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U-Pb Geochronology of the Miocene Peach Spring Tuff Supereruption and Precursor Cook Canyon Tuff, Western Arizona, USA

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U-Pb Geochronology of the Miocene Peach Spring Tuff Supereruption and Precursor Cook Canyon Tuff, Western Arizona, USA San Jose State University SJSU ScholarWorks Master's Theses Master's Theses and Graduate Research Fall 2014 U-Pb Geochronology of the Miocene Peach Spring Tuff Supereruption And Precursor Cook Canyon Tuff, Western Arizona, USA Marsha Izabella Lidzbarski San Jose State University Follow this and additional works at: https://scholarworks.sjsu.edu/etd_theses Recommended Citation Lidzbarski, Marsha Izabella, "U-Pb Geochronology of the Miocene Peach Spring Tuff Supereruption And Precursor Cook Canyon Tuff, Western Arizona, USA" (2014). Master's Theses. 4502. DOI: https://doi.org/10.31979/etd.c2xh-zwh9 https://scholarworks.sjsu.edu/etd_theses/4502 This Thesis is brought to you for free and open access by the Master's Theses and Graduate Research at SJSU ScholarWorks. It has been accepted for inclusion in Master's Theses by an authorized administrator of SJSU ScholarWorks. For more information, please contact [email protected]. U-PB GEOCHRONOLOGY OF THE MIOCENE PEACH SPRING TUFF SUPERERUPTION AND PRECURSOR COOK CANYON TUFF, WESTERN ARIZONA, USA A Thesis Presented to The Faculty of the Department of Geology San José State University In Partial Fulfillment of the Requirements for the Degree Master of Science by Marsha I. Lidzbarski December 2014 ©2014 Marsha I. Lidzbarski ALL RIGHTS RESERVED The Designated Thesis Committee Approves the Thesis Titled U-PB GEOCHRONOLOGY OF THE MIOCENE PEACH SPRING TUFF SUPERERUPTION AND PRECURSOR COOK CANYON TUFF, WESTERN ARIZONA, USA by Marsha I. Lidzbarski APPROVED FOR THE DEPARTMENT OF GEOLOGY SAN JOSÉ STATE UNIVERSITY December 2014 Dr. Jonathan Miller Department of Geology Dr. Robert Miller Department of Geology Dr. Jorge Vazquez United States Geological Survey ABSTRACT U-PB GEOCHRONOLOGY OF THE MIOCENE PEACH SPRING TUFF SUPERERUPTION AND PRECURSOR COOK CANYON TUFF, WESTERN ARIZONA, USA by Marsha I. Lidzbarski The 18.8 Ma Peach Spring Tuff, Arizona, is a >600 km 3 ignimbrite formed from the Miocene supereruption of Silver Creek caldera, Black Mountains, Arizona, and is an important Miocene stratigraphic bed in the southwestern United States. Peach Spring Tuff overlies the undated and less-voluminous Cook Canyon Tuff. Ion-microprobe and high-precision thermal ionization U-Pb dating of chemically abraded zircon crystals from Peach Spring Tuff and Cook Canyon Tuff reveal the crystallization history of both magma systems leading to eruption. A spread of U-Pb dates from ca. 18.1 to 22.0 Ma for Peach Spring Tuff relative to its 40 Ar/39 Ar age indicates variable Pb loss, with potential additional uncertainty due to complexities associated with 40 Ar/ 39 Ar dating. The youngest U-Pb crystallization date for Cook Canyon Tuff zircon crystals constrains the maximum eruption age to ca. 18.9 Ma, and indicates that eruption of the Cook Canyon Tuff preceded the Peach Spring Tuff eruption by no more than 2-3 x 10 5 years. The complex U-Pb zircon age spectra for both units indicate several 10 5 years of pre-eruptive magma residence, likely in a crystal mush state. When combined, the ages and trace elements for Peach Spring Tuff and Cook Canyon Tuff zircon crystals suggest that these two silicic magmas were derived from discrete but temporally and spatially overlapping magma systems. ACKNOWLEDGEMENTS Support for this research came from National Science Foundation grants EAR-0911728 and EAR-0409882 At this moment of accomplishment, I would like to gratefully acknowledge my adviser Professor Jonathan Miller, whose brilliance and ambitious spirit in regard to research successfully guided me through this can of worms. I would like to thank my committee members, Professor Robert Miller for his constructive reviews, timely edits, and campfire dance lessons, and Dr. Jorge Vazquez for his endless encouragement and motivation. He was once my professor, now he is my colleague and he will forever be my mentor. I would also like to thank the faculty, staff, and students of the San José State Geology Department for making my graduate experience an unforgettable one. Most of the results described in this thesis would not have been possible without the close collaboration of a few laboratories. I owe a deep debt of gratitude to Roland Mundil for his time and invaluable assistance at the Berkeley Geochronology Center. I would also like to thank Charlie Bacon, Joe Wooden and Matt Coble for their assistance at the Stanford USGS Micro Analysis Center, with whose wealth of knowledge and pep talks, I was able to retain my sanity. I am most grateful to the collaborators of this research project, specifically Calvin Miller, Susanne McDowell, Charles Ferguson and Sarah Overton for their unparalleled enthusiasm, sharing their data, listening to my crazy ideas, and lending me their expertise and inspiration. v I deeply thank my family, especially my mother Maria, my sister Megan, and my brother Mark for their unconditional support, encouragement and endless patience. I sincerely thank Dr. Yan Xin and my friends in Connecticut, who, along with my family, were there at the start of this journey, and helped mold me into the responsible, successful adult I am today. I cannot forget friends who went through hard times, cheered me on, made sure I remembered to eat, and who have shared as much anticipation for this day as I have. Thank you Esther, Danielle, Raquel, and my Changos. I expand my thanks to Trials Pub for treating me like family while I’m so far from my own and allowing me to us your establishment as my living room and writing headquarters. I especially thank Syrus and Thane (my emergency contact), without whose hugs, back-cracking ability, thinking juice, and unfailing support I would not have completed this work. vi TABLE OF CONTENTS LIST OF FIGURES………………………………………………………………………………………………………….….x LIST OF TABLES………………………………………………………………………………………………………….…xiv INTRODUCTION ................................................................................................................... 1 Zircon U-Pb Dating.......................................................................................................... 3 TIMS vs. SIMS summary ................................................................................................. 9 GEOLOGIC BACKGROUND AND SETTING .......................................................................... 10 Previous Work: Peach Spring and Cook Canyon Tuffs ................................................. 12 Growth of the Silver Creek magma system and eruption of the Peach Spring Tuff .... 17 METHODS .......................................................................................................................... 20 Sample Descriptions ..................................................................................................... 21 Zircon extraction and processing ................................................................................. 22 TIMS sample preparation and analysis ........................................................................ 23 SIMS sample preparation and analysis ........................................................................ 25 RESULTS............................................................................................................................. 27 Zircon zoning and trace element variation .................................................................. 27 Peach Spring Tuff ..................................................................................................... 35 Type 1. ................................................................................................................. 35 Type 1a……………………………………………………………………………………………………….…..35 Type 1b……………………………………………………………………………………………………….…..36 Type 2. ................................................................................................................ 37 Type 3. ................................................................................................................. 37 vii Cook Canyon Tuff ..................................................................................................... 38 Type 1. ................................................................................................................. 38 Type 1a……………………………………………………………………………………………………….…..38 Type 1b……………………………………………………………………………………………………….…..39 Type 2 .................................................................................................................. 39 SIMS U-Pb zircon geochronology ................................................................................. 40 Cook Canyon Tuff Zircon: No chemical abrasion ..................................................... 40 Sectioned zircons. ................................................................................................ 40 Zircon rims ........................................................................................................... 42 Cook Canyon Tuff Zircon: Chemically abraded zircons ............................................ 44 All zircons: rims and edges…………………………………………………………………….………..44 Zircon rims ........................................................................................................... 44 Zircon edges ......................................................................................................... 44 Peach Spring Tuff Zircon: No chemical abrasion ..................................................... 47 Sectioned zircons ................................................................................................. 47 Zircon rims ..........................................................................................................
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