Photomicrographs showing the positions of the laser spots for in situ Pb isotopic analyses of the granitic dike KIG13-14  359xxiiiLIST OF ABBREVIATIONSAnalytical: BSE = backscattered electron cm = centimeterg = grams Ga = billion years, billion years ago HFSE = high field strength elementsHR-ICP-MS = high resolution-inductively coupled plasma-mass spectrometryHz = hertzICP-OES = inductively coupled plasma-optical emission spectrometryJ = joulekg = kilogram km = kilometer L = liter LA-ICP-MS = laser ablation-inductively coupled plasma-mass spectrometry LILE = large ion lithophile elementsm = meters Ma = million years, million years ago MC-ICP-MS = multiple collector-inductively coupled plasma-mass spectrometry mg = milligram mL = milliliter mm = millimeter xxivLIST OF ABBREVIATIONSnm = nanometer PFA = perfluoroalkoxy alkanespg = picogram ppb = parts per billion ppm = parts per million REE = rare earth elementsRSD = relative standard deviation (can also be reported as 2RSD)RSE = relative standard error (can also be reported as 2RSE)SD = standard deviation (typically reported as 2SD)SE = standard error (typically reported as 2SE)SEM = scanning electron microscope SSB = sample standard bracketingT = transmissionTE = trace elementTIMS = thermal ionization mass spectrometryXRD = X-ray diffractionW = wattwt% = weight percentε = epsilon notation for Nd and Hf isotopes – variations of 1 part in 10000μg = microgram μL = microliter μm = micrometer Σ = sum xxvLIST OF ABBREVIATIONSMinerals: antiperth = antiperthite: intergrowth of alkali feldspar ((K,Na)AlSi3O8) in plagioclase ((Na,Ca)(Al,Si)4O8) hostap = apatite: Ca5(PO4)3(OH,F,Cl)aug = augite: (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6bt = biotite: K(Mg,Fe)3(AlSi3O10)(F,Cl,OH)2chl = chlorite: (Mg,Al,Fe)6(Si,Al)4O10(OH)8cp = chalcopyrite: CuFeS2cpx = clinopyroxene: (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6hbl = hornblende: (K,Na)0-1(Ca,Na,Fe,Mg)2(Mg,Fe,Al)5(Si,Al)8O22(OH)2 fay = fayalite: Fe2SiO4mag = magnetite: Fe3O4ol = olivine: (Mg,Fe)2SiO4opx = orthopyroxene: (Mg,Fe)2SiO6 plag = plagioclase:  (Na,Ca)(Al,Si)4O8pn = pentlandite: (Fe,Ni)9S8 po = pyrrhotite: Fe1-xSPPL = plane-polarized light px = pyroxene: (Ca,Na,Mg,Fe)(Mg,Fe,Al,Cr)(Si,Al)2O6qtz = quartz: SiO2ser = sericite: (K,Na)Al2(Si3Al)O10(OH,F)2serp = serpentine: (Mg,Fe)3Si2O5(OH)4XPL = cross-polarized light xxviLIST OF ABBREVIATIONSReference materials and institutes: GSJ = Geological Survey of JapanIGGE = Institute of Geophysical and Geochemical Exploration, ChinaMINTEK = Council for Mineral Technology, South AfricaNIST = National Institute of Standards and Technology, USA SARM = Service d’Analyse des Roches et des Minéraux, FranceSRM = standard reference materialULB = Université Libre de BruxellesUSGS = United States Geological SurveyKiglapait intrusion: C-P = Caplin-Patsy traverseCP = Churchill ProvinceD-B = David-Billy traverseFBG = Falls Brook GroupIBZ = Inner Border Zone LZ = Lower Zone NP = Nain ProvinceNPS = Nain Plutonic SuitePCS = volume percent solidifiedS-L = Sally Lake traverseUBZ = Upper Border Zone UZ = Upper Zone xxviiACKNOWLEDGEMENTSDuring the six and a half years of this PhD, I have benefitted from the support, encouragement, and contributions of many colleagues and friends. First and foremost, I thank my two thesis supervisors, Drs. Dominique Weis and James Scoates whose mentorships, scientific support, edits, geochemical and petrological expertise, and advice allowed for the progress of this dissertation and my professional development. Thank you both for giving me the opportunity to conduct this research, for always being enthusiastic about this project, and for your help and support.I thank Dr. Stearns A. (Tony) Morse for providing most of the samples from the Kiglapait intrusion, for his enthusiastic emails and discussions about this work, and for an amazing field conference held on the rocks on the Kiglapait intrusion itself in the summer of 2013. I am honored to contribute, even if it is just a little, to the exhaustive work you have done on the Kiglapait intrusion.I also thank Dr. Michael Hamilton for giving me access to his unpublished isotope geochemistry from the Nain Plutonic Suite. This comprehensive dataset added important constraints on the geochemical modeling presented in this study.I owe many thanks to the members of the research staff at PCIGR, who work very hard to keep the clean lab and instruments running, who spent many hours teaching me how to use the mass spectrometers, and who always had advice for analyzing “tricky” samples. Thank you to Richard Friedman, Kathy Gordon, Bruno Kieffer, Vivian Lai, Hai Lin, Taylor Ockerman, and Liyan Xing. I am especially grateful to Marghaleray Amini who accepted to be part of my committee, who provided great insights over the years, and who spent many hours with me on the AttoM and laser for the tests and analyses of Pb isotopes. Thanks also to Dr. Mati Raudsepp, Edith Czech, Elisabetta Pani, Jenny Lai, and Lan Kato for the XRD analysis of reference xxviiiACKNOWLEDGEMENTSmaterials, and for assistance with the SEM and electron microprobe.I very much thank the Layered Intrusions working group at UBC, Laura Bilenker, June Cho, Matt Manor, Nichole Moerhuis, Tom Ver Hoeve, and Corey Wall, for their helpful feedback and advice during our group meetings, and also for their friendships during conferences and field trips.Thank you to all my friends who have made these years such a great experience. I want to especially thank my 305-301 office mates who provided necessary support, editing, and friendship through these years, and for all the discussions during our bi-weekly coffee (tea)-runs and over Friday beers. Additional thanks go to those who were there when I started and made me feel welcome, Corey Wall, Lauren Harrison, Marina Martindale, Genna Patton, Mariko Ikeata, Kang Wang, and Aram Goodwin. My life in Vancouver would not have been as enjoyable without all the moments with you all. Many thanks go to the many past and current roommates I had over the years at the “Zenhouse”. They managed to keep me out of the lab from time to time and make my life so fun and agreeable here. Finally, a big thank you goes to my family who supported me, with understanding and patience, during all this years. Merci! xxixDEDICATIONTo my family, Who always supports my choices even when it implies moving very far away from home. Merci!1 2.CHAPTER 1Introduction1.1 Introduction and Scope of the ProjectMafic layered intrusions represent fossil magma chambers that contain remarkable rock records of the evolution of magmatic processes during the solidification of basaltic magmas. These plutonic bodies form natural laboratories for examining crystallization processes of mostly mantle-derived magma in the crust (Wager & Brown, 1968; Cawthorn, 1996; Charlier et al., 2015; O’Driscoll & VanTongeren, 2017). Mafic layered intrusions are present worldwide and throughout geologic history from the Archean to the Cenozoic (Scoates & Wall, 2015). Evidence of their potential presence on Mars (Francis, 2011) underscores their importance in understanding the nature and timescales of planetary differentiation, the origin of diversity of rocks observed in the Earth’s crust, and magmatic pathways between the mantle and crust (Walker & McCallum, 1982; Francis, 2011; O’Driscoll & VanTongeren, 2017). Layered intrusions are also host to world-class ore deposits of chromium, platinum group elements, and vanadium and their study has economic and resource implications (Cawthorn et al., 2005). Studies of layered intrusions over the last 100 years have yielded knowledge on many key processes involved in their formation, however, there remain important unanswered questions (Wager & Brown, 1968; Cawthorn, 1996; Charlier et al., 2015; O’Driscoll & VanTongeren, 2017). These questions concern their age and emplacement (e.g., timescale, tectonic setting), their mantle source and significance of crustal contamination, the physical nature of the magma chamber or reservoir, and the specific magmatic processes that occur during their crystallization (Boudreau et al., 2016; O’Driscoll & VanTongeren, 2017). Radiogenic isotopes are crucial to answering some of these questions as they are not fractionated during melting or crystal fractionation and can thus constrain the magmatic processes involved in emplacement and crystallization of layered intrusions (e.g., DePaolo & Wasserburg, 1979; Kruger & Marsh, 1982; 2CHAPTER 1Palacz, 1984; DePaolo, 1985; Stewart & DePaolo, 1992; Lambert et al., 1994; Harmer et al., 1995; Barling et al., 2000; Tegner et al., 2005). Radiogenic isotope ratios, especially those in the rubidium-strontium (Rb-Sr), samarium-neodymium (Sm-Nd), lutetium-hafnium (Lu-Hf), and lead-lead (Pb-Pb) systems, have long been used for exploring mantle heterogeneity through time (Manhes et al., 1980), for identifying magma sources (e.g., Stillwater, DePaolo & Wasserburg, 1979; Kiglapait, DePaolo, 1985; Bjerkreim–Sokndal, Barling et al., 2000; Bushveld, Maier et al., 2000), for determining the ages of crystallization of layered intrusions (e.g., Stillwater, DePaolo & Wasserburg, 1979; Wall & Scoates, 2016; Kiglapait, DePaolo, 1985; Muskox, Stewart & DePaolo, 1996; Bushveld, Scoates & Friedman, 2008), for detecting the effects of crustal contamination (e.g., Kiglapait, DePaolo, 1985; Hidra massif, Weis, 1986; Bjerkreim–Sokndal, Weis, 1986; Barling et al., 2000; Tegner et al., 2005; Skaergaard, Stewart & DePaolo, 1990; Bushveld, Harmer et al., 1995; Maier et al., 2000; Hasvik, Tegner et al., 2005), and for tracing magma mixing (e.g., Bushveld, Kruger & Marsh, 1982; Harmer et al., 1995; Maier et al., 2000; Stillwater, Lambert et al., 1994; Muskox, Stewart & DePaolo, 1996). Surprisingly, recent studies that have measured isotopic ratios at the mineral scale by solution techniques (Weis et al., 2003; Prevec et al., 2005; Roelofse & Ashwal, 2012) and in situ techniques (Mathez & Waight, 2003; Mathez & Kent, 2007; Chutas et al., 2012; Yang et al., 2013) are revealing that initial isotopic differences between coexisting minerals in major layered intrusions can be significant. These observations have generated debate on the processes involving during emplacement and crystallization of layered intrusions and they highlight the importance of careful and detailed isotopic investigations of well-characterized intrusions.The research presented in this dissertation aims to establish an integrated Pb-Sr-Nd-Hf isotopic and trace element framework for evaluation of the source, parent magma composition, and differentiation of layered intrusions from a study of the ca. 1307 Ma Kiglapait layered intrusion, the largest troctolitic body of the vast Nain Plutonic Suite, Labrador (Morse, 1969; 2015). The Kiglapait intrusion represents a key end-member among layered intrusions as it is considered to represent a pristine example of extreme fractionation of a single batch of high-Al 3CHAPTER 1basaltic magma under closed-system conditions (e.g., Morse, 1969, 1979a, 1979b, 1981, 1996, 2015; Huntington, 1979; Kalamarides, 1984, 1986; Morse & Ross, 2004). It is very well-exposed in coastal Labrador, it contains a complete 8 km-thick stratigraphic section of cumulates, and it ranges in composition from a troctolitic Lower Zone (0-84 percent solidified or PCS) through to an olivine gabbroic to ferrosyenitic Upper Zone (84-100 PCS) (Morse, 1969, 1979a, 2015).The accurate and precise measurement of the isotopic compositions of individual minerals, such as those preserved in layered intrusions, by multiple collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) requires the analysis of sample–matrix-matched reference materials (e.g., Kane & Pott, 1997; Woodhead & Hergt, 2000; Weis et al., 2005, Nobre Silva et al., 2009; Chauvel et al., 2011; Jochum & Ensweiler, 2014). In the case of ultramafic samples, robust and systematic isotopic characterizations of reference materials were relatively sparse prior to this study. The first part of this dissertation involves establishing a new database of mafic to ultramafic reference materials to serve as a reference dataset for the isotopic study of the Kiglapait intrusion. Radiogenic isotopic compositions (Pb-Nd-Hf-Sr) of 10 mafic to ultramafic reference materials, carefully selected to match the matrix of samples from layered intrusions, were analyzed by MC-ICP-MS and thermal ionization mass spectrometry (TIMS).The primary goal of this research is to constrain the sources and processes involved in the crystallization of the Kiglapait intrusion. This goal was accomplished through the measurement of four isotope systems (Pb-Pb, Rb-Sr, Sm-Nd, Lu-Hf) and trace elements on mineral separates, leached and unleached plagioclase, and whole rocks, and through the application of a newly developed in situ technique for analyzing Pb isotopes directly in thin section. Using this isotopic and trace element framework, the results of this dissertation research identify 1) the trace element composition of the Kiglapait parent magma, 2) the magma source(s) of this plutonic body, 3) the role of contamination of the Upper Zone during crystallization. Combined, the results allow for an evaluation of the possible mechanisms responsible for the observed isotopic differences with potential application to plutonic rocks in general. The following sections contain background information relevant to the main components 4CHAPTER 1of this dissertation. These sections include an overview of mafic layered intrusions and their radiogenic isotope compositions, the analytical techniques used during the different studies, and the geological setting of the Kiglapait intrusion in the Nain Plutonic Suite. This introductory chapter ends with a summary of the contents of the dissertation and a series of conference, workshop, and field opportunities related to this research.1.2 Mafic layered intrusions1.2.1 Layered intrusions and their significance in the geological recordMafic to ultramafic layered intrusions are crystallized magma chambers whose rocks record the effects of fractional crystallization and mineral accumulation in magma reservoirs, and they have been fundamental in understanding differentiation and crystallization processes in terrestrial magmas (e.g., Bowen, 1956; Wager & Brown, 1968; Walker & McCallum, 1982; Parsons, 1987; Cawthorn, 1996; Francis, 2011; Charlier et al., 2015; O’Driscoll & VanTongeren, 2017) (Fig. 1.1). They consist of rocks called cumulates (Fig. 1.1A-B) and comprise cumulus minerals or primocrysts, which fractionated from magma, and postcumulus or interstitial minerals, which crystallized from fractionated intercumulus or interstitial liquid (e.g., Wager et al., 1960; Wager & Brown, 1968; Irvine, 1982) (Fig. 1.1B-D). Conventionally, layered intrusions have been considered to form from the crystallization of a crystal-free magma (i.e., super-liquidus) in the crust. The mineralogy and mineral compositions of the cumulus phases follow a predictable crystallization sequence (i.e., from high-Mg/Fe to low-Mg/Fe olivine, from high-Ca/Na to low Ca/Na plagioclase) as the magma loses heat, crystals nucleate and grow, and then accumulate on the floor of the magma chamber due to density differences (Wager & Brown, 1968; Naslund & McBirney, 1996). In situ crystallization in boundary zones along the margins of the magma chamber may also occur when plagioclase is the main crystallizing phase as it is slightly buoyant (or neutrally buoyant) in basaltic melts and should not accumulate on the floor (Naslund & McBirney, 1996; Scoates, 2000; Namur et al., 2015).5CHAPTER 1B2 cmA2 mCPlagOlCpx0.5 cmDPlagOlCpx0.5 mmFigure 1.1. Photographs and photomicrographs of igneous layering and textures in the Kiglapait intrusion, Labrador, Canada. A. Modal layering in the Lower Zone, 10 PCS, Slambang Bay. B. Troctolite of the Lower Zone of the Kiglapait intrusion, 40 PCS, Thalia Point. C. Thin section in cross-polarized light of a troctolite from the Lower Zone, 60 PCS (KI3267). D. Photomicrograph showing cumulus plagioclase and olivine with interstitial clinopyroxene (KI3267). Pl = plagioclase; Cpx = clinopyroxene (augite); Ol = olivine. Scales as indicated on images.6CHAPTER 1There are two end-member magmatic systems, those that crystallize under closed-system conditions from a single batch of magma and those that crystallize under open-system conditions involving multiple injections of magma (Wager & Brown, 1968; Cawthorn, 1996; Charlier et al., 2015). When a layered intrusion forms in a closed system, the entire crystallization sequence originates from one injection of magma and its subsequent cooling (e.g., Kiglapait, Morse, 1969; Skaergaard, Wager & Brown, 1968). In an open system, the intrusion is formed by many injections of fresh magma, from the same or multiple sources, causing repetition and discontinuities in the sequences of layers, and changes in elemental and isotopic compositions (e.g., Bushveld, Kruger & Marsh, 1982; Maier & Barnes, 1998; Muskox, Irvine, 1975, 1977; Rum, Palacz, 1984; Stillwater, Lambert & Simmons, 1987; Wall et al., 2018). Layered intrusions have also been considered to result from the crystallization of “crystal-rich slurries” (Marsh, 2013). Recent high-precision U-Pb zircon dating of layered intrusions has revealed that some large open-system layered intrusions, such as the Bushveld and the Stillwater complexes, were not formed by progressive crystallization of a magma chamber periodically replenished from base to top, but rather formed as a stack of amalgamated sills of different age (not necessarily in sequence) resulting from multiple injections of magma (Scoates & Wall, 2015; Mungall et al., 2016; Wall et al., 2018).1.2.2 Isotopic studies of layered intrusionsRadiogenic isotopic systems (Pb-Pb, Rb-Sr, Sm-Nd, Lu-Hf) are important tracers of the parent magma and source(s) of layered intrusions (e.g., DePaolo & Wasserburg, 1979; Manhes et al., 1980; Kruger & Marsh, 1982; Stewart & DePaolo, 1990; DePaolo, 1985; Palacz, 1984; Lambert et al., 1994). Radiogenic isotopes are powerful geochemical tools as, unlike elemental concentrations or stable isotopes, they do not fractionate during magmatic processes such as fractional crystallization. The initial isotopic compositions (i.e., corrected for the in situ decay of the parent isotope since crystallization or obtained using isochron diagrams) of rocks or minerals will reflect the composition of the magma that they crystallized from. Due to the relatively short 7CHAPTER 1period of crystallization compared to the half-lives of the radioactive parents, the initial isotopic compositions of the samples will monitor the homogeneity, or change, in the source(s) isotopic composition(s). The isotopic ratios of samples from layered intrusions are thus an essential tool for defining their mantle source compositions (e.g., DePaolo & Wasserburg, 1979; DePaolo, 1985; Harmer et al., 1995; Barling et al., 2000; Maier et al., 2000) and for tracing compositional changes in magma chambers as a result of assimilation and magma mixing (e.g., Kruger & Marsh, 1982; DePaolo, 1985; Stewart & DePaolo, 1990, 1996; Lambert et al., 1994; Harmer et al., 1995; Barling et al., 2000; Maier et al., 2000; Tegner et al., 2005; Wilson et al., 2017).1.2.3 Isotopic differences between minerals in layered intrusionsIn the past 15 years, there have been significant advances in microsampling techniques to assess elemental and isotopic differences within and between minerals (Mathez & Waight, 2003; Tepley & Davidson, 2003; Mathez & Kent, 2007; Ramos & Tepley, 2008; Chutas et al., 2012; Yang et al., 2013). Isotopic differences in initial ratios between co-existing mineral phases have been observed in volcanic and plutonic rocks (Ramos & Tepley, 2008). These differences are variably referred to as “isotopic disequilibrium”, “isotopic variations”, or “isotopic heterogeneities”. In this study, the preferred terminology is “isotopic differences”.Minerals coexisting in cumulates within a single mafic layered intrusion have long been considered to have crystallized from the same magma and thus should share the same initial radiogenic isotopic compositions. However, an increasing number of studies, as summarized in Table 1.1, report isotopic differences between different crystals in cumulates from mafic layered intrusions, including the Bushveld Complex (Mathez & Waight, 2003; Prevec et al., 2005; Mathez & Kent, 2007; Chutas et al., 2012; Roelofse & Ashwal, 2012), the Skaergaard intrusion (McBirney & Creaser, 2002), the Kiglapait intrusion (Weis & Morse, 1993, 1995; Weis et al., 2003, 2004), the Rum intrusion (Palacz et al., 1984; Tepley & Davidson, 2003), and the Stillwater Complex (McCallum et al., 1999). These observations have opened up an ongoing debate on how these minerals crystallize and form cumulates (e.g., different compositions prior 8CHAPTER 1Reference Layered Intrusion Observations HypothesisPost-crystallization alterationWooden et al. (1991), Bosch et al. (1991)Stillwater Complex, USADifference of Pbi between leached and unleached plagioclasePlagioclase Pbi modified by mixing with radiogenic Pb after crystallization of the complexMcCallum et al. (1999)Stillwater Complex, USADifference of initial Pbi between coexisting sulfide (more radiogenic) and plagioclase; leaching of sulfide results in lower Pbi; evidence of sulfide recrystallization and presence of secondary mineralsPost-crystallization changes in sulfides during hydrothermal eventMathez & Waight (2003)Bushveld Complex, South AfricaVariations of Pbi between coexisting sulfide and plagioclase; both sulfide and plagioclase show isotopic variations within samplesRadiogenic Pb component from the country rock introduced during percolation of interstitial, possibly subsolidus, fluidMathez & Kent (2007)Bushveld Complex, South AfricaSulfides have higher 206Pb/204Pb for equivalent 207Pb/204Pb than coexisting plagioclaseRemobilization by fluid of radiogenic Pb from U-Th-rich minerals in host rocks to the Bushveld Complex Late-magmatic processesMcBirney & Creaser (2002)Skaergaard intrusion, GreenlandVariation of Sri and Ndi at variable scales (whole rock and coexisting minerals); dominant minerals in both mafic and felsic rocks have lower Sri than respective residual mineralsMigration of late-stage liquids disturb initial compositionWeis et al. (2003, 2004)Kiglapait intrusion, LabradorDifference of Pbi and Sri between whole rock, plagioclase, and bulk maficsLate apatite, Fe-rich residual liquids disturb the isotopic composition of the maficsS.A. Morse (personal communication, 2006)Kiglapait intrusion, LabradorDifference of Pbi between whole rock, plagioclase, and bulk mafics; difference of Pb solubility between sulfide melt and crystallized solidRadiogenic Pb carried by sulfide melt, expelled during sulfide crystallization, and taken up by the surrounding mineralsChutas et al. (2012) Bushveld Complex, South AfricaPlagioclase from the Critical Zone has rims more radiogenic than cores (no intra-mineral variability in Upper Zone); plagioclase has higher initial Sri and lower Pbi than orthopyroxeneRadiogenic Sr component migrated through partly solidified crystal pile, followed by Pb contamination of the late-crystallized orthopyroxeneWei et al. (2014) Xiahohaizi intrusion, ChinaSr and Nd isotopic difference between clinopyroxene and plagioclase (lower Sri and higher εNd in clinopyroxene); positive correlation between Sri and Zr/Nb in clinopyroxeneInterstitial plagioclase crystallized from