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Magma Genesis, Degassing, and Mixing in Rifts and Arcs

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Magma Genesis, Degassing, and Mixing in Rifts and Arcs Magma Genesis, Degassing, and Mixing in Rifts and Arcs by Thomas R. Hudgins A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology) in the University of Michigan 2015 Doctoral Committee: Associate Professor Adam C. Simon, Chair Professor Kristina I. Håkansson Professor Rebecca A. Lange Research Scientist Gordon Moore © Thomas R. Hudgins 2015 ACKNOWLEDGEMENTS I would like to thank my advisor, Adam Simon, for his continuing support and mentorship throughout the three years we have worked together. He has helped shape my views of igneous petrology and geochemistry from rifts to arcs to ore deposits. I could not have accomplished any of what is presented here without his continuous support, financial and intellectual, and the numerous opportunities to travel and present this research at conferences. I am honored to have been accepted into his research group and to have been allowed to grow as an academic under his supervision. I would also like to thank Sam Mukasa for my initiation into a PhD program, as well as the exciting research opportunities presented in my first two years at the University of Michigan. During these two years I learned a great deal about how to ask the right questions, develop research goals, and see them through. I owe many thanks to Gordon Moore for our conversations about anything igneous, which provided a great deal of expansion of my own ideas. I also have learned more about analytical methods talking to and teaching under Gordon than I ever did by using the instruments. I would like to thank Becky Lange for always challenging my views and assumptions, providing me with new outlooks and perspectives on ideas that I thought I understood. Thanks to my committee, Gordon, Becky, and Kicki Håkansson, for their countless hours of defense and dissertation discussion, as well as working with me to get everything done on time. I owe thanks and so much more to Laura Waters for our countless discussions, all of which provided new insight and perspectives on geochemistry and petrology, for improving my ability to conduct research, and for being an incredible friend. Thanks to Udo Becker for many ii interesting conversations about potential career paths, publishing advice, and other topics unrelated to academia; to the past and current members of my extended research group: Chris Stefano, Stephen Crabtree, Laura Waters, Laura Bilenker, Adrian Fiege, Jaayke Knipping, Liz Tanis, Brian Konecke, Tristan Childress, Xiaofei Pu, James Jolles, Sean Hurt, Daniel Korfeh; to the staff members who seem to keep this crazy department functioning, Anne Hudon and Bill Wilcox. I owe a special thanks to my family, who have put up with me and supported me in all of my endeavors, no matter how ridiculous; to Meghan Taylor for being a source of joy, inspiration, support, and so much more for the past four years; to my officemates who have made this office incredibly enjoyable: Laura Waters, Tim Gallagher, James Jolles, Peng Ni; and to the incredible group of friends that this entire department has been. Thank you all so much. iii TABLE OF CONTENTS ACKNOWLEDGEMENTS ......................................................................................................... ii LIST OF FIGURES .................................................................................................................... vii LIST OF TABLES ....................................................................................................................... ix LIST OF APPENDICES ...............................................................................................................x CHAPTER I INTRODUCTION ..................................................................................................1 1.1. VOLATILES IN RIFT ENVIRONMENTS .............................................................................1 1.2. PETROGENESIS IN ARC ENVIRONMENTS ......................................................................3 1.3. REFERENCES .........................................................................................................................6 CHAPTER II MELT INCLUSION EVIDENCE FOR CO 2-RICH MELTS BENEATH THE WESTERN BRANCH OF THE EAST AFRICAN RIFT: IMPLICATIONS FOR LONG-TERM STORAGE OF VOLATILES IN THE DEEP LITHOSPHERIC MANTLE ......................................................................................................................................11 2.1. ABSTRACT ............................................................................................................................11 2.2. INTRODUCTION ..................................................................................................................12 2.3. BACKGROUND GEOLOGY ................................................................................................14 2.4. ANALYTICAL METHODS ..................................................................................................15 2.5. RESULTS ...............................................................................................................................20 2.6. DISCUSSION .........................................................................................................................22 2.7. CONCLUSIONS.....................................................................................................................30 2.8. REFERENCES .......................................................................................................................51 iv CHAPTER III INVESTIGATING MAGMA MIXING THROUGH CHEMICAL AND TEXTURAL OBSERVATIONS OF PLAGIOCLASE FROM MUTNOVSKY VOLCANO, KAMCHATKA ............................................................................................................................61 3.1. ABSTRACT ............................................................................................................................61 3.2. INTRODUCTION ..................................................................................................................62 3.3. BACKGROUND GEOLOGY ................................................................................................63 3.4. METHODS .............................................................................................................................66 3.5. RESULTS ...............................................................................................................................67 3.6. PLAGIOCLASE CHEMICAL AND TEXTURAL EVIDENCE FOR MAGMA MIXING .........................................................................................................................................68 3.7. CONCLUSIONS.....................................................................................................................71 3.8. REFERENCES .......................................................................................................................82 CHAPTER IV A MODEL TO INVESTIGATE THE PLAUSIBILITY OF THE HYBRIDIZATION OF THERMALLY AND COMPOSITIONALLY DISTINCT MAGMAS .....................................................................................................................................85 4.1. ABSTRACT ............................................................................................................................85 4.2. INTRODUCTION ..................................................................................................................86 4.3. BACKGROUND GEOLOGY ................................................................................................87 4.4. MELTS MODELING .............................................................................................................87 4.5. RESULTS ...............................................................................................................................88 4.6. ASSESSING THE PLAUSIBILITY OF PHYSICAL MIXING OF BASALT AND DACITE .........................................................................................................................................89 4.7. CONCLUSIONS.....................................................................................................................94 v 4.8. REFERENCES .....................................................................................................................103 CHAPTER V CONCLUSIONS ................................................................................................106 APPENDICES ............................................................................................................................110 vi LIST OF FIGURES Figure 2.1 Map of the East African Rift System...........................................................................31 Figure 2.2 Carbon signal intensity vs. melt inclusion depth .........................................................32 Figure 2.3 Total-alkali vs. silica plots of melt inclusion data .......................................................33 Figure 2.4 Major-element vs MgO plots of melt inclusion data ...................................................34 Figure 2.5 Trace-element vs MgO plots of melt inclusion data ....................................................35 Figure 2.6 Primitive-mantle normalized spider diagrams of melt inclusions and whole rock .....36 Figure 2.7 Volatile cross-plots ......................................................................................................37 Figure 2.8 Volatile/trace element vs volatile plots .......................................................................38
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