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Post-Caldera Volcanism in Yellowstone National Park

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Post-Caldera Volcanism in Yellowstone National Park POST-CALDERA VOLCANISM IN YELLOWSTONE NATIONAL PARK: PETROGENESIS OF THE INTRACALDERA UPPER BASIN MEMBER OF THE PLATEAU RHYOLITE AND EXTRA-CALDERA MINGLED MAGMA COMPLEXES By CHAD JAMES PRITCHARD A dissertation submitted in partial fulfillment of The requirements for the degree of Doctor of Philosophy WASHINGTON STATE UNIVERSITY School of Earth and Environmental Sciences MAY 2011 ©Copyright by CHAD JAMES PRITCHARD, 2011 All Rights Reserved ©Copyright by CHAD JAMES PRITCHARD, 2011 All Rights Reserved To the Faculty of Washington State University: The members of the Committee appointed to examine the dissertation of CHAD JAMES PRITCHARD find it satisfactory and recommend that it be accepted. Peter B. Larson, Ph.D., Chair Terry L. Spell, Ph.D. John A. Wolff, Ph.D. ii ACKNOWLEDGMENTS I could have only conducted this research with the support and understanding of my wife, Meghan Lunney, of whom I am super-duper grateful. Peter Larson, chair of this committee, was extremely helpful and kind, which is greatly appreciated. I would also like to thank the other members of my committee for their time and energy. World class assistance in the field was given by Allen Anderson, William Starkel, and Kevin Tarbert. Sample analyses were conducted at Washington State University GeoAnalytical Laboratories with appreciated help from Dr. Rick Conrey, Charles Knaack, Dr. Garret Hart, and Dr. Jeffery Vervoort. Sampling permits were issued by Yellowstone National Park, Research Permit Office, with help from Christie L. Hendrix. Acknowledgments specific to each research project are present for Chapters 2 and 3. I would also like to thank the kindly folks and friends in the School of Earth and Environmental Sciences. This study was funded by National Science Foundation grant #EAR-0609475, awarded to Dr. Peter B. Larson; the Washington State University Graduate School; and by the School of Earth and Environmental Sciences, Washington State University. iii POST-CALDERA VOLCANISM IN YELLOWSTONE NATIONAL PARK: PETROGENESIS OF THE INTRACALDERA UPPER BASIN MEMBER OF THE PLATEAU RHYOLITE AND EXTRA-CALDERA MINGLED MAGMA COMPLEXES ABSTRACT by Chad James Pritchard, Ph.D. Washington State University May 2011 Chair: Peter B. Larson The Plateau Rhyolite erupted following the last large Yellowstone caldera collapse and may have erupted from a rejuvenating magmatic system. Our preferred model for rhyolite genesis is by assimilation of continental crust by mafic magmas, followed by fractional crystallization. This model focuses on the extra-caldera mingled magma complexes and the eastern Upper Basin Member. Radiogenetic isotope trends of the mingled magma complexes show that the rhyolite and basalt portions are isotopically distinct and that cryptic mixing between rhyolite and basalt may have occurred in a number of other extra-caldera rhyolites. Rhyolites of the eastern Upper Basin Member contain petrologic textures and increased radiogenic 87Sr/86Sr in plagioclase phenocrysts (0.7134 to 0.7185) when compared to the groundmass and whole rock radiogenic values (0.7099 to 0.7161). δ18O depletions on the order of 5‰ found in the Tuff of Sulphur Creek and Canyon flow indicate at least a two-stage petrogenesis involving assimilation and fractional crystallization. The presence of a low-δ18O rhyolite outside the caldera indicates that country rock was hydrothermally altered at depth and then assimilated to form the Dunraven Road flow. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS .................................................................................................................................. iii ABSTRACT ..................................................................................................................................................... iv LIST OF TABLES ........................................................................................................................................... viii LIST OF FIGURES ........................................................................................................................................... ix CHAPTER 1 Introduction to the Geology of the Yellowstone Plateau Area 1. Introduction ............................................................................................................................. 1 2. Geologic Background ............................................................................................................... 4 3. History of Volcanism – Yellowstone Caldera ........................................................................... 6 4. Geothermal History................................................................................................................ 10 5. Whole Rock Geochemistry ..................................................................................................... 11 6. Isotopes .................................................................................................................................. 15 7. EC-RAxFC Models ................................................................................................................... 16 8. Summary of Conclusions From This Dissertation .................................................................. 21 9. References ............................................................................................................................. 22 CHAPTER 2 Mixed magma complexes and extra-caldera volcanism in the Norris-Mammoth Corridor 1. Abstract .................................................................................................................................. 28 2. Introduction ........................................................................................................................... 29 3. Geologic Background ............................................................................................................. 31 4. Material and Methods ........................................................................................................... 32 v 5. Results .................................................................................................................................... 36 6. Discussion .............................................................................................................................. 48 7. Acknowledgments .................................................................................................................. 51 8. References ............................................................................................................................. 52 CHAPTER 3 Evolution of the Upper Basin Member of the Plateau Rhyolites 1. Abstract .................................................................................................................................. 57 2. Introduction ........................................................................................................................... 57 3. Sampling and Methods .......................................................................................................... 63 4. Results .................................................................................................................................... 69 5. Discussion .............................................................................................................................. 86 6. Conclusions ............................................................................................................................ 96 7. Acknowledgments .................................................................................................................. 97 8. References ............................................................................................................................. 98 APPENDICES A. WHOLE ROCK MAJOR AND TRACE ELEMENT DATA ............................................................. 104 B. RESULTS FROM EC-RAxFC MODELS ..................................................................................... 130 C. RESOURCES FOR CHAPTER 2 – MICROPROBE ANALYSES OF FELDSPAR FROM THE MINGLED MAGMAS.............................................................................................................................. 151 D. RESOURCES FOR CHAPTER 2 – MICROPROBE ANALYSES OF XENOCRYSTS FROM THE MINGLED MAGMAS ............................................................................................................. 204 E. RESOURCES FOR CHAPTER 2 – MICROPROBE ANALYSES OF PYROXENE FROM THE MINGLED MAGMAS.............................................................................................................................. 209 vi F. RESOURCES FOR CHAPTER 2 – MICROPROBE ANALYSES OF OLIVINE FROM THE MINGLED MAGMAS.............................................................................................................................. 223 G. RESOURCES FOR CHAPTER 2 – MICROPROBE ANALYSES OF GROUNDMASS FROM THE MINGLED MAGMAS ............................................................................................................. 234 H. RESOURCES FOR CHAPTER 3 – MICROPROBE ANALYSES OF GROUNDMASS GLASS FROM THE EUBM ............................................................................................................................ 263 I. RESOURCES FOR CHAPTER 3 – MICROPROBE ANALYSES OF GLASS FEATURES FROM THE EUBM ................................................................................................................................... 281 J. RESOURCES FOR CHAPTER 3 – MICROPROBE ANALYSES
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