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Wrangellia flood basalts in Alaska, Yukon, and British Columbia : exploring the growth and magmatic history… Greene, Andrew R. 2008

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WRANGELLIA FLOOD BASALTS IN ALASKA, YUKON, AND BRITISH COLUMBIA: EXPLORING THE GROWTH AND MAGMATIC HISTORY OF A LATE TRIASSIC OCEANIC PLATEAU  By ANDREW R. GREENE  A THESIS SUBMITTED iN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  THE FACULTY OF GRADUATE STUDIES (Geological Sciences)  UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  August 2008  ©Andrew R. Greene, 2008  ABSTRACT The Wrangellia flood basalts are parts of an oceanic plateau that formed in the  eastern Panthalassic Ocean (ca. 230-225 Ma). The volcanic stratigraphy presently extends >2300 km in British Columbia, Yukon, and Alaska. The field relationships, age, and geochemistry have been examined to provide constraints on the construction of oceanic plateaus, duration of volcanism, source of magmas, and the conditions of melting and magmatic evolution for the volcanic stratigraphy. Wrangellia basalts on Vancouver Island (Karmutsen Formation) form an emergent sequence consisting of basal sills, submarine flows (>3 km), pillow breccia and hyaloclastite (<1 1cm), and subaerial flows (>1.5 km). Karmutsen stratigraphy overlies Devonian to Permian volcanic arc (—‘380-355 Ma) and sedimentary sequences and is overlain by Late Triassic limestone. The Karmutsen basalts are predominantly homogeneous tholeiitic basalt (6-8 wt% MgO); however, the submarine part of the stratigraphy, on northern Vancouver Island, contains picritic pillow basalts (9-20 wt% MgO). Both lava groups have overlapping initial  and ENd, indicating a common, ocean  island basalt (OIB)-type Pacific mantle source similar to the source of basalts from the Ontong Java and Caribbean Plateaus. The major-element chemistry of picrites indicates extensive melting (23 -27%) of anomalously hot mantle (‘—1500°C), which is consistent with an origin from a mantle plume head. Wrangellia basalts extend —-‘450 km across southern Alaska (Wrangell Mountains and Alaska Range) and through southwest Yukon where <3.5 km of mostly subaerial flows (Nikolai Formation) are bounded by Pennsylvanian to Permian volcanic (312-280 Ma) and sedimentary strata, and Late Triassic limestone. The vast majority of the Nikolai ) with uniform plume-type 2 basalts are LREE-enriched high-Ti basalt (1.6-2.4 wt% Ti0 Pacific mantle isotopic compositions. However, the lowest ‘-.400 m of stratigraphy in the Alaska Range, and lower stratigraphy in Yukon, is light rare earth element (LREE) ) with pronounced negative-HFSE anomalies 2 depleted low-Ti basalt (0.4-1.2 wt% Ti0 and high Elf values that are decoupled from Nd and displaced well above the OIB mantle array. The low-Ti basalts indicate subduction-modified mantle was involved in the formation of basalts exposed in Alaska and Yukon, possibly from mechanical and thermal erosion of the base of the lithosphere from an impinging mantle plume head.  11  TABLE OF CONTENTS fi  Table of Contents List of Tables List of Figures Acknowledgements Dedication Co-authorship statement  ffl vii ix  xvi xvii  CHAPTER 1 Introduction 1 Introduction and motivation for this study 2 The Wrangellia oceanic plateau 7 Methodology and rationale for this study 10 Previous research 11 The importance of LIPs and mantle plumes 12 An overview of the four manuscripts in this dissertation and additional references...15 Contributions to this project 18 References 19 CHAPTER 2 Wrangeffia Flood Basalts on Vancouver Island: Significance of Picritic and Tholeiitic Lavas for the Melting History and Magmatic Evolution of a Major Oceanic Plateau Introduction Geologic setting Wrangellia on Vancouver Island Age of the Karmutsen Formation Volcanic stratigraphy and petrography Sample preparation and analytical methods Whole-rock chemistry Major- and trace-element compositions Sr-Nd-Hf-Pb isotopic compositions Alteration Olivine accumulation in picritic lavas Discussion Melting conditions and major-element composition of primary magmas Source of Karmutsen lavas REE modeling: Dynamic melting and source mineralogy Magmatic evolution of Karmutsen tholeiitic basalts Conclusions Acknowledgements References  26 27 28 28 31 31 37 44 44 56 62 63 63 65 68 71 75 78 79 79  111  CHAPTER 3 Wrangeffia Flood Basalts in Alaska: A Record of Plume-Lithosphere Interaction in a Late Triassic Accreted Oceanic Plateau 86 Introduction 87 Geologic setting 89 Wrangellia in Alaska 89 Wrangell Mountains 89 Eastern Alaska Range 91 Age of the Nikolai Formation 93 Volcanic stratigraphy and petrography 93 Whole-rock chemistry 104 Major- and trace-element compositions 104 Sr-Nd-Hf-Pb isotopic compositions 115 Alteration 115 Flood basalt chemostratigraphy 123 Discussion 125 Source of Nikolai basalts 125 Lithospheric involvement in derivation of the low-titanium basalts 128 Nature of underlying Paleozoic arc lithosphere 128 Trace-element and isotopic source constraints of the low titanium basalts... 129 Origin of decoupled Hf and Nd isotopic compositions of low-titanium basalts 134 Melting conditions and estimated major-element composition of 138 primary low-Ti magma Conclusions 142 Acknowledgements 143 References 143 CHAPTER 4 Geochemistry of Flood Basalts from the Yukon (Canada) Segment of the Accreted Wrangeffia Oceanic Plateau Introduction Geologic setting and age constraints Field relations and petrography Whole-rock chemistry Major- and trace-element compositions Sr-Nd-Hf-Pb isotopic compositions Discussion Effects of alteration and comparison to Nikolai basalts in Alaska Relationship between chemistry and stratigraphic position Source characteristics of Nikolai basalts in Yukon Melting of arc mantle in formation of the low-titanium basalts Conclusion Acknowledgements References  151 152 153 156 161 161 171 171 171 179 180 182 188 189 189  iv  CHAPTER 5 The Age and Volcanic Stratigraphy of the Accreted Wrangeffia Oceanic Plateau in Alaska, Yukon and British Columbia Introduction Wrangellia flood basalts: The volcanic stratigraphy of an accreted oceanic plateau Geographic distribution and aerial extent of the Wrangellia flood basalts Geologic history of Wrangellia Stratigraphy of Wrangellia Wrangellia of southern Alaska Talkeetna Mountains and eastern Alaska Range Wrangell Mountains Wrangellia in southwest Yukon Wrangellia in southeast Alaska Wrangellia in the Queen Charlotte Islands (Haida Gwaii) Wrangellia on Vancouver Island Central and southern Vancouver Island Northern Vancouver Island Geochronology of Wrangellia Previous geochronology for Wrangellia flood basalts and related plutonic rocks Ar in this study 39 Ar/ Information about samples analyzed by 40 4O,39 geochronological results Summary of isotopic age determinations for Wrangellia flood basalts Paleontological studies Discussion Overview of geology and age of Northern and Southern Wrangellia Eruption environment for Wrangellia flood basalts Northern Wrangellia Southern Wrangellia The accumulation and subsidence of the Wrangellia flood basalts Conclusion Acknowledgements References  CHAPTER 6 Conclusions Conclusions and Directions for Future Research References  195 196  198 200 200 203 203 205 209 215 218 221 222 222 228 233 233 235 236 243 243 245 245 248 248 249 251 254 255 255  267 271  v  Appendices. Appendix A. Geologic map of the Mount Arrowsmith area Appendix B. XRF whole-rock analyses of a subset of Karmutsen basalts, Vancouver Island, B.C Appendix C. PCIGR trace-element analyses of Karmutsen basalts, Vancouver Island, B.C Appendix D. Sample preparation and analytical methods for Alaska samples Appendix E. Sample preparation and analytical methods for Yukon samples Appendix F. Major element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Late Paleozoic Station Creek Formation, Yukon Appendix G. Previous research on Wrangellia Appendix H. 40 Ar analytical methods 39 Ar/ Appendix I. Analytical results of reference material from Actlabs whole-rock analyses for Vancouver Island and Yukon Appendix J. Description of supplementary electronic files on CD-ROM  273 274 276 279 284 288 290 306 308 310  Supplementary electronic files on CD-ROM Supplementary data files (SD) SD 1- Endnote database for Wrangellia (.enl file) SD 2- Reference list for Wrangellia (.doc file) Ar samples (.xls file) 39 Ar/ SD 3- Geochemistry for 40 SD 4- 40 Ar analytical data (.xls file) 39 Ar/ SD 5- Wrangellia ages and biostratigraphy (.xls file) Supplementary Google Earth ifies (SGE) SGE 1- Mapped Wrangellia flood basalts (.kniz file) SGE 2- Major faults in Alaska and Yukon (.kml file) SGE 3- Major faults in southwest B.C. (.kml file) SGE 4- Alaska sample locations (.kml file) SGE 5- Yukon sample locations (.kml file) SGE 6- Vancouver Island sample locations (.kml file) SGE 7- Alaska Range photograph locations (.kmz file) SGE 8- Wrangell Mountains photograph locations (.kmz file) SGE 9- Yukon photograph locations (.kmz file) SGE 10- Vancouver Island photograph locations (.kmz file) Supplementary photo ifies (SP) SP 1- Alaska Range photographs (.pdf file) SP 2- Wrangell Mountains photographs (.pdf file) SP 3- Ed MacKevett Jr. Wrangell Mountains photographs (.pdf file) SP 4- Yukon photographs (.pdf file) SP 5- Vancouver Island photos (.pdf file)  Greene_2008_PhD_dissertation_UBC (.pdf file of complete dissertation)  vi  LIST OF TABLES CHAPTER 2  Table 2.1 Summary of petrographic characteristics and phenocryst proportions of Karmutsen basalts on Vancouver Island, B.C  39  Table 2.2 Major element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Karmutsen basalts, Vancouver Island, B.C  46  Table 2.3 Sr and Nd isotopic compositions of Karmutsen basalts, Vancouver Island, B.C  59  Table 2.4 Hf isotopic compositions of Karmutsen basalts, Vancouver Island, B.C  60  Table 2.5 Pb isotopic compositions of Karmutsen basalts, Vancouver Island, B.C  61  Table 2.6 Estimated primary magma compositions for Karmutsen basalts and other oceanic plateaus/islands  67  CHAPTER 3  Table 3.1 Summary of petrographic characteristics and phenocryst proportions of Nikolai basalts in Alaska  102  Table 3.2 Major element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Nikolai basalts, Alaska  106  Table 3.3 Sr and Nd isotopic compositions of Nikolai basalts, Alaska  118  Table 3.4 Hf isotopic compositions of Nikolai basalts, Alaska  119  Table 3.5 Pb isotopic compositions of Nikolai basalts, Alaska  120  Table 3.6 Estimated primary magma compositions for Nikolai basalts and other oceanic plateaus/islands  141  CHAPTER 4 Table 4.1 Summary of petrographic characteristics and phenocryst proportions of Nikolai basalts in Yukon  160  Table 4.2 Major element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Nikolai basalts, Yukon  163  vii  Table 4.3 Sr and Nd isotopic geochemistry of Nikolai basalts, Yukon  174  Table 4.4 Hf isotopic compositions of Nikolai basalts, Yukon  175  Table 4.5 Pb isotopic compositions of Nikolai basalts, Yukon  176  CHAPTER 5  Table 5.1 Areal extent and volumetric estimates for the Wrangellia flood basalts  201  Table 5.2 Compilation of previous geochronology of Wrangellia flood basalts and associated plutonic rocks  234  Table 5.3 Ar/ 40 dating results for 13 samples of Wrangellia flood Ar 39 basalts and 6 samples from the Wrangellia Terrane  241  Table 5.4 Comparison of geology and ages of Northern and Southern Wrangellia  246  vi”  LIST OF FIGURES CHAPTER 1  Figure 1.1 Distribution of Phanerozoic LIPs on Earth  3  Figure 1.2 Schematic diagrams of mantle plumes in the Earth’s interior  4  Figure 1.3 “Pin-pricking” the giant Ontong Java Plateau  6  Figure 1.4 Map showing distribution of Wrangellia flood basalts in Alaska, Yukon, and British Columbia  8  Figure 1.5 Estimated distribution of the continental landmasses in the Middle to Late Triassic (226 Ma)  9  Figure 1.6 Age difference between peak eruption ages of LIPs from the last 260 Myr versus the age of a stratigraphic boundary  14  Figure 1.7 Photographs showing the different modes of transportation used for field work in remote areas of Alaska, Yukon, and BC as part of this project  17  CHAPTER 2 Figure 2.1 Simplified map of Vancouver Island showing the distribution of the Karmutsen Formation  30  Figure 2.2 Geologic map and stratigraphy of the Schoen Lake Provincial Park and Karmutsen Range areas  33  Figure 2.3 Photographs of picritic and tholeiitic pillow basalts from the Karmutsen Range area (Alice and Nimpkish Lake area), northern Vancouver Island  34  Figure 2.4 Photographs showing field relations from the Schoen Lake Provincial Park area, northern Vancouver Island  35  Figure 2.5 Photomicrographs of picritic pillow basalts, Karmutsen Formation, northern Vancouver Island  38  Figure 2.6 Whole-rock major-element, Ni, and LOl variation diagrams for the Karmutsen Formation  45  Figure 2.7 Whole-rock REE and trace-element concentrations for the Karmutsen Formation  53  ix  Figure 2.8 Whole-rock trace-element concentrations and ratios for the Karmutsen Formation  55  Figure 2.9 Whole-rock Sr, Nd, and Hf isotopic compositions for the Karmutsen Formation  57  Figure 2.10 Pb isotopic compositions of leached whole-rock samples by MC-ICP-MS for the Karmutsen Formation  58  Figure 2.11 Relationship between abundance of olivine phenocrysts and whole-rock MgO contents for Keogh Lake picrites  64  Figure 2.12 Estimated primary magma compositions for three Keogh Lake picrites using the forward and inverse modeling technique of Herzberg et a!. (2007)  66  Figure 2.13 Comparison of age-corrected (230 Ma) Sr-Nd-Hf-Pb isotopic compositions for Karmutsen flood basalts on Vancouver Island to age-corrected OIB and MORB  69  Figure 2.14 Evolution of 8 Hf with time for picritic and tholeiitic lavas for Karmutsen Formation the  72  Figure 2.15 Trace-element modeling results for incongruent dynamic mantle melting for picritic and tholeiitic lavas from the Karmutsen Formation  74  Figure 2.16 Forward fractional crystallization modeling results for major elements from MELTS (Ghiorso & Sack, 1995) compared to picritic and tholeiitic lavas from the Karmutsen Formation  77  CHAPTER 3  Figure 3.1 Simplified map of south-central Alaska showing the distribution of the Nikolai Formation  90  Figure 3.2 Geologic map and stratigraphy of the Wrangell Mountains, Alaska  92  Figure 3.3 Photographs of the base of the Nikolai Formation in the Wrangell Mountains, Alaska  94  Figure 3.4 Photograph of —1000 m of continuous flood basalt stratigraphy at the top of the Nikolai Formation along Glacier Creek in the Wrangell Mountains, Alaska  95  Figure 3.5 Photographs showing the top of the Nikolai Formation in the Wrangell Mountains, Alaska  97  x  Figure 3.6 Simplified geologic map and stratigraphy of the Amphitheater Mountains, Alaska  98  Figure 3.7 Photographs of the base of the Nikolai Formation in the Amphitheater Mountains, east-central Alaska Range (Tangle Lakes, West), Alaska  99  Figure 3.8 Geologic map and stratigraphy of the Clearwater Mountains, Alaska  101  Figure 3.9 Representative photomicrographs of Nikolai basalts, Alaska  103  Figure 3.10 Whole-rock major-element and Ni variation diagrams vs. MgO for the Nikolai Formation in Alaska with data for the Nikolai Formation in Yukon  105  Figure 3.11 Whole-rock REE and trace-element concentrations for the Nikolai Formation in Alaska  113  Figure 3.12 Whole-rock trace-element concentration variations and ratios for the Nikolai Formation in Alaska, with data for the Nikolai Formation in Yukon  114  Figure 3.13 Whole-rock Sr, Nd, and Hf isotopic compositions for the Nikolai Formation in Alaska  116  Figure 3.14 Pb isotopic compositions of leached whole-rock samples by MC-ICP-MS for the Nikolai Formation in Alaska  117  Figure 3.15 Loss-on-ignition versus MgO and isotopic ratios for the Nikolai Formation in Alaska  122  Figure 3.16 Chemostratigraphy of the Nikolai Formation in three areas of Alaska (Clearwater, Amphitheater, and Wrangell Mountains)  124  Figure 3.17 Comparison of age-corrected (230 Ma) Sr-Nd-Hf isotopic compositions for Nikolai basalts in Alaska to age-corrected OIB and MORE  126  Figure 3.18 Comparison of Pb isotopic compositions of the Nikolai Formation in Alaska to OIB and MORE  127  Figure 3.19 Trace-element ratios and isotopic compositions of the Nikolai Formation in Alaska  130  Figure 3.20 Th-Nb and Ti-Yb proxies of the Nikolai Formation in Alaska with data compilation and modeling results  132  xi  Figure 3.21 Global Hf-Nd isotope systematics with age-corrected data of the Nikolai Formation in Alaska  136  Figure 3.22 Comparison of initial Hf, Nd, and Sr isotopic compositions of the Nikolai Formation in Alaska to Pacific arcs (Tonga Kermadec, Mariana, Vanuatu, New Britain) and Pacific MORB  137  Figure 3.23 Estimated primary magma compositions for two picrites from the Nikolai Formation using the forward and inverse modeling technique of Herzberg et al. (2007)  140  ChAPTER 4 Figure 4.1 Simplified map of southwest Yukon showing the distribution of the Nikolai Formation  154  Figure 4.2 Geologic map and stratigraphy of the northern part of the Kluane Ranges, Yukon  155  Figure 4.3 Photographs of the Nikolai Formation in the Kluane Ranges, Yukon  158  Figure 4.4 Photomicrographs of representative Nikolai basalts in southwest Yukon  159  Figure 4.5 Whole-rock major-element variation diagrams for the Nikolai Formation in Yukon with data for the Nikolai Formation in Alaska  162  Figure 4.6 Whole-rock REE and trace-element concentrations for the Nikolai Formation in Kluane Ranges, Yukon  170  Figure 4.7 Whole-rock trace-element concentrations for the Nikolai Formation in Yukon, with data for the Nikolai Formation in Alaska  172  Figure 4.8 Whole-rock Sr, Nd, and Hf isotopic compositions for the Nikolai Formation in Yukon, with fields for the Nikolai Formation in Alaska  173  Figure 4.9 Comparison of trace-element compositions of the Nikolai basalts in Yukon to averages for basalts from Alaska  178  Figure 4.10 Comparison of age-corrected (230 Ma) Sr-Nd-Hf isotopic compositions of the Nikolai Formation in Yukon and Alaska to age-corrected OIB and MORB  181  Figure 4.11 Th-Nb and Ti-Yb systematics for the Nikolai Formation in Yukon with data compilation and modeling results  183  xii  Figure 4.12 Trace-element ratios of high- and low-titanium basalts of the Nikolai Formation in Yukon with Paleozoic arc samples and fields for Nikolai basalts in Alaska  184  Figure 4.13 Schematic diagrams of two stages of melting of Nikolai basalts in Yukon and Alaska that produced the low- and high-titanium basalts in Yukon and Alaska  185  Figure 4.14 Trace-element abundances of low-titanium basalts from Yukon compared to arc mantle compositions of the Early to Middle Jurassic Talkeetna arc and incongruent dynamic melting modeling results  187  CHAPTER 5  Figure 5.1 Map showing the distribution of Phanerozoic large igneous provinces  197  Figure 5.2 Simplified map showing the distribution of Wrangellia flood basalts in Alaska, Yukon, and British Columbia  199  Figure 5.3 Simplified map of eastern south-central Alaska showing the distribution of Wrangellia flood basalts and stratigraphic columns  204  Figure 5.4 Geology and magnetic map of the Amphitheater Mountains  207  Figure 5.5 Photographs of base of Nikolai Formation in Tangle Lakes area of the Amphitheater Mountains  208  Figure 5.6 Photographs of the base of Nikolai Formation north of Skolai Creek in Wrangell-St. Elias National Park  210  Figure 5.7 Photographs of flood basalts in the Glacier Creek area in Wrangell-St. Elias National Park and map of the southern part of the Wrangell Mountains  211  Figure 5.8 Photographs of the top of the Nikolai Formation around Hidden Lake Creek in Wrangell-St. Elias National Park  212  Figure 5.9 Photographs and map of the Nikolai Formation in southwest Yukon  216  Figure 5.10 Simplified map of southeast Alaska showing the distribution of Triassic 219 basalts that may be correlative with Wrangellia flood basalts Figure 5.11 Simplified map of Vancouver Island showing the distribution of the Karmutsen Formation  223  xlii  Figure 5.12 Field notes, photographs, and geologic map for the Schoen Lake area, Vancouver Island  226  Figure 5.13 Generalized geology and photographs of Buttle Lake area, Vancouver Island  227  Figure 5.14 Generalized geology of the Karmutsen Formation on northern Vancouver Island in the Port Alice-Robson Bight area  229  Figure 5.15 Photographs of intra-Karmutsen sedimentary lens near the top of the Karmutsen southwest of Nimpkish Lake, northern Vancouver Island  231  Figure 5.16 Photographs from near Holberg Inlet, northern Vancouver Island  232  40 age spectra for 6 analyses of plagioclase separates Ar 39 Figure 5.17 ArI from Vancouver Island  237  40 age spectra of 1 biotite and 2 plagioclase separates Ar 39 Figure 5.18 Ar/ from Yukon  238  Figure 5.19 Ar/Ar age spectra for 6 analyses of plagioclase separates from Alaska  239  40 age spectra for 6 analyses of homblende separates Ar 39 Figure 5.20 Ar/ from Alaska  240  40 and UiPb ages of Wrangellia flood basalts and Figure 5.21 Ar/Ar plutomc rocks  244  Figure 5.22 Summary of geochronology and biostratigraphy for Wrangellia  247  xiv  ACKNOWLEDGEMENTS  This project has involved help from numerous people who I am extremely grateful to. James Scoates and Dominique Weis proposed and guided this study. I am grateful for the opportunity they gave me and for their enthusiastic guidance and support. I also have greatly appreciated help from Graham Nixon of the BC Geological Survey and Steve Israel of the Yukon Geological Survey. Advice was also offered from Jeanine Schmidt (USGS Anchorage), David Brew (USGS Menlo Park), Nick Massey (BCGS), Mikkel Schau, and Don Carlisle. Kelly and Natalie Bay of Wrangell Mountain Air in McCarthy, Alaska provided extensive knowledge of the Wrangell Mountains. Jeff Trop (Bucknell University) and Danny Rosenkrans (Wrangell-St. Elias National Park) offered assistance with backcountry advice about Wrangell-St. Elias National Park. Great thanks go to Bruno Kieffer, Frederico Henriques, and James Scoates for help with field work and making time in the field lots of fun. Katrin Breitsprecher was helpful with reviewing and discussions. Bruno Kieffer, Jane Barling, and Bert Mueller provided training for analytical work. I would also like to thank Mark Jellinek and Jim Mortensen for being a part of my thesis committee and posing thought-provoking questions that inspired me to explore different areas.  xv  DEDICATION  This dissertation is dedicated to my Mom and Dad, Sue and Art Greene. It is special to share this achievement with them.  xvi  CO-AUTHORSifiP STATEMENT  The four manuscripts in this dissertation are all co-authored by colleagues. My supervisors James Scoates and Dominique Weis are co-authors on each of the manuscripts and they significantly contributed to each manuscript. Their contributions included ideas, advice, comments, and reviewing, as well as financial support. The contributions from other co-authors on each manuscript are described below. CHAPTER 2 Wrangellia flood basalts on Vancouver Island: Significance of picritic and tholeiltic lavas for the melting history and magmatic evolution of a major oceanic plateau Authors: Andrew R. Greene, James S. Scoates, Dominique Weis, Graham T. Nixon, Bruno Kieffer Bruno Kieffer analyzed a suite of 24 samples from Vancouver Island for isotopic and trace-element compositions. Graham Nixon helped with field work and advice on field relationships and geochemistry. CHAPTER 3 Wrangeffia flood basalts in Alaska: A record of plume-lithosphere interaction in a Late Triassic accreted oceanic plateau Authors: Andrew R. Greene, James S. Scoates, and Dominique Weis  James Scoates and Dominique Weis contributed to many aspects of this manuscript. CHAPTER 4 Geochemistry of flood basalts from the Yukon (Canada) segment of the accreted Wrangeffia oceanic plateau Authors: Andrew R. Greene, James S. Scoates, Dominique Weis, Steve Israel Steve Israel assisted with field work, and contributed funding for field work and analytical data. Steve provided major- and trace-element whole-rock analyses of twentysix samples of Nikolai basalt and 8 Station Creek samples. CHAPTER 5 The age and volcanic stratigraphy of the accreted Wrangeffia oceanic plateau in Alaska, Yukon and British Columbia Authors: Andrew R. Greene, James S. Scoates, Dominique Weis, Erik C. Katvala, Steve Israel, and Graham T. Nixon Erik Katvala assisted with field work on Vancouver Island, provided fossil determinations, and helped with revisions on the manuscript. Ar/Ar age date and provided revisions on the Steve Israel contributed a single 40 manuscript. Graham Nixon offered advice and revisions on the manuscript.  xvii  I  uornporn  I HLJAVID  INTRODUCTION AND MOTIVATION FOR THIS STUDY  The largest melting events on Earth have led to the formation of transient large igneous provinces (LIPs). LIPs are features that can extend over millions of square kilometers of the Earth’s surface and consist of flood basalt sequences up to 6 km thick. These voluminous outpourings of lava occur over short intervals of geologic time (i.e. several million years) and have been linked to major changes in the global climate and biosphere in Earth history. This project is an extensive field and geochemical study of one of the major transient LIPs on Earth, the Triassic Wrangellia oceanic plateau. Transient and persistent LIPs cover large areas of the oceans and continents (Fig. 1.1). Approximately 13 major transient LIPs have formed in the last 260 Myr (Courtillot & Renne, 2003), including the Siberian (ca. 251 Ma) and Deccan traps (ca. 65 Ma); volcanism usually takes place in less than a few million years. Examples of persistent LIPs, or hotspots, are Ninetyeast Ridge and the Hawaiian-Emperor chain, where volcanism occurs over tens of millions of years. Large igneous province is an umbrella term that includes continental flood basalts (CFBs), volcanic rifled margins, oceanic plateaus, and aseismic ridges (Saunders, 2005). Common attributes of these provinces are that they form from an unusually high magmatic flux, they are mostly basaltic in composition, and they are not directly associated to seafloor spreading processes. The origin of most LIPs is best explained by mantle plumes. Mantle plumes are buoyant upwellings of hot mantle that may rise through the surrounding mantle as large spherical heads fed by narrower conduits (Griffiths & Campbell, 1990), or a variety of plume shapes, possibly without heads (Farnetani & Samuel, 2005). Transient LIPs are the initial eruptive products that form from melting of a new mantle plume head at the base of the lithosphere, and persistent LIPs form from melting within the narrower plume tail (Campbell, 2005) (Fig. 1.2). Continental flood basalts are closely associated with continental breakup. The formation of the Paraná-Etendeka (ca. 133 Ma) preceded the opening of the South Atlantic Ocean and formation of the North Atlantic Volcanic Province (ca. 62-60 Ma) preceded the opening of the North Atlantic Ocean. The Ethiopian traps (ca. 30 Ma) are an example of the eruption of flood basalts prior to rifling of Arabia and Africa. CFBs are at 2 and are emplaced as hundreds (or over a least 1 km thick and greater than 100,000 km  2  (30±1 Ma) Ethiopia  (65.5±0.5 Ma) (259±3 Ma)  Deccan  Emeishan  (Ca. 230 Ma)  (250±1 Ma)  wrangellia  Siberia  a  (16±1 Ma)  Columbia River  Ontong Java-H (122±1 Ma)  (123±1.5 Ma)  (201±1 Ma)  Caribbean (89±1 Ma)  • ,  (56±1 Ma; 61±2 Ma)  North Atlantic  Paraná-Etendeka (133±1 Ma)  Figure 1.1 Distribution of Phanerozic LIPs on Earth. Transient LIPs are indicated in yellow (continental) and orange (oceanic) with peak eruption ages. Persistent LIPs are mostly in red. Map modified from base map by A. Goodlife and F. Martinez in Mahoney and Coffin (1997). The peak eruption ages of each LIP are from the compiled references within Courtillot and Renne (2003) and Taylor (2006).  3  _._r .  lox vertical exaggeration  Figure 1.2 Schematic diagrams of mantle plumes in the Earth’s interior. (a) A view of the deep-mantle complexities beneath the central Pacific Ocean showing the Hawaiian hotspot, a D” high-velocity reflector, and heterogeneity at the base of the lower mantle where mantle plumes may originate. Mantle plume head is hypothetical. Drawing modified from Gamero (2004) with parts of a plume model by Farnetani and Samuel (2005). (b) A drawing of a model of plumelithosphere interaction beneath oceanic lithosphere that produces basalts erupted in an oceanic plateau. Dashed line marks the base of the mechanical boundary layer. Arrows indicate flattening of the plume head. Model developed primarily after work of Saunders et al. (1992). Parts of the diagrams were adapted from a drawing by J. Holden in Fodor (1987) and a plume model by Fametani and Samuel (2005).  4  thousand) of inflated compound pahoehoe flow fields that form a tabular flow stratigraphy (Self et a!., 1997). CFBs have been well-studied due to their accessibility as subaerial land-based features. Oceanic plateaus are not nearly as well-studied as CFBs because they are mostly submerged in the oceans. Several extant oceanic plateaus in the ocean basins have been broken up by seafloor spreading since their formation (Fig. 1.1). The Ontong Java, Manihiki and Hikurangi plateaus may have formed together at ca. 120 Ma and together cover 1 % Earth’s surface (Taylor, 2006). Ontong Java (2 x 106 k 2 in area; 30-35 km thick) formed from the largest magmatic event recorded on Earth and covers an area of the western Pacific Ocean comparable to the size of western Europe, or approximately one-third the size of the conterminous United States (Fitton eta!., 2004). The Kerguelen (2 x 106 km 2 in area; 20 km thick) and Broken Ridge Plateaus formed together, beginning ca. 118 Ma, and have since been separated by seafloor spreading along the Southeast Indian Ridge (Weis & Frey, 2002; Fig. 1.1). An important feature of the basalts erupted in some oceanic plateaus is that they are unaffected by continental lithosphere and are thus better suited for understanding the composition of the mantle source of LIPs than CFBs. The basalt stratigraphy of oceanic plateaus remains largely unsampled because of the difficulty in sampling more than the uppermost few hundred meters of flows from drilling ships (Fig. 1.3). For example, the Ontong Java Plateau, which rises to depths of 1700 m below sea level, has been the focus of several Deep Sea Drilling Project (DSDP; Site 289) and Ocean Drilling Program (ODP; Leg 192, Sites 803 and 807) legs to sample the basaltic basement of the plateau (Fig. 1.3; Mahoney et a!., 2001). These efforts have been described as “pin-pricking the elephant” (Tejada eta!., 2004); drilling of Ontong Java has only penetrated a maximum 338 m of approximately 6 km or more of the basalt stratigraphy (Mahoney et a!., 2001). Drilling of the Kerguelen Plateau has only penetrated a maximum 233 m of the basalt stratigraphy (Frey et a!., 2000). Ocean drilling of extant plateaus submerged in the ocean is an extremely difficult and expensive tool to study oceanic plateaus. The most efficient and comprehensive way to study oceanic plateaus is by observing and sampling exposures of oceanic plateaus where they have been accreted at  5  Distance (km)  Figure 1.3 “Pin-pricking” the giant Ontong Java Plateau. (a) Representation of drilled stratigraphic sections from 8 DSDP and ODP drilling sites (locations shown in panel b). Diagram adapted from Mahoney et al. (2001). The most volcanic rock sampled from drilling is 338 m of volcaniclastic rock at Site 1184 and 217 m of pillowed and massive basalt at Site 1185. (b) Predicted bathymetry (after Smith & Sandwell, 1997) of the Ontong Java Plateau and surrounding region showing the location of drill sites from ODP Leg 192 (stars) and previous drill sites (white and black circles). Map adapted from Mahoney et a!. (2001). The broken black line (labeled W-E) indicates a transect where multichannel seismic reflection (MCS) investigations acquired data for the plateau by RJV Hakuho Maru KH98-1 Leg 2 in 1998 (shown in panel c). (c) Composite east-west MCS transects of the Ontong Java Plateau with reflecting horizons (location shown in panel b). Figure modified from Inoue et a!. (2008). Sediments and the top of the igneous basement are indicated. Vertical red lines indicate depth of drilling at 3 labelled sites on the transect. Red circle indicates location of ‘eye structure’ (see Inoue et a!., 2008). Vertical exaggeration = 1 00:1. This figure serves to illustrate the difficulty of sampling and studying extant oceanic plateaus in the ocean basins. The black rectangle in panel c indicates the extent of stratigraphy that is exposed and accessible in obducted oceanic plateaus on land, such as the Wrangellia oceanic plateau.  6  continental margins or accreted onto island arcs, as in the case of the Ontong Java Plateau and the Solomon island arc. However, Phanerozoic examples of accreted oceanic plateaus are rare. Accreted sections of flood basalts around the Caribbean Sea and in Central and South America are several kilometers thick in areas (e.g. Kerr et a!., 1998; Révillon et al., 1999; Kerr, 2003). Several small sections of the Ontong Java Plateau are exposed on land in the Solomon Islands (Tejada et a!., 1996; Babbs, 1997; Petterson et a!., 1999; Tejada et a!., 2002). These are the two major oceanic plateaus where obducteci parts of the plateau have been studied. THE WRANGELLL4 OCEANIC PLATEAU  Wrangellia flood basalts in the Pacific Northwest of North America are part of one of the best exposed accreted oceanic plateaus on Earth and can provide information about oceanic plateaus that is rarely accessible elsewhere on Earth. Wrangellia flood basalts formed as part of a transient LIP in the Middle to Late Triassic, with accretion to westem North America occurring either in the Late Jurassic or Early Cretaceous. Although their original areal distribution was likely considerably larger, current exposures of the flood basalts extend over 2300 km in British Columbia (BC), Yukon, and Alaska (Fig. 1.4). Parts of the entire volcanic stratigraphy, from the base to the top, are accessible for close examination on land. From a geochemical perspective, the Wrangellia flood basalts have remained relatively poorly studied and have been the focus  of only one study in the last twenty years using modem analytical geochemistry (Lassiter eta!., 1995). In this study, the Wrangellia oceanic plateau has been intensively studied to establish the stratigraphical and geochemical architecture of an oceanic plateau and the nature of the episodic melting events that lead to the formation of oceanic plateaus. The Wrangellia flood basalts erupted mostly within the Late Ladinian and Camian stages of the Triassic (ca. 230 Ma; e.g. Carlisle & Suzuki, 1974; Parrish & McNicoll, 1992), as the continents were gathered into a great landmass referred to as Pangaea (Fig. 1.5). They erupted atop different-aged Paleozoic arc volcanic and marine sedimentary sequences and are overlain by Late Triassic limestone. Paleontological and paleomagnetic studies indicate that the Wrangellia flood basalts probably erupted in the eastem Panthalassic  7  Figure 1.4 Map showing distribution of Wrangellia flood basalts in Alaska, Yukon, and British Columbia. Map derived from Wilson et a!. (1998), Israel (2004), Massey et a?. (2005a, b), Wilson et a!. (2005), and Brew (2007, written comm.). Outlines for the Peninsular and Alexander Terranes are shown in orange and blue, respectively. As labeled, the Wrangellia Terrane is referred to as Northern and Southern Wrangellia in this study. Major faults in Alaska and parts of Yukon and BC are shown with purple lines. The Wrangellia, Alexander, Peninsular terranes, which are part of the Wrangellia Composite Terrane, share similar elements or have a linked geologic history [as defined by Plafker et aL (1989), Nokleberg et a?. (1994), Plafker and Berg (1994), and Plaficer et a?. (1994)]. Geochronology from a single pluton in Alaska is proposed to link the Proterozoic to Triassic Alexander Terrane to Wrangellia by late Pennsylvanian time (Gardner et a?., 1988). The Wrangellia and Peninsular Terranes may have been in close proximity by the Late Triassic or Early Jurassic (Rioux eta!., 2007).  8  Figure 1.5 Estimated distribution of the continental landmasses in the Middle to Late Triassic (226 Ma). Map modified from Ogg (2004), based on the reconstruction of Scotese (2004). Global Stratotype Sections and Points (GSSP) are indicated for stages of the Triassic. Blue arrow indicates estimated location of the Wrangellia oceanic plateau.  9  Ocean in equatorial latitudes (Jones et al., 1977; Katvala & Henderson, 2002). The eruption of Wrangellia flood basalts broadly coincides with major biotic and environmental changes worldwide that occurred at the end of Carnian time (Furin et al., 2006). A global-scale environmental crisis, referred to as the Reingrabener turnover, occurred in the Carnian (e.g. Furin et a!., 2006) This event is preserved by the collapse of rimmed carbonate platforms, a global shift in sedimentological and geochemical proxies, and a strong radiation of several groups, including scleractinian reef builders, calcareous nannoplankton, and dinosaurs (Furin et al., 2006 and references therein). The accretion of the Wrangellia oceanic plateau to western North America was a major tectonic event and represents a significant addition of oceanic mantle-derived material to the North American crust (Condie, 2001). The volcanic stratigraphy of the Wrangellia plateau is defined as the Karmutsen Formation on Vancouver and Queen Charlotte Islands (Haida Gwaii), and as the Nikolai Formation in southwest Yukon and south-central Alaska (Fig. 1.4). On Vancouver Island, the volcanic stratigraphy is a tripartite succession of submarine, volcaniclastic, and subaerial flows approximately 6 km thick. In Alaska and Yukon, the volcanic stratigraphy is predominantly massive subaerial flows with a small proportion of submarine flows along the base. Smaller elements in southeast Alaska may be correlative with the Wrangellia flood basalts. Rapid eruption of the Wrangellia flood basalts is supported by the absence of intervening sediments between the flows, except in the uppermost part of the stratigraphy as volcanism waned. Paleomagnetic measurements of the Wrangellia flood basalts have not revealed any magnetic reversals, which also testifies to the short duration of eruptions (Hillhouse, 1977; Yole & Irving, 1980; Hilihouse & Coe, 1994). METHODOLOGY AND RATIONALE FOR THIS STUDY  This study represents the first comprehensive study of the Wrangellia oceanic plateau. The integration of geochemical, volcanological, stratigraphic, and geochronological results provide constraints on the formation of the Wrangellia oceanic plateau. The volcanological and stratigraphic studies yield insights about the emplacement of flows, eruptive environment, original tectonic setting, and construction  10  of the plateau. The geochronological and paleontological studies allow for estimation of the age and duration of volcanism. The petrologic and geochemical studies provide information about the composition of the source, conditions of melting, and the magmatic evolution of lavas that formed the Wrangellia plateau. The interpretation of these different results will help to develop our understanding of the physical and chemical processes that occur in mantle plumes, as they decompress and impinge on the base of oceanic lithosphere and produce the basaltic magmas which erupt though oceanic lithosphere and form oceanic plateaus. The contributions in the four major chapters in this dissertation (described below) address some of the enduring questions about the origin of oceanic plateaus. PREVIOUS RESEARCH  In the 1 970s, Jones and co-workers (1977) defined the fault-bound blocks of crust that contain diagnostic Triassic flood basalts in BC, Yukon, and Alaska as Wrangellia, named after the type section in the Wrangell Mountains of Alaska. Early paleomagnetic and paleontological studies of Wrangellia indicated long-distance displacement of the basalts from equatorial latitudes (Hillhouse, 1977) and similar Daonella bivalves were found in sediments directly beneath the flood basalts on Vancouver Island and in the Wrangell Mountains (Jones et aL, 1977). A back-arc setting was initially proposed for the formation of Karmutsen basalts on Vancouver and Queen Charlotte Islands based on major- and trace-element geochemistry of 12 samples (Barker et al., 1989). Richards and co-workers (1991) proposed a plume initiation model for the Wrangellia flood basalts based on evidence of rapid uplift prior to volcanism, lack of evidence of rifting associated with volcanism (few dikes and abundant sills), and the short duration and high eruption rate of volcanism. A geochemical study of 36 samples of Wrangellia flood basalts, 29 samples from Buttle Lake on Vancouver Island and 9 samples from the Wrangell Mountains in Alaska, was undertaken by Lassiter and co-workers (1995) as part of the only modem geochemical and isotopic study of Wrangellia flood basalts until the initiation of this project. Lassiter and co-workers (1995) suggested mixing of a plume type source with low Nb/Th arc-type mantle could reproduce variations in the Wrangellia flood basalts.  11  TUE IMPORTANCE OF LIPS AND MANTLE PLUMES  Since the recognition of oceanic plateaus in the early 1 970s (Edgar et al., 1971; Donnelly, 1973; Kroenke, 1974), there have been significant advances in our understanding of oceanic plateaus. A wide range of scientific approaches have been used to study oceanic plateaus; however, we only partially understand the physical and chemical processes that lead to the formation of oceanic plateaus. Oceanic plateaus have formed for at least the last several hundred million years and likely well back into Earth history. Archean and Proterozoic greenstone belts have been interpreted to be remnants of oceanic plateaus (e.g. Kerr, 2003) and komatiites (>18 wt % MgO, with spinifex-textured olivines) may be the high-temperature melting products of ancient mantle plumes (e.g. Arndt & Nesbet, 1982) and some Phanerozoic plume heads (e.g. Storey et aL, 1991). Phanerozoic oceanic plateaus may form from mantle plumes that originate at the core-mantle boundary (Campbell, 2005). The large temperature and density contrasts that exist between the outer core and mantle are expected to produce an unstable boundary layer above the core that episodically leads to the formation of mantle plumes (Jellinek & Manga, 2004). Oceanic plateaus are thus the surface manifestations of a major mode of heat loss from the interior of the Earth. The geochemical study of flood basalts is one important way by which we gain information about mantle plumes rising from their origin to the eruption of their melting products at the Earth’s surface. Although mantle plumes are considered the strongest hypothesis for the origin of LIPs, there are a number of alternative interpretations: meteorite impacts (Rogers, 1982), enhanced convection at the edge of continental cratons (King & Anderson, 1998), delamination of lithosphere causing rapid mantle upwelling (Elkins-Tanton, 2005), and melting of fertile eclogitic mantle (Korenaga, 2005). One example of evidence that mantle plumes are responsible for the formation of most LIPs is the high melt production rates that form LIPs, which make them difficult to explain by an origin related to plate tectonic processes (Jellinek & Manga, 2004). Perhaps the best evidence for the high source temperatures required to explain the melting that produces LIPs is the presence of O+ 2 picrites (e.g. Saunders, 2005), with MgO between 12 and 18 wt % and 1-2 wt % Na 0 (Le Bas, 2000). In this study, high-Mg picritic lavas have been discovered for the 2 K  12  first time within the Wrangellia oceanic plateau on northern Vancouver Island and in Alaska and modeling of their compositions indicate high source temperatures and high degrees of melting. The eruption of basalts in LIPs has the potential to significantly affect the composition of the atmosphere and oceans by releasing large amounts of gas (primarily ) and aerosols that may trigger heating via runaway greenhouse effect or 2 2 and SO CO cooling via the spread of stratospheric sulphate aerosols that backscatter and absorbe the sun’s radiation (e.g. Rampino & Stothers, 1988; Wignall, 2001). Although CO 2 emissions in LIPs are small compared to the amount of CO 2 present in the atmosphere and the landocean-atmosphere flux of C0 , the gradual buildup of CO 2 2 from LIP eruptions may tip the balance enough to initiate release of other greenhouse gases, such as methane hydrates on the seafloor (Saunders, 2005). The release of SO 2 in LIP eruptions is incomparable to inputs at any other time during the Phanerozoic (Self et a!., 2006). The eruption of a single <2400 km 3 flow field is estimated to release as much as 6,500 Tg a 1 for a 10-year duration, which is enormous compared to the background amount of S in the atmosphere (<1 Tg) (Self et a!., 2006). In the oceans, a series of variables that are consequences of large releases of CO 2 lead to warmer polar waters, decreased solubility of CO 2 and 02, and increased biogenic productivity in surface waters (e.g. Kerr, 2005). These effects can potentially lead to a shutdown of the ocean circulation system and anoxic conditions. It is likely that the eruption of Wrangellia flood basalts would have significantly affected the chemical composition of the ocean and atmosphere. The close correlation between major mass extinctions in Earth history and the formation of most transient LIPs suggests a causal link between LIP eruptions and environmental change (Rampino & Stothers, 1988; Fig. 1.6). The three most recent large diversity depletion events in the Phanerozoic (Permian-Triassic, Triassic-Jurassic, Cretaceous-Tertiary) coincide with the timing of peak volcanic activity in the formation of a continental flood basalt province (Siberia, Central Atlantic Magmatic Province (CAMP), and Deccan, respectively) (Courtillot & Renne, 2003). The eruption of the Siberian traps may have played a key role in the End Permian extinction event because of the high proportion of pyroclastic eruptions and intrusion of magmas into carbon- and methane-bearing strata (Wignall, 2001). Recent studies of the CAMP and the Deccan  13  Age Difference (Myr) 0  .  .  10 .  •  10  .  I  Large igneous province 0i2 event  Ethiopian Traps (30 Ma)  50  stratigraphic boundary  End Palaeocene End Early Palaeocene End Cretaceous  North Atlantic Province (56 Ma) .  Deccan Traps (65.5 Ma) Madagascar (88 Ma) Caribbean (89 Ma)  End Cen omanian  100  LIP Age (Ma) 150  Early Aptian Ontong Java (122 Ma EarlyAptian Kerguelen/Rajmahal (118 MaFd_1d Paraná-Etendeka (133 Ma)————— End Valanginian  Karoo-Ferrar (183 Ma)—  200  300  End Pliensbachian  Central Atlantic Magmatic Province (201 Ma) —•— End Triassic Wrangellia (230 Ma)  250  i—  ? —1 i—? End Camian  Siberian Traps (250 Ma) Emeishan Traps (259 Ma)—  End Permian End Guadalupian  —  LIP pre-dates boundary  LIP post-dates boundary  stratigraphic boundary Figure 1.6 Age difference between peak eruption ages of LIPs from the last 260 Myr versus the age of a stratigraphic boundary associated with major sudden environmental changes. Diagram modified from Kelley (2007). Ages are mostly from the compilation of Courtillot and Renne (2003). The possible connection between Wrangellia and a climatic and biotic crisis recognized in the Carnian is hypothetical and needs to be explored further (Furin eta!., 2006).  14  Traps support a close temporal relationship between the End Triassic and End Cretaceous extinctions, respectively. A recent study by Courtillot and Olsen (2007) suggests there may be a connection between magnetic superchrons, where the Earth’s magnetic field does not reverse polarity for abnormally long periods of time (30-50 Myr), and the timing of mantle plumes. The -‘50 Myr long Kaiman Long Reverse Superchron (310 to 260 Ma) ended 10 Myr before eruption of the Siberian Traps and the 35 Myr long Cretaceous Long Normal Superchron (118 to 83 Ma) ended -l 8 Myr before eruption of the Deccan Traps (Courtillot & Olsen, 2007). Courtillot and Olsen (2007) suggest a mechanism whereby a major change in heat flow at the core-mantle boundary may lead to the end of a superchron and cause initiation of “killer” mantle plumes. Along with aerially-extensive flood basalt sequences, radiating dike swarms are impressive aspects of transient LIPs which extend >2800 km and are a major mode of lateral transport of LIP magmas in the crust. Radiating dike swarms are diagnostic of major magmatic events linked to mantle plumes and associated continental break-up and serve as indicators of plume centers and magma transport (Ernst et al., 2001). Dike swarms have been identified in every Mesozoic and Cenozoic CFB on Earth and are expected to form in oceanic plateaus (Ernst & Buchan, 2003). Where the flood basalts are largely eroded, such as the CAMP, dike swarms can be used to reconstruct plate motions and identify plume events through Earth’s history (Ernst & Buchan, 1997). There are many important and fascinating aspects of LIPs. The study of LIPs holds great relevance in a variety of large-scale Earth processes and this study provides constraints which help to further our understanding of these geological phenomena. AN OVERVIEW OF THE FOUR CHAPTERS IN THIS DISSERTATION AND ADDITIONAL REFERENCES  The chapters in this dissertation were written in manuscript form for submission to major international geological journals. Three of the first four manuscripts are detailed studies of the Wrangellia flood basalts from different regions of western North America (Vancouver Island, Alaska, and Yukon). These three manuscripts parallel one another in that similar analytical techniques are used, but each study has distinct results and  15  interpretations. Each study involved extensive field work using different modes of transportation in remote areas of western North America (Fig. 1.7). Additional contributions from this project that are not included in the dissertation are four government geological survey papers (Greene et a!., 2005b, 2005c, 20060; Nixon eta!., 2008b) and eight abstracts to international geological conferences (Greene et a!., 2005 a, 2006a, 2006b, 2007a, 2007b, 2007c, 2008a, 2008b). Contributions to other conference proceedings include studies of platinum-group elements (Scoates et a!., 2006, 2007, 2008) and stratigraphic successions of Wrangellia flood basalts (Nixon et a!., 2008a). The first manuscript in this dissertation is a comprehensive study of the Karmutsen Formation on Vancouver Island, which has major implications for the evolution of this large oceanic plateau. Karmutsen basalts on Vancouver Island comprise one of the thickest and most complete examples of the volcanic stratigraphy of an emergent oceanic plateau on Earth. My co-authors and I examine the field relationships, stratigraphy, petrography, and geochemical and isotopic compositions of the Karmutsen Formation to assess the nature of the mantle source and to evaluate the melting history and subsequent magmatic evolution of basalts involved in the construction of this major oceanic plateau. The second manuscript is a study of the Nikolai Formation in Alaska. This study integrates field relationships in widespread areas of Alaska and geochemistry of continuous sections of volcanic stratigraphy to understand the physical and chemical processes that occur as a mantle plume head impinges on the base of oceanic arc lithosphere. This information provides insights into the temporal and spatial variation of the magmas in a major oceanic plateau that result from plume-lithosphere interaction. The third manuscript is a field, petrographic, and geochemical study of Nikolai basalts in Yukon, where volcanic stratigraphy and bounding sedimentary sequences are similar to Alaska. Nikolai basalts in Yukon are more altered than their counterparts in Alaska and a comparative geochemical study of Nikolai basalts from Yukon and Alaska allows for analysis of the effects of alteration and regional differences in basalts erupted in the northern part of Wrangellia. This study also examines the geochemistry of the underlying Paleozoic arc sequences and their role in the generation of the Nikolai basalts.  16  Figure 1.7 Photographs showing the different modes of transportation used for field work in remote areas of Alaska, Yukon, and BC as part of this project. (a) Canoe access to the Amphitheater Mountains in the Alaska Range, Alaska. (b) Helicopter access in the Kluane Ranges, southwest Yukon. (c) Transportation by Super Cub in Wrangell-St. Elias National Park, Alaska. (d) Four-wheel drive vehicle access on logging roads on northern Vancouver Island. Photograph by Graham Nixon.  17  The fourth manuscript is a stratigraphic and geochronological study of Wrangellia flood basalts from throughout BC, Yukon, and Alaska. This synthesis integrates observations from field work and dozens of government geological survey reports and maps to provide detailed descriptions of the volcanic stratigraphy and the pre- and postvolcanic rock stratigraphy of Wrangellia. This overview is presented in the form of stratigraphic columns and descriptions, compiled geologic maps, photographic databases, interactive Google Earth files, and a review and compilation of previous research on Wrangellia. The maps, photographs, and archiving of information are presented differently than in the previous chapters and offer users interactive electronic tools to visualize and explore information about the Wrangellia oceanic plateau. This work, in combination with 40 Ar geochronology of flood basalts throughout Wrangellia, 39 Ar/ provides an over-arching contribution that brings together past and present research on Wrangellia in a new light. CONTRIBUTIONS TO THIS PROJECT  This project benefited from the assistance of many people. Assistance with field work in Alaska, Yukon, and BC was provided by Bruno Kieffer, Frederico Henriques, and James Scoates. Advice for field work was provided by Graham Nixon (British Columbia Geological Survey), Nick Massey (British Columbia Geological Survey), Don Carlisle, Steve Israel (Yukon Geological Survey), Jeanine Schmidt (United States Geological Survey-Anchorage), David Brew (United States Geological Survey-Menlo Park), Danny Rosenkrans (Wrangell-St. Elias National Park), and Jeff Trop (Bucknell University). Isotopic and trace-element analyses for a suite of 24 samples on Vancouver Island were made by Bruno Kieffer and Jane Barling. Bruno Kieffer, Jane Barling, and Bert Mueller also provided training for analytical work for Yukon and Alaska samples at the Pacific Centre for Isotopic and Geochemical Research (PCIGR). The analyses for Ar geochronology were carried out by Tom Ulfrich from samples that were 39 Ar/ 40  crushed, separated, picked, and leached by me. This project was made possible from funding provided by the BC & Yukon Chamber of Mines (Association of Mineral Exploration BC) from the 2004 Rocks to Riches Program, the BC Geological Survey, the Yukon Geological Survey, and by  18  NSERC Discovery Grants to James Scoates and Dominique Weis. The author was also supported by a University Graduate Fellowship at UBC. Major- and trace-element analyses for this project were performed by Activation Laboratories (ActLabs) in Ontario, Canada and at the Ronald B. Gilmore X-Ray Fluorescence Laboratory (XRF) at the University of Massachussetts. Claude Herzberg (Rutgers University), Julian Pearce (Cardiff University), and Haibo Zou (University of California Los Angeles) offered assistance with geochemical modeling. My supervisors, James Scoates and Dominique Weis, offered invaluable assistance and guidance with all aspects of this project. REFERENCES Arndt, N. T. & Nisbet, E. G. (1982). Geochemistry of Munro township basalt. In: Arndt, N. T. & Nisbet, E. G. (eds.) Komatiites. Allen and Unwin: Winchester, MA, pp. 19-27. T. Babbs, L. (1997). Geochemical and petrological investigations of the deeper portions of the Ontong Java Plateau: Malaita, Solomon Islands. Unpublished Ph.D. dissertation, Leicester University, U.K., 254 pp. Barker, F., Brown, A. S., Budahn, J. R. & Plafker, G. (1989). Back-arc with frontal-arc component origin of Triassic Karmutsen basalt, British Columbia, Canada. Chemical Geology 75, 8 1-102. Brew, D. A. C. (2007, written comm.). Unpublished map showing the distribution of the Late Triassic Wrangellia, Hyci Group, and Perserverance group rocks in southeastern Alaska, scale 1:600,000 (Based on Brew, D. A. (Compiler), Unpublished bedrock geologic map of southeastern Alaska.) Campbell, I. H. (2005). Large igneous provinces and the mantle plume hypothesis. Elements 1, 265-269. Carlisle, D. & Suzuki, T. (1974). Emergent basalt and submergent carbonate-clastic sequences including the Upper Triassic Dilleri and Welleri zones on Vancouver Island. Canadian Journal ofEarth Sciences 11, 254-279. Condie, K. C. (2001). Mantle Plumes and Their Record in Earth History. Cambridge University Press: Cambridge, 306 p. Courtillot, V. & Olsen, P. E. (2007). Mantle plumes link magnetic superchrons to Phanerozoic mass depletion events. Earth and Planetary Science Letters 260, 495-504. Courtillot, V. E. & Renne, P. R. (2003). On the ages of flood basalt events. Comptes Rendus Geoscience 335, 113-140. Donnelly, T. W. (1973). Late Cretaceous basalts from the Caribbean: a possible flood basalt province of vast size. EOS 54, 1004. Edgar, N. T., Ewing, J. I. & Hennion, J. (1971). Seismic refraction and reflection in the Caribbean Sea. American Association ofPetroleum Geologists Bulletin 55, 833870.  19  Elkins-Tanton, L. (2005). Continental magmatism caused by lithospheric delamination. In: Foulger, G. R., Natland, J. H., Presnall, D. C. & Anderson, D. L. (ecis.) Plates, Plumes and Paradigms. Geological Society of America Special Paper 388, pp. 449-462. Ernst, R. E. & Buchan, K. L. (1997). Giant radiating dyke swarms: Their use in identifring pre-Mesozoic large igneous provinces and mantle plumes. In: Mahoney, J. 3. & Coffin, M. F. (eds.) Large Igneous Provinces: Continental, Oceanic, and Planetary Flood Volcanism. American Geophysical Union Geophysical Monograph 100, pp. 297-333. Ernst, R. E. & Buchan, K. L. (2003). Recognizing mantle plumes in the geologic record. Annual Review ofEarth and Planetay Sciences 31, 469-523. Ernst, R. E., Grosfils, E. B. & Mège, D. (2001). Giant dike swarms: Earth, Venus and Mars. Annual Review ofEarth and Planetary Science 29,489- 534. Farnetani, C. G. & Samuel, H. (2005). Beyond the thermal plume paradigm. Geophysical Research Letters 32(L073 11), doi: 10.1 029/2005GL022360. Fitton, J. G., Mahoney, J. J., Wallace, P. J. & Saunders, A. D. (eds.) (2004). Origin and Evolution of the Ontong Java Plateau. Geological Society of London Special Publication 229. Y74pp. Fodor, R. V. (1987). Low- and high-Ti0 2 flood basalts of southern Brazil: origin from picritic parentage and a common mantle source. Earth and Planetary Science Letters 84, 423-43 0. Frey, F. A., et al. (2000). Origin and evolution of a submarine large igneous province: the Kerguelen Plateau and Broken Ridge, southern Indian Ocean. Earth and Planetary Science Letters 176, 73-89. Furin, S., Preto, N., Rigo, M., Roghi, G., Gianolla, P., Crowley, J. L. & Bowring, S. A. (2006). High-precision U-Pb zircon age from the Triassic of Italy: Implications for the Triassic time scale and the Camian origin of calcareous nannoplankton and dinosaurs. Geology 34(12), 1009-1012, 10.11 30/g22967a. 1. Gardner, M. C., Bergman, S. C., Cushing, G. W., MacKevett, E. M., Jr. Plafker, G., Campbell, R. B., Dodds, C. J., McClelland, W. C. & Mueller, P. A. (1988). Pennsylvanian pluton stitching of Wrangellia and the Alexander terrane, Wrangell Mountains, Alaska. Geology 16, 967-971. Garnero, E. 3. (2004). A new paradigm for Earth’s core-mantle boundary. Science 304, 834-836. Greene, A., Scoates, J. S., Weis, D. & Kieffer, B. (2006a). Wrangellia Flood Basalts: Exploring the architecture and composition of an accreted oceanic plateau. Geological Society ofAmerica Cordilleran Section Anchorage, Alaska. 38: 5, p. 25. Greene, A. R., Scoates, J. S., Weis, D. & Kieffer, B. (2006b). Wrangellia Flood Basalts: Exploring the architecture and composition of an accreted oceanic plateau. Geological Association of Canada 2006 Annual Meeting, Montreal, Quebec. Greene, A. R., Scoates, J. S., Nixon, G. T. & Weis, D. (2006c). Picritic lavas and basal sills in the Karmutsen flood basalt province, Wrangellia, northern Vancouver Island. In: Grant, B. (ed.) Geological Fieldwork 2005. British Columbia Ministry of Energy, Mines and Petroleum Resources Paper 2006-1, pp. 39-52. ,  20  Greene, A. R., Scoates, J. S. & Weis, D. (2005a). Wrangellia Terrane in B.C. and Yukon: Where are its Ni-Cu-PGE deposits? Cordilleran Mineral Roundup Expo, Vancouver, BC. Greene, A. R., Scoates, J. S. & Weis, D. (2005b). Wrangellia Terrane on Vancouver Island: Distribution of flood basalts with implications for potential Ni-Cu-PGE mineralization. In: Grant, B. (ed.) Geological Fieldwork 2004. British Columbia Ministry of Energy, Mines and Petroleum Resources Paper 2005-1, pp. 209-220. Greene, A. R., Scoates, J. S. & Weis, D. (2008a). Wrangellia flood basalts in Alaska: A record of plume-lithosphere interaction in a Late Triassic accreted oceanic plateau. Goldschmidt 2008 Conference, Vancouver, BC. Greene, A. R., Scoates, J. S., Weis, D. & Israel, S. (2005c). Flood basalts of the Wrangellia Terrane, southwest Yukon: Implications for the formation of oceanic plateaus, continental crust and Ni-Cu-PGE mineralization. In: Emond, D. S., Lewis, L. L. & Bradshaw, G. D. (eds.) Yukon Exploration and Geology 2004. Yukon Geological Survey, pp. 109-120. Greene, A. R., Scoates, J. S., Weis, D., Israel, S., Nixon, G. T. & Kieffer, B. (2007a). Geochemistry and geochronology of the Wrangellia Flood Basalts in British Columbia, Yukon, and Alaska. Cordilleran Mineral Roundup Expo, Vancouver, BC. Greene, A. R., Scoates, J. S., Weis, D. & Nixon, G. T. (200Th). Significance of picritic and tholeiitic lavas within Wrangellia Flood Basalts on Vancouver Island for the melting history and magmatic evolution of a major oceanic plateau. AGU 2007 Fall Meeting San Francisco, CA. Abstract V33A-1 153 Greene, A. R., Scoates, J. S., Weis, D. & Nixon, G. T. (2008b). Picritic and tholeiitic lavas within Wrangellia Flood Basalts on Vancouver Island for the melting history and magmatic evolution of a major oceanic plateau. Cordilleran Tectonics Workshop, Vancouver, BC. Greene, A. R., Weis, D. & Scoates, J. S. (2007c). Wrangellia Flood Basalts: Exploring the architecture and composition of an accreted oceanic plateau. Geological Association of Canada, NUNA 2007 Conference: The Pulse ofthe Earth and Planetary Evolution, Sudbury, Ontario. Griffiths, R. W. & Campbell, I. H. (1990). Stirring and structure in mantle starting plumes. Earth and Planetary Science Letters 99, 66-78. Hilihouse, J. W. (1977). 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Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach terranes along the Trans Alaskan Crustal Transect in the northern Chugach Mountains and southern Copper River basin, Alaska. Journal of Geophysical Research 94, 4,255-4,295. Rampino, M. R. & Stothers, R. B. (1988). Flood basalt volcanism during the past 250 million years. Science 241, 663-668. Révillon, S., Arndt, N. T., Hallot, E., Kerr, A. C. & Tarney, J. (1999). Petrogenesis of picrites from the Caribbean Plateau and the North Atlantic magmatic province. Lithos49, 1-21. Richards, M. A., Jones, D. L., Duncan, R. A. & DePaolo, D. 3. (1991). A mantle plume initiation model for the Wrangellia flood basalt and other oceanic plateaus. Science 254, 263-267. Rioux, M., Hacker, B., Mattinson, J., Kelemen, P., Blusztajn, 3. & Gehrels, G. (2007). Magmatic development of an intra-oceanic arc: High-precision U-Pb zircon and whole-rock isotopic analyses from the accreted Talkeetna arc, south-central Alaska. 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S., Greene, A. R., Weis, D., Israel, S. & Nixon, G. T. (2007). PGE geochemistry and suiphide saturation state of the Triassic Wrangellia basalts, Vancouver Island and Yukon. Cordilleran Mineral Roundup Expo, Vancouver, BC Scotese, C. R. (2004). PALEOMAP project. http://www.scotese.com/research.htm. Self, S., T., T. & L., K. (1997). Emplacement of continental flood basalt lava flows. In: Mahoney, J. J. & Coffm, M. F. (eds.) Large Igneous Provinces: Continental, Oceanic, and Planetaiy Flood Volcanism. American Geophysical Union: Washington. Geophysical Monograph 100, pp. 38 1-410. Self, S., Widdowson, M., Thordarson, T. & Jay, A. E. (2006). Volatile fluxes during flood basalt eruptions and potential effects on the global environment: A Deccan perspective. Earth and Planetary Science Letters 248, 518-532. Smith, W. H. F. & Sandwell, D. T. (1997). Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings. Science 277, 1956-1962. Storey, M., Mahoney, J. J., Kroenke, L. W. & Saunders, A. D. (1991). Are oceanic plateaus sites of komatiite fonnation? Geology 19, 376-379. Taylor, B. (2006). The single largest oceanic plateau: Ontong Java-Manihilci-Hikurangi. Earth and Planetary Science Letters 241(3-4), 372-380. Tejada, M. L. G., Mahoney, 3. 3., Castillo, P. R., Ingle, S. P., Sheth, H. C. & Weis, D. (2004). Pin-pricking the elephant: evidence on the origin of the Ontong Java Plateau from Pb-Sr-Hf-Nd isotopic characteristics of ODP Leg 192 basalts. In: Fitton, J. G., Mahoney, 3. J., Wallace, P. 3. & Saunders, A. D. (eds.) Origin and Evolution of the Ontong Java Plateau. Geological Society of London, Special Publication 229, pp. 133-150. Tejada, M. L. G., Mahoney, 3. 3., Duncan, R. A. & Hawkins, M. P. (1996). Age and geochemistry of basement and alkalic rocks of Malaita and Santa Isabel, Solomon Islands, Southern Margin of Ontong Java Plateau. Journal ofPetrology 37(2), 361-394. Tejada, M. L. G., Mahoney, J. J., Neal, C. R., Duncan, R. A. & Petterson, M. G. (2002). Basement geochemistry and geochronology of Central Malaita, Solomon Islands, with implications for the origin and evolution of the Ontong Java Plateau. Journal ofPefrology 43(3), 449-484.  24  Weis, D. & Frey, F. A. (2002). Submarine basalts of the northern Kerguelen plateau: interaction between the Kerguelen plume and the southeast Indian Ridge revealed at ODP Site 1140. Journal ofPetrology 43(7), 1287-1309. Wignall, P. B. (2001). Large igneous provinces and mass extinctions. Earth-Science Reviews 53, 1-33. Wilson, F. H., Dover, J. D., Bradley, D. C., Weber, F. R., Bundtzen, T. K. & Haeussler, P. J. (1998). Geologic map of Central (Interior) Alaska. U S. Geological Survey Open-File Report 98-133-A. http://wrgis.wr.usgs.gov/open-file/of98- 1 33-al. Wilson, F. H., Labay, K. A., Shew, N. B., Preller, C. C., Mohadjer, S. & Richter, D. H. (2005). Digital Data for the Geology of Wrangell-Saint Elias National Park and Preserve, Alaska U S. Geological Survey Open-File Report 2005-1342, http://pubs.usgs.gov/of’2005/1 342/. Yole, R. W. & Irving, E. (1980). Displacement of Vancouver Island, paleomagnetic evidence from the Karmutsen Formation. Canadian Journal ofEarth Sciences 17, 1210-1228.  25  CHAPTER 2  Wrangellia Flood Basalts on Vancouver Island: Significance of Picritic and Tholeiitic Lavas for the Melting History and Magmatic Evolution of a Major Oceanic Plateau  ‘A version of this chapter has been submitted for publication.  26  INTRODUCTION  The largest magmatic events on Earth have led to the formation of oceanic plateaus. Oceanic plateaus are transient large igneous provinces (LIPs) that cover up to two million square kilometers of the ocean floor and form crustal emplacements 20-40  km thick with submarine or subaerial flood basalt sequences six or more kilometers thick (Coffin & Eldholm, 1994). LIPs typically form in one or more pulses lasting less than a few million years. Three key aspects of LIPs are that they form from unusually high melt production rates, they are predominantly basaltic in composition, and their formation is often not directly attributable to seafloor spreading processes (e.g. Saunders, 2005). The high melt production rates are best explained by high mantle source temperatures of rapidly upwelling mantle (i.e. mantle plumes) and direct evidence of high mantle temperatures is eruption of high-MgO, near-primary lavas (Kerr & Mahoney, 2007). Studies of oceanic plateaus may provide important information about their construction and growth history, the temperature and depth of melting of the mantle source, the volume of magma and melt production rates, and the composition of the mantle source. Combined, this information serves to constrain aspects of the mantle plume hypothesis from the origin of components in the source to emplacement of voluminous lava sequences. From a geochemical perspective, study of oceanic plateaus is important because the lavas erupted in oceanic plateaus are generally unaffected by continental contamination. Presently, one of the great challenges in studying oceanic plateaus in the ocean basins is the difficulty in sampling more than the uppermost few hundred meters of flows (e.g. Kerguelen, Ontong Java, etc.). Accreted sections of oceanic plateaus (e.g. Caribbean, Ontong Java) provide an opportunity to closely examine their volcanic stratigraphy. Wrangellia flood basalts in the Pacific Northwest of North America are parts of an immense LIP that erupted in a marine setting and accreted to western North America in the Late Jurassic or Early Cretaceous (Richards et al., 1991). Although their original areal distribution was likely considerably larger, current exposures of the flood basalts extend in a thin belt over 2300 km in British Columbia (BC), Yukon, and Alaska and retain a large part of their original stratigraphic thickness (—‘6 km on Vancouver Island; —‘3.5 km in Alaska). The present extent of the Wrangellia oceanic plateau  27  remnants is primarily a result of transform fault motions that occurred along western North America after accretion, rather than an indication of the original size of the plateau. The flood basalts erupted in the Middle to Late Triassic (—23 1-225 Ma; Richards et a!., 1991) atop different-aged Paleozoic arc volcanic and marine sedimentary sequences and are overlain by Late Triassic limestone. On Vancouver Island, a tripartite succession of flood basalts includes submarine, volcaniclastic, and subaerial flows formed as part of an enormous emergent oceanic plateau. Richards et a!. (1991) proposed a plume initiation model for the Wrangellia flood basalts based on evidence of rapid uplift prior to volcanism, lack of evidence of rifting associated with volcanism (i.e. few dikes and abundant sills), and the short duration and high eruption rate of volcanism. Wrangellia flood basalts are perhaps the most extensive aecreted remnants of an oceanic plateau in the world where parts of the entire volcanic stratigraphy are exposed, but they have been the focus of only one study in the last 20 years using multiple types of isotopic and geochemical data (Lassiter et al., 1995). In this study, we examine the field relationships, stratigraphy, petrography, major and trace elements, and Sr-Nd-Hf-Pb isotopic compositions of Wrangellia flood basalts from different areas of Vancouver Island to assess the nature of the mantle source and to evaluate the melting history and subsequent magmatic evolution of basalts involved in the construction of this major oceanic plateau. The geochemistry of picritic and tholeiitic basalts that form the volcanic stratigraphy of this oceanic plateau offers a view of the melting history of plume-derived magmas that does not involve continental lithosphere and where source heterogeneity does not have a major role. This study is one part of a large research project on the nature, origin and evolution of the Triassic Wrangellia flood basalts in British Columbia, Yukon and Alaska. GEOLOGIC SETTING Wrangeffia on Vancouver Island  Wrangellia flood basalts form the core of the Wrangellia terrane, or Wrangellia, one of the largest outboard terranes accreted to western North America (Jones et a!., 1977). Middle to Late Triassic flood basalts extend in a discontinuous belt from Vancouver and Queen Charlotte Islands (Karmutsen Formation), through southeast  28  Alaska and southwest Yukon, and into the Wrangell Mountains, Alaska Range, and Talkeetna Mountains in east and central Alaska (Nikolai Formation) (Fig. 2.1). Wrangellia covers approximately 80% of Vancouver Island, which is 460 km long by 130 km wide (Fig. 2.1). Wrangellia is the uppermost sheet of a stack of southwest vergent thrust sheets that form the crust of Vancouver Island and has a cumulative thickness of>10 km (Monger & Journeay, 1994). Pre-Karmutsen units of Wrangellia on Vancouver Island are Devonian arc sequences of the Sicker Group and Mississippian to Early Permian siliciclastic and carbonate rocks of the Buttle Lake Group (Muller, 1980; Sutherland-Brown eta!., 1986). The Paleozoic formations have varied estimated thicknesses (—P2-5 km) (Muller, 1980; Massey, 1 995a) and are only exposed on central and southern Vancouver Island (Fig. 2.1). The Karmutsen Formation is overlain by the shallow-water Quatsino Limestone (30-750 m) and deeper-water Parson Bay Formation (-600 m), which is intercalated with and overlain by Bonanza arc volcanics (169-202 Ma; Nixon et a!., 2006b). Bonanza arc plutonic rocks (167-197 Ma) also intrude the Karmutsen Formation and are some of the youngest units of Wrangellia that formed prior to accretion with North America (Nixon et a!., 2006b). Following accretion, Wrangellia units were intruded by the predominantly Cretaceous Coast Plutonic Complex (Wheeler &McFeely, 1991). The Karmutsen Formation (19,142 km , based on mapped areas from digital 2 geologic maps) is composed of basal sediment-sill complexes, a lower member of pillowed and unpillowed submarine flows, a middle member of mostly pillow breccia and hyaloclastite, and an upper member of predominantly massive subaerial flows (Carlisle & Suzuki, 1974). The pillow basalts directly overlie thick sediment-sill complexes composed of mafic sills intruding Middle Triassic pelagic sediments and Late Paleozoic formations. The boundary between pillow breccialhyaloclastite and massive lava flows represents the transition from a submarine to a subaerial eruptive environment. The uppermost flows of the Karmutsen are intercalated and overlain by shallow-water limestone and local occurrences of submarine flows occur within the upper subaerial member. The Karmutsen Formation and Wrangellia on Vancouver Island were the focus of mapping efforts and stratigraphic descriptions by Carlisle (Carlisle, 1963; Carlisle, 1972; Carlisle & Suzuki, 1974) and Muller (Muller et a!., 1974; Muller, 1977). Recent  29  -5ON 12W W  Middle—Late Triassic Karmutsen Formation Paleozoic—Middle Triassic Sicker and Buttle Lake Groups Karmutsen Range (Alice—Nimpkish Lake> Schoen Lake Provincial Park area Mount Arrowsmith area L) Buttle Lake Holberg Inlet  Figure 2.1 Simplified map of Vancouver Island showing the distribution of the Karmutsen Formation (gray) and underlying Paleozoic formations (black; after Massey eta?., 2005a, 2005b). The main areas of field study are indicated with boxes or circles with capital letters (see legend). Ocean is light gray. The inset shows the extent of the Wrangellia flood basalts (gray) in British Columbia, Yukon, and Alaska.  30  descriptions of the Karmutsen Formation on northern Vancouver Island have been made during regional mapping studies (1:50,000 scale) on northern Vancouver Island by Nixon et al. (Nixon eta!., 2006b; Nixon & Orr, 2007; Nixon eta!., 2008). Age of the Karmutsen Formation  The age and duration of Karmutsen volcanism are constrained by fossils in the underlying and overlying sedimentary units and by three U-Pb isotopic age determinations on intrusive rocks that are likely related to the Karmusten volcanics. Daone!la-bearing shale 100-200 m below the base of the pillow basalts on Schoen Mountain and Halobia-rich shale interlayered with flows in the upper part of the Karmutsen indicate eruption of the flood basalts in the Upper Ladinian (Middle Triassic) to Upper Carnian (Late Triassic; Carlisle and Suzuki, 1974). The only published U-Pb age is based on a single concordant analysis of a multi-grain baddeleyite fraction from a U age of 227.3 238 Pb/ gabbro on southern Vancouver Island that yielded a 206  ±  2.6 Ma  U baddeleyite ages, also from a 238 Pb/ (Parrish & McNicoll, 1992). Two unpublished 206 gabbro on southern Vancouver Island, are 226.8  ±  0.5 Ma (5 fractions) and 228.4 ± 2.5 (2  fractions; Sluggett, 2003). VOLCANIC STRATIGRAPHY AND PETROGRAPIIY Field studies undertaken on Vancouver Island in 2004-2006 explored the volcanic stratigraphy of the Karmutsen flood basalts in three main areas: the Karmutsen Range (between Alice and Nimpkish lakes), the area around Schoen Lake Provincial Park, and around Mount Arrowsmith (Greene eta!., 2005; Greene eta!., 2006), and also around  Holberg Inlet, on northernmost Vancouver Island, and Buttle Lake (Fig. 2.1). The character and thickness of the flood basalt sequences vary locally, although the tripartite succession of the Karmutsen Formation appears to be present throughout Vancouver Island. The stratigraphic thicknesses for the pillow, pillow breccia, and massive flow members are estimated at —‘2600 m, 1100 m, and 2900 m, respectively, in the type area around Buttle Lake (Surdam, 1967); on northern Vancouver Island estimated thicknesses are >3000 m, 400-1500 m, and >1500 m, respectively (Nixon et al., 2008); on Mount  31  Arrowsmith and nearby areas on southern Vancouver Island estimates are 1100 m, 950 m, and 1200 m, respectively (Yorath et a!., 1999; Fig. 2.1). Picritic pillow lavas occur west of the Karmutsen Range on northern Vancouver Island, in a roughly triangular-shaped area (30 km across) bounded by Keogh, Maynard and Sara lakes (Figs 2.2 and 2.3; Greene et a!., 2006; Nixon et al., 2008). Excellent exposures of picritic pillow lavas occur in roaclcuts along the north shore of Keogh Lake, the type locality (Greene eta!., 2006). The Keogh Lake picrites mostly form pillowed flow units (<15 m thick), with pillows and tubes of varied dimensions (typically <1 m wide), and unpillowed flows. Numerous thermal contraction features in the pillows are filled with quartz-carbonate, such as drain-back ledges, tortoise-shell jointing, and interpillow voids containing spalled rims (Fig. 2.3; Greene eta!., 2006). The picritic pillow basalts are not readily distinguishable in the field from basalt, except by their density and non-magnetic character and minor interpillow quartz-carbonate. Recent fieldwork and mapping indicates that the picrites occur mostly near the transition between pillow lava emplacement and hyaloclastite deposition (Nixon et a!., 2008). In and around Schoen Lake Provincial Park, there is a well-preserved sedimentsill complex at the base of the Karmutsen Formation (Figs 2.2 and 2.4). Middle Triassic marine sedimentary rocks overlie Pennsylvanian to Permian limestone and siliceous sedimentary rocks, and both successions are intruded by mafic sills related to the overlying flood basalts (Carlisle, 1972). Carlisle (1972) estimated the sediment-sill complex to be approximately 600-900 m thick with a total thickness of 150-200 m of pre intrusive sedimentary rocks. The Triassic sedimentary rocks range from thinly-bedded siliceous and calcareous shale to banded chert and finely-laminated, Daonella-bearing shale (Carlisle, 1972). The basal sediment-sill complex is immediately overlain by thick successions of submarine flows (Fig. 2.4). Basal sills and pre-Karmutsen sediments are also exposed around Buttle Lake. Exposures with large vertical relief around Mount Arrowsmith (Appendix A) and Buttle Lake preserve thick successions of pillow basalt, breccias, and subaerial flows and there are rarely sediments between flows or in interpillow voids. Unpillowed submarine flows interspersed with pillowed flows are locally recognizable by irregular, hackly columnar jointing. The massive subaerial flows form monotonous sequences marked  32  BONANZA VOLCANICS waterlain pyroclastics, subaerial basalt, rhyolite flows, tuff, and intrusive suites (Island Plutonic Suite) HARBLEDOWN FORMATION calcareous siltstone, feldspathic wacke  PARSON BAY FORMATION 1J  ]  well—bedded siliceous limestone and wacke, with minor volcanics  QUATSINO FORMATION massive to well—bedded micritic and locally bioclastic limestone intra—Karmutsen limestone lenses  KARMUTSEN FORMATION subaerial flows with minor pillow basalt and hyaloclastite (—3000 m)  pillowed and unpillowed flows, breccia and hyaloclastite (—2500 m)  Early-MIddle Jurassic Island Plutonic Suite  Late Triassic- Early Jurassic  silicified shale, chert and limestone with Daonella beds intruded by mafic sills  []  Parson Bay Formation  massive bioclastic limestone (Mount Mark Fm.), variety of chert, thinly— bedded shale, and limestone (Fourth Lake Fm.)  o  Quatsino Limestone  /  /  sill I gabbro  • pillow lava shale or chert  Karmutsen Formation  o  Shale-chert-limestone  (b)  Buttle Lake Group (sedimentary rocks) massive lava  MIddle-Lower Triasslc  BUTTLE LAKE GROUP  — (a)  Mississlpplan-Permlan  —  fault river  park boundary  LEMARE LAKE VOLcANIcS  subaerialbasalt and  rhyolite flows, breccia, and tuff minor pillow lava, hyaloclastite, debris—flow and epiclastic deposits  ‘U  a —  I  plag—megacrystic flows  -interbedded volcaniclastic and sedimentary rocks PARSON BAY FORMATION well—bedded shale, limestone, wacke, with minor volcanics c breccia, tuff, reworked cs, minor pillows and INOF  N  -  massive lava i pillow lava picrite  limestone lenses  fKARMUTSEN FORMATION subaerial flows with minor pillow basalt and hyaloclastite I  pillow breccia and hyaloclastite Keogh Lake picrite (mostly pillow lavas)  It  -J  T...  .._.,  Late Triassic-Middle Jurassic Bonanza Group  Alert Bay Volcanics  pillowed and unpillowed flows —  (c)  jabz I  /  ]  Upper Cretaceous Nanaimo Group equivalents  Parson Bay Formation TJ  Undivided Parson Bay  and Bonanza sediments  L.._.  e to Late Triassic uatsino Formation  Karmutsen Formation Early to Middle Jurassic l5tsfld Plutonic Suite  Figure 2.2 Geologic map and stratigraphy of the Schoen Lake Provincial Park and Karmutsen Range areas (locations shown in Figure 2.1, northern Vancouver Island). (a) Stratigraphic column depicts units exposed in the Schoen Lake area, derived from Carlisle (1972) and fieldwork. (b) Generalized geology for the Schoen Lake area with sample locations. Map derived from Massey et a!. (2005a). The exposures in the Schoen Lake area are the lower volcanic stratigraphy and base of the Kannutsen Formation. (c) Stratigraphic column for geology in the Alice-Nimpkish Lake area, derived from Nixon & Off (2007). (d) Geologic map from mapping of Nixon & Orr (2006a) and Nixon et a!. (2008). Sample sites and lithologies are denoted in the legend. The Keogh Lake picrites are exposed near Keogh, Sara, and Maynard lakes and areas to the east of Maynard Lake (Nixon eta!., 2008).  33  2.3 P1 of picritic and tholeiitic pillow basalts from the Karmutsen Range area (Alice and Nimpkish Lake area), northern Vancouver Island. (a) Stack of dense, closely packed, asymmetric picritic pillows with radial vesicle infillings (circled sledgehammer 8O cm long for scale). (b) Picritic pillow basalts in cross-section near Maynard Lake. Note vesicular upper margin to pillows. (c) Unpillowed submarine flow with coarse, hackly columns (marked with arrows) draped over high-MgO pillow basalt. (d) Spalled rims from pillows filling voids between tholeiitic pillow basalt (coin for scale). (e) Cross-section of a large picritic pillow lobe with infilling of quartz-carbonate in cooling-contraction cracks (sledgehammer for scale). (f) High-MgO pillow breccia stratigraphically between submarine and subaerial flows (lens cap for scale --7 cm diameter). -  -  -  34  Figure 2.4 Photographs showing field relations from the Schoen Lake Provincial Park area, northern Vancouver Island. (a) Sediment-sill complex at the base of the Karmutsen Formation on the north side of Mount Adam (see Fig. 2.2 for location). (b) Interbedded mafic sills and deformed, finely-banded chert and shale with calcareous horizons, from location between Mt. Adam and Mt. Schoen.  35  Arrowsmith and nearby areas on southern Vancouver Island estimates are 1100 m, 950 m, and 1200 m, respectively (Yorath et al., 1999; Fig. 2.1). Picritic pillow lavas occur west of the Karmutsen Range on northern Vancouver Island, in a roughly triangular-shaped area (--‘30 km across) bounded by Keogh, Maynard and Sara lakes (Figs 2.2 and 2.3; Greene et a!., 2006; Nixon et al., 2008). Excellent exposures of picritic pillow lavas occur in roadcuts along the north shore of Keogh Lake, the type locality (Greene eta!., 2006). The Keogh Lake picrites mostly form pillowed flow units (<15 m thick), with pillows and tubes of varied dimensions (typically <1 m wide), and unpillowed flows. Numerous thermal contraction features in the pillows are filled with quartz-carbonate, such as drain-back ledges, tortoise-shell jointing, and interpillow voids containing spalled rims (Fig. 2.3; Greene et a?., 2006). The picritic pillow basalts are not readily distinguishable in the field from basalt, except by their density and non-magnetic character and minor interpillow quartz-carbonate. Recent fieldwork and mapping indicates that the picrites occur mostly near the transition between pillow lava emplacement and hyaloclastite deposition (Nixon et aL, 2008). In and around Schoen Lake Provincial Park, there is a well-preserved sedimentsill complex at the base of the Karmutsen Formation (Figs 2.2 and 2.4). Middle Triassic marine sedimentary rocks overlie Pennsylvanian to Permian limestone and siliceous sedimentary rocks, and both successions are intruded by mafic sills related to the overlying flood basalts (Carlisle, 1972). Carlisle (1972) estimated the sediment-sill complex to be approximately 600-900 m thick with a total thickness of 150-200 m of pre intrusive sedimentary rocks. The Triassic sedimentary rocks range from thinly-bedded siliceous and calcareous shale to banded chert and finely-laminated, Daonel!a-bearing shale (Carlisle, 1972). The basal sediment-sill complex is immediately overlain by thick successions of submarine flows (Fig. 2.4). Basal sills and pre-Karmutsen sediments are also exposed around Buttle Lake. Exposures with large vertical relief around Mount Arrowsmith (Appendix A) and Buttle Lake preserve thick successions of pillow basalt, breccias, and subaerial flows and there are rarely sediments between flows or in interpillow voids. Unpillowed submarine flows interspersed with pillowed flows are locally recognizable by irregular, hackly columnar jointing. The massive subaerial flows form monotonous sequences marked  36  mainly by amygdaloidal horizons and brecciated flow tops are rarely observed. A single locality with well-preserved pahoehoe flow features is exposed north of Holberg Inlet (Nixon & Orr, 2007; Nixon et al., 2008). There is no evidence of significant detrital material from a continental source in sediments associated with the flood basalts anywhere on Vancouver Island. The uppermost Karmutsen flows are interbedded with thin (>4 m) lenses of limestone, and rarely siliciclastic sedimentary rocks (Nixon et a!., 2006b). Plagioclase-phyric (>0.8 mm) trachytic-textured flows are also commonly found near the top of the Karmutsen Formation (Nixon et a!., 2006b). A total of 129 samples were collected from the Karmutsen Formation on Vancouver Island and 63 samples were selected for geochemical work based on the relative degree of alteration and geographic distribution of the samples. Fifty-six of these samples have been divided into four groups based on petrography (Table 2.1) and geochemistry, including tholeiitic basalt, picrite, high-MgO basalt, and coarse-grained mafic rocks. The tholeiitic basalts are dominantly glomeroporphyritic with an intersertal to intergranular groundmass (Table 2.1). Plagioclase forms most of the phenocrysts and glomerocrysts and the groundmass is fme-grained plagioclase microlites, clinopyroxene granules, small grains of Fe-Ti oxide, devitrified glass, and secondary minerals; there is no fresh glass. The picritic and high-MgO basaltic lavas exhibit plagioclase and clinopyroxene with spherulitic morphologies with abundant euhedral olivine phenocrysts (Fig. 2.5; Table 2.1). Only olivine is strongly altered and is completely pseudomorphically replaced by talc/tremolite. Plagioclase and clinopyroxene phenocrysts are not present in the high-MgO samples. The coarse-grained mafic rocks are  characterized petrographically by subophitic texture with average grain size typically >1mm, and are generally non-glomeroporphyritic. The coarse-grained mafic rocks are  mostly from the interiors of massive flows, although some may be from sills.  SAMPLE PREPARATION AND ANALYTICAL METHODS  Only the freshest rocks in the field were sampled and only the least altered samples were selected for chemical and isotopic analysis based on thorough petrographic inspection. Sixty-three of the 129 collected samples (including 7 non-Karmutsen  37  Figure 2.5 Photomicrographs of picritic pillow basalts, Karmutsen Formation, northern Vancouver Island. Scale bars are 1 mm long. (a) Picrite with abundant euhedral olivine pseudomorphs from Keogh Lake type locality (Fig. 2.2) in cross-polarized transmitted light (sample 4722A4; 19-19.8 wt % MgO, 4 analyses). Samples contain dense clusters (24-42 vol %) of olivine pseudomorphs (<2 mm) in a groundmass of curved and branching sheaves of acicular plagioclase and intergrown with clinopyroxene and altered glass. In many cases, plagioclase nucleated on the edges of the olivine phenocrysts. (b) Sheaves of intergrown plagioclase and clinopyroxene in aphyric picrite pillow lava from west of Maynard Lake (Fig. 2.2) in cross polarized transmitted light (sample 4723A2; 10.8 wt % MgO).  38  Table 2.1 Summary of oetroaraohic characteristics and ohenocrist orooortions of Karmutsen basalts on Vancouver Island. B.C.  Sampie 4718A1 471 8A2 471 8A5 471 8A6 4718A7 4719A2 471 9A3 4720A2 4720A3 4720A4 4720A5 4720A8 4720A9 4721A1 4721A2 4721A3 4721A4 4721A5 4722A2 4723A10 4724A5 5614A10 5614A11 5614A13 561 5A1 5615A8 5615A10 5616A2 5618A1  Areab FIOWC MA PIL MA PIL MA PLO MA BRE MA PIL MA PIL MA PIL SL BRE SL FLO SL FLO SL PLO SL FLO SL FLO SL PIL SL FLO SL FLO SL FLO SL FLO KR FLO KR PLO SL PLO KR FLO KR FLO KR FLO KR PIL PIL KR KR PIL KR FLO Cl FLO  Groupd THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL THOL  Texture intersertal intersertal, glomero intersertal, glomero porphyritic glomero porphyritic, intersertal glomero glomero glomero glomero senate glomero glomero glomero glomero glomero glomero, ophimottled glomero, ophlmottled intengranular, intersertal intengranular porphyritic intergranular, intersertal intergranular, intersertal lntergranular, porphynitlc aphyric, Intersertal intengranular intengranular intergranular, intersertal intergranular  93G171 4722A4 4723A3 4723A4 4723A13 5614A1 5615A7 5615A12 5616A1  KR KR KR KR KR KR KR KR KR  4723A2 5614A3 561 4A5 561 6A7  PIL PIL PIL PIL PIL PIL PIL PIL PIL  PlC PlC PlC PlC PlC PlC PlC PlC PlC  subophitic cumulus, intergranular spherulitic intergranular, intersertal spherulitic spherulitic cumulus, intergranular spherulltic iritengranular, intersertal  23 35 31 0 24 24 42 13 25  KR KR KR KR  PIL PIL BRE PIL  HI-MG HI-MG HI-MG HI-MG  spherulitic spherulitic, intrafasciculate porphyritic, ophimottled intersertal  0 12 13 2  4722A5 KR 5615A11 KR  FLO PIL  OUTLIER intersertal OUTLIER intersertal  4720A6 4720A7 4720A10 4724A3 5614A14 5614A15 5615A5 561 5A6 5616A3 5617A1 5617A5  PLO FLO SIL FLO SIL SIL GAB GAB GAB SIL SIL  CG CG CG CG CG CG CG CG CG CG CG  SL SL SL SL KR KR KR KR KR SL SL  subophitic subophitic subophltic, Intrafasciculate ophimottled, subophitic intergranular subophitic intergranular, plag-phynic intergranular, plag-phynic subophitic intergranular, lntergrowths intergranular, intersertal  voi% 011 PIag Cpx Ox 9 Alteration Note” 20 5 3 few plag glcr <2 mm, cpx <1 mm 15 1 plag glcr <2 mm, very fresh 10 2 mottled, few plag glcr <4 mm 20 2 plag 5-6 mm, sericite alteration 10 3 plag glcr<3 mm 5 3 plag glcr <2 mm 10 2 plag glcr <3 mm 5 plag glcr <2 mm 3 3 3 plag glcr <3 mm 5 1 plag glcr <5 mm, slightly cg, very fresh 20 plag glcr <2 mm, plag needles and laths 3 20 2 plag glcr <2 mm, plag needles and laths 10 2 plag glcr<1.5 mm 15 plagglcr<1.5mm, plag needles aligned 3 10 1 plag glcr<3 mm, very fresh 20 plag glcr <2 mm, plag needles 3 20 5 1 plag glcr <1.5 mm, cpx <1 mm (oik), very fresh 5 15 3 plag glcr <1.5 mm, cpx <1 mm (01k) 1 1 few plag phenos <2 mm 5 3 10 3 few plag glcr <1 mm, ox 0.5-1 mm 25 plag 7-8mm 3 2 5 3 ox <0.5mm 7 ox 0.5-1 mm 5 3 5 5 3 ox 0.5-1 mm 1 2 f.g., no phenos 1 f.g., abundant small ox, very fresh 3 3 3 2 plag glcr <4 mm 5 7 3 ox 0.2-0.5mm 3 2 10 3 ox 0.5-2 mm, c.g., plag laths >2 mm 10  10  15 25 5  30 10 25  30 15 25 30 1  5 5 5 3 5 10 5  3 3 3 3 1 1 1 1  01<2.3 mm, cpx<1 .5 mm, partially enc plag 01<1.5 mm, cpx<2 mm enc plag 01<1 mm, swtl plag <1.5mm swtl plag <1 mm, no ci phenos swtl plag <1 mm 01<1.5 mm, swtl plag <1 mm 01<1.5 mm, cpx <1.5mm enc plag 01 <2 mm, swtl plag <1 mm 01 <2mm  3 1 2 2  swtl plag <2 mm, no ol phenos 01<1.5 mm, swtl plag <2mm ol <2 mm, cpx <2 mm enc plag ol <2 mm, plag needles <1 mm  3 3  mottled, very f.g., v. small p1 needles mottled, very f.g., v. small p1 needles  1 1 3 3 3 1 3 3 1 3 1  plag glcr <3 mm, cpx <3 mm plag chad <1.5 mm, cpx oik <2mm, very fresh plag chad<2 mm, cpx oik <3 mm, ox <1 mm, c.g. plag glcr 4-5 mm, cpx olk <2mm, ox <1 mm plag<lmm,cpx<2mm plag<1 mm, CPX 01k <3 mm, ox <0.2mm ox <0.5 mm, plag laths <4 mm plag<3mm,oxo.5-1.5mm plag laths <1 mm, cpx 01k <2mm, ox 0.5-1 mm plag <3 mm, cpx <5 mm, cpx-plag intergrowths plag <1 mm, f.g., mottled  5617A4 SL SIL MIN intersertal 5 3 to. asample number: last digit year, month, day, initial, sample station (except 93G171).bMA, Mount Arrowsmith; SL, Schoen Lake; KR, Karmutsen Range. °PIL, pillow; BRE, breccia; PLO, flow; SIL,sill; GAB, gabbro.dTHOL, tholeiitic basalt; PlC, picrite; HI-MG, high-MgO basalt; CG,coarse-grained; MIN, mineralized sill. °glomero, glomeroporphyrltic.OIivine modes for picrites based on area calculations from scans (see Olivine accumulation in picritic lavas section and Figure 2.13). 9 Visual alteration index based primarily on degree of plagioclase alteration and presence of secondary minerals (1, least altered; 3, most altered). Plagioclase phenocrysts commonly altered to albite, pumpellyite, and chlorite; divine is altered to talc, tremolite, and clinochiore (determined using the Rietveld method of X-ray powder diffraction); clinopyroxene is unaltered; Fe-Ti oxide commonly replaced by sphene.’glcr, glomerocrysts; f.g., fine-grained; c.g., coarse grained, oik, oikocryst; chad, chadacryst; enc, enclosing, swtl, swallow-tail. Mineral abbreviations: 01, olivine pseudomorphs; plag, plagioclase; cpx, clinopyroxene; ox, oxides (includes ilmenite + titanomagnetite).  39  samples) were crushed (400 g) into small pieces <2 mm in diameter in a Rocklabs hydraulic piston crusher between WC-plates to minimize contamination. The coarsecrush was mixed and 100 g was powdered in a planetary mill using agate jars and balls cleaned with quartz sand between samples. ActLabs Analytical Methods  The major- and trace-element compositions of the whole rock powders were determined at Activation Laboratories Ltd. (Actlabs) in Ancaster, Ontario. Analytical techniques and detection limits are also available from Actlabs (http://www.actlabs.com/methsub_code4ere.htm). The particular analytical method for each of the elements analyzed is indicated in Table 2.2. For the major elements, a 0.2 g sample was mixed with a mixture of lithium metaborate/lithium tetraborate and fused in a graphite crucible. The molten mixture was poured into a 5% HNO 3 solution and shaken until dissolved (30 minutes). The samples were analyzed for major oxides and selected trace elements on a combination simultaneous/sequential Thermo Jarrell-Ash Enviro II inductively coupled plasma optical emission spectrometer (ICP-OES). Internal calibration was achieved using a variety of international reference materials (e.g. W-2, BIR- 1, DNC- 1) and independent control samples. Additional trace elements were analyzed by both the INAA (instrumental neutron activation analysis) and ICP-MS (inductively couple plasma mass spectrometry) methods. For the 1NAA analyses, 1.5-2.5 g of sample was weighed into small polyethylene vials and irradiated with control international reference material CANIVIET WMS- 1 and NiCr flux wires at a thermal 2 s in the McMaster Nuclear Reactor. Following a 7-day neutron flux of 7 x 1012 n cm waiting period, the samples were measured on an Ortec high-purity Ge detector linked to a Canberra Series 95 multichannel analyzer. Activities for each element were decay- and weight-corrected and compared to a detector calibration developed from multiple international certified reference materials. For the ICP-MS analyses, 0.25 g of sample 3 and HC1O , heated and taken to 4 was digested in HF, followed by a mixture of HNO  dryness. The samples were brought back into solution with HC1. Samples were analyzed using a Perkin Elmer Optima 3000 ICP. In-lab standards or certified reference materials  40  (e.g. W-2, BIR- 1, DNC- 1) were used for quality control. A total of 15 blind duplicates were analyzed to assess reproducibility and the results were within analytical error. University ofMassachussetts XRF Analytical Methods  Fourteen sample duplicate powders (high-MgO basalts and picrites) were also analyzed at the Ronald B. Gilmore X-Ray Fluorescence (XRF) Laboratory at the University of Massachussetts. Major elements were measured on a fused La-bearing lithium borate glass disc using a Siemens MRS-400 spectrometer with a Rh X-ray tube operating at 2700 W. Trace element concentrations (Rb, Sr, Ba, Ce, Nb, Zr, Y, Pb, Zn, Ga, Ni, Cr, V) were measured on a separate powder pellet using a Philips PW2400 sequential spectrometer using a Rh X-ray tube. Loss-on-ignition (LOl) and ferrous iron measurements were made as described by Rhodes and younger (2004). Precision and accuracy estimates for the data are described by Rhodes (1996) and Rhodes and younger (2004). Results for each sample are the average of two separate analyses (shown in Appendix B). PCIGR Analytical Methods  A subset of 19 samples was selected for high-precision trace-element analysis and Sr, Nd, Pb, and Hf isotopic analysis at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia (UBC). Samples were selected from the 63 samples analyzed for whole-rock chemistry at ActLabs, based on major- and trace-element chemistry, alteration (low LOT and petrographic alteration index), and sample location. Samples were prepared for trace-element analysis at the PCIGR by the technique described by Pretorius et al. (2006) on unleached rock powders. Sample powders (—100 mg) were weighed in 7 mL screw-top Savillex® beakers and dissolved in 3 and 5 mL 48% HF on a hotplate for 48 hours at 130°C with periodic 1 mL --‘l4N HNO ultrasonication. Samples were dried and redissolved in 6 mL 6N HC1 on a hotplate for 24 3 for 24 hours before hours and then dried and redissolved in 1 mL concentrated HNO  final drying. Trace element abundances were measured with a Thermo Finnigan Element2 High Resolution-Inductively Coupled Plasma-Mass Spectrometer (HR-ICP MS) following the procedures described by Pretorius et al. (2006) within 24 hours of  41  redissolution. High field strength elements (HFSE) and large ion lithophile elements (LILE) were measured in medium resolution mode at 2000x dilution using a PFA teflon spray chamber washed with Aqua Regia for 3 minutes between samples. Rare earth elements (REE) were measured in high resolution mode, and U and Pb in low resolution 3 between mode, at 2000x dilution using a glass spray chamber washed with 2% HNO samples. Total procedural blanks and reference materials (BCR-2, BHVO-2) were analyzed with the batch of samples. Indium was used as an internal standard in all samples and standard solutions. Background and standard solutions were analyzed after every 5 samples to detect memory effects and mass drift. Results for PCIGR traceelement analyses are shown in Appendix C. Sample digestion for purification of Sr, Nd Hf, and Pb for column chemistry ,  began by weighing each sample powder (400-500 mg) prior to leaching. All samples were leached with 6N HC1 and placed in an ultrasonic bath for 15 minutes. Samples were 0 between each leaching step (15 total) until the 2 rinsed two times with 18 mega 2-cm H  supernatant was clear (following the technique of Mahoney, 1987). Samples were then dried on a hotplate for 24 hours and weighed again. Sample solutions were then prepared 3 and 10 by dissolving -400-250 mg of the leached powder dissolved in 1 mL l4N HNO mL 48% HF on a hotplate for 48 hours at 130°C with periodic ultrasonication. Samples were dried and redissolved in 6 mL 6N HC1 on a hotplate for 24 hours and then dried. Pb was separated using anion exhange columns and the discard was used for Sr, REE, and Hf separation. Nd was separated from the other REE and Hf required two additonal purification steps. Detailed procedures for column chemistry for separating Sr, Nd, and Pb at the PCIGR are described in Weis et al. (2006) and Hf purification is described in Weis et a!. (2007). Sr and Nd isotope ratios were measured on a Thermo Finnigan Triton Thermal Ionization Mass Spectrometer (TIMS) in static mode with relay matrix rotation on a single Ta and double Re-Ta filament, respectively. Four to 5 filaments per barrel of 21 were occupied by standards (NBS 987 for Sr and LaJolla for Nd) for each barrel where samples were run. Sample Sr and Nd isotopic compositions were corrected for 46 ‘ N 1 d = 0.7219. Each sample was 5r = 0.1194 and NdJ 88 Sr/ mass fractionation using 86  then normalized using the barrel average of the reference material relative to the values of Sr=0.710248 (Weis et al., 2006). During the course of 86 Sr/ 43 = 0.511858 and 87 ‘ Nd 44 Nd/’  42  the Vancouver Island analyses, the La Jolla Nd standard gave an average value of 0.511856 ± 6 (n=7) and NBS987 standard gave an average of 0.710240 ± 8 (n=1 1) (2a error is reported as times 106). SmJ’Nd 47 ratio errors are approximately —1.5%, or ‘ —0.006. United States Geological Survey (USGS) reference material BHVO-2 was processed with the samples and yielded Sr and Nd isotopic ratios of 0.703460 ± 7 and 0.512978 ± 6, respectively. These are in agreement with the published values of 0.703479 ±  20 and 0.5 12984 ± 11, respectively (Weis et a!., 2006). Pb and Hf isotopic compositions were analyzed by static multi-collection on a Nu  Plasma (Nu Instruments) Multiple Collector-Inductively Coupled Plasma-Mass Spectrometer (MC-ICP-MS). The detailed analytical procedure for Pb isotopic analyses on the Nu Plasma at the PCIGR is described in Weis et al. (2006). The configuration for Pb analyses allows for collection of Pb, Tl, and Hg together. Ti and Hg are used to monitor instrumental mass discrimination and isobaric overlap, repectively. All sample solutions were analyzed with approximately the same Pb/Tl ratio (-.4) as the reference material NIST SRM 981. To accomplish this, a small aliquot of each sample solution from the Pb columns was analyzed on the Element2 to determine the precise amount of Pb available for analysis on the Nu Plasma. The SRM 981 standard was run after every two samples on the Nu Plasma. During the time samples were run, analyses of the SRM 981 Pb reference material gave values of 206 Pb= 16.9403 204 Pb/ ±  23, and 208 Pb=36.7 131 204 Pb/  ±  ±  22, 207 Pb= 15.4958 204 Pb/  64 (n=6 1; 2a error is reported as times 1 0); these values  are in excellent agreement with reported TIMS triple-spike values of Galer & Abouchami (1998). Fractionation-corrected Pb isotopic ratios were further corrected by the samplestandard bracketing method or the in-In correction method described by White et a!. (2000) and Blichert-Toft eta!. (2003). Leached powders of USGS reference material Pb= 18.6454 ± 8, 207 204 Pb/ Pb= 15.4910 ± 204 Pb/ BHVO-2 yielded Pb isotopic ratios of 206 Pb= 18.8046 ± 6, 204 Pb/ Pb= 38.2225 ± 14 and BCR-2 yielded 206 204 Pb/ 5, and 208 Pb 15.6251 204 Pb/ 207  ±  8, and 208 Pb= 38.8349 ± 6 (2a error is reported as times 204 Pb/  10). These values are in agreement with leached residues of BITVO-2 and BCR-2 from Weis et a!., (2006). Hf isotopic compositions were analyzed following the procedures detailed in Weis eta!. (2007). The configuration for Hf analyses monitored Lu mass 175 and Yb  43  mass 172 to allow for interference correction to masses 174 and 176. Hf isotopic ratios 79 ratio of 0.7325 using an ‘ Hf 77 were normalized internally for mass fractionation to a Hf/’ exponential correction. Standards were run after every two samples and sample results 76 ratio for JMC ‘ Hf 77 were normalized to the ratio of the in-run daily average and a Hf/’ 475 of 0.282160. During the course of analyses, the Hf standard JMC-475 gave an average value 0.282 167 ± 9 (n=l30). USGS reference materials BCR-2 and BHVO-2 were processed with the samples and yielded Hf isotopic ratios of 0.282867 ± 5 and 0.283100± 5, respectively. Published values for BCR-2 and BHVO-2 are 0.28287 1  ±  7  and 0.283104 ± 8, respectively (Weis et a!., 2007).  WHOLE-ROCK CHEMISTRY Major- and trace-element compositions  The most abundant type of lava in the Karmutsen Formation is tholeiitic basalt with a restricted range of major- and trace-element compositions. The tholeiitic basalts have similar compositions to the coarse-grained mafic rocks, and both groups are distinct from the picrites and high-MgO basalts (Fig. 2.6). The tholeiitic basalts have lower MgO 2 (1.4-2.2 wt % Ti0 ) than the picrites (13.0-19.8 wt 2 (5.7-7.7 wt % MgO) and higher Ti0 ) and high-MgO basalts (9.1-11.6 wt % MgO, 0.5-0.8 wt % 2 % MgO, 0.5-0.7 wt % Ti0 ) (Fig. 2.6; Table 2.2). Almost all data plot within the tholeiitic field in a total alkalis 2 Ti0 versus silica plot, although there has been substantial K-loss in most samples from the , 2 Karmutsen Formation (Fig. 2.7), and the tholeiitic basalts generally have higher Si0 0+K Na 0 2 , CaO, and FeOT (total iron expressed as FeO) than the picrites. The tholeiitic basalts also have noticeably lower LOl (mean 1.72 ± 1.3 wt %) than the picrites (mean 5.39 ± 0.8 wt %) and high-MgO basalts (mean 3.84 ± 1.5 wt %; Fig. 2.6) reflecting the presence of abundant altered olivine phenocrysts in the latter groups. Ni concentrations are significantly higher for the picrites (339-755 ppm) and high-MgO basalts (122-551 ppm) than the tholeiitic basalts (58-125 ppm, except for one anomalous sample) and coarse-grained rocks (70-213 ppm) (Fig. 2.6; Table 2.2). An anomalous tholeiitic pillowed flow (3 samples; outlier in Tables 2.1 and 2.2), from near the picrite type locality at Keogh Lake, and a mineralized sill (disseminated sulfide), from the basal  44  4.0 +  Picnte  3.5 -1102  O High-MgO basalt 0 Coarse-grained  3.0  9 Tholelitic basalt  2.5  -  .,  2.0  0  :.  1.5  X Pillowed flow + Mineralized sill  •  ,.  1.0  *  •  0  Karmutsen Form.. (compiled data)  +  0.5 —(b) 40  50 2 (wt%) Si0  45 II  II  60  55 liii  II  .111.111.1..  0.0  5  10  11111111111  I  IIIIIIIIIII  I  0  14 -CaO  6*  -(wt%)  +•.  13  600  I.... 20  MgO (wt%)  15 -  Ni (ppm)  15  •.  0  -  12 11  400  x .  -  10 —  00  200  06  16 15 14  I  0  5 —  : LO (wt  I  I  I  I  I  I  •  I  I  12  11 10  2  10 15 MgO(wt%)  5  20  3 0 2 A1  (w  0  l.  ••  .  5  10  MgO (wt  LA  20  15  0  25  e  •• 6*  *  16  ..  15  AA €0 0O*OA  AA  14 13  8  12  6  +  5  9  7  1  Ocr.  *  :fE  13  -  .()....I....I....I  oo0 0  14  A  •  . .  I  10 MgO (wt%)3  i—I—I  •  FeO(T) (wt%)  I  •  •  :00  (C)  0  ‘cc  (f)  11 -  11111  I....  I....  I  •* .  (g)  I  —  -  .l.  —  —  —  I  —  25 10 20 250 15 5 15 20 10 0 5 MgO (wt%) MgO (wt%) Figure 2.6 Whole-rock major-element, Ni, and LOT variation diagrams for the Karmutsen Formation. New samples from this study (Table 2.2) are shown by symbols with black outlines (see legend). Previouslypublished analyses are shown in small gray symbols without black outlines. The boundary of the alkaline and tholeiitic fields is that of MacDonald and Katsura (1964). Total iron expressed as FeO, LOT is loss-onignition, and oxides are plotted on an anhydrous, normalized basis. References for the 322 compiled analyses for the Karmutsen Formation are G. Nixon (unpublished data), Barker et a!. (1989), Kuniyoshi (1972), Lassiter eta!. (1995), Massey (1995a; 1995b), Muller eta!. (1974); Surdam (1967), and Yorath et a!. 2 (>52 wt (1999). Note that the compiled data set has not been filtered; many of the samples with high Si0 %) are probably not Karmutsen flood basalts, but younger Bonanza basalts and andesites. Three pillowed flow samples (x) and a mineralized sill (+) are distinguished separately because of their anomalous chemistry. Coarse-grained samples are indicated separately and generally have subophitic texture. Three 3 contain 10-25 modal % of large 0 2 tholeiitic basalt samples (4724A5, 4718A5, 4718A6) with >16 wt % A1 plagioclase phenocrysts (7-8 mm) or glomerocrysts (>4 mm).  45  Table 2.2 Maior element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Karmutsen basalts, Vancouver Island, B.C. 4719A3 4719A2 4720A3 4718A6 4720A2 4718A5 4718A7 4718A1 4718A2(1) 4718A2(2) Sample THOL THOL ThOL THOL THOL THOL THOL TI-IOL Group THOL THOL MA MA MA SL MA SL MA MA MA MA Area Brenda Flow Pillow Pillow Pillow Brenda Pillow Flow Flow Pillow Pillow 5454625 5454625 5455280 5567712 5567305 5455518 5455150 5455459 5455150 5455062 UTM EW 707890 708686 381761 381761 382261 383237 384260 383424 384260 384113 UTMNS Unnormalized Major Element Oxides (Wefght %): 49.68 48.47 48.69 49.24 48.41 49.08 2 Si0 49.07 48.44 47.93 48.65 1.716 1.676 1.705 1.359 1.487 1.577 1.402 2 Ti0 1.857 1.835 1.646 14.93 14.74 13.54 13.52 15.92 14.06 14.15 14.30 14.41 15.89 203 * 3 0 2 Fe 11.61 9.75 12.21 12.13 11.30 10.74 12.48 9.90 12.07 12.29 0.185 0.212 0.178 0.181 0.167 0.185 0.171 0.157 0.155 0.183 MnO 6.55 7.12 6.74 6.09 6.81 6.98 6.89 6.25 6.21 6.16 MgO 11.94 10.94 14.00 10.96 11.56 11.31 10.76 11.70 10.22 11.85 CaO 2.24 2.18 2.89 2.12 2.23 2.39 3.22 2.51 0 2 Na 2.25 2.28 0.31 0.24 0.27 0.29 0.34 0.10 0.35 0.18 0.14 0.24 1(20 0.13 0.12 0.08 0.12 0.12 0.12 0.10 5 0 2 P 0.14 0.15 0.15 1.97 1.63 1.95 1.15 2.17 2.28 1.64 2.72 1.38 1.22 LOl 99.11 98.75 99.00 99.81 99.45 99.24 99.01 99.98 99.33 99.09 Total Trace Elements (ppm): 720 7.88 7.02 7.17 6.58 6.10 6.50 9.03 8.72 7.88 La 18.0 17.7 17.3 19.0 16.2 21.6 15.5 15.4 19.0 22.2 Ce 2.72 2.20 2.62 2.52 2.23 2.42 2.71 3.02 2.15 3.10 Pr 12.5 13.2 13.5 11.2 11.4 12.2 10.7 14.5 13.0 15.2 Nd 3.85 3.66 3.43 3.67 3.13 3.42 3.57 3.03 4.05 4.11 Sm 1.47 1.20 1.39 1.33 1.47 1.25 1.40 1.18 1.48 1.57 Eu 4.24 4.32 4.48 3.64 4.12 4.77 4.87 3.90 4.39 3.59 Gd 0.78 0.71 0.74 0.68 0.76 0.64 0.63 0.82 0.82 0.76 Tb 4.78 4.68 4.41 4.12 4.28 3.80 3.87 4.79 4.55 5.02 Dy 0.95 0.87 0.94 0.89 0.84 0.77 0.78 0.96 0.99 0.90 I-to 2.45 2.69 2.27 2.34 2.48 2.20 2.66 2.79 2.72 2.57 Er 0.34 0.38 0.35 0.37 0.32 0.33 0.32 0.40 0.39 0.36 Tm 2.11 2.05 2.33 1.96 1.90 2.23 2.00 2.15 2.39 2.32 Yb 0.33 0.30 0.30 0.28 0.29 0.27 0.32 0.27 0.33 0.31 Lu 46.2 42.8 42.8 38.3 41.1 40.4 40.2 40.7 41.3 38.9 Sc 344 341 341 279 317 325 285 328 353 351 V 131 168 297 151 130 252 290 125 93 146 Cr 56.2 53.4 51.4 53.1 45.4 50.5 46.1 49.9 48.9 48.7 Co 93 83 125 122 103 115 94 87 88 90 Ni 184 168 167 180 167 158 198 159 201 177 Cu 87 88 79 86 82 77 73 91 83 91 Zn 19 17 18 18 16 19 17 19 20 19 Ga 1.5 1.9 1.1 1.5 1.1 1.5 0.7 1.6 1.5 1.4 Ge 6 5 5 4 4 6 6 2 2 Rb 286 281 214 332 192 282 263 418 228 231 Sr 26 27 25 22 26 24 25 22 28 28 Y 90 83 86 71 77 83 72 94 86 97 Zr 7.3 7.4 8.6 7.9 10.0 7.0 6.8 6.5 8.4 10.1 Nb 02 0.2 0.2 0.2 0.2 0.5 0.5 0.7 Cs 0.3 133 143 81 28 71 49 62 98 173 50 Ba 2.6 2.5 2.4 2.6 2.1 2.0 2.2 2.8 2.6 2.8 Hf 0.49 0.60 0.46 0.51 0.45 0.53 0.41 0.59 0.65 0.68 Ta 7 9 11 7 4 10 7 7 6 4 Pb 0.61 0.57 0.64 0.53 0.52 0.61 0.54 0.65 0.74 0.72 Th 0.20 0.18 0.22 0.19 0.17 0.16 0.24 0.17 0.23 0.20 U Abbreviations for group are: THOL, tholeiilic baaalt; PlC, picrite; HI-MG, high MgO basalt; CG, coarse-grained (sill or gabbro); MIN SIL, mineralized sill; OUTLIER, anomalous pillowed flow in plots. Abbreviations for area are: MA, Mount Arrowsmith; SL, Schoen Lake; KR, Karmutsen Range; 01, Quadra Island. Sample locations are given using the Universal Transverse Mercator (UTM) coordinate system (NAD83; zones 9 and . LOl is loss-on-ignition. AU major 3 0 2 10). Analyses were perfoiTned at Activation Laboratoiy (AcilLabs). Fe 203 is total ron expressed as Fe elements, &, V, andY were measured by CF quadrupole OES on solutions of fused samples; Cu, Ni, Pb, and Zn were measured by total dilution ICP; Cs, Ga, Ge, Hf, Nb, Rb, Ta, Th, U, Zr, and REE were measured by magnetic-sector ICP on solutions of fused samples; Co Cr, and Sc were measured by INAA. Blanks are below detection lwnit. Ni concentrations for these high-MgO samples by XRF. See Appendices B and C for complete XRF data and PCIGR trace element data, respectively. Major elements for sample 93G1 7 are normalized, anhydrous. Samples from Quadra Island are not shown in figures.  46  4720A5 4720A5 4720A4 Sample THOL THOL ThOL Group SL SL Area SL Breccia Flow Flow Flow 5563304 5566984 UTM EW 5563304 705978 705978 707626 UTM NS Unnrxmalized Major Element Oxides (Weight %): 49.16 50.25 48.88 5102 2 riO 1.781 1.736 1.776 3 0 2 A1 13.84 13.43 14.00 * 3 0 2 Fe 13.03 13.46 13.30 0.179 0.194 0.175 MnO 6.12 6.39 5.93 MgO 11.43 11.05 11.85 CaO 2.16 1.86 2.12 0 2 Na 0.14 0.14 0.12 1<20 0.15 5 0 2 P 0.16 0.15 1.44 1.42 0.93 LOl 99.75 99.42 99.56 Total Trace Elements (ppm): 8.44 8.07 7.81 La 18.8 19.5 20.5 Ce 2.88 2.63 2.73 Pr 13.5 13.1 14.3 Nd 4.07 3.87 3.68 Sm 1.49 1.45 1.43 Eu 4.74 4.70 4.60 Gd 0.81 0.83 0.79 Th 4.77 4.92 4.90 Dy 0.96 0.98 0.99 Ho 2.79 2.81 2.80 Er 0.40 0.40 0.39 Tm 2.47 2.46 2.31 Yb 0.35 0.35 0.33 Lu 44.5 41.0 42.9 Sc 354 349 362 V 156 133 122 Cr 54.8 53.7 50.8 Co 105 92 99 Ni 185 174 202 Cu 93 92 90 Zn 19 20 19 Ga 1.6 1.6 1.6 Ge 1 1 2 Rb 179 183 188 Sr 28 27 28 Y 92 93 97 Zr 8.2 9.1 8.6 Nb 0.1 0.2 0.1 Cs 34 38 37 Ba 2.6 2.7 2.7 Hf 0.56 0.57 0.60 Ta 8 7 8 Pb 0.68 0.61 0.63 Th 0.21 0.19 0.20 U  4720A6 CG SL Flow 5566161 704411  4720A7(1) CG SL Flow 5566422 703056  4720A7(2) CG SL Flow 5566422 703056  4720A8 ThOL SL Flow 5566800 700781  4720A9 TI-IOL SL Flow 5564002 703739  4720A10 CG SL SIU 5560585 702230  4721A1 ThOL SL PUlow 5563843 704932  48.90 1.799 14.21 11.78 0.195 6.40 12.08 1.82 0.31 0.12 1.38 99.00  49.60 1.811 14.34 13.37 0.199 5.93 11.69 1.97 0.15 0.16 0.75 99.97  49.53 1.809 14.36 13.39 0.199 5.94 11.68 1.97 0.13 0.15 0.75 99.90  48.02 1.768 14.34 13.18 0.195 6.73 11.37 1.97 0.11 0.15 1.91 99.73  48.06 1.767 14.11 13.73 0.185 6.35 11.61 2.08 0.11 0.16 1.37 99.52  47.38 0.829 14.42 10.58 0.161 7.69 11.66 2.77 0.12 0.06 4.07 99.75  48.17 1.890 14.96 11.40 0.180 6.39 11.75 1.93 0.10 0.13 2.11 99.01  7.75 19.0 2.71 13.9 4.03 1.43 4.62 0.81 5.01 1.01 2.89 0.41 2.51 0.36 43.4 363 152 52.5 107 188 96 18 1.2 10 155 27 94 8.7 0.9 39 2.7 0.57 7 0.64 0.21  7.84 19.0 2.67 13.3 3.86 1.42 4.73 0.81 4.95 1.01 2.92 0.42 2.49 0.34 44.2 366 154 52.6 97 212 93 19 1.6 2 173 29 94 8.6 0.3 45 2.7 0.56 14 0.61 0.19  7.74 19.3 2.74 13.7 3.89 1.43 4.66 0.82 4.97 1.01 2.89 0.40 2.44 0.35  6.86 17.5 2.54 12.6 3.72 1.37 4.40 0.77 4.86 0.98 2.78 0.40 2.51 0.35 42.0 362 155 54.5 116 218 109 19 1.8  7.06 17.3 2.46 12.3 3.51 1.36 4.19 0.75 4.62 0.93 2.65 0.37 2.27 0.33 44.0 362 166 55.5 112 187 90 18 1.4 1 196 28 88 7.8 0.1 35 2.6 0.53 8 0.61 0.18  2.24 5.6 0.85 4.8 1.76 0.75 2.58 0.50 3.38 0.76 2.31 0.34 2.16 0.31 49.9 288 311 49.5 121 134 64 14 1.4 2 130 21 38 1.7 0.3 68 1.2 0.09  7.31 18.9 2.78 13.5 4.06 1.47 4.72 0.81 4.99 1.03 2.96 0.41 2.50 0.36 44.4 378 158 54.8 106 208 86 18 1.3 2 174 30 97 8.5 0.6 36 2.9 0.58 14 0.68 022  367  85 210 94 19 1.7 2 174 28 93 8.7 0.3 43 2.8 0.55 6 0.61 0.19  174 28 95 8.3 0.2 33 2.7 0.55 8 0.62 0.19  0.24 0.11  47  Sample Group Area Flow UTM EW IJTM NS  4721A2 THOL SL Flow 5563936 704941  4721A3 THOL SL Flow 5564229 704928  4721A4 THOL SL Flow 5564285 704896  4721A5 4722A2(1)* 4722A2(2)* 472(3)* 4722(4)* 4722A4(1)* 4722A4(2)* THOL THOL THOL THOL THOL PlC PlC SL KR KR KR KR KR KR Flow Flow Flow Flow Flow Pillow Pillow 5564343 5590769 5590769 5590769 5590769 5595528 5595528 705008 634318 634318 634318 634318 629490 629490  Unnormalized Major Element Oxides (Weight %): Si0 2 1102 3 0 2 Al * 3 0 2 Fe MnO MgO GaO 0 2 Na 0 2 K 5 0 2 P LOl Total Trace La Ce Pr Nd  Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Cs Ba Hf Ta Pb Th U  49.56 1.770 13.92 13.07 0.174 6.06 12.15 2.01 0.09 0.16 0.76 99.73 Elements (ppm): 7.86 19.2 2.70 13.5 3.84 1.46 4.47 0.79 4.75 0.96 2.72 0.38 2.35 0.32 42.1 351 118 51.6 91 195 90 19 1.7 I 187 26 97 9.0 0.2 39 2.8 0.60 8 0.69 0.21  48.17 1.768 14.16 13.24 0.183 6.61 11.30 2.03 0.15 0.14 1.78 99.53  49.49 1.791 13.98 13.13 0.176 6.46 11.76 1.92 0.12 0.14 0.87 99.85  49.37 1.806 13.98 13.53 0.201 5.98 11.59 1.92 0.15 0.15 1.04 99.71  48.33 1.799 13.59 13.75 0.185 6.97 11.42 2.03 0.14 0.15 1.48 99.84  48.67 1.816 13.74 13.05 0.187 7.02 11.42 2.05 0.13 0.14 1.34 99.56  47.23 1.783 13.77 14.13 0.187 7.09 11.43 2.02 0.06 0.14 1.38 99.22  48.16 1.782 13.62 13.76 0.187 7.09 11.48 2.08 0.14 0.12 1.37 99.79  43.85 0.425 11.56 10.11 0.161 17.74 9.43 0.53 0.10 0.04 5.45 99.39  43.84 0.425 11.74 9.65 0.158 17.51 9.36 0.53 0.13 0.00 5.33 98.66  7.42 18.3 2.66 13.3 3.84 1.40 4.59 0.79 4.88 0.98 2.82 0.39 2.42 0.35 42.3 364 164 54.9 115 206 87 19 1.3 1 162 28 95 8.5 0.4 34 2.8 0.57 9 0.62 0.20  7.21 17.9 2.57 13.0 3.81 1.38 4.28 0.77 4.77 0.97 2.80 0.40 2.40 0.34 42.2 364 151 53.3 108 211 92 19 1.7 1 160 29 95 8.6 0.3 28 2.7 0.55 9 0.62 0.19  7.62 18.8 2.73 13.9 3.91 1.47 4.73 0.83 5.12 1.04 2.99 0.42 2.55 0.35 39.7 367 122 46.5 90 210 92 19 1.6 1 171 29 96 8.5 0.2 34 2.9 0.59 5 0.67 0.20  6.95 17.8 2.53 12.9 3.72 1.41 4.42 0.77 4.61 0.94 2.65 0.38 2.32 0.32 39.2 365 143 50.0 107 189 104 19 1.4 2 190 27 96 8.3 0.2 34 2.8 0.55 11 0.66 0.19  7.34 18.5 2.64 12.7 3.66 1.42 4.62 0.77 4.60 0.94 2.70 0.38 2.27 0.34 29.2 365 98 37.7 105 189 103 19 1.5 2 193 28 87 8.4 0.2 34 2.6 0.54 12 0.64 0.20  7.65 19.3 2.94 13.6 4.05 1.55 4.76 0.83 4.92 0.92 2.64 0.389 2.41 0.349 41.6 362 162 55.7 93 178 98 20 1.5 2 178 26 94 8.5 0.4 28 2.8 0.6 91 0.59 0.23  6.95 17.8 2.67 13.3 3.77 1.42 4.59 0.80 4.77 0.95 2.69 0.37 2.28 0.34 41.5 362 165 53.5 93 174 94 17 1.2 2 190 27 102 8.5 0.2 33 2.8 0.57  1.06 2.6 0.41 2.6 0.92 0.38 1.40 0.30 2.16 0.49 1.53 0.24 1.58 0.23 38.3 201 1710 80.3 755 92 77 10 1.0 5 100 16 16 0.7 2.8 19 0.5 0.09 7 0.10 0.05  0.96 2.5 0.38 2.3 0.84 0.37 1.42 0.30 2.17 0.50 1.54 0.23 1.52 0.23 40.1 189 1830 84.6 755 83 55 9 0.7 4 97 13 19 0.9 2.7 18 0.6 0.03 4 0.11 0.03  0.68 0.15  48  Sample Group Area Flow UTMEW UTMNS  4722A4(3)* 4722A5(1)* 4722A5(2r OUTLIER PlC OUTLIER KR KR KR Pillow Flow Flow 5595528 5595029 5595029 629490 627605 627605  4723A2* HI-MG KR Pillow 5588266 626698  4723A3* PlC KR Pillow 5588274 626641  --  PlC KR Pillow 5586081 626835  4723A10 4723A1 3(1 )* 4723A13(2)* THOL PlC PlC KR KR KR Flow Pillow Pillow 5578863 5599233 5599233 630940 616507 616507  4724A3 CG SL Flow 5581870 704472  Unnormalized Major Element Oxides (Weight %): Si0 2 1102 3 0 2 A1 3 0 2 Fe MnO MgO GaO 0 2 Na 0 2 K  42.94 0.42 11.26 10.82 0.161 18.28 8.98 0.54 0.02 0.03 LOl 5.7 Total 99.16 Trace Elements (ppm): La 1.08 Ce 2.6 Pr 0.43 Nd 2.5 Sm 0.87 Eu 0.405 1.45 Gd Th 0.3 Dy 2.11 Ho 0.47 Er 1.54 Tm 0.242 1.62 Yb Lu 0.244 36.4 Sc V 194 Cr 1750 Co 80 Ni 755 Cu 83 Zn 55 Ga 11 Ge 1.2 Rb 6 Sr 93 Y 15 Zr 16 0.7 Nb Cs 5.8 Ba 27 Hf 0.6 Ta Pb 22 Th 0.09 [I  007  48.95 2.295 13.61 12.56 0.188 6.18 9.33 3.26 0.30 0.13 2.00 98.80  48.45 2.333 12.51 15.24 0.191 5.99 8.99 3.30 0.30 0.19 1.95 99.45  46.73 0.611 15.24 10.26 0.158 10.27 9.93 2.26 0.38 0.06 3.70 99.60  44.41 0.539 12.75 10.33 0.148 15.42 8.73 0.78 0.07 0.05 5.61 98.83  44.39 0.663 14.93 10.11 0.139 13.02 9.73 1.56 0.07 0.06 4.91 99.58  50.03 2.083 12.31 15.21 0.223 5.66 9.19 2.94 0.70 0.18 1.55 100.07  44.62 0.443 13.71 10.38 0.138 14.47 9.37 0.86 0.06 0.05 5.59 99.68  44.71 0.442 13.75 10.37 0.138 14.48 9.36 0.86 0.07 0.05 5.59 99.81  49.08 1.457 14.77 11.60 0.128 8.73 11.02 1.99 0.15 0.12 0.98 100.02  8.77 23.0 3.37 17.2 5.20 1.74 6.39 1.11 6.59 1.34 3.85 0.55 3.31 0.45 38.7 481 79.7 45.6 59 116 106 17 0.7 6 225 39 127 10.0 0.3 87 3.7 0.67 6 1.08  9.46 25.2 3.68 17.9 5.21 1.79 6.63 1.20 7.08 1.39 3.94 0.57 3.48 0.51 33.1 495 59.0 40.7 59 114 103 20 1.3 6 229 39 126 10.6 0.4 88 3.7 0.70 7 1.08 oq  1.94 5.0 0.74 4.2 1.41 0.52 2.09 0.42 2.91 0.67 2.10 0.32 2.06 0.31 47.2 261 358 48.8 163 111 61 13 1.2 10 271 20 33 1.5 6.5 84 1.0 0.08  1.78 4.5 0.71 4.1 1.48 0.63 2.16 0.42 2.79 0.60 1.79 0.26 1.67 0.25 38.1 235 725 60.4 339 106 63 13 1.1 2 132 18 36 1.1 0.8 20 1.0 0.05 0.10  8.93 21.5 3.10 15.5 4.20 1.62 5.21 0.90 5.40 1.11 3.23 0.45 2.71 0.39 38.3 496 34.2 47.1 61 306 107 20 1.6 12 299 32 110 9.7 0.4 152 3.1 0.65 5 0.77  1.40 3.4 0.52 3.0 1.00 0.46 1.71 0.36 2.54 0.59 1.89 0.29 1.89 0.29 43.5 219 1370 72.2 583 142 106 12 1.2 2 73 16 24 0.8 0.7 13 0.7 0.04 8 0.15  1.36 3.4 0.51 2.9 1.01 0.44 1.69 0.35 2.50 0.56 1.79 0.28 1.84 0.28  0.23  1.80 4.5 0.67 3.8 1.27 0.51 1.86 0.37 2.60 0.59 1.86 0.29 1.85 0.28 41.0 218 1570 72.9 656 110 60 12 1.1 2 64 17 29 1.3 0.9 15 0.9 0.06 4 0.20  0.14  5.57 14.3 2.09 10.4 2.98 1.21 3.85 0.65 4.01 0.81 2.27 0.33 1.98 0.28 35.1 287 352 52.4 209 208 83 19 1.6 2 167 23 73 6.5 0.3 55 2.1 0.42 7 0.43  010  009  005  027  005  007  015  0R  222  583 98 62 12 1.3 1 73 17 22 0.7 0.7 13 0.7 0.04  49  5614A3’ 4724A5 5614AV Sample THOL PlC HI-MG Group KR SL KR Area Pillow Pillow Flow Flow 5599183 UTMEW 5580653 5599183 704736 616472 616472 UTMNS Unnormalized Major Element Oxides (Weight %): 2 Sb 48.08 46.24 48.43 0.477 0.471 1.729 1102 14.9 16.39 14.57 2O3 * 3 0 2 Fe 7.59 11.13 8.57 0.145 0.134 MnO 0.196 10.66 12.11 MgO 5.54 10.68 12.38 10.81 CaO 1.3 1.51 0 2 Na 2.01 0.01 0.06 0 2 K 0.10 0.04 0.04 0.15 p205 4.13 4.91 LOI 1.29 99.01 99.14 98.6 Total Trace Elements (ppm): 1.71 7.98 1.79 La 4.0 19.4 4.3 Ce 0.65 0.59 Pr 2.72 3.2 3.4 Nd 13.3 1.09 1.11 Sm 3.69 0.483 1.42 0.501 Eu 1.71 4.58 1.74 Gd 0.37 0.37 0.75 Th 2.67 2.66 Dy 4.53 0.59 0.6 Ho 0.89 2.54 1.87 1.87 Er 0.292 0.297 0.36 Tm 1,99 2.26 2.01 Yb 0.308 0.312 0.32 Lu 48.8 45 Sc 34.4 217 222 V 299 1420 207 1370 Cr 76.1 43.1 68.7 Co 564 551 98 NI 104 111 Cu 198 76 53 51 Zn 12 21 11 Ga 0.8 1.5 0.9 Ge Rb 120 130 272 Sr 18 17 25 Y 24 22 Zr 92 0.8 8.6 0.7 Nb 0.4 0.4 0.1 Cs 18 20 Ba 32 0.7 0.7 Hf 2.7 0.60 Ta 28 26 Pb 0.17 0.69 0.15 Th nii fl9 nil ii  5614A5 HI-MG KR Breccia 5599192 614756  5I4A1Q THOL KR Flow 5595261 615253  5614A11 THOL KR Flow 5593546 615098  5614A13 THOL KR Flow 5588018 618867  5614A14 CG KR Sill 5588246 618183  5614A15 CG KR Flow 5589935 615917  5615A1 THOL KR Pillow 5599424 620187  47.1 0.512 14,52 9.12 0.135 10,92 10.78 2.1 0.01 0.05 4.67 99.89  46.69 1.761 13.32 12.72 0.168 7.09 10.62 3.49 0.01 0.14 3.53 99.43  48.06 1.741 13.35 12.96 0.187 6.38 10.51 3.23 0.44 0.13 2.39 99.37  47.78 1.86 12.91 14.23 0.211 6.47 10.24 2.91 0.44 0.15 2.02 99.21  46.17 1.773 13.8 13.53 0.136 8.25 1041 2.01 0.21 0.14 2.87 99.3  46.2 1.605 14.77 10.89 0.123 9.37 10.22 1.55 0.08 0.13 4.07 99.03  47.61 1.873 13.55 14.34 0.188 7.42 9.86 2.87 0.21 0.15 1.92 100  0.91 2.5 0.43 2.7 1,02 0.526 1.6 0.34 2.35 0.52 1,67 0.27 1.8 0.267 43.7 206 797 68.6 315 96 48 13 0.9  8.04 19.7 2.96 13.7 3.88 1.44 4.47 0.79 4.59 0.85 2.47 0.37 2.27 0.325 43.8 354 195 48.9 93 134 80 20 1.4 86 26 90 8.1 0.8 11 2.7 0.6 97 0.75 n  8.51 20.9 3.08 14.7 4.2 1.59 4.79 0.87 5.12 0.98 2.83 0.413 2.54 0.375 424 372 71.9 51.5 65 165 102 20 1.6 8 274 29 98 9.0 0.1 85 2.9 0.7 98 0.66  7.31 18.7 2.81 13.2 3.89 1.47 4.61 0.81 4.76 0.9 2.55 0.375 2.35 0.336 39.3 332 328 58.9 147 83 86 20 1.3 3 283 28 91 8.2 0.1 62 2.8 0.5 94 0.54 n’i  6.88 17.6 2.68 12.5 3.43 1.34 4.03 0.7 4.11 0.76 2.18 0.324 2 0.29 32.3 271 400 56.8 213 111 72 19 1.1  141 16 19 0.5  7.23 18.0 2.68 12.3 3.6 1,39 4.24 0.77 4.57 0.89 2.53 0.36 2.26 0.329 43.8 362 76 53.6 67 181 93 17 0.9 9 381 27 86 8.0 0.4 80 2.5 0.5 97 0.62 n4  8.17 20.2 3,01 14.3 4,12 1.58 4.88 0.85 5.01 0.94 2.7 0.404 2.51 0.365 44.5 380 172 57.4 86 182 84 19 1.3 5 287 29 98 8.6 0.9 39 3.0 0.6 97 0.64 (127  9 0.6 29 0.08 nn  183 23 86 7.7 0.2 32 2.6 0.5 82 0.52 n92  50  Sample Group Area Flow UTM EW UTM NS  5615A5 CG KR Flow 5601095 624103  5615A6 5615A7(1) 5615A7(2)* PlC PlC CG KR KR KR Pillow Sill Pillow 5595569 5601095 5595569 629573 629573 624103  5815A8 ThOL KR Pillow 5595513 629434  5615A10 ThOL KR Pillow 5595376 629069  5615A11 OUTLIER KR Pillow 5595029 627605  5615A1 PIG KR Pillow 5586126 626824  5616A1* PlC KR Pillow 5598448 616507  5616A2 ThOL KR Flow 5585731 623077  48.31 1.745 13.45 13.48 0.196 6.78 11.77 1.8 0.03 0.14 1.74 99.43  47.29 1.807 13.7 14.23 0.195 6.77 10.65 2.58 0.21 0.14 1.57 99.14  49.08 2.304 11.86 15.2 0.215 5.73 9.84 3.25 0.04 0.22 2.07 99.81  45.35 0.643 14.07 10.4 0.142 12.56 9 2.11 0.02 0.06 4.68 99.02  43.7 0.439 13.66 10.47 0.158 15.55 8.71 0.98 0.04 0.04 6.05 99.8  46.72 1.939 13.21 14.11 0.235 6.29 11.19 2.49 0.01 0.16 3.38 99.66  7.32 18.4 2.69 12.9 3.78 1.47 4.4 0.79 4.65 0.89 2.58 0.379 2.34 0.339 40.4 353 173 53 96 175 88 20 1.4 2 194 28 91 8.0 0.6 39 2.7 0.6 91 0.59 0,22  7.34 18.5 2.84 13.2 3.92 1.48 4.65 0.81 4.79 0.91 2.58 0.38 2.42 0.348 39.8 363 166 52,4 94 185 86 20 1.3 9 279 28 96 8.5 1.3 61 2.8 0.6 92 0.61 0.24  6.41 17.3 2.89 15.6 5.06 1.88 6.19 1.13 6.65 124 3.67 0.547 3.44 0.493 43.8 520 107 53.4 56 208 94 18 0.7  1.73 4.7 0.77 4.4 1.47 0.607 2.13 0.42 2.78 0.59 1,78 0.267 1.75 0.269 38.3 215 906 67.2 368 83 50 14 1.1 2 189 16 35 1.4 0.6 15 1.1  1.52 3.6 0.55 3.0 1.02 0.454 1.57 0.34 2.44 0.55 1.73 0268 1.77 0.277 37.5 204 3000 67.9 559 77 53 12 1.1  8.87 21.0 3.02 14.4 4.16 1.59 4.81 0.86 5.07 0.92 2.72 0.413 2.62 0.378 41.6 401 76 50.8 58 210 85 22 1.6  112 16 22 0.9 0.8 20 0.7  67 30 100 9.2  34 0.09 0.07  22 0.14 0.1  Unnomialized Major Element Oxides (Weight %): Si0 2 2 riO O 2 AJ * 3 0 2 Fe MnO MgO  CaO Na 0 2 O 2 K 5 0 2 P LOI Total  47.76 2.125 14.41 12.5 0.191 5.71 8.81 4.16 0.2 0.18 3.17 99.2  46.53 2.119 14.06 13.01 0.177 5.7 10 3.64 0.09 0.19 345 98.96  47.16 0.466 11.84 11.54 0.172 18.59 9.45 0.42 0.01 0.03 99.67  45.73 0.442 11.48 11.22 0.166 18.19 9.14 0.41 0.16 0.05 2.86 99.84  11.7 26.9 3.95 17.7 4.76 1.73 5.32 0.93 5.31 0.98 2.86 0.43 2.73 0.391 38.5 376 164 43.7 85 148 102 21 1.4 2 170 31 121 13.0  1.09 2.7 0.44 2.5 0.88 0.381 1.42 0.3 2.16 0.49 1.55 0.253 1.71 0247 39.2 224 1910 87.1 729 86 57 10 1.1 6 124 15 16 0.9 4.4 27 0.6  1.02 2.6 0.41 2.4 0.85 0.361 1.35 0.3 2.12 0.46 1.46 0.236 1.58 0.245 39.5 222 1850 89.3 680 80 54 10 0.9 6 120 15 15 0.7 4.5 24 0.5  24 0.1 0.07  22 0.08 0.07  Trace Elements (ppm): La Ce Pr Nd Sm Eu Gd Th Dy Ho Er Tm Yb Lu Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Cs  Ba Hf Ta Pb Th U  11.6 28.4 4.01 17.7 4.74 1.78 5.49 0.93 5.49 1.02 2.91 0.441 2.75 0.392 35.7 381 127 39.4 73 105 86 21 1.4 128 32 116 12.7 0.2 36 3.4 0.9 110 0.92 0.34  34 3.5 0.9 118 0.93 0.33  -  143 39 124 9.9 0.1 20 3.8 0.7 113 1.01 0.41  -  8 2.9 0.6 96 0.63 0.25  51  Sample Group Area Flow UTM EW UTMNS  5616A3 CG KR Flow 5584647 623236  5616A7 HI-MG KR Pillow 5589833 626879  5617A1 CG SL Sill 5560375 702240  5617A4 5617A5(1)* 5617A5(2)* MINSIL CG CG SL SL SL Sill Sill Sill 5557712 5557712 5557712 700905 700905 700905  5618A1 THOL 01 Flow 5557892 338923  5618A3 THOL QI Pillow 5552258 341690  5618A4 THOL QI Breccia 5552258 341690  93G171 PlC KR Pillow 5599395 616613 47.93 0.461 14.02 9.9 0.19 15.8 10.42 1.02 0.11 0.08  Unnormalized Major Element Oxides (Weight %): Si0 2 1102 3 0 2 Al * 3 0 2 Fe MnO MgO CeO 0 2 Na 0 2 K 5 0 2 P LOl Total  46.77 1.814 14.23 12.85 0.185 7.28 10.92 1.86 0.16 0.13 2.92 99.14  46.75 0.732 15.92 10.88 0.153 8.7 11.69 2.12 0.07 0.04 2.86 99.91  49.1 0.901 13.72 11.34 0.16 6.99 10.96 3.46 0.03 0.08 3.23 99.97  48.06 3.505 12.79 16.78 0.164 5.25 648 2.31 0.69 0.35 3.22 99.6  49.31 1.713 13.39 12.39 0.174 7.5 12.01 1.83 0.22 0.13 1.28 99.95  47.4 1.71 13.33 12.71 0.174 7.46 11.93 1.8 0.17 0.14 1.38 98.21  48.61 1.749 12.82 13.81 0.211 6.96 10.54 2.76 0.5 0.14 1.8 99.9  47.9 1.362 13.79 11.62 0.158 6.57 12.08 3.13 0.12 0.1 3.17 99.99  40.29 2.159 16.27 18.1 0.28 9.7 6.78 0.58 0.52 0.18 4.77 99.63  1.51 3.8 0.59 3.5 1.36 0.638 2.05 0.43 2.9 0.61 1.91 0.305 2.02 0.302 50.7 270 346 56.7 122 111 51 15 1  2.84 6.9 1.1 6.1 2.14 0.888 3.05 0.63 4.19 0.86 2.65 0.415 2.66 0.401 54.5 327 210 46.8 70 160 69 16 1.3  181 19 26 1.1 0.3 23 0.8  58 27 45 2.1 0.2 12 1.4 0.1 48 0.28 0.16  22.3 51.5 7.19 32.7 8.86 3.33 9.84 1.64 9.58 1.78 5.06 0.73 4.56 0.637 44.2 517 64.4 38.3 39 232 160 27 2 21 197 52 229 19.7 1.2 771 6.4 1.4 151 2.09 0.88  8.13 19.7 2.89 13.3 3.83 1.45 4.36 0.75 4.35 0.83 2.37 0.341 2.13 0.304 40.8 342 274 51.8 98 161 77 19 1.1 7 255 24 89 8.9 0.2 38 2.6 0.6 85 0.61 0.23  7.94 19.2 2.85 13.3 3.77 1.43 4.32 0.75 4.25 0.81 2.31 0.342 2.14 0.298 37.7 338 255 47.6 97 160 76 19 0.7 7 254 23 86 8.5 0.2 37 2.5 0.6 83 0.57 0.25  7.72 19.1 2.85 13.5 3.98 1.47 4.56 0.79 4.71 0.88 2.56 0.375 2.35 0.342 42.9 367 114 53 79 25 89 19 1.5 8 227 27 89 8.1 0.4 103 2.7 0.6 83 0.57 0.22  6.57 15.4 2.22 10.5 2.98 1.21 3.56 0.63 3.84 0.75 2.16 0.331 2.12 0296 41.8 313 194 46 67 125 92 18 1.5 3 170 21 67 6.6  10.7 24.3 3.48 15.9 4.53 2.04 5.64 0.99 5.95 1.15 3.36 0.495 3.11 0.455 54.2 499 159 62 68 109 75 24 1.3 10 220 38 112 9.8 0.6 109 3.3 0.7 65 0.71 0.34  100.00  Trace Elements (ppm): La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sc V Cr Co Ni Cu Zn Ga Ge Rb Sr Y Zr Nb Ca Ba Hf Ta Pb Th U  7.14 17.9 2.72 12.9 3.82 1.47 4.49 0.79 4.66 0.9 2.6 0.373 2.35 0.34 40 349 317 52.6 110 164 87 20 1.3 3 237 25 91 8.1 1.2 39 2.7 0.6 93 0.52 0.23  37 0.14 0.09  17 2 0.5 66 0.45 0.22  1.4 3.6 0.56 2.9 1.23 0.47 2.10 0.32 2.38 0.64 2.11 0.297 1.97 0.282 140 606 491 91 57  13 24 0.9 20 0.8 0.1 0.15  52  pu ‘(q>j pu ;o ssoj Ajjids) ‘-jj’-j IUo!IA p ioj o&iu.i iuaijjip (ro oi uop spux) q jud ni ‘suoid pu ij uo uoi.i jo soojj p iiioii pQJ 1u-33fl uoq uo3uSip StLJUA UO!z!1UUUOU liv •SUiU pjTJ UTUW ijo •(c661) mis pu nouoao woij jo tp wo sjdmUs ioj stuUd 3uwp-ooI3 pzquuou-uw A!w!.Id ai (j) pu ‘(p) ‘(q) •pusj JA1LOOUEA pzquuou-upuotp ai () pu ‘(a) ,jo tp wog sjdwUs io; sud uo saro pjg WUW ‘to) uo uuo usnuuj ioj suoirnIouoo 1um -jqdmoou ipO pu 3J 3pOJ-Ou L1 a.In,I rn  13  A OH 1(53 qlpD 03 ‘1 IH JZWS IS PH d 3) 1  •  •  II  •  •  •  •  •  •  •  •  •  ,  •,  fl  ELqN ) ,  qj •  ,  q 5)  •  I  fl  •  WL  13  •  •  OH  .  1(53  •  qI  •  p9  •  553 •  W5 Wd  •  •  PN  •  14  •  3)  •  ,  •  1  ()  (1) II!S P2Z!TeJ3Ui +  3 0L3  MO p3MOfld X ieseq !w3Ior1 e )OJ iJew p3u1e16-3s13o) 0 3 eseq 6 w O ’ H -1 0 !J’Id V 0L  qWSMoJJ UflOfiJ till  fl1cVJ3  P!WSMOIJV  11111111111111  AoHXaqIpDn3  ‘  ,0L  1;H,zwsJspNJda)e1eLqN  )1  fl  UflOjAJ I  1  1  1  1  1  1  1 —  qLeaqus)  fl  •  I  I  CIJ WI p  •  13 i  OH  p  1(53 (Ii. p9 i  •  •  fl3 W5 Wd •  I  I  I  I  14  PN  3) I  00L  3 I  (D)  I  If,  3  3 01  • liii  111111  •,••,  ••,  PN d  3)  l 1qN )I fl qj  1111111  liii  q  liii  SD  1111  fl(  10  •  (•t  ee,uq)S  001  fl 53), 13 A oHXoqIp9 flJ 1. JH JZU.JS iS  (oo’3psirS  CI), p  Wj •  13 p  OH •  1(53 (Ij i  •  p9  •  fl3 W Wd PN •  •  •  OOL  14  3)  •  •  s,  •  SSIeS)  e6eJ3Ae oow pesidea  usnw 111111111  •  I  I  001  I  I  I  I  I  I  I  I  I  I  I  I  001  sediment-sill complex at Schoen Lake, are distinguished by higher Ti0 2 and FeOT than the main group of tholeiitic basalts. The tholeiitic basalts are similar in major-element composition to previously published results for samples from the Karmutsen Formation; however, the Keogh Lake picrites, which encompass the picritic and high-MgO basalt pillow lavas, extend to —20 wt % MgO (Fig. 2.6, and references therein). The tholeiitic basalts from the Karmutsen Range form a tight range of parallel light rare earth element (LREE)-enriched patterns (La/YbcN=2.1-2.4; mean 2.2 ± 0.2), whereas the picrites and high-MgO basalts from the Karmutsen Range form a range of parallel LREE-depleted patterns (LaJYbcN=0.3-0.7; mean 0.6 ± 0.2) with lower REE abundances than the tholeiitic basalts (Fig. 2.7). Tholeiitic basalts from the Schoen Lake and Mount Arrowsmith areas have similar REE patterns to samples from the Karmutsen Range (Schoen Lake- LaJYbCN=2.l-2.6; mean 2.3  ±  0.3; Mount Arrowsmith  LaJYbCN=1.9-2.5; mean 2.2 ± 0.4), and the coarse-grained mafic rocks have similar REE patterns to the tholeiitic basalts (LaJYbCN=2.l-2.9; mean 2.5  ±  0.8). Two LREE-depleted  coarse-grained mafic rocks from the Schoen Lake area have similar REE patterns (LaJYbCN=0.7) to the picrites from the Keogh Lake area, indicating that this distinctive suite of rocks is exposed as far south as Schoen Lake (Fig. 2.7). The anomalous pillowed flow from the Karmutsen Range has lower La/YbCN (1.3-1.8) than the main group of tholeiitic basalts from the Karmutsen Range (Fig. 2.7). The mineralized sill from the Schoen Lake area is distinctly LREE-enriched (La/YbCN=3.3) with the highest REE abundances (La=94.0) of all Karmutsen samples, which may reflect contamination by adjacent sediment. The primitive mantle-normalized trace-element patterns (Fig. 2.7), and traceelement variations and ratios (Fig. 2.8), highlight the differences in trace-element concentrations between the four main groups of Karmutsen flood basalts on Vancouver Island. The tholeiitic basalts from all three areas have relatively smooth, parallel trace element patterns; some samples have small positive Sr anomalies, relative to Nd and Sm, and many samples have prominent negative K anomalies relative to U and Nb, reflecting K-loss during alteration (Fig. 2.7). The large ion lithophile elements (LILE) in the tholeiitic basalts (mainly Rb and K, not Cs) are depleted relative to HFSE and LREE, and LILE segments, especially for the Schoen Lake area (Fig. 2.7d), are remarkably parallel.  54  15  •  •  .  .  1.6  ,  Nb(ppm)  Nb/La 1.2-  10  8o  .  0.8  oo  -  5 •  •  Q (a)  I  0 0  I  I  I  I  50  Picrite High-MgO basalt 0 Coarse-grained 0 Tholeiltic basalt X Pillowed flow I I I I I  04  -  (b) 0  5  10  15  20  25  MgO (wt%)  Zr (ppm) 1.25  ‘  00 150  100  -  1.2  ....i....i.,..i....i,.,.  i  Th (ppm)  i  i  i  i  Th (ppm)  i  i  I  I  >X  :: 0.25  (d)  0.2 561 5A1 2 I I  (C)  0.00 0  1  2  •  I  3  •  I  4  I  0.0  •  5  0.0  I 0.1  I  I 0.2  I  I 0.3  I  0.4  0.5  Hf(ppm) U(ppm) Figure 2.8 Whole-rock trace-element concentrations and ratios for the Karmutsen Formation (except panel b is versus MgO). (a) Nb vs. Zr. (b) Nb/La vs. MgO. (c) Th vs. Hf. (d) Th vs. U. There is a clear distinction between the tholeiitic basalts and picrites in Nb and Zr, both in concentration and the slope of each trend.  55  The picrites and high-MgO basalts form a tight band of parallel trace-element patterns and are depleted in HFSE and LREE with positive Sr anomalies and relatively low Rb. The coarse-grained mafic rocks from the Karmutsen Range have identical trace-element patterns to the tholeiitic basalts. Samples from the Schoen Lake area have similar traceelement patterns to the Karmutsen Range, except for the two LREE-depleted coarse grained mafic rocks and the mineralized sill (Fig. 2.7d). Sr-Nd-Hf-Pb isotopic compositions The nineteen samples of the Karmutsen Formation from the four main groups, selected on the basis of major and trace-element variation, stratigraphic position, and location to cover the range of these parameters, have indistinguishable age-corrected Hf and Nd isotope ratios and distinct ranges of Sr isotopic compositions (Fig. 2.9). The tholeiitic basalts, picrites, high-MgO basalt, and coarse-grained mafic rocks have initial Hf— 8  +8.7 to +12.6 and 5 Nd= +6.6 to +8.8 corrected for in situ radioactive decay since 230  Ma (Fig. 2.9; Tables 2.3 and 2.4). All the Karmutsen samples form a well-defined linear array in a Lu-Hf isochron diagram corresponding to an age of 241  ±  15 Ma (Fig. 2.9).  This is within error of the accepted age of the Karmutsen Formation and indicates that the Hf isotope systematies have behaved as a closed system since ca. 230 Ma. The anomalous pillowed flow has similar initial Epj (+9.8) and slightly lower initial ENd (+6.2) than the other Karmutsen samples. The picrites and high-MgO basalt have higher initial Sr =0.70306-0.70381) 86 Sr/ Sr (0.70398-0.705 18) than the tholeiitic basalts (initial 87 86 Sr/ 87 Sr =0.70265-0.70428) overlap the 86 Sr/ and the coarse-grained mafic rocks (initial 87 ranges of the picrites and tholeiitic basalts (Fig. 2.9; Table 2.3).  The measured Pb isotopic compositions of the tholeiitic basalts are more radiogenic than those of the picrites and the most magnesian Keogh Lake picrites have the least radiogenic Pb isotopic compositions. The range of initial Pb isotope ratios for Pb 204 Pb/ Pb = 15.547-15.562, and 208 204 Pb/ the picrites is 206 Pb = 18.142-18.580, 207 204 Pb/ =  Pb = 18.782-19.098, 204 Pb/ 37.873-38.257 and the range for the tholeiitic basalts is 206  Pb = 37.312-38.587 (Fig. 2.10; Table 2.5). The 204 Pb/ Pb = 15.570-15.584, and 208 204 Pb/ 207 coarse-grained mafic rocks overlap the range of initial Pb isotopic compositions for the Pb = 15.568-15.588, and 204 Pb/ Pb = 18.652-19.155, 207 204 Pb/ tholeiitic basalts with 206  56  0.5132  -  0.2834  -  11•1J•  d 143 N 1 Nd/  I  I  I  I  Hf 177 Hf/ 176 0.2833  0.5131  Age=241 ± l5Ma (0=+9.90±  -  0.2832 0.5130  0.5129  a  A Picrite  X -  (a) 0.5128  i  ‘  0.17  0.15  0.2831  High-MgO basalt 0 Coarse-grained • tholeütic basalt X Pillowed flow  0 0.2830  L_  0.2829 0.21  0.19  0.23  0.25  I  —I  0.02  0.00  I  I  •  ‘  i  Hf 177 Lu/ 176 14  •  (230 Ma)  ‘  I  ‘  I  ‘  0 0  8  •  0  -  0  LOl (wt 96)  6  t  A  4 X  6  10  (d) ê 0.702  i  8 “Sri Sr  0.703  0.704  0.705  0.706 •  0.703  0.704  x  A 4723A2  dD (c)  0.702  I  I  EHf (230Ma)  12  Nd  4  0.10  0.08  0.06  0.04  Nd 144 5m/ 147 10  i  0.705  Sr (230 Ma) Sr/ 86 87  0.706  -  (e) I  6 5  I  6  i  I  i  7  I  I  I  9  8  i  10  Ma) Nd  d vs. 43 ‘ N 1 Figure 2.9 Whole-rock Sr, Nd, and Hf isotopic compositions for the Karmutsen Formation. (a) NW Hf. The slope of the best-fit line for all samples corresponds to an age 77 LuJ’ 47 (b) 176 ‘ Sm/’Nd. Hf vs. 176 177 Hf/ Sr. (e) Initial CHf VS. 86 Sr/ Sr. Age correction to 230 Ma. (d) LOT vs. 87 86 Sr/ of 241 ± 15 Ma. (c) Initial ENd VS. 87 Nd Average 2a error bars are shown in a corner of each panel. Complete chemical duplicates, shown in Tables 6 2.3 and 2.4 (samples 4720A7 and 4722A4), are circled in each plot.  57  15.68  I  I  I  I  I  I  I  I  I  15.60  I  I  •  I  •  I  •  I•I•1•I•I•  4723A2  4723A2  • 207 pb 204 pb/  15.66 15.58  15.64  0  (230 Ma)  -  •  15.56  -  —  15.62  4722A4  15.54  —  —  4723A13 _‘><•s4723A3  ‘  -  15.60  Picrite  15.52  15,58  <>High-MgO basalt 0 Coarse-grained Tholeiitic basalt Pillowed flow  -  4723A4  (a) I  15.56 18.6  I  I  19.0  I  I  194  I  I  I  202  19.8  (b)  I  I  I  20.6  21.0  1530 17.8  18.0  18.2  Pb 204 pb/ 206 39.6  •  ‘  i  ‘  i  •  18.4  18.6  18.8  Pb 204 Pb/ 206 i  ‘  39.0  i  4723A2  39.2  38.6  5  (230 Ma)  —  6 0  LOl (wt %) -  19.4  (230 Ma)  X 38.8  19.2  111111111111111  -  -  19.0  38.2  A  0  4723A2  0 0 384  0  (d) 186 c  (c) 38.0 18.6  ‘  ‘  19.0  I  194  4723  37.8  2  I  •  19.0 I  19.8  19A I  19.8 I  20.2  I  -  Pb 204 Pb’ 20 20.2 I  20.6  (e)  20.6 21.0 I I  21.0  ililililili 17.8  18.0  18.2  18.4  18.6  18.8  pb 204 pb/ 206  liii 19.0  19.2  19.4  (230 Ma)  Figure 2.10 Pb isotopic compositions of leached whole-rock samples measured by MC-TCP-MS for the Pb vs. 206 204 Pb/ Pb. (b) Initial 4 ° 2 Pb/ Karmutsen Formation. Error bars are smaller than symbols. (a) Measured 207 Pb vs. 206 204 Pb/ Pb. (d) LOT vs. 4 PbP° Pb vs. 206 204 Pb/ 207 Pb. Age correction to 230 Ma. (c) Measured 208 4 PbP° Pb vs. 206 204 Pb/ Pb. Complete chemical duplicates, shown in Table 2.5 (samples 204 Pb/ Pb. (e) Initial 208 204 Pb/ 206 4720A7 and 4722A4), are circled in each plot. The dashed lines in panels b and e show the differences in agecorrections for two picrites (4723A4, 4722A4) using the measured U, Th, and Pb concentrations for each sample (black triangles) and the age-corrections when concentrations are used from the two picrites (4723A3, 4723A13) that appear to be least affected by alteration.  58  SL KR KR KR KR KR KR  CG  PlC  PlC  PlC  PlC  PlC  HI-MG  5617A1  4722A4  4722A4(dup)  4723A3  4723A4  4723A13  4723A2  Sr  8.23  0.67  1.43  1.65  3.16  3.16  2.00  3.00  1.44  0.11  1.79  2.18  6.11  4.46  1.65  1.58  2.54  3.49  3.27  3.78  1.28  5.7 13.2 12.9 6.06 2.70 2.48 5.91  2.05  135  3.84 3.82 2.14 1.07 0.97 2.09 2.14 1.33 1.99  0.70332 0.70373 0.70391 0.70483 0.70483 0.70398 0.70423 0.70403 0.70518  0.0310 0.0366  269  63  110  69  77  77  58  0.0998 0.1184 0.1 184 0.0696 0.0375 0.0312 0.0885  7 8  0.703421  0.705466  0.704132  0.704352  0.704209  0.705214  7  8  8  9  7  8  7  0.704241 0.705220  7  0.703849  5.79  3.54  5.90  0.513122  16.0  4.56  0.70295  b  8.5 7.6 8.5 7.9  0.51278 0.51273 0.51278 0.51275  0.2142 0.2192 0.2268 0.2081  9.0 8.2 9.4 8.2  7 10 7  0.513098 0.513060 0.513118  8  8.3 0.51277  0.513059  8.1 0.51276 0.2361  8.5 0.51278 0.2384 6  0.513115  7.2 0.51271  9.4  0.2135  9.0 7 0.513097  6.9 0.51270  9.3  0.1790  6.7  7.7 8.7 0.51279  6  0.1757  6.3 6  0.512961  6  9.4 7  0.512983  0.1722 0.2191  6.9 6  0.512994 0.513120  0.51273  8.0 0.1735  0.513012  7.3  0.70428  0.0369 0.0055  9  0.703067 0.704294  0.703078  6  17.3  4.96  0.70295  0.0401  0.51275  6  7.3 0.51272 0.1711  6.6  7  0.512976  16.8  4.75  0.70265  9  0.1438  6.2 0.51266 0.1756  5.5  6  0.512922  6.10  0.70366  6.6  0.51268 0.1691  5.8  6  0.512933  0.0678  0.703121  237  21.0  5.48  0.70297  7.6 7.2 0.51271  0.1675  6.4  7  0.512965  0.0277  123  60  19.6  4.05  0.70300  0.0220  7.2 0.51273  0.1662  6.7  7  0.51271  0.1718  0.512984  7 7  140  21.0  5.77  0.70295  0.0341  7.3  0.51272  6.5  7.7  0.51274  0.1742  8.1  CNd(t)  0.1688  0.51275  0.1656  230 Ma  d 143 147 N 1 Sm/ Nd 1 Nd/  6  7.0 6.5  6  7.1  Nd 6  6  6  am 2  0.512972  0.703062 0.703877  157  14.8  4.22  0.70361  0.0441  14.6  0.512972  16.1  4.48  0.70368  0.0387  7  8  6  0.51 2998  16.6  4.79  0.70358  0.0387  0.513004  16.8  4.60  0.0183  0.70319  d 143 N 1 NW  Nd  (ppm)  Sm  r 1 S 6 5r/° 81  230 Ma  (ppm)  Rb/Sr 87  0.703076  0.703066  0.703757  9  8  0.703702 0.703811  6  am 2  0.703247  SrISr 87  191  172  209  215  229  244  283  202  (ppm) (ppm)  Rb  °  THOL, tholentic basalt, CG, coarse-grained rnafic rock, PlC, picrite, HI-MG, high-MgO basalt; OUTLIER, anomalous pillowed flow in plots. Abbreviations for area are: KR, Karmutsen Range, SL, Schoen Lake, MA, Mount Arrowsmith. (dup) indicates complete chemistly duplicate. All isotopic and elemental analyses carried out at the PCIGR the complete trace element analyses are shown in Appendix C.  SL KR  SL  CG  4720A7  CG  5L  CG  4720A6  CG  KR  OUTLIER  4722A5  5616A3  SL  THOI  4721A4  4724A3  SL  THOL  4721A2  SL  SL  THOL  4720A4  SL  MA  THOL  4719A3  CG  MA  THOL  471 9A2  CG  MA  THOL  471 8A7  4720A7(dup)  MA  THOL  471 8A2  4720A10  Areab  Groups  Sample  Table 2.3 Sr and Nd isotopic geochemistiy ofKarmutsen basalts, Vancouver Island, B.C.  Table 2.4 Hfisotopic compositions ofKarmutsen basalts, Vancouver Island, B.C. Sample  Groupa  Areab  Lu  Hf  (ppm)  (ppm)  Hf 76 Hff’ 177  45  m 2  Hf 1 Lu/ 176  Hf 176 Hf/ 177  (t) 45  230 Ma  4718A2  THOL  MA  0.38  2.53  0.283007  4  8.3  0.0211  0.28291  4718A7  THOL  MA  0.46  2.41  0.283001  7  8.1  0.0271  0.28288  9.1  4719A2  THOL  MA  0.40  2.16  0.283079  5  10.9  0.0262  0.28296  12.0  4719A3  THOL  MA  0.37  2.12  0.283024  9  8.9  0.0246  0.28291  10.2  4720A4  THOL  SL  0.53  3.04  0.283002  7  8.1  0.0247  0.28289  9.5  4721A2  THOL  SL  0.36  2.99  0.283004  10  8.2  0.0173  0.28293  10.7  4721A4  THOL  SL  0.53  2.79  0.283006  6  8.3  0.0268  0.28289  9.3  4722A5  OUTLIER  KR  0.56  3.15  0.283015  6  8.6  0.0254  0.28290  9.8  4720A6  CG  SL  0.45  2.38  0.283012  5  8.5  0.0269  0.28289  9.5  4720A7  CG  SL  0.46  2.23  0.283012  6  8.5  0.0291  0.28288  9.1  4720A7(dup)  CG  SL  0.43  2.35  0.283012  4  8.5  0.0260  0.28290  9.6  4720A10  CG  SL  0.36  1.00  0.283179  7  14.4  0.0515  0.28295  11.5  4724A3  CG  SL  0.34  1.41  0.283035  8  9.3  0.0339  0.28288  9.2  5616A3  CG  KR  0.34  2.70  0.283024  7  8.9  0.0179  0.28294  11.3  5617A1  CG  SL  0.40  140  0.283161  4  13.8  0.0407  0.28298  12.6  4722A4  PlC  KR  0.29  0.48  0283321  10  194  0.0857  0.28294  11.2  4722A4(dup)  PlC  KR  0.29  0.45  0.283350  11  20.4  0.0915  0.28294  11.3  4723A3  PIG  KR  0.45  0.98  0.283197  6  15.0  0.0649  0.28291  10.1  4723A4  PIG  KR  0.35  0.90  0.283121  26  12.3  0.0561  0.28287  8.7  4723A13  PlC  KR  0.35  0.63  0.283250  7  16.9  0.0791  0.28290  9.7  4723A2  HI-MG  KR  0.43  1.06  0.283186  7  14.7  0.0579  0.28293  10.8  10.2  a THOL, tholeiitic basalt, CG, coarse-grained mafic rock, PlC, picrite, HI-MG, high-MgO basalt; OUTLIER, anomalous pillowed  flow in plots. b Abbreviations for area are: KR, Karmutsen Range, SL, Schoen Lake, MA, Mount Arrowsmith. (dup) indicates complete chemistry duplicate. All isotopic and elemental analyses carried out at the PCIGR; the complete trace element analyses are shown in Appendix C.  60  Th  0.06 0.05  0.03  KR KR  KR KR KR  PlC  PIG  PlC  PlC  HI-MG  4722A4(dup)  4723A3  4723A4  4723A13  4723A2  0.0017  KR  PIG  4722A4  37.676 15.590 19.242 134.7  0.298 41.0  39.2295 0.0073 0.0030  15.6656  20.7321 0.0037  0.09  37.873 15.561 18.580 41.5 0.067 9.2 38.3518 0.0030  0.0011  15.5784  18.9131 0.0011  0.19  0.11  0.18  37.858 17.868 55.5  0.261 35.9 384984 0.0033  0.0012  15.5832  19.1733 0.0013  0.09  37.996  15.517  0.083  38.4434 0.0027  0.0011  15.5820  18.9873 0.0012  0.32  0.19  38.257 15.561  18.573 38.8  11.4  15.5890  0.16  15.548 18.142 14.1 0.162 22.4  0.03  38.074 15.547  18.197 28.8  0.151 20.8  38.4186 0.0029  18.9539 0.0013  38.4063 0.0041  0.0012  15.5852  18.9514 0.0017  0.17  0.07  38.603  b °THOL, tholelitic basalt, CG, coarse-grained mafic rock, PlC, picrite, HI-MG, high-MgO basalt; OUTLIER, anomalous pillowed flow in plots. Abbreviations for area are: KR, Karmutsen Range, SL, Schoen Lake, MA, Mount Arrowsmlth. (dup) indicates complete chemistry duplicate. All isotopic and elemental analyses carried out at the PCIGR; the complete trace element analyses shown in Appendix C.  0.06  0.05  0.05  38.4401 0.0016  39.0679 0.0015  0.0006 0.0006  15.5910  19.1202 0.0007  CG  15.5986  5617A1  0.0013  15.5880  0.30 19.4845 0.0007  0.09  19.2520 0.0014  CG  5616A3  15.570 18.900  0.60  SL KR  CG  4724A3  38.153 38.519  15.568  18.652 14.3 0.070  33.6 9.7  38.9072 0.0032  0.044  6.1  38.3176 0.0042  0.0016  15.5788  18.8745 0.0018  0.51  0.11  0.05  SL  CG  4720M0  38.638 38.735 15.588 19.154  48.8  0.108  14.9  39.2975 0.0022  0.0006  15.6157  19.6951 0.0006  0.61  0.44  0.14  SL  CG  4720A7(dup)  15.588 53.5  0.103  14.2  15.584 54.4  0.112  15.4  39.2547 0.0019  19.6640 0.0009  0.61  38.448  39.2307 0.0039  19.149  0.0006  15.6138  19.062  0.0013  15.6124  19.6209 0.0017  0.56  0.13  SL  CG  4720A7  0.48  0.45  0.13  SL  GG  4720A6  15.568  18.673 68.0  26.3  39.2322 0.0034  0.191  0.0012  15.6164  19.6272 0.0016  38.587 15.584 19.098  0.81  0.82  0.33  KR  OUTLIER  4722A5  38.454  15.576 18.859  76.7  39.4709 0.0020  53.1  17.6 20.9  39.0661 0.0039 0.151  0.0008  15.6229  19.8552 0.0009  0.54  0.127  0.0015  15.6084  19.4972 0.0019  0.91  0.61  0.17  SL  ThOL  4721A4  0.72  0.25  SL  ThOL  4721A2  38.527  0.153  21.0  39.3997 0.0026  0.0010  15.6218  19.8169 0.0012  15.583  19.053  75.7  0.65  0.72  0.21  SL  THOL  4720A4  38.524 15.573  19.007  58.8  0.131  18.0  392027 0.0042  0.0015  15.6066  19.6614 0.0017  0.52  0.45  0.14  MA  THOL.  4719A3  38.312 38.501  15.581  18.940  46.4  0.127  17.6  39.0359 0.0032  0.0012  15.6130  19.5780 0.0015  0.68  0.47  0.18  MA  THOL  15.570  18.782  65.7  0.146  4719A2  38.455  15.581  18.957  53.2  0.116  16.0 20.1  0.52  0.17  MA  39.0697 0.0042  230 Ma  Pb 204 Pbl 208  39.0684 0.0035  230 Ma  Pb 204 Pb/ 207  0.0015  230 Ma  / 232 2 U 5 M Pb Pb 206 204 Thl Pb 204 Pb/  0.0017  / Pb U 2 °  15.6070  m 2  15.6105  b wPb/ 2 P 4 o  19.5133 0.0016  m 2  19.5369 0.0021  b/ 204 P 7 ° 2 Pb  0.54  m 2  0.71  0.56  0.18  MA  THOL  SL  Pb 4 b °Pbfl° 2 P  (ppm) (ppm) (ppm)  U  THOL  kea’  4718A7  Groups  4718A2  Sample  Table 2.5 Pb isotopic compositions ofKarmutsen basalts, Vancouver Island, B.C.  Pb 204 Pb/ Pb = 38.153-38.735. One high-MgO basalt has the highest initial 206 204 Pb/ 208 Pb (37.676). The Pb 204 Pb/ (19.242) and 207 Pb (15.590), and the lowest initial 208 204 Pb/ isotopic ratios for Karmutsen samples define broadly linear relationships in Pb isotope plots. The age-corrected Pb isotopic compositions of several picrites have been affected by U and Pb (andlor Th) mobility during alteration (Fig. 2.10). ALTERATION  The Karmutsen basalts have retained most of their original igneous structures and textures; however, secondary alteration and low-grade metamorphism generated zeolitic and prehnite-pumpellyite-bearing mineral assemblages (Table 2.1) (Cho et a?., 1987), which have primarily affected the distribution of the LILE and the Sr isotopic systematics. The Keogh Lake picrites show the strongest effects of alteration and have higher LOT (up to 5.5 wt %), variable LILE, and higher measured Sr, Nd, and Hf and lower measured Pb isotope ratios than tholeiitic basalts. As a result, Sr and Pb isotopes show a relationship with LOl (Figs 2.9 and 2.10), whereas Nd and Hf isotopic compositions do not correlate with LOI (not shown). The relatively high initial Sr isotopic compositions for high-MgO lavas (up to 0.7052) likely resulted from an increase in 8 Sri S r through addition of seawater Sr (e.g. Hauffet a?., 2003). High-MgO lavas Sr compared to basalts (Révillon et 86 Sr/ from the Caribbean plateau have similarly high 87 a?., 2002). The correction for in situ decay on initial Pb isotopic ratios has been affected by mobilization of U and Pb (andlor Th) in whole rocks since their formation. A thorough acid leaching during sample preparation was used that has been shown to effectively remove alteration phases (Weis et a?., 2006; Nobre Silva et a?., submitted). The HFSE abundances for tholeiitic and picritic basalts exhibit clear linear correlations in binary diagrams (Fig. 2.8), whereas plots of Lll.E versus HFSE are highly scattered (not shown) due to the mobility of some of the alkali and alkaline earth LILE (Cs, Rb, Ba, K) and Sr for most samples during alteration. The degree of alteration in the Karmutsen samples does not appear to be related to eruption environment or depth of burial. Pillow rims are compositionally different from pillow cores (Surdam, 1967; Kuniyoshi, 1972), and aquagene tuffs are chemically different from isolated pillows within pillow breccia, but submarine and subaerial basalts  62  exhibit a similar degree of alteration. There is no clear correlation between the submarine and subaerial basalts and some commonly used chemical alteration indices [e.g. Ba/Rb 0/P (Huang & Frey, 2005)]. There is also no definitive correlation between the K 5 0 vs. 2 petrographic alteration index (Table 2.1; 1-least altered, 3-intensely altered) and chemical alteration indices, although 10 of 13 tholeiitic basalts with the highest K and LILE abundances have a petrographic alteration index of 3. OLIVINE ACCUMULATION IN PICRITIC LAVAS  Geochemical trends and petrographic characteristics indicate that accumulation of olivine played an important role in the formation of the Keogh Lake picrites on northern Vancouver Island. The Keogh Lake picrites show a strong linear correlation in plots of , Ti0 3 0 2 Al , Sc, Yb, and Ni versus MgO and many of the picrites have abundant clusters 2 of olivine pseudomorphs (Table 2.1; Fig. 2.11). There is a strong linear correlation between modal percent olivine and whole-rock magnesium content for the Keogh Lake picrites (Fig. 2.11). Magnesium contents range between 10 and 19 wt % MgO and the proportion of olivine phenocrysts in these samples varies from 0 to 42 vol % (Fig. 2.11). With a few exceptions, the size range and median size of the olivine phenocrysts in most samples is comparable. The clear correlation between proportion of olivine phenocrysts and whole-rock magnesium contents indicates that accumulation of olivine was directly responsible for the high MgO contents (>10 wt %) for most of the picritic lavas. DISCUSSION  The Wrangellia oceanic plateau on Vancouver Island was constructed in a threelayered structure of mostly tholeiitic basalt with a restricted range of composition. The plateau formed rapidly during a single phase (ca. 230 Ma) and hiatuses between eruptions were not long-lasting so there was very little accumulation of sediments. The pillowed and unpillowed flows that built up the submarine volcanic edifice from the deep seafloor resulted primarily from different effusive rates and local topography. Some of the unpillowed flows represent master tubes for the delivery of lava to distal parts of submarine flow fields. Abundant picritic pillow lavas erupted during the middle and latter stages of submarine growth (Nixon et aL, 2008), in areas of the plateau exposed on  63  20  MgO (wt %) Figure 2.11 Relationship between abundance of olivine phenocrysts and whole-rock MgO contents for Keogh Lake picrites. (a) Tracings of olivine grains (gray) in six high-MgO samples made from high resolution (2400 dpi) scans of petrographic thin-sections. Scale bars are 10 mm in length and sample numbers are indicated in upper left. (b) Modal % olivine vs. whole-rock MgO. Black line is the best-fit line for ten high MgO samples. The areal proportion of olivine was calculated from raster images of olivine grains using ImageJ® image analysis software, which provides an acceptable estimation of the modal abundance (e.g. Chayes, 1954).  64  northern Vancouver Island. The overlying volcaniclastic units formed as a consequence of eruption in shallow water. A broad subaerial platform was constructed of well-layered sheet flows and, as volcanism waned, local interfiow carbonate deposits developed, along with plagioclase megacrystic flows and local volcaniclastic deposits. The geochemical and stratigraphic relationships observed in the Karmutsen Formation on Vancouver Island provide constraints on the construction of oceanic plateaus, the source of magmas for a plume head impinging on oceanic lithosphere, and the conditions of melting and subsequent magmatic evolution of basaltic magmas involved in the formation of an oceanic plateau. Studies of the formation of this oceanic plateau in the following sections examine the (1) temperature and extent of melting of picritic lavas; (2) composition of the mantle source; (3) the depth of melting and residual mineralogy in the source region; and (4) low-pressure evolution of the Karmutsen basalts. Melting conditions and major-element composition of primary magmas  The primary melts to most flood basalt provinces are believed to be picritic (e.g. Cox, 1980) and they have been found in many continental and oceanic flood basalt provinces worldwide [e.g. Siberia; Karoo; Parana-Etendeka; Caribbean; Deccan (Saunders, 2005)). Near-primary picritic lavas with low total alkali abundances require high-degree partial melting of the mantle source (e.g. Herzberg & O’Hara, 2002). The Keogh Lake picrites from northern Vancouver Island are the best candidates for leastmodified partial melts of the mantle plume source, despite having accumulated olivine phenocrysts, and can be used to estimate conditions of melting and the composition of primary magmas for the Karmutsen Formation. Herzberg et al. (2007) have provided a thorough description of a technique for inverse and forward modeling for estimating mantle temperature, melt fraction, primary magma composition, and source residue composition using major elements. The estimated melting conditions and primary magma compositions for the picritic lavas of the Karmutsen Formation, and a brief summary of the modeling method, are presented in Figure 2.12 and Table 2.6. If Karmutsen picritic lavas were derived from accumulated fractional melting of fertile peridotite, the primary magmas would have contained 15-17 wt % MgO and -40 wt % CaO (Fig. 2.12; Table 2.6), formed from 23-  65  14 2 Si0 (wt%)  12  Dashed fines  —  =  Melting model initial melting pressure —  10 8  7 Solidus Garnet Peridosite  (b)  KR-4G03  40  6 4  14 Liquid compositions Fertile peridotite source Accumulated Fractional Melting model Thick black lines = initial melting pressure Gray lines = final melting pressure  12  10  30 MgO (wt%)  8 6  Karmutsen flood basalts A Picrite D High-MgO basalt e Tholeiitic basalt OIMne addition model Olivine addition (5% increment) $ Pnmary magma  —  4  +  Figure 2.12 Estimated primary magma compositions for three Keogh Lake picrites (samples 4723A4, 4723A13, 5616A7) using the forward and inverse modeling technique of Herzberg et a!. (2007). Karmutsen compositions and modeling results are overlain on diagrams provided by C. Herzberg. (a) Whole-rock FeO vs. MgO for Karmutsen samples from this study. Total iron estimated to be FeO is 0.90. Gray lines show olivine compositions that would precipitate from liquid of a given MgO-FeO composition. Black lines with crosses 2 vs. MgO show results from olivine addition (inverse model) using PRIMELT1 (Herzberg et al., 2007). (b) Si0 with Kanntusen lavas and model results. (c) FeO vs. MgO with Karmutsen lava compositions and results of forward model for accumulated fractional melting of fertile peridotite. (d) CaO vs. MgO with Karmtusen lava compositions and model results. To briefly summarize the technique [see Herzberg et a!. (2007) for complete description], potential parental magma compositions for the high-MgO lava series were selected (highest MgO and appropriate CaO) and, using PRIMELTI software, olivine was incrementally added to the selected compositions to show an array of potential primary magma compositions (inverse model). Then, using PRIMELT 1, the results from the inverse model were compared to a range of accumulated fractional melts for fertile peridotite, derived from parameterization of the experimental results of Walter (1998) (forward model; Herzberg & O’Hara, 2002). A melt fraction was sought that was unique to both the inverse and forward models (Herzberg et al., 2007). A unique solution was found when there was a common melt fraction for both models -Si0 (CMAS) projection space. This modeling assumes olivine was the 3 0 CaO-MgO-A1 in FeO-MgO and 2 only phase crystallizing and ignores chromite precipitation, and possible augite fractionation in the mantle (Herzberg & O’Hara, 2002). Results are best for a residue of spinel lherzolite (not pyroxenite). The presence of accumulated olivine in samples of Keogh Lake picrites used as starting compositions does not significantly affect the results because we are modeling addition of olivine. The tholeiitic basalts cannot be used for modeling because they are all plag + cpx + ol saturated.  66  Table 2.6 Estimated primary magma compositions for Karmutsen basalts and other oceanic plateaus/islands Sample  4723A4  4723A13  561 6A7  93G171  Average  OJPa  Mauna Keab  Gorgona  (Weight %): 2 Si0  47.0  47.6  46.9  47.8  47.3  48.0  46.3  46.1  2 Ti0  0.68  0.46  0.60  0.46  0.55  0.62  1.93  0.56  3 0 2 A1  15.3  14.3  13.0  13.9  14.1  12.3  9.6  11.7  3 0 2 Cr  0.10  0.20  0.04  0.09  0.11  0.07  0.26  0.16  3 0 2 Fe  1.18  1.03  1.08  0.89  1.09  1.02  0.90  1.08  FeO  8.7  9.0  9.5  8.9  9.0  9.2  10.3  10.1  MnO  0.15  0.15  0.16  0.19  0.16  0.17  0.18  0.18  MgO  15.3  16.3  17.4  16.1  16.3  16.8  18.3  18.8  9.6  10.3  9.9  10.3  10.1  10.0  1.31  1.36  1.67  1.04  0.41  0.03  CaO 0 2 Na  9.9 1.59  9.8 0.90  1.74  1.01  0 2 K  0.07  0.06  0.05  0.11  0.07  0.08  NO  0.05  0.08  0.08  0.07  0.07  0.10  0.08  0.11  Eruption T(°C)  1354  1375  1397  1369  1374  1382  1415  1422  1467  1491  1517  1486  1490  1500  91.2  91.3  90.5  0.26  0.27  7.9  18  Potential T(°C) Fo content (olMne) Melt fraction %ol addition  91.2 0.23 4.2  91.2 0.27 2.5  91.6 0.26 24.3  0.27 0.8  1606 91.4  90.6 0.28  Ontong Java primary magma composition for accumulated fraction melting (AFM) from Herzberg (2004). Mauna Kea primary magma composition is average of 4 samples in Table I of Herzberg (2006). Gorgona primary magma composition for AFM for 1 F, fertile source, in Table 4 of Herzberg and OHara (2002). Total iron estimated to be FeO is 0.90.  67  27% partial melting, and would have crystallized olivine with a Fo content of --91 (Fig. 2.12; Table 2.6). Calculated mantle temperatures for the Karmutsen picrites (—‘1 490°C) indicate melting from anomalously hot mantle (100-200°C) compared to ambient mantle that produces mid-ocean ridge basalt (MORB; ‘--1280-1400°C; Herzberg et al., 2007). Several picrites are near-primary melts and required very little addition of olivine (e.g. sample 93G1 71, with measured 15.8 wt % MgO). These temperature and melting estimates of the Karmutsen picrites in this study are consistent with the decompression of hot mantle peridotite in an actively convecting plume head (i.e. plume initiation model). The estimated primary magma compositions and melting conditions for some other LIPs (e.g. the Ontong Java Plateau) are similar to estimates for the Karmutsen Formation (Table 2.6). Herzberg (2004) found that primary magma compositions for Ontong Java basalts, assuming a peridotite source, would contain —17 wt % MgO and —l0 wt % CaO (Table 2.6), and these magmas would have formed by 27% melting with mantle potential temperatures of —1500°C, and first melting occurring at —-3.6 GPa. Fitton & Godard (2004) estimated 30% partial melting of the Ontong Java lavas based on the Zr contents of primary magmas calculated by incremental addition of equilibrium olivine to analyses of Kroenke-type basalt. If a considerable amount of eclogite was involved in the formation of the Ontong Java Plateau, the excess temperatures estimated by Herzberg et a!. (2007) may not be required (Korenaga, 2005). Estimated primary magmas for Mauna Kea and Gorgona have higher MgO (18-19 wt % MgO) and comparable CaO (10 wt % CaO) (Table 2.6; Herzberg (2006)). Source of Karmutsen lavas  Karmutsen samples have isotopic compositions belonging to the field of ocean island basalts (OIB) and provide a sampling of the Pacific mantle Ca. 230 Ma (Fig. 2.13). Sr that fall within the range of 86 Sr/ The Karmutsen tholeiitic basalts have initial ENd and 87 basalts from the Caribbean Plateau (e.g. Kerr et a!., 1996; Kerr et al., 1997; Hauff et a!., 2000; Kerr, 2003), a range of Hawaiian isotope data (e.g. Frey eta!., 2005), and lie within and just above the range for the Ontong Java Plateau (Tejada et a!., 2004; Fig 2.13). Karmutsen tholeiitic basalts with the highest initial  Nd 8  5r 86 Sr/ and lowest initial 87  lie just below the field for northern East Pacific Rise (EPR) MORB (e.g. Niu eta!., 1999;  68  14  II  t  12  I  liii  •S I.  10  I  16  Indian__.  • •  EHfinitiah  4•  8  ft-’ 6  4  • Indian MORB  6  .1  •  (b) 2 0.703  0.705  0.704  0.706  •  -4  I  -2  I  0  I  I 2  I  I  4  I  I  I  I  I  I  I  I  I  F F  FI1  I  1  I  I  6  I 8  I  I 10  I  12  14  E Nd(t1ao)  SrI 86 87 Sr (initial) I1F[ I  Karmutsen high-MgO lava  I  I  •  -2 0.702  Hawaii  • Karmutsen tholeiitic basalt  iOlB array i\  0  0  • Ontong Java  I  2  .  Caribbean Plateau  —  £  4 2  • East Pacific Rise  .F •  I  I  •• 15.60  0 •  15.55  I.. • I  15.50  • East Pacific Rise • • • •  Juan de Fuca/Gorda Explorer Ridge Caribbean Plateau Ontong Java Hawaii  -  o Karmutsen Formation (measured)  15.45  —  • Karmutsen Formation (initial) • Karmutsen Formation (different age-correction for 3 picrites) I  17.5  I  I  I  I  18.0  I  I  I  I 18.5  IIIIIIIIIIIII  19.0  19.5  I  20.0  17.5  18.0  18.5  19.0  19.5  20.0  pb 204 pb/ 206  Figure 2.13 Comparison of age-corrected (230 Ma) Sr-Nd-Hf-Pb isotopic compositions for Karmutsen flood basalts on Vancouver Island to age-corrected OIB and MORB. (a) Initial 8 Sr. (b) Initial 8 86 Sr/ Nd vs. 87 Hf vs. 8 Nd Both fields Pb vs. 206 204 Pb/ Pb. (d) Measured and initial 204 Pb/ with dashed lines are Indian MORE. (c) Measured and initial 207 Pb. Most of the compiled data was extracted from the GEOROC database (http://georoc.mpch 4 PbP° Pb vs. 206 204 Pb/ 208 mainz.gwdg.de/georocl). Data for Ontong Java from Mahoney et a?. (1993), Babbs (1997), and Tejada et a?. (2004); Indian MORE from Salters (1996), Kempton et a?. (2002), and Janney et a?. (2005); Pacific MORE from Mahoney et a?. (1992, 1994), Nowell et a?. (1998), Salters and White (1998), and Chauvel and Blichert-Toft (2001); Explorer Ridge data from Cousens and Weis (pers. conmi., 2007); OTB array line from Vervoort et a?. (1999). EPR is East Pacific Rise. Several high-MgO samples affected by secondary alteration were not plotted for clarity in Pb isotope plots. Dashed lines indicate Bulk Silicate Earth (B SE). An extended reference list is available upon request.  69  Regelous et a!., 1999). Initial Hf and Nd isotopic compositions place the Karmutsen basalts on the edge of the field of OIB (age-corrected), with slightly higher initial  Nd 8  and  similar initial 8 Hf to Ontong Java, and slightly lower initial £Hf and similar initial ENd to the range of compositions for Hawaii and the Caribbean Plateau (Fig. 2.13). Karmutsen samples are slightly offset to the low side of the OIB array (Vervoort et a!., 1999), slightly overlap the low 8 Hf end of a field for Indian MORB (Kempton et a!., 2002; Janney et aL, 2005), and samples with the highest initial  Hf 8  and 8 Nd lie just at the edge of  the presently defined field for Pacific MORB (Mahoney et aL, 1992, 1994; Nowell et al., 1998; Chauvel & Blichert-Toft, 2001). Karmutsen Pb isotope ratios overlap a broad range for the Caribbean Plateau and the linear trends for Karmutsen samples intersect fields for Pb space, but do not intersect these 206 PbEPR MORB, Hawaii, and Ontong Java in 208 Pb for a given 204 Pb/ Pb space (Fig. 2.13). The more radiogenic 207 206 Pbfields in 207 Pb of Karmutsen basalts indicate they are isotopically enriched in comparison to 204 Pb/ 206 EPR MORB, Hawaii, and Ontong Java. The Hf-Nd isotopic geochemistry of volcanic rocks of the Karmutsen Formation on Vancouver Island indicates an isotopically rather uniform mantle source. The Hf and Nd isotopic compositions of Karmutsen basalts indicate long-term depletion of the more highly incompatible elements in the mantle source and are distinct from MORE; they are less depleted than the source of MORE and there is no clear evidence of involvement of MORE-type mantle. The limited variation of Hf and Nd isotopic compositions is slightly greater than in the isotopically very uniform mantle source of Ontong Java. Small-scale heterogeneities in the mantle source of Karmutsen lavas may have been diluted by the high degrees of partial melting, similar to Ontong Java (Tejada et al., 2004). Lassiter et a!. (1995) suggested that mixing of a plume-type source with 8 Nd +6 to +7 with arc material with low Nb/Th could reproduce variations in the Karmutsen basalts, but the absence of low Nb/La ratios in most of the basalts restricts the amount of arc lithospheric involvement (based on major and trace elements and Sr, Nd, and Pb isotopic compositions for a suite of 29 samples from Buttle Lake in Strathcona Provincial Park on central Vancouver Island; Fig. 2.1). The isotopic composition and trace-element ratios of Karmutsen basalts in this study do not indicate significant involvement of Paleozoic arc  70  lithosphere on Vancouver Island. There are no clear HFSE-depletions in Karmutsen tholeiitic basalts. The Sr-Nd-Hf-Pb isotope systematics for Karmutsen basalts distinguish the source of Karmutsen basalts from MORB and some OIB. The Hf and Nd isotope systematics provide the firmest constraints on the character of the source for Karmutsen lavas. The LU/Hf ratios of the picritic lavas (mean 0.08) are considerably higher than in tholeiitic basalts (mean 0.02), but the small range of initial £Hf for the two lava suites suggests that these differences in trace-element compositions were not long-lived, and do not correspond to intrinsic differences in the mantle plume source. Evolution of Hf isotopes with time shows that if the picritic and tholeiitic lavas originally had a similar range of 8 Hf it would take —l55 m.y. for Hf isotope ratios to evolve so there would be no overlap in  Hf 8  (Fig. 2.14); this is similar to a concept emphasized by Arndt et a!. (1997)  using Nd isotopes of lavas from Gorgona Island. Therefore, it is unlikely that the picrites had high LU/Hf ratios long before ascent of the plume and the different Lu/Hf ratios likely developed during the melting process within the plume during ascent. The similar initial Hf and Nd isotopic ratios of the picrites and tholeiitic basalts preclude the limited isotopic range being simply the result of mixing of magmas. The slightly different Pb isotope ratios of the picrites and tholeiitic basalts are at least partly a result of alterationrelated effects. As observed in the Caribbean Plateau, the radiogenic Pb in Karmutsen basalts is systematically different than in MORB, Ontong Java, and OIB from Hawaii, but Hf and Nd isotope compositions indicate a homogeneous, OIB-type enriched mantle source. REE modeling: Dynamic melting and source mineralogy  The combination of isotopic and trace-element geochemistry of picritic and tholeiitic Karmutsen lavas indicates that differences in trace elements may have originated from different melting histories within a predominantly homogeneous, depleted (but not MORE) mantle source. Dynamic melting models simulate progressive decompression melting where some of the melt fraction is retained by the residue and only when the degree of partial melting is greater than the critical mass porosity, and the source becomes permeable, is excess melt extracted from the residue (Zou, 1998). For the  71  25  20  15  —  •  Picrite High-MgO basalt Tholelitic basalt  1  - -  —155 m.y.—+I II /  -  -  j.-’  -  Hf 10  hypothetical  •  0 500  •  400  ‘  I 230 Ma  a  I  300  I  200  actual  I  I  100  I  0  Age (Ma)  Figure 2.14 Evolution of EHf with time for picritic and tholeiitic lavas for the Karmutsen Formation. The different Lu/Hf ratios of the Karmutsen lavas likely originated during melting processes within the plume. For example, if the picritic and tholeiitic lavas possessed the Lu/Hf ratios that they did at 230 Ma more than 155 m.y. before their formation, they would have evolved to have a different range of Hf isotopic compositions by 230 Ma (shown by the gray and white vertical boxes for tholeiitic and picritic lavas, respectively). This is shown by hypothetical compositions at 400 Ma (using EHf( O 23 evolution trends using Ma) for each sample) and Hf for each sample. Picritic lavas have high Lu! 77 Lu!’ 176 Hf ratios so they accumulate radiogenic Hf within a relatively short geologic timespan. Decay constant of yr’ used from Scherer et a!. (2001). Error 1.87 x 10 1 bars are smaller than symbols.  72  Karmutsen lavas, evolution of trace element concentrations was simulated using the incongruent dynamic melting model developed by Zou & Reid (2001). Melting of the mantle at pressures greater than -4 GPa involves incongruent melting (e.g. Longhi, 2002) with olivine being produced during reaction of cpx + opx + sp for spinel peridotites. Modeling was separated into two intervals of melting, for a garnet therzolite (gt lherz) and spine! lherzolite (sp lherz) source, using coefficients for incongruent melting reactions based on experiments on lherzolite melting (e.g. Kinzler & Grove, 1992; Longhi, 2002). The model solutions are non-unique and a range in degree of melting, partition coefficients, melt reaction coefficients, and proportion of mixed source components is possible to achieve acceptable solutions. The LREE-depleted high-MgO lavas require melting of a depleted spinel lherzolite source (Fig. 2.15). The modeling results indicate a high degree of melting (2225%), similar to results from major-element modeling using PRIMELT1 (discussed  above), from a LREE-depleted source, and melting of garnet was probably not involved in formation of the high-MgO lavas. The enriched tholeiitic basalts involved melting of both garnet and spinel lherzolite and represent aggregate melts produced from continuous melting throughout the depth of the melting column (Fig. 2.15), which were subsequently homogenized and fractionated in magma chambers at low pressure. The modeling results indicate that these aggregate melts would have involved lesser proportions of enriched, small-degree melts (1-6% melting) generated at depth and greater amounts of depleted, high-degree melts (12-25%) generated at lower pressure (ratio of gt lherz to sp lherz melt would have been approximately ito 3, or 1 to 4; see Fig. 2.15). The degree of melting was high (23-27%), similar to the degree of partial melting of primary melts that erupted as the Keogh Lake picrites, from a source that was likely depleted in LREE. Although the modeling results indicate that the depleted high-MgO Karmutsen lavas were formed from high-degree partial melting within the spinel therzolite stability field (—0.9-2.5 GPa), the source was not necessarily more depleted in incompatible trace elements than the source of the tholeiitic lavas. It is possible that early high-pressure, low-degree melting left a residue within parts of the plume (possibly the hotter, interior portion) that was depleted in trace elements (e.g. Elliott et al., 1991); further decompression and high-degree melting of such depleted regions could then have  73  100  hoiclavas  High-MgO lavas 20% melting  Melting of spinel lherzolite C 0 -C U  C  10  .210 U  0.8 enriched melt + 0.2 depleted high-MgO melt  0.  EC,  E  Spirl lherzolite melt (from panel B)  Spinel lherzolite + garnet lherzolite melt (from panel C)  30% melting urce(O.7DM+O3PM  (a)  . .  A.  La Ce Pr Nd Pn-fSm Eu Gd Tb Dy[lo Er Tm Yb Lu 100  ‘  ‘  ‘  ‘  La  Ce Pr 1.5  Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu I  o’Ie,it’ic lva  ‘  •  I  I  •  •  Melting of spinel lherzolite  14 13  melting  C,  C 0 L)  12  xgtlherz+4xspiherz  10  DyIYb  -—  1.1  Spinel lherzolite + garnet lherzolite melt  C,  0.  EC,  0.7DM +0.3PM 1.0  3 ÷ D 7 .e(O. E M P O. (C)  1  1  I  La/Srn  (d)  os  0. 0  L Ce Pr Nd P4Sm Eu Gd Tb DyHo Er • TmYb ‘ • Lu 100  melting 30% melting  0.9  0.5  1.5  1  ‘  Tholeiitic lavas -  1.4  1% melting  -  .  .....J_  -  !eltin  10  2.(  13•  ____  0 C 0 -C U  1.0 1.5 % melting ratio, x gnt lherz ÷ 3x sp lherz 10% 25% 20%  12  Spinellherzolite+ 25 .garnetlherzolitemelts  Dy/Yb  %meltinp ratio xgntlherz÷4xsplherz  1.1  C,  0.  EC,  U,  (e)  0.7DM+O.3PM) •  •  I  I  I  I  I  I  •  •  La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu  1.0  •  0.9  -  A Picrite 0 High-MgO basalt 0 Coarse-g rained A.  .  0.8  0.0  03  1.0 La/SmCN  • Tholeiitic basalt •  1.5  2.0  Figure 2.15 Trace-element modeling results for incongruent dynamic mantle melting for picritic and tholeiitic lavas from the Karmutsen Formation. Three steps of modeling for tholeiitic lavas are shown (order of modeling is shown going upwards from panel e to c to a, following the arrows): (e) Melting of garnet lherzolite, (c) Mixing of garnet and spinel therzolite melts, and (a) Mixing of enriched tholeiitic and depleted picritic melts. (b) Melting of spinel therzolite for high-MgO lavas. Shaded field is the range of REE patterns for Karmutsen tholeiitic basalts in panels a, c, and e and for picrites in panel b. Patterns with symbols in panels a, b, c, and e are modeling results (patterns are 5% melting increments in panels a and c and 1% increments in panel e. Abbreviations are: PM, primitive mantle; DM, depleted MORB mantle; gt therz, garnet therzolite; sp lherz, spinel lherzolite. The ratios of percent melting for garnet and spinel therzolite are indicated in panel c. A range of proportion of source components (0.7DM:0.3PM to 0.9DM:0.1PM) can reproduce the variation in high-MgO lavas. (d) Dy!YbCN vs. La! SmcN for results of spinel Iherzolite melting modeling and Karmutsen samples. Tickmarks are 5% increments and proportions of mantle source components are labelled next to curves. (f) Dy/YbCN vs. La/SmCN for results of spinel lherzolite + garnet therzolite melting modeling and Karmutsen samples. Melting modeling uses the formulation of Zou & Reid (2001), an example calculation is shown in their Appendix. PM from McDonough & Sun (1995) and DM from Salters & Stracke (2004). Melt reaction coefficients of spinel lherzolite from Kinzler & Grove (1992) and garnet lherzolite from Walter (1998). Partition coefficients from Salters & Stracke (2004) and Shaw (2000) were kept constant. Source mineralogy for spinel lherzolite (0.l8cpx:0.27opx:0.52o1:0.O3sp) from Kinzler (1997) and for garnet therzolite (0.34cpx:0.O8opx:0.53o1:0.OSgt) from Salters & Stracke (2004). A source composition with mantle components up to 0.3 PM and 0.7 depleted mantle can reproduce REE patterns similar to those of the high-MgO lavas, with best fits for a melt fraction of 0.22-0.25. Concentrations of tholeiitic basalts cannot easily be reproduced from an entirely primitive or depleted source. A range of source compositions (0.7DM:0.3PM to 0.3DM:0.7PM) and garnet and spinel lherzolite melt mixtures generate similar results (x gtlherz + 3x splherz to x gtlherz + 4x splherz; where x is percent melting in the interval of modeling; the ratio of the respective melt proportions in the aggregate melt was kept constant).  74  generated the depleted high-MgO Karmutsen lavas. However, the modeling results indicate that this earlier melting was not necessary for their formation, depending on the original trace-element composition of the source. Shallow, high-degree melting would preferentially sample depleted regions, whereas deeper, low-degree melting may not sample more refractory, depleted regions (e.g. Caribbean; Escuder-Viruete et al., 2007). Decompression melting within the mantle plume initiated within the garnet stability field at high mantle potential temperature (T>l450°C) and proceeded beneath oceanic arc lithosphere within the spinel field where more extensive degrees of melting could occur. Magmatic evolution of Karmutsen tholelitic basalts  Primary magmas in LIPs leave extensive coarse-grained residues within or below the crust and these mafic and ultramafic plutonic sequences represent a significant proportion of the original magma that partially crystallized at depth (e.g. Farnetani et al., 1996). For example, seismic and petrological studies of Ontong Java (e.g. Farnetani et al., 1996), combined with the use of MELTS (Ghiorso & Sack, 1995), indicate that the volcanic sequence may have been only -40% of the total magma reaching the Moho. Neal et al. (1997) estimated between 7 and 14 km of cumulate thickness corresponding with 11 to 22 km of flood basalt, depending on the presence of pre-existing oceanic crust and the total crustal thickness (25-3 5 km), and that 3 0-45% fractional crystallization took place for Ontong Java magmas. Interpretations of seismic velocity measurements suggest the presence of pyroxene and gabbroic cumulates --9-16 km thick beneath the Ontong Java Plateau (e.g. Hussong et al., 1979). Wrangellia is characterized by high crustal velocities in seismic refraction lines, which is indicative of mafic plutonic rocks extending to depth beneath Vancouver Island (Clowes et al., 1995). Wrangellia crust is —25-30 km thick beneath Vancouver Island and is underlain by a strongly reflective zone of high velocity and density that has been interpreted as a major shear zone where lower Wrangellia lithosphere was detached (Clowes et a!., 1995). The vast majority of Karmutsen flows are evolved tholeiitic lavas (e.g. low MgO, high FeOIMgO) indicating an important role for partial crystallization of melts at low pressure, and a significant portion of the crust beneath Vancouver Island has seismic properties that are consistent with crystalline residues from partially crystallized  75  Karmutsen magmas. To test the proportion of the primary magma that fractionated within the crust, MELTS (Ohiorso & Sack, 1995) was used to simulate fractional crystallization using several estimated primary magma compositions from modeling results using P1UMELT1. The major-element composition of primary magmas could not be estimated for the tholeiitic basalts due to extensive plag + cpx + ol fractionation, and thus the MELTS modeling of the picrites is used as a proxy for the evolution of major elements in the volcanic sequence. A pressure of 1 kbar was used with variable water contents 0), calculated at the quartz-fayalite-magnetite (QFM) 2 (aithydrous and 0.2 wt % H oxygen buffer. Experimental results from Ontong Java indicate that most crystallization occurs in magma chambers shallower than 6 km deep (<2 kbar; Sano & Yamashita, 2004); however, some crystallization may take place at greater depths (3-5 kbar; Farnetani et aL, 1996). A selection of the MELTS results are shown in Figure 2.16. Olivine and spinel crystallize at high temperature until —P15-20 wt % of the liquid mass has fractionated, and the residual magma contains 9-10 wt % MgO (Fig. 2.16). At 1235-1225°C, plagioclase begins crystallizing and between 1235 and 1190°C olivine ceases crystallizing and clinopyroxene saturates (Fig. 2.16). As expected, the addition of clinopyroxene and plagioclase to the crystallization sequence causes substantial changes in the composition 3 and CaO decrease, while the 0 2 2 increase and A1 of the residual liquid; FeO and Ti0 decrease in MgO lessens considerably (Fig. 2.16). Tn general, the compositions of the predicted residual liquids follow trends for compositions of Karmutsen lavas, but miss some of the low MgO, high CaO basalts (some of which are due to plag accumulation). 3 and CaO of Karmutsen basalts are not clearly decreasing with 0 2 Also, trends in Al decreasing MgO. Increasing the crystallization pressure slightly and water content of the melts does not systematically improve the match to the observed data. The MELTS results indicate that a significant proportion of crystallization takes place before plagioclase (‘-15-20% crystallization) and clinopyroxene (-35-45% crystallization) join the crystallization sequence. These results suggest >45% crystallization of primary magmas occurred (estimated from residual liquid % in Fig. 2.16) and, if the original flood basalt stratigraphy on Vancouver Island was —6 1cm, at least an equivalent amount of complementary plutonic rocks should have crystallized.  76  LL  ssd uizqjs&I jo siut pjqj inrndw SA pmbij TP!so1 uaoj () .OZH ou q (ETVZLI7 jduius) urn jJji uo wo. sssd Pz!TIms jo suoTijodoid TuI!N () coi i puu uoruuonJj %L si OH % i o tpA si usi snoip(qu s ioj uod-puS 11 .OZH pu c pu uot uoT.g o,’i .ioj iuod-pus o pu OH OU 1{IA p5511 SuA P 5UOJP1(11I ! ‘II )1°1 N1O PIt1O1 ‘OH % % O ! 1I!I iqj j jo ainsssid v sjnsaz ‘W’! pi IL 10E6 pu £VEZL ssidwus iOj swuw i(iuiud psuwss sqj ij ut uos ‘EIvlLt sjdws oj (/f) iv is sqz.Is-{JO snbimps &IiJspouI si woi,j ssuss uuj jo uonisodwoo sq usn ‘(sjaip i) uoiiisodmos &iiis suo ioj uMo1s st io; uwui &Iuuiud pswmtss sm sijnsai si ‘i(iup io suornsoduioo uu ussnuuj o paidwoo sprnbJ Jrnlpsa1jo suornsodwoo usuisjs (p) puu ‘(o) ‘(q) ‘(s) uouuoj ussnuu stp wo SA1 siiiisJo pu o!.Is!d o psidwoo (c661 -iofw si  ‘i°s ‘ oslon{9) S1iN WO SU5UI5S 1018W JOj SflUSSJ U!j5pOw RO13uZqSAJO 1’°!3° pJAUO{ 91Z ‘flLI (%M)  OE  8L  9L  VL  L  06W OL  8  9  V  0  O  8L  9t  Vt  (%IM) OW L  OL  8  9  V  0  9 (3)  (p)  LL  L 8  EL  6  V V  V  VV V  OL  Vt EL  LL 9L  V  LL  (%IM) I  I (%IM)  St  0  9L  L  VL  !1!!IOq.1. • seq 6 WH 0 ! -L1 1!J)!d  Qe3,  I  I  EL  I  St  @ y 1 Z 0 (%M) S  8  9  OZ  0  1’  8L  9t  6t  V I  I  I  (%M)  W 6 0  OL  VL  t  I  I  I  I  W 6 0  OL  8  9  V  Z  0 9  0•0  (q)  (8)  W 6 0  c.0  L 8  0• 6 c•  OL LL  (%) p!nb!I ienpsi OL  O  OS  O  00  09  OL  09  06 OOL  (J)  0ZH%1MO /  c. EL  -i 0OLL  0.E Vt  0611  0H OU’  0ZL  0056  (%) 5 01j. I  ed 6uIIsAj pue PiflbII IeflP!S9°  SE  EL  O•V  I  ••  9L  The Karmutsen basalts and their plutonic residues thus represent a significant addition of crust (perhaps >12 km thickness), previously thickened by Paleozoic arc activity. CONCLUSION 2 of Vancouver Island, British The Karmutsen Formation covers —20,000 km Columbia, and was constructed as a large oceanic plateau during a single phase over a geologically short interval (ca. 230 Ma). The tripartite volcanic stratigraphy on Vancouver Island is upwards of 6 km of submarine flows, volcaniclastic deposits, and massive sheet flows; these volcanological differences are primarily related to the eruption environment (deep-water, shallow-water, subaerial). The rapid growth of the plateau prevented intervening sediments from accumulating, except in the uppermost stratigraphy where isolated limestone lenses commonly associated with pillowed and volcaniclastic basalts preserve a record of the subsidence history of the plateau. The Wrangellia plateau on Vancouver Island was constructed dominantly of tholeiitic basalt with a restricted major- and trace-element, and isotopic, composition. Picritic pillow basalts erupted in the middle to latter portion of the submarine phase. Modeling results of Karmutsen picrites indicate melting of anomalously hot mantle (—4500°C) and extensive degrees of partial melting (23-27%) and are consistent with a plume initiation model. The lavas that built the volcanic edifice were derived from an isotopically relatively uniform depleted mantle source distinct from the source of MORE. There are compositional similarities between the source of Karmutsen basalts on Vancouver Island and the sources of ocean islands (e.g. Hawaii) and plateaus (e.g. Ontong Java) in the Pacific Ocean. The Karmutsen basalts erupted atop Paleozoic arc volcanic sequences, but there is no clear evidence from our work on Vancouver Island of significant involvement of arc or continental material in formation of the basalts. Picrites formed from melting of spinel lherzolite with a depleted mantle isotopic composition similar to the source of the tholeiitic basalt. The tholeiitic basalts underwent extensive low-pressure fractionation (<2-3 kbar) and seismic work indicates some of the Wrangellia crust beneath Vancouver Island may correspond to the plutonic residues of the Karmutsen Formation.  78  ACKNOWLEDGEMENTS  We would like to thank Nick Arndt for helping us get this project started and Nick Massey for insights into Vancouver Island geology. 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Geochemistry Geophysics Geosystems 7(Q08006), doi: 10.1 029/2006GC00 1283. Weis, D., Kieffer, B., Hanano, D., Silva, I. N., Barling, J., Pretorius, W., Maerschalk, C. & Mattielli, N. (2007). Hf isotope compositions of U.S. Geological Survey reference materials. Geochemistry Geophysics Geosystems 8(Q06006), doi: 10.1 029/2006GC00 1473. Weis, D., Kieffer, B., Maerschalk, C., Barling, J., de Jong, J., Williams, G. A., Hanano, D., Mattielli, N., Scoates, 3. 5., Goolaerts, A., Friedman, R. A. & Mahoney, J. B. (2006). High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS. Geochemistry Geophysics Geosystems 7(Q08006), doi: 10.1 029/2006GC00 1283. Wheeler, 3. 0. & McFeely, P. (1991). Tectonic assemblage map of the Canadian Cordillera and adjacent part of the United States of America. Geological Survey of Canada Map 1712A. White, W. M., Albarêde, F. & Télouk, P. (2000). High-precision analysis of Pb isotope ratios by multi-collector ICP-MS. Chemical Geology 167, 257-270. Yorath, C. J., Sutherland Brown, A. & Massey, N. W. D. (1999). LITHOPROBE, southern Vancouver Island, British Columbia. Geological Survey of Canada. LITHOPROBE, southern Vancouver Island, British Columbia Bulletin 498, 145 p. Zou, H. (1998). Trace element fractionation during modal and non-model dynamic melting and open-system melting: A mathematical treatment. Geochimica et CosmochimicaActa 62(11), 1937-1945. Zou, H. & Reid, M. R. (2001). Quantitative modeling of trace element fractionation during incongruent dynamic melting. Geochimica et Cosmochimica Acta 65(1), 153-162.  85  CHAPTER 3  Wrangellia Flood Basalts in Alaska: A Record of Plume-Lithosphere Interaction in a Late Triassic Accreted Oceanic Plateau  ‘A version of this chapter has been submitted for publication.  86  INTRODUCTION  Oceanic plateaus and continental flood basalts (CFBs) are produced from the largest melting events recorded on Earth. Oceanic plateaus and CFBs are transient large igneous provinces (LIPs) that form from unusually high magmatic fluxes over several million years or less (Saunders, 2005). The presence of transient LIPs in a variety of tectonic settings attests to large thermal anomalies that are not directly attributable to seafloor spreading processes. A longstanding controversy in many transient LIPs worldwide is the role of the mantle lithosphere in generation of the basaltic magmas. CFBs have compositions that indicate involvement of subcontinental lithospheric mantle and continental crust (e.g. Peate & Hawkesworth, 1996). Compositional evidence of plume-lithosphere interaction in oceanic plateaus, however, remains elusive because oceanic plateaus are less accessible. Oceanic plateaus are enormous volcanic edifices (2-4 km high) that are isolated from continents and form upon mid-ocean ridges, extinct arcs, detached or submerged continental fragments, or intraplate settings (Coffin et a!., 2006). The basalts that form oceanic plateaus have a better chance of avoiding interaction with continental lithosphere than basalts erupted along the margins or in the interiors of continents (Kerr & Mahoney, 2007). A significant issue in the geochemistry of flood basalt provinces has been the origin of high- and low-titanium basalts within the flood basalt stratigraphy (e.g. Arndt et a?., 1993). Numerous flood basalt provinces have been found to possess two or more distinguishable groups of basalts based on titanium contents [e.g. Siberia (Wooden et a?., 1993); Emeishan (Xu eta?., 2001); Karoo (Cox eta?., 1967); Ferrar (Hornig, 1993); Paraná-Etendeka (Peate, 1997); Deccan (Melluso et a?., 1995); Ethiopia (Pik et a?., 1998); Columbia River Basalts (looper & Hawkesworth, 1993)]. In several of these provinces, the high- and low-titanium basalts are geographically distributed, and in several provinces these different lava types have a distinct stratigraphic distribution. However, all of these LIPs formed upon continental crust and are thought to have involved interaction with metasomatized lithospheric mantle or continental crust during parts of their eruptive history. The Wrangellia flood basalts in Alaska erupted in the eastern Panthalassic Ocean over <5 Myr in the Middle to Late Triassic, with accretion to western North America  87  occurring in the Late Jurassic or Early Cretaceous (Jones et aL, 1977). The Wrangellia flood basalts form thick successions of flood basalts bounded by marine sediments that extend over widespread areas of Alaska, Yukon, and British Columbia (>2300 km in length). In south-central Alaska, parts of the complete flood basalt stratigraphy overlie Late Paleozoic oceanic arc crust and marine sediments and are overlain by Late Triassic limestone. Most of the 3.5-4 km of flood basalts in Alaska erupted subaerially, however, in areas of Alaska there are pillowed and volcaniclastic basalts in the lower part of the volcanic stratigraphy. The Wrangellia flood basalts in Alaska provide an exceptional opportunity to examine the volcanic stratigraphy of an accreted oceanic plateau. While Ocean Drilling Program (ODP) and Deep Sea Drilling Program (DSDP) legs have drilled extant oceanic plateaus in the ocean basins, the vast majority of the stratigraphic sequence of oceanic plateaus remains generally unsampled and undescribed. This study examines volcanic stratigraphy, petrography, and geochemistry of flood basalts in the Wrangell Mountains and Alaska Range in south-central Alaska to determine the source and origin of high- and low-titanium basalts in the accreted Wrangellia oceanic plateau and the role of the pre existing Paleozoic oceanic arc lithosphere. A mantle plume origin was proposed for Wrangellia flood basalts by Richards et aL (1991) based on the large volume of flood basalts erupted in a short duration, the absence of evidence of rifting, and evidence of uplift prior to eruption of the flood basalts. The only previous modem analytical study of the Wrangellia flood basalts in Alaska involved major- and trace-element chemistry, and Sr, Nd, and Pb isotopic analyses, of 9 basalts from the Wrangell Mountains (Lassiter et al., 1995). This present study is part of a larger research project on the origin and evolution of the Triassic Wrangellia flood basalts in British Columbia, Yukon, and Alaska (Greene et a!., 2008, submitted-b). The generation of compositionally distinct basalts in part of the Wrangellia oceanic plateau has implications for the interaction of mantle plumes and oceanic mantle modified by subduction.  88  GEOLOGIC SETTING Wrangeffia in Alaska  The Wrangellia Terrane, or Wrangellia, was defined by Jones et a!. (1977) as a set of fault-bound crustal blocks with similar stratigraphy along the margin of western North America (Fig. 3.1). The Wrangellia flood basalts have been mapped as the Nikolai Formation in Alaska and Yukon (Northern Wrangellia) and the Karmutsen Formation on Vancouver and Queen Charlotte Islands (Southern Wrangellia). Three key aspects of Wrangellia led Jones and co-workers (1977) to suggest these crustal blocks formed as part of a once-contiguous terrane: thick sections of tholeiitic flood basalts directly overlie shale with Middle to Late Ladinian Daonella; similar-aged Late Triassic limestones overlie the flood basalts; and paleomagnetic evidence indicated that eruption of the flood basalts occurred at low latitude. Wrangellia may have joined with parts of the Alexander Terrane, primarily in southeast Alaska, as early as the Late Pennsylvanian (Gardner et aL, 1988) and may have been in close proximity to the Peninsular Terrane of southern Alaska by the Late Triassic (Rioux et al., 2007). Wrangellia extends 450 km in an arcuate belt in the Wrangell Mountains, Alaska Range, and Tailceetna Mountains in southern Alaska (Fig. 3.1). The northwest margin of Wrangellia is one of the most prominent geophysical features in south-central Alaska and is exposed along the Talkeetna Suture Zone (Glen eta!., 2007). The suture between Wrangellia and transitional crust to the northwest is well-defined geophysically by a series of narrow gravity and magnetic highs along the Talkeetna Suture Zone, between dense, strongly magnetic Wrangellia crust and less dense, weakly magnetic crust beneath flysch basins to the northwest (Glen et a!., 2007). This area lies directly in the axis of the major orocline of southern Alaska, where structures curve from northwest- to northeasttrending (e.g. Plafker eta!., 1994; Fig. 3.1). The Wrangellia terrane is bounded by the Denali Fault to the northeast and extends more than 300 km to the southeast in Yukon where Wrangellia stratigraphy is very similar to Alaska (Fig. 3.1). Wrangell Mountains Wrangellia stratigraphy is well-exposed in a northwest-trending belt extending l00 km along the southern flank of the Wrangell Mountains in Wrangell-St. Elias  89  Figure 3.1 Simplified map of south-central Alaska showing the distribution of the Nikolai Formation (black), derived from the GIS-based digital map compilations of Wilson et a!. (1998, 2005) and Schmidt (pers. comm, 2006). The three main areas that were studied are outlined with boxes and indicated in the legend. The inset shows the extent of the Wrangellia flood basalts (green) in Alaska, Yukon, and British Columbia. The red lines are faults.  90  National Park (Fig. 3.2). The Nikolai Formation disconformably overlies the Skolai Group, which comprises Pennsylvanian to Early Permian volcanic arc sequences and marine sediments of the Station Creek and Hasen Creek Formations, respectively (Smith and MacKevett, 1970; Fig. 3.2). In most areas, Nikolai basalts unconfomably overlie parts of the Hasen Creek Formation called the Golden Horn Limestone Lentil (<250 m thick), which forms prominent yellow- and red-stained cliffs of bioclastic Early Permian limestone. Isolated lenses of Daonella-bearing Middle Triassic argillite (<100 m thick) lie between the top of the Golden Horn Limestone and the base of the Nikolai Formation (Smith and MacKevett, 1970). The Skolai Group is intruded by mafic and ultramafic 2 intrusive bodies related to the Nikolai basalts. The Nikolai basalts cover l 057 km (4.2% of all Wrangellia flood basalts from Vancouver Island to central Alaska) within the McCarthy and Nabesna Quadrangles in Wrangell-St. Elias National Park and are approximately 3.5-4 km in total thickness. A cumulative thickness of over 3.5 km of marine sedimentary rocks, ranging in age from Late Triassic to Late Jurassic, overlies the Nikolai Formation in the Wrangell Mountains (MacKevett et al., 1997). Volcanic successions of the Miocene to Holocene Wrangell volcanic field unconformably overlie Jurassic and Cretaceous sedimentary sequences (MacKevett, 1978; Richter et al., 1990). Eastern Alaska Range  The Nikolai Formation in the eastern Alaska Range and small areas of the 2 (2.6% of all Wrangellia flood basalts) mostly in the Tailceetna Mountains covers 666 km Mount Hayes and Healy Quadrangles, and is 3.5-4 km thick in the Amphitheater and Clearwater Mountains (Fig. 3.1). Volcanic and marine sedimentary sequences similar to the Late Paleozoic successions in the Wrangell Mountains underlie the Nikolai basalts in the Alaska Range (Nokleberg eta?., 1994). In the Amphitheater Mountains, a major feeder system for the Nikolai Formation stratigraphically underlies flood basalt stratigraphy within a well-preserved synform that contains exposures of mafic and ultramafic intrusive units. These are the most significant occurrence of plutonic rocks associated with flood basalts within Wrangellia. The upper part of the volcanic stratigraphy contains interbedded volcanic and sedimentary horizons (argillite and  91  Figure 3.2 Geologic map and stratigraphy of the Wrangell Mountains, Alaska (location shown in Figure 1). (a) Stratigraphic column depicts Late Paleozoic to Jurassic units on the south side of the Wrangell Mountains, derived from Smith and MacKevett (1970) and MacKevett (1978). (b) Simplified map showing the distribution of the Nikolai Formation (green) in the Wrangell Mountains, derived from the GIS-based digital map compilation of Wilson et al. (2005). The four areas of field study are outlined with labelled boxes. The red lines are faults.  92  limestone) that give way to fine-grained sedimentary strata, which are poorly exposed in the Amphitheater Mountains. Age of the Nikolai Formation  Biostratigraphy and geochronology provide bounds on the age and duration of emplacement of the Nikolai basalts. Fossil assemblages in finely laminated shale immediately beneath the Nikolai basalts in the Wrangell Mountains indicate a Middle to Late Ladinian age (McRoberts, pers. comm. 2007; Jones etal., 1977) and fossils in limestone disconformably overlying the Nikolai Formation are Late Carnian to Early Norian (Armstrong & MacKevett, 1977; Plaficer et al., 1989). Five 40 Ar plateau ages 39 Ar/ for hornblende and biotite from intrusive rocks in the Amphitheater Mountains in the Alaska Range interpreted to be comagmatic with Nikolai basalts indicate formation of these rocks at 23 1-225 Ma (Bittenbender et al., 2007; Schmidt & Rogers, 2007). Three Ar step-heating ages 39 Ar/ Nikolai basalt samples from the Wrangell Mountains yielded 40 of 228.3  ±  5.2, 232.8  ±  11.5, and 232.4 ± 11.9 Ma (Lassiter, 1995).  VOLCANIC STRATIGRAPHY AND PETROGRAPHY Field studies in Alaska focussed in three general areas where parts of the entire flood basalt stratigraphy are well-exposed: the southern flank of the Wrangell Mountains, and the Amphitheater and Clearwater Mountains in the southern part of the eastern Alaska Range (Fig. 3.1). In the Wrangell Mountains, field studies focussed in 4 areas: Skolai Creek, Glacier Creek, Hidden Lake Creek, and Nugget Creek (Fig. 3.2). The base of the Nikolai Formation is well-exposed near Skolai Creek, the type section for the underlying Paleozoic Skolai Group. At Skolai Creek, the base of the Nikolai Formation is basalt flow-conglomerate, pillow breccia, and minor pillow basalt. (Figs 3.2 and 3.3). Pebbles and cobbles comprise >30% of the basal flow-conglomerate and all the clasts appear to be derived from the underlying Skolai Group (Fig. 3.3). Middle to upper portions of the flood basalt stratigraphy are well-exposed above Glacier Creek, where massive maroonand green-colored flows form monotonous sequences with amygdaloidal-rich horizons and no discernible erosional surfaces or sediments between flows (Fig. 3.4). The top of  93  S  Figure 3.3 Photographs of the base of the Nikolai Formation in the Wrangell Mountains, Alaska. (a) Westward-dipping Paleozoic arc volcanic rocks of the Station Creek Formation overlain by Early Permian shale and limestone (Phc-Hasen Creek Formation; Pgh-Golden Horn Limestone Lentil), isolated lenses of Middle Triassic ‘Daonella-beds’ (TRd), basalt flow-conglomerate with local pillows, and massive subaerial flows on the north side of Skolai Creek. Photograph by Ed MacKevett, Jr. (b) Close-up photograph of area b in photo a. (c) Close-up photograph of area c in photo b showing basal flow-conglomerate with clasts of rounded cobbles of white limestone (<20 cm) derived from Golden Horn Limestone Lentil and red basalt (<40 cm) from Station Creek Formation. Pen (14 cm) in middle of photo for scale.  94  Figure 3.4 Photograph of —4000 m of continuous flood basalt stratigraphy at the top of the Nikolai Formation along Glacier Creek in the Wrangell Mountains, Alaska. The yellow line marks the contact between Nikolai basalts and the overlying Chitistone Limestone.  95  the flood basalts are best exposed around Hidden Lake Creek where a sharp contact between Nikolai basalts and overlying Chitistone Limestone is mostly a smooth surface with minimal evidence of weathering (Fig. 3.5; Armstrong & MacKevett, 1982). Several occurrences of a thin zone (<1 m) of highly-oxidized subangular cobble-sized clasts of Nikolai basalt and minor thinly-bedded siltstone occur along the contact (Fig. 3.5). In the Amphitheater Mountains, fieldwork concentrated in five areas: Glacier Gap Lake, Landmark Gap Lake, Tangle Lakes (West), Sugarloaf Mountain, and Rainy Creek (Fig. 3.6). The Amphitheater Mountains are formed of exceptionally well-preserved flood basalt sequences flanked by associated underlying mafic and ultramafic plutonic rocks. South of the Eureka Creek fault is a broad synform with approximately 3.5 km of basaltic flows with basal sill complexes exposed along the outer margins (Fig. 3.6). The lower —‘500 m of volcanic stratigraphy are submarine flows and subaerial flows comprise most of the remainder of the volcanic stratigraphy. Within the synform, several north-southtrending, U-shaped glacial valleys (e.g. Lower Tangle Lakes) provide excellent crosssectional exposures of sediment-sill complexes and the base of the flood basalt stratigraphy (Figs 3.6 and 3.7). The lowest part of over 1000 m of continuous volcanic stratigraphy consists of unfossiliferous shale and siliceous argillite (<4 m thick) interbedded with massive mafic sills (2-30 mthick), in turn overlain by pillow basalt (Fig. 3.7). The basal pillowed flow is 13 m thick and pillows are typically <1 m in diameter with sediment between pillows along the base of the flow. Sills interbedded with thinly bedded basaltic sandstone and minor hyaloclastite also occur slightly higher in the stratigraphy, within the submarine stratigraphy (Figs 3.6 and 3.7). Middle and upper sections of the Nikolai Formation are massive amygdaloidal flows (mostly <15 m thick) with no discernible erosional surfaces or sediments between flows. A small segment of Wrangellia consisting of a heterogeneous assemblage of mafic and ultramafic plutonic and volcanic rocks forms a wedge between the Broxson Gulch Thrust and the Eureka Creek fault in the northern part of the Amphitheater Mountains (Fig. 3.6). A complex steeply-dipping sequence of picritic tuff and volcaniclastic rocks, mafic and ultramafic intrusives and dikes, and limestone occurs within several ridges near Rainy Creek. These units have distinct lithologic character from the volcanic stratigraphy of the Nikolai Formation south of the Eureka Creek Fault  96  : Figure 3.5 Photographs showing the top of the Nikolai Formation in the Wrangell Mountains, Alaska. (a) Chitistone Limestone overlying the Nikolai Formation above Hidden Creek in the Wrangell Mountains. Faulting has offset the contact. (b) Close-up photograph of uppermost Nikolai flow and base of the Chitistone Limestone from where photo a was taken. (c) Cobbles <10 cm long along the contact between the Chitistone Limestone and Nikolai Formation. The oxidized cobbles are subangular, closely packed, aligned along their long axis, and are glomeroporphyritic basalt identical to the uppermost flows of the Nikolai Formation. Sledgehammer handle (4 cm wide) for scale.  97  Amphitheater Mountains  Figure 3.6 Simplified geologic map and stratigraphy of the Amphitheater Mountains, Alaska (location shown in Figure 3.1). (a) Stratigraphic column with sample lithologies and estimated vesicularity for flood basalts from the lower part of the volcanic stratigraphy, derived from three traverses marked by red lines in b. Vesicularity estimated visually from thin-sections. (b) Generalized geology of the Nikolai Formation and related plutonic rocks in the Amphitheater Mountains. Five main field areas are outlined with numbered boxes (see legend). Map derived Nokleberg et a!. (1992) and digital compilation of Wilson et aL (1998). (c) Schematic cross-section of Amphitheater Mountains from A to A? in panel b, adapted from Nokleberg et aL (1985).  98  neater Mountains, Alaska Range  Figure 3.7 Photographs of the base of the Nikolai Formation in the Amphitheater Mountains, east-central Alaska Range (Tangle Lakes, West), Alaska. (a) Basal sill and sediments beneath submarine flows. Letters denote locations of other photographs. (b) Fissile shale (—4 m thick) and a mafic sill from the lowermost exposure of shale. (c) Pillow basalt with shale between pillows lying directly above shale similar to photograph b. (d) Pillow basalt (pillow tubes are <1 m diameter in cross-section) in the lowermost flow (13 m thick) in the Tangle section. Photograph c is from the base of this flow. Sledgehammer (80 cm long) for scale. (e) Sequence of at least 4 massive sills (<8 m thick) interbedded with fine-grained tuff (<2 m thick). Tuff layers interbedded with sills contain plagioclase crystals (<0.5 mm), curvilinear shards, and local areas of volcanic breccia containing basaltic clasts with abundant small acicular plagioclase (<0.5 mm).  99  within the broad synform. A small suite of eight samples, including several highly altered olivine-bearing picritic tuffs, were collected for comparison to Nikolai basalts within the synform and are referred to as Rainy Creek picrites. In the Clearwater Mountains, a small mountain range 40 km west of the Amphitheater Mountains, the lowest level of exposure is pelagic sedimentary sequences interbedded with mafic sills, very similar to units in the Amphitheater Mountains (Fig. 3.8). The lowest flows of the Nikolai Formation are pillow basalt directly overlying thin beds of shale and argillite (<3 m thick) with sediment commonly filling interpillow voids in the lowermost pillows. Picritic pillow lavas have been found in the submarine stratigraphy in the Clearwater Mountains. Similar to the Amphitheater Mountains, the lower <400 m of the volcanic stratigraphy is submarine flows and the remainder of the stratigraphy is primarily subaerial flows. Upper parts of the volcanic stratigraphy contain subaerial flows (or sills) with columnar jointing, minor occurrences of tuff and volcanic breccia, and limestone and argillite lenses interbedded with flows are overlain by fine grained sediments with diagnostic index fossils (bivalve Halobia and ammonoid Tropite; Smith, 1981). A total of 111 samples of the Nikolai Formation and several Paleozoic, Late Mesozoic, and Cenozoic volcanic and sedimentary rocks were collected for petrography and geochemical analysis. Fifty-three of these samples were selected for geochemistry based on the visual degree of alteration (Table 3.1; 1-least altered, 3-intensely altered) and are grouped into high- and low-titanium basalts, sills, and picrites based on geochemistry. The high- and low-titanium basalts have similar petrographic textures with simple mineralogy and aphyric or glomeroporphyritic texture (Fig. 3.9; Table 3.1). Half of the 26 high-titanium basalts are glomeroporphyritic and about half of the low-titanium basalts are aphyric (Table 3.1). Phenocrysts and glomerocrysts in the Nikolai Formation are almost exclusively plagioclase and the primary minerals in the groundmass are plagioclase, clinopyroxene, and Fe-Ti oxide, and olivine is rarely present (Fig. 3.9; Table 3.1). High-titanium basalts have a higher proportion of Fe-Ti oxide than low-titanium basalts (Table 3.1). Several of the uppermost flows in the Wrangell Mountains are plagioclase-rich (>50% plagioclase laths —1mm long with —5:1 aspect ratio) with  100  Figure 3.8 Geologic map and stratigraphy of the Clearwater Mountains, Alaska. (a) Stratigraphic column with sample lithologies and estimated vesicularity for flood basalts from the lower part of the stratigraphy, derived from three traverses and maps of Smith (1973) and Silberling et a!. (1981). Vesicularity estimated visually from thin-sections. (b) Generalized geology of the Nikolai Formation and related plutonic rocks in the Clearwater Mountains, adapted from Silberling et a!. (1981). Sample locations are shown by red dots. Location of map shown in Figure 3.1. (c) Schematic cross-section of Clearwater Mountains from A to A’ in panel b, adapted from Silberling eta!. (1981).  101  Table 3.1 Summaiyofpefrographic characteristics and phenoc,yst proportions of Nikolai basalts in Alaska Sample’ Areab Flow’ 5710A2 WM FLO 5801A2 CL PLO 5806A3 GG PLO 5708A2 WM PLO 5801A9 CL PIL 5725A2 TA SIL?? 5716A2 WM PLO 5806A5 GG PLO 5716A3 WM PLO 5707A3 WM PLO 5710A3 WM PLO 5719A6 WM PLO 5719A5 WM PLO CL PLO 5801A5 5806A6 GG PLO 5712A2 WM PLO TA PIL 5726A1 5726A6 TA PIL 5725A4 TA SIL?? 5726A3 TA PLO 5810AtO TA PIL WM PLO 57’15A1 5714A1 WM PLO 5716A1 WM PLO 5726A2 TA PLO 5714A3 WM PLO  Groupd high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti sill high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti high-TI high-Ti high-Ti high-Ti high-Ti sill high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti high-Ti  Texture’ glomero glomero aphyric, recrystallized trachylic, glomero aphyric, intersertal glomero intergranular, aphyric aphyric, intersertal plag-phyric, intersertal intergranular, intersertal glomero, intergranular glomero, intergranular glomero, intergranular glomero, intergranular aphyric, intersertal glomero aphyric glomero, intersertal aphylic, ophimottled intersertal aphyiic, Intersertal trachylic, glomero trachylic, glomero plag-phyric aphyric, intersertal intergranular, glomero  5715A5 5801A8 5802A5 5731A5 5802A6 5810A4 5802A1 5731A6 5810A6 5727A3 5810A1 5727A5 5727A7 5810A2 5727A2 5731A3 5802A3 5727A6 5802A2 5731A4 5811A1  WM CL CL CL CL TA CL CL TA TA TA TA TA TA TA CL CL TA CL CL TA  PLO PLO PIL PIL SIL SIL PIL PIL PIL SIL PIL PIL PIL SIL SIL PIL PIL SIL PIL PIL GAB  low-Ti low-Ti low-Ti low-Ti low-Ti low-Ti sill low-Ti low-Ti low-Ti low-Ti sill low-Ti low-Ti low-Ti low-Ti sill low-Ti sill low-Ti low-Ti low-Ti sill low-Ti low-Ti low-Ti sill  relict glomero intergranular, aphyric intergranular, ophimotfied intergranular, ophimottied intergranular glomero, intersertal interaertal intergranular, intersertal glomero, intersertal subophitic aphyric, intersertal aphyric, intersertal aphyric, intersertal aphyiic, intersertal intergranular intergranular, intersertal aphyric, intersertal subophilic, ophimottied variolitic subophitic, ophimotfied intergranular  571 SAl  WM  BRE  basal  trachytic  5802A4  CL  PIL  CWPIC  spherulitic  5808A3 5808A8 5808A2 5808A1 5808A6  RC RC RC RC RC  TUP SIL TUP TUP DIK  RCPIC RC RCPIC RC RC  tuffaceous tuffaceous tuffaceous tutfaceous interaranular  vnl ôi  Plan  Cnx  Os  20 20 10 15  3 15  10 10 15  30 3 10 10 10 15  10 15 15 15 20  5  15  20 7 10 5 10 10 5 3 3  1 20 10 5 10  5 5 15  1  25 2 10 5  3 1 2 1  5 5 2 20  1 1  15 30 5  3 1 3 2 3 2 2 3 3 3 3 2 1 2 3 2 2 2 2 3 1 1 2 3 2 3  Notch plag glcr <3 mm abundant ox abundant ox, few relict phenos abundant ox, plag glcr <2 mm aphyric plag glcr <2mm, cpx <0.5mm plag laths <1.5 mm, plag-rich, secondary mm abundantox,aphyric abundant plag phenos and glcr <4 mm fewplag<2mm plag glcr<3 mm, plag laths <1 mm, ox-rich abundant ox, plag glcr <3 mm, plag-rich abundant ox, plag glcr <3 mm, plag-rich abundant ox, plag glcr <2 mm plag <0.5 mm, cpx <0.5 mm plag glcr <3 mm, plag laths <0.5 mm vesicles 3%, very f.g., I plag glcr <3 mm plag glcr <2 mm, plag needles <0.5 mm plag <0.5 mm, cpx <0.5 mm plag phenos <2 mm plag <0.5 mm, cpx <0.5 mm plag glcr <3 mm, aligned p1 <0.5 mm plag glcr <3mm, aligned plag laths <0.5mm plag <6 mm, very c.g., plag laths <1 mm vesicles <0.5 mm, plag needles <0.5mm c.g., abundant sec mi plag glcr <3 mm  3 3 2 2 1 1 2 3 1 3 2 2 2 2 3 2 2 2 3 3 2  altered, abundant sec mm, plag glcr <3 mm blocky ox <0.5 mm aphyric aphyric plag laths <1 mm, cpx <1.5mm plag glcr <3 mm plag needles <0.5 mm, cpx <1.5mm plag <0.5 mm 10% vesicles, plag glcr <3 mm plag <I mm, cpx <I mm, ox <0.5mm 15% vesicles, tiny plag needles <0.3 mm plag needles <0.5 mm vesicular, plag needles <0.5 mm, cpx<0.5 mm f.g., plag needles <0.5mm plag laths <1 mm, cpx <1 mm few ol<1.5 mm few oI<1 mm cpx <2 mm enc plag <1 mm highly altered, glomero, aligned plag cpx <1 mm enc tiny plag needles cpx <2 mm filling Interstices  2  calcite and qtz <3 mm, plag needles <1 mm  2  01 <2 mm, swfl plag <1 mm  Alferatlnna  3 3 3 3 2  blocky ox <0.5 mm  elonoate hbl (<1.5 mmt with atz cement ‘Sample number: last digit year, month, day, initial, sample station (except 93G171). ‘WM, Wrangell Mountains; TA, Tangle Lake; GG, Glacier Gap Lake; CL, Clearwater Mountains; RC, Rainy Creek; °PIL, pillow; BRE, breccia; FLO, flow; SIL,sill; GAB, gabbro; TUP, tuft; DIK, dike. dbasal basal flow-conglomerate; RC, Rainy Creek; RCPIC, Rainy Creek picrite; CWPIC, Cleaiwater picrite. °glomero, glomeroporphyritic.Modal proportions were visually estimated. alteration index based primarily on degree of plagioclase alteration and presence of secondary minerals (1, least altered; 3, most altered). Plagioclase is commonly replaced by epidote, chlorite, sericite, clmnozoisite, and clay minerals and zoning is obscured in many samples due to albitization; clinopyroxene is mosty unaltered compared to plagiodase; Pe-Ti oxides are altered to sphene and leucoxene minerals; amygdules (<20 volume %) are prevalent throughout most subaerial flows and are usually filled with quartz, calcite, epidote, prehnite and pumpellyite. hglcr, glomerocrysts; f.g., fine-grained; c.g., coarse-grained, oik, swtl, swallow-tail. Mineral abbreviations: 01, olivine pseudomorphs; plag, plagioclase; cpx, clmnopyroxene; ox, oxides (includes ilmenite + titanomagnetite). High- and low-titanium basalte are listed from highest (top) to lowest (bottom) TiO 2 contents.  102  Figure 3.9 Representative photomicrographs of Nikolai basalts, Alaska. (a) Aphyric pillow basalt from the Tangle Lake (West) in the Amphitheater Mountains in cross-polarized transmitted light (sample 5810A10). (b) Hyaloclastite from near the top of the submarine section at Tangle Lake (West) in plane-polarized transmitted light (sample 5810A9, no chemistry). (c) Hyaloclastite interbedded with sills from Tangle Lake (West) in plane-polarized transmitted light (sample 581 OA3b, no chemistry). (d) Glomeroporphyritic pillow basalt with abundant amygdules (—10 vol %) from Tangle Lake (West) in cross-polarized transmitted light (sample 5810A6). (e) Variolitic picritic pillow basalt with olivine pseudomorphs (<2 mm) and acicular plagioclase with swallow-tail terminations from the Clearwater Mountains, in plane-polarized transmitted light (sample 5802A4). (f) Rainy Creek picritic tuff with pseudomorphed olivine phenocyrsts, undeformed recrystallized angular and cuspate shards, and lithic particles in a fine-grained matrix, in plane-polarized transmitted light (sample 5808A2). Some clasts appear to be clusters of grains, some of which contain thin green rims.  103  trachytic-like texture and abundant oxides. Picrite from the Clearwater Mountains preserve spherulitic textures with bow-tie and fan-shaped bundles of acicular plagioclase, typically with swallow-tail terminations. Olivine (<2 mm) pseudomorphed by secondary minerals comprises —20 vol % of the picrite and plagioclase commonly radiates from the edges of olivine pseudomorphs and is intergrown with clinopyroxene. The sample preparation and analytical methods for whole-rock chemistry, major elements, trace elements, Sr, Nd, Hf, and Pb isotopes are described in Appendix D. WHOLE-ROCK CHEMISTRY Major- and trace-element compositions  The most noteworthy feature of the major-element chemistry of the Nikolai Formation is two clearly distinguishable groups of high- and low-titanium basalt (Fig. 3.10). The low-titanium basalts range from 0.4 to 1.2 wt % Ti0 2 and the high-titanium 2 (Fig. 3.10; Table 3.2). The high-titanium basalts basalts range from 1.6 to 2.4 wt % Ti0 have a limited range in MgO (5.7-7.9 wt % MgO, except for one plagioclase-rich flow with 4.8 wt % MgO) and Si0 2 (49.2-52.1 wt %), whereas the low-titanium basalts extend 2 to higher MgO and have a significantly larger range in MgO (6.4-12.0 wt %) and Si0 (46.7-52.2 wt %). Almost all of the Nikolai basalts in Alaska fall within the tholeiitic  field in a total alkalis versus silica plot, with low-titanium basalts generally having lower total alkalis than the high-titanium basalts. The low-titanium basalts exhibit broadly decreasing trends of Ti0 , FeOT, and Na 2 0 with increasing MgO (Fig. 3.10) and have 2 higher loss on ignition (LOl; mean LOI=2.7 ± 1.3 wt %) than the high-titanium basalts (mean LOI=1.9 ± 1.5 wt %; Table 3.2). Low-titanium basalts with >8 wt% MgO have higher concentrations of Ni than the high-titanium basalts and the three picrite samples have noticeably higher Ni concentrations (525-620 ppm) than all basalts (Fig. 3.10). Both the high- and low-titanium basalts have a large range in CaO, which appears to be independent of MgO variation. A single Clearwater picrite (13.6 wt % MgO) and two , FeOT, 2 Rainy Creek picrites (15.5-16.2 wt % MgO) have higher MgO with similar Ti0 and alkali contents to the low-titanium basalts, however, the Rainy Creek picrites have 3 (Fig. 3.10). The basal flow-conglomerate from the Wrangell 0 2 notably lower A1 Mountains has distinct major-element chemistry compared to the other Nikolai basalts.  104  0  lillIllIll  —  •  7  .  —.—  x  0 2 Na  •  -  +  0  4.  0  cP  1.5  tholeiitic  D •00  0  3  o  2.0 0  0  high-titanium basalt  D low-titanium basalt low-titanium sill A Clearwaterpicrite Rainy Creek picrite X basalfiow 0 Yukon high-Ti basalt o Yukon low-Ti basalt  0  -  0  5  •  • high-titanium sill  2 T10  2.5  .  alkalic  K 0 2 (wt%)  6  111111111  0  i.o  21-  0  a) III  0  I  I  40  1111111111  I  45  50  ‘(b)  III  55  0.0 60  0  2  4  10 12 8 MgO (wt%)  6  5102 (%) 15  I  14  I  I  I  CaO  I  I  I  I  I  I  I  I  I  I  20  I  12  16  18  III  0  x  3 0 2 A1 18 • (wt%)  0 C  o  17  QD  11  11111  ‘III’  19  D  o  13 • (wt%)  I  14  000  C  16  oVoLc  10  15  9  14 W70(  •  i  8 600  7  0.  Ni(ppm) A  x  6  • (C)  II  5 0  I  2  6  I  i  I  I  I  C  6 8 MgO (wt%)  300  I  •  200  i  (e?  400  4  .  ,  6  8  10  MgO(wt%)  4  12  1•1111•  14  16  0  18  FeO fr) (wt%)  00  00  10  0  •_-8 dj:l  9  2  8 7  0 I  2  4  6  DC 0  .  0  18  12 11  (f)  16  •J 4  0  14  0  ;(d)  .0000  3  10 12 8 MgO (wt%)  6  100  Na X 0 2 (wt%)  5  o  500 I  °  •o  I  10 12 8 MgO (wt%)  I  -  14  I  --  I  16  C C I  -  18  0  2  I  4  I  I  6  8  10  12  14  16  18  MgO (wt%)  Figure 3.10 Whole-rock major-element and Ni variation diagrams vs. MgO for the Nikolai Formation in Alaska with data for the Nikolai Formation in Yukon (see chapter 4). The boundary of the alkaline and tholeiitic fields is that of MacDonald and Katsura (1964). Total iron expressed as FeO, LOT is loss-on-ignition, and oxides are plotted on an anhydrous, normalized basis. Note the clear distinction between the high- and low-titanium basalts in panel b and the difference in alkali contents between the Nikolai basalts in Alaska and Yukon in panel a.  105  Table 3.2 Major element (wt% oxide) and trace element (ppm) abundances in whole rock samples of Nikolai basalts, Alaska. 5714A1 5714A3 5715A1 (1) 5715A1 (2) SAMPLE 5707A3 5708A2 5710A2 5710A3 5712A2 5715A5 HI-TI HI-TI HI-TI HI-TI HI-TI HI-TI HI-TI HI-TI HI-TI LOW-TI Group WM Area WM WM WM WM WM WM WM WM WM Flow FLO PLO FLO FLO PLO FLO FLO FLO PLO FLO 6838178 6826371 6826390 6827794 6828050 UTM EW 6816521 6813830 6838676 6836850 6827794 430777 428595 356266 353987 384783 384806 383399 383399 383641 UTM NS 356035 Unnormalized Major Element Oxides (Weight %): 2 Si0 49.74 48.40 48.81 50.02 49.90 49.31 50.21 49.61 49.41 50.25 2 TiO 2.36 2.4 1.95 1.89 1.66 1.6 1.69 1.68 1.14 1.96 3 O 2 A1 16.01 15.56 13.37 13.49 15.21 14.45 13.76 15.58 15.75 16.69 * 3 O 2 Fe 16.14 12.94 13.39 13.76 13.21 10.99 13 12.97 10.39 14.05 0.24 0.17 0.16 0.2 0.2 0.18 MnO 0.27 0.27 0.23 0.18 5.89 6.74 6.6 6.64 6.63 6.62 7.94 MgO 6.69 6.85 6.56 9.97 CaO 10.61 10.09 9.16 8.56 11.35 10.8 11.09 11.04 9.48 O 2 Na 2.47 3.15 1.87 2.08 3.77 1.84 1.82 3.36 2.64 3.56 0.61 1.03 0.22 0.42 0.28 0.2 0.2 0.67 0.29 0.58 1<20 0.16 0.14 0.15 0.14 0.09 0.16 0.23 0.21 0.18 0.15 1.41 2.37 2.47 1.28 2.39 3.12 0.84 1.84 3.57 LOI 1.68 99.77 99.97 100.19 Total 99.78 99.95 99.54 99.88 99.89 99.98 99.83 Trace elements (ppm): 3.74 La 10.32 8.08 6.56 6.56 21.79 17.07 17.07 10.69 Ce 24.25 2.35 2.35 1.49 Pr 3.66 2.90 12.20 12.20 7.68 Nd 18.83 14.73 4.19 3.51 3.51 2.32 Sm 5.22 1.25 1.25 0.90 1.73 1.43 Eu 4.17 3.80 3.80 2.55 Gd 5.57 0.72 0.72 0.50 1.02 0.77 Tb 3.34 6.84 5.04 4.77 4.77 Dy 0.98 0.98 0.69 Ho 1.35 0.99 1.98 4.02 2.85 2.86 2.86 Er 0.36 0.36 0.25 Tm 0.51 0.33 2.37 2.59 2.59 1.77 Yb 3.58 0.40 0.28 0.53 0.36 0.40 Lu 42.52 41.17 41.17 38.50 Sc 44.06 276 354 352 249 362 411 349 337 346 329 V 167 119 133 156 282 165 167 460 Cr 165 62 44 44 39 47 45 Co 73 82 81 85 85 116 Ni 75 57 89 69 126 126 64 19 1067 Cu 108 113 109 88 110 111 68 Zn 121 176 126 15 21 19 19 19 17 20 19 Ga 19 20 2.6 1 1 8.5 3.4 9.7 6.1 15 2.2 5.2 Rb 437 263 481 184 334 394 184 184 Sr 237 162 26 26.2 18.3 28.1 36.1 31.6 27.8 25.8 26.2 22.6 Y 145 115 110 99 93 98 98 60 Zr 113 148 7.7 7.3 7.7 7.7 4.4 10.1 12.5 12.2 9.7 9.9 Nb 0.28 0.83 0.14 0.28 Cs 0.08 63 56 55 56 129 Ba 79 108 147 246 70 2.78 2.78 1.79 4.10 3.15 Hf 0.48 0.48 0.30 0.74 0.67 Ta 0.44 0.81 0.52 0.52 Pb 1.59 0.64 0.64 0.34 0.98 0.72 Th 0.19 0.09 0.20 0.19 U 0.31 4 6 6 2 6 7 8 7 6 6 La(XRF) 24 22 21 16 13 17 16 8 Ce(XRF) 21 27 Abbreviations for group are: HI-TI, hIgh-titanium; LOW-TI, low-titanium; RC, Rainy Creek; RCPIC, Rainy Creek picnte; CWPIC, Clearwater picrite. Abbreviations for flow are: PLO, massive flow; PIL, pillow basalt; FLO-BRE, flow-conglomerate-pillow breccia; SIL, sill; TUF, tuff. Abbreviations for area are: WM, Wrangell Mountains; TANGLE, Tangle Lakes; GLAC, Glacier Gap Lake; CLEAR, Clearwater Mountains; RAINY, Rainy Creek. Sample locations are given using the Universal Transverse Mercator (UTM) coordinate system (NAD83; zones 6 and 7). XRF analyses were * is total iron expressed as Fe 3 O 2 . LOI is loss-on-ignition. 3 O 2 performed at University of Massachusetts Ronald B. Gilmore XRF Laboratory. Fe Elements by XRF: Sc, V, Cr, Ni, Zn, Ga, Rb, Sr, Y, Zr, Nb, Ba. Elements by ICP-MS: REE, Co, Cu, Cs, Hf, Ta, Pb, Th, U.  106  5716A2 SAMPLE 5716A1 5716A3 Group HI-TI HI-TI HI-TI WM WM Area WM Flow FLO FLO FLO 6824809 6825071 UTM EW 6824771 UTM NS 384884 384800 384853 Unnormalized Major Element Oxides (Weight %): 2 SIO 50.52 50.76 50.89 2 TiO 1.66 2.12 1.96 3 0 2 A1 13.56 15.57 15.82 * 3 O 2 FC 12.03 14.22 13.37 0.19 0.18 MnO 0.18 MgO 6.13 7.83 4.8 7.94 7.01 8.1 CaO 0 2 Na 4.26 4.52 4.71 0 2 K 0.58 0.08 0.23 0.19 0.15 0.18 LOI 2.96 3.57 3.54 99.87 Total 99.64 100.23 Trace elements (ppm): La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sc 289 393 319 V 70 Cr 157 133 Co 47 Ni 66 61 Cu 82 Zn 94 97 17 21 Ga 15 0.6 2 Rb 5.8 97 Sr 321 56 26.4 30.8 28.5 V 120 118 Zr 98 7.6 9.7 10.2 Nb Cs Ba 115 14 47 Hf Ta Pb Th U La(XRF) 4 4 7 18 18 Ce(XRF) 16  5719A1 LOW-TI WM FLO-BRE 6840607 430357  5719A5 (1) HI-TI WM FLO 6840632 430204  5719A5 (2) HI-TI WM FLO 6840632 430204  5719A6 HI-TI WM FLO 6840632 430204  5725A2 HI-TI TANGLE SIL 7001750 556168  5725A4 HI-TI TANGLE SIL 7002024 555867  5726A1 HI-TI TANGLE PIL 7002334 553245  55.72 0.67 18.59 7.84 0.16 3.37 6.07 5.14 2.18 0.38 5.14 100.12  49.54 1.92 14.57 12.84 0.21 6.52 11.47 2.01 0.29 0.17 1.05 99.54  49.62 1.93 14.55 12.86 0.21 6.55 11.5 2.02 0.3 0.17 1.09 99.71  49.76 1.92 14.45 12.79 0.21 6.65 11.45 2.12 0.24 0.17 2.66 99.76  50.53 2.19 14.98 11.73 0.2 5.99 11.74 1.99 0.46 0.21 1.26 100.02  50.43 1.82 14.31 12.36 0.2 6.66 12.13 1.78 042 0.16 1.03 100.27  49.01 1.88 13.96 13.13 0.23 7.07 11.74 2.26 0.25 0.16 1.88 99.69  18.10 36.95 4.56 20.65 4.26 1.31 3.96 0.52 3.40 0.66 2.12 0.26 1.94 0.31 11.02 170 0 16 1 25 83 17 25.4 158 19.5 81 6.3 0.06 1277 2.30 0.36 2.96 4.18 1.91 17 34  9.13 21.43 3.05 16.26 4.45 1.48 4.58 0.79 5.31 0.97 2.94 0.35 2.46 0.36 41.37 366 162 42 77 167 104 19 5.8 200 26.3 113 10.1 0.09 94 3.23 0.63 0.85 0.87 0.25 7 23  9.13 21.43 3.05 16.26 4.45 1.48 4.58 0.79 5.31 0.97 2.94 0.35 2.46 0.36 41.37 367 160 42 76 167 104 19 5.9 200 26.1 113 10 0.09 91 3.23 0.63 0.85 0.87 0.25 8 23  8.57 21.35 3.00 15.16 4.30 1.43 4.32 0.77 4.89 0.94 2.69 0.32 2.17 0.30 38.05 325 127 42 80 160 101 20 16.5 207 24.3 107 9.2 0.53 83 3.08 0.57 0.66 0.83 0.25 5 19  7.52 19.80 2.74 14.35 4.07 1.08 4.15 0.74 4.92 0.91 2.59 0.30 2.03 0.27 41.02 359 217 42 90 138 110 17 2.1 239 24.3 110 9.4 0.07 191 2.66 0.52 0.95 0.86 0.23 5 18  340 164  358 140  78  68  104 19 4.1 275 25.6 112 9.9  96 20 16.2 213 29.6 140 12.1  85  245  8 21  8 23  107  5726A3 5726A6 5726A2 SAMPLE HI-TI I-Il-TI HI-TI Group TANGLE TANGLE TANGLE Area FLO PIL FLO Flow 7002270 7002475 7002466 UTM EW 553826 553495 553936 UTM NS Unnarmalized Major Element Oxides (Weight %): 49.90 50.11 2 S1O 51.41 1.81 1.85 2 T1O 1.63 14.74 3 O 2 A1 14.73 13.83 * 3 O 2 FC 12.34 11.71 12.16 0.21 0.19 MnO 0.19 6.72 6.75 MgO 6.96 11.96 12.7 11.25 CaO 1.94 1.95 O 2 Na 2.2 0.09 0.13 O 2 K 0.11 0.16 0.16 5 O 2 P 0.14 1.29 1.6 1.35 LOI 99.87 100.28 Total 99.88 Trace elements (ppm): La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sc 332 333 324 V 136 118 148 Cr Co 84 85 79 Ni Cu 100 84 102 Zn 20 19 18 Ga 0.4 3.4 0.7 Rb 178 195 198 Sr 24.6 24.7 22.2 Y 106 94 109 Zr 92 9.4 8 Nb Cs 45 47 48 Ba Hf Ta Pb Th U 7 6 6 La(XRF) 18 19 17 Ce(XRF)  5727A2 LOW-TI TANGLE SIL 6999661 550468  5727A3 LOW-TI TANGLE SIL 6999663 550377  50.70 0.54 14.49 11.21 0.19 9.41 12.3 1.09 0.06 0.04 2.18 100.03  50.97 0.58 15.85 10.79 0.19 7.75 11.96 1.76 0.1 0.05 2.3 100.00  1.13 3.19 0.49 2.92 1.22 0.56 1.47 0.36 2.62 0.56 1.67 0.22 1.61 0.27 44.90 242 555 51 178 96 81 14 1.7 76 15.1 23 0.9 0.36 98 0.80 0.04 0.55 0.17 0.07 0 2  1.13 3.22 0.51 2.92 1.23 0.49 1.47 0.34 2.60 0.60 1.70 0.22 1.61 0.26 43.02 254 269 44 106 116 77 14 1.8 117 15.5 24 0.9 0.28 76 0.87 0.05 0.50 0.17 0.07 1 2  5727A6 (2) LOW-TI TANGLE SIL 6999646 550324  5727A7 LOW-TI TANGLE PIL 6999646 550270  5731A3 LOW-TI CLEAR PIL 6993085 483499  48.89 0.48 15.06 10.51 0.18 11.51 12.43 0.79 0.05 0.06 3 99.96  48.89 0.48 15.06 10.51 0.18 11.51 12.43 0.79 0.05 0.06 3 99.96  46.13 0.56 17.97 11.84 0.17 9.09 12.78 1.19 0.1 0.07 2.75 99.90  50.94 0.53 15.51 9.75 0.17 10.52 10.68 1.22 0.22 0.1 3.15 99.64  1.25 3.56 0.54 3.05 1.11 0.37 1.33 0.34 2.35 0.55 1.63 0.21 1.53 0.25 45.67 233 521 54 214 98 74 12 0.6 123 14 15 0.8 0.12 46 0.57 0.04 0.20 0.07 0.03 1 3  1.27 3.58 0.56 3.09 1.13 0.36 1.37 0.32 2.37 0.53 1.58 0.21 1.53 0.24 49.00 233 521 54 214 96 74 12 0.6 123 14 15 0.8 0.12 46 0.57 0.04 0.18 0.07 0.03 1 3  2.56 5.66 0.80 3.86 1.30 0.67 1.63 0.38 2.80 0.64 1.93 0.25 1.91 0.33 50.33 268 199 57 163 131 92 15 1.5 155 17.2 20 0.8 0.23 54 0.70 0.05 1.21 0.29 0.10 2 3  5727A5 5727A6 (1) LOW-TI LOW-TI TANGLE TANGLE SIL PIL 6999646 6999658 550324 550351 47.43 0.57 15.81 11.04 0.19 10.35 13.12 1.06 0.09 0.07 2.87 99.73  257 455 157 84 13 1.2 146 15.8 17 1 130  1 2  217 605 191 68 12 4.6 205 17.2 38 2.2 125  4 11  108  5731A5 SAMPLE 5731A4 5731A6 Group LOW-TI LOW-TI LOW-TI CLEAR CLEAR Area CLEAR Flow PIL PIL PIL 6993131 6993230 6993320 UTMEW UTM NS 483495 483531 483566 Unnormalized Major Element Oxides (Weight %): 2 Sb 48.12 49.13 48.61 2 TiO 0.48 0.92 0.64 3 O 2 A1 16.1 15.9 15.89 * 3 0 2 Fe 10.32 11.5 9.69 0.19 0.16 MnO 0.19 9.63 9.67 8.37 MgO 11.71 13.54 CaO 12 O 2 Na 1.87 1.35 2.13 0.63 0.28 0.29 1<20 0.1 0.06 0.16 3.1 3.34 3.77 LOI Total 99.68 99.94 100.01 Trace elements (ppm): La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Sc 232 256 237 V 578 412 Cr 373 Co 232 137 Ni 141 Cu 72 62 Zn 67 13 Ga 12 15 15.9 6.5 3.3 Rb 272 484 Sr 392 13.8 20.4 16.2 V 45 35 Zr 26 1.6 2.8 Nb 1.4 Cs 108 190 Ba 173 Hf Ta Pb Th U La(XRF) 3 2 6 7 9 14 Ce(XRF)  5801A2 HI-TI CLEAR FLO 6992862 480105  5801A5 HI-TI CLEAR FLO 6992750 480328  5801A8 LOW-TI CLEAR FLO 6992452 480516  5801A9 HI-TI CLEAR PIL 6992443 480528  5802A1 LOW-TI CLEAR PIL 6993172 483888  5802A2 LOW-TI CLEAR PIL 6993140 483867  5802A3 LOW-TI CLEAR PIL 6993104 483847  50.00 2.37 14.02 13.68 0.21 6.08 11.77 1.74 0.13 0.22 1.26 100.22  49.75 1.91 15.17 13.13 0.21 5.76 11.84 1.69 0.28 0.17 1.25 99.91  50.82 1.09 15.06 12.51 0.22 7.16 10.44 1.99 0.27 0.15 2.13 99.71  49.97 2.33 13.95 12.28 0.19 6.69 11.77 1.85 0.38 0.22 1.5 99.63  49.18 0.71 16.27 10.82 0.19 9.41 10 2.82 0.63 0.17 3.64 100.20  49.94 0.48 15.33 10.44 0.19 8.85 12.67 1.88 0.11 0.06 3.43 99.95  47.76 0.52 16.76 10.42 0.18 9.85 12.31 1.2 0.59 0.06 2.7 99.65  12.70 28.04 4.14 21.10 5.55 1.79 5.49 0.93 6.21 1.13 3.25 0.37 2.66 0.38 37.45 386 211 43 80 207 115 20 1.7 225 29.4 146 13.1 0.12 57 4.03 0.76 1.01 1.24 0.36 9 31  8.65 21.65 3.07 15.51 4.25 1.46 4.40 0.80 5.22 1.01 2.93 0.35 2.50 0.36 38.99 358 58 41 56 182 111 20 5.9 187 26.2 113 10.3 0.09 70 3.17 0.61 0.72 0.84 0.24 7 20  285 69  330 129  265 360  56  81  142  118 16 4.6 148 26.7 59 3.9  95 19 5 190 24.8 109 9.4  73 12 16.3 485 18.1 40 3.1  118  73  186  6 13  5 21  6 13  3.00 6.92 1.00 4.04 1.31 0.45 1.57 0.34 2.53 0.57 1.76 0.23 1.75 0.39 50.28 247 364 44 127 89 68 11 2.1 303 15.3 23 1.3 0.30 44 0.78 0.08 0.21 0.56 0.20 3 6  242 346 151 70 13 16.9 260 14.9 29 1.7 198  4 8  109  SAMPLE 5802A5 5802A4 (1) 5802A4 (2) Group LOW-TI CWPIC LOW-TI Area CLEAR CLEAR CLEAR Flow PIL PIL PIL UTMEW 6993057 6993057 6993004 483801 UTM NS 483801 483762 Unnormalized Major Element Oxides (Weight %): 2 Si0 48.26 48.28 46.68 2 Ti0 0.5 0.5 0.93 3 0 2 A1 15.81 15.83 16.19 * 3 0 2 Fe 10.73 10.75 12.21 MnO 0.19 0.19 0.2 13.47 MgO 13.49 1021 CaO 9.2 9.19 12.16 0 2 Na 1.48 1.51 1.23 0.05 0.05 0.12 1<20 5 0 2 P 0.1 0.09 0.09 LOl 4.51 4.53 3.32 Total 99.86 100.03 99.80 Trace elements (ppm): 5.18 5.18 La 3.58 Ce 12.40 12.40 9.28 148 1.32 Pr 148 6.61 Nd 6.61 6.68 Sm 1.69 1.69 2.19 0.51 0.84 Eu 0.51 Gd 1.84 1.84 2.53 Tb 0.40 0.40 0.54 Dy 2.62 2.62 3.76 Ho 0.56 0.56 0.79 Er 1.76 1.76 2.30 Tm 0.23 0.23 0.29 Yb 1.69 1.69 2.12 Lu 0.27 0.27 0.33 40.80 40.80 45.91 Sc V 202 203 257 Cr 1596 1577 633 Co 60 60 58 Ni 539 538 244 Cu 78 78 103 Zn 74 74 82 13 13 16 Ga Rb 0.4 0.5 3 Sr 183 184 252 20.7 Y 15.4 15.2 Zr 35 35 46 2 2.1 1.5 Nb Cs 0.50 0.50 0.30 37 40 Ba 39 Hf 1.05 1.05 1.51 Ta 0.11 0.11 0.08 Pb 0.13 0.13 0.50 Th 0.89 0.89 0.34 0.32 0.32 0.11 U La(XRF) 4 5 2 Ce(XRF) 7 11 4  5802A6 LOW-TI CLEAR SIL? 6992950 483733  5806A3 HI-TI GLAC FLO 7000695 538926  5806A5 HI-TI GLAC FLO 7000232 538787  5806A6 HI-TI GLAC FLO 6999795 538622  5808A1 RC RAINY TUF 7021484 556534  5808A2 RCPIC RAINY TUF 7021213 556314  5808A3 RCPIC RAINY TLJF 7021298 556392  51.77 0.9 14.82 11 0.19 7.95 11.72 147 0.3 0.09 1.56 100.21  49.67 2.37 13.98 13.53 0.21 6.4 10.36 2.14 0.68 0.22 1.82 99.56  49.86 1.97 14.58 12.98 0.21 6.6 10.83 2.25 0.57 0.17 1.62 100.02  50.25 1.89 13.96 12.79 0.21 6.62 12.24 1.59 0.29 0.17 1.67 100.01  49.93 1.01 14.09 13.4 0.22 7.31 11.9 1.61 0.31 0.1 1.98 99.88  46.44 1.06 10.72 10.72 0.15 15.42 9.59 1.34 0.35 0.09 3.2 99.86  46.89 1.18 10.72 10.72 0.18 14.78 9.42 0.88 1.12 0.11 2.4 100.01  5.99 15.32 1.96 9.85 2.69 0.94 2.77 0.51 3.25 0.66 1.79 0.21 1.48 0.22 2729 285.54 1327 67 620 123 60 13 6.11 126.86 16.01 58.73 6.00 0.43 72 1.71 0.35 0.76 0.70 0.26 6 15  6.52 18.08 2.33 11.57 3.01 1.09 3.02 0.54 3.23 0.63 1.79 0.22 1.45 0.25 29.39 297.75 1250 63 525 79 63 13 2643 92.53 15.81 65.10 8.11 1.10 191 1.88 048 0.65 1.06 0.38 7 18  254 448  369 213  339 141  327 123  313 138  128  89  87  78  76  85 16 8.8 188 18.5 49 3  119 21 13.9 215 29.1 144 12.9  112 20 11.8 208 25.4 116 10.4  101 19 4.9 205 25.4 112 9.6  111 16 5.8 185 28.5 41 5.3  92  182  118  108  140  2 4  9 27  7 21  6 19  3 7  110  SAMPLE 5808A6 5808A8 5810A1 (1) 581 OAI (2) Group RC RC LOW-TI LOW-TI Area RAINY RAINY TANGLE TANGLE Flow DIK SIL PIL PIL UTMEW 7021445 7021631 6999686 6999686 UTMNS 556560 557160 550380 550380 Unnormalized Major Element Oxides (Weight %): 2 SiO 49.27 50.04 47.02 46.82 2 Ti0 0.93 1.14 0.57 0.57 3 0 2 A1 14.71 13.39 15.84 15.8 * 3 0 2 Fe 10.76 15.35 10.94 10.96 MnO 0.2 0.25 0.18 0.18 MgO 8.88 6.57 11.23 11.16 CaO 11.31 11.27 13.14 13.09 O 2 Na 1.73 1.52 1.19 1.04 O 2 K 1.57 0.06 0.06 0.07 0.27 0.11 0.07 0.07 LOI 2.16 1.96 2.68 2.65 Total 99.63 99.70 100.24 99.76 Trace elements (ppm): La 1.16 1.16 3.40 Ce 3.40 Pr 0.57 0.57 Nd 3.31 3.31 Sm 1.26 1.26 Eu 0.43 0.43 1.51 1.51 Gd Tb 0.36 0.36 Dy 2.59 2.59 Ho 0.57 0.57 Er 1.74 1.74 Tm 0.24 0