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Postcollapse Volcanism in the Valles Caldera, New Mexico: the Transition from Large Volume Explosive to Small Volume Effusive Eruptions

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Postcollapse Volcanism in the Valles Caldera, New Mexico: the Transition from Large Volume Explosive to Small Volume Effusive Eruptions UNLV Retrospective Theses & Dissertations 1-1-2007 Postcollapse volcanism in the Valles Caldera, New Mexico: The transition from large volume explosive to small volume effusive eruptions Kati Gibler University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Gibler, Kati, "Postcollapse volcanism in the Valles Caldera, New Mexico: The transition from large volume explosive to small volume effusive eruptions" (2007). UNLV Retrospective Theses & Dissertations. 2166. http://dx.doi.org/10.25669/4mwl-n577 This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Thesis has been accepted for inclusion in UNLV Retrospective Theses & Dissertations by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. POSTCOLLAPSE VOLCANISM IN THE VALLES CALDERA, NEW MEXICO: THE TRANSITION FROM LARGE VOLUME EXPLOSIVE TO SMALL VOLUME EFFUSIVE ERUPTIONS By Kati Gibier Bachelor of Science University of Alaska 2004 A thesis in partial fulfillment of the requirements for the Master of Science Degree in Geoscience Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas August 2007 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 1448398 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. UMI UMI Microform 1448398 Copyright 2007 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thesis Approval The Graduate College University of Nevada, Las Vegas May 30 .2007 The Thesis prepared by Kati I. Gibier Entitled Postcollapse Volcanism in the Valles Caldera. New Mexico: The Transition from Large Volume Explosive to Small Volume Effusive Eruptions _______ is approved in partial fulfillment of the requirements for the degree of Master of Science Examination Committee Chair Dean of the Graduate College Examination Coinmittee Member Examination Committee Member Graduate College Faculti/ Representative 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT Postcollapse volcanism in the Valles Caldera, New Mexico: The Transition from Large Volume Explosive to Small Volume Effusive Eruptions By Kati I. Gibier Dr. Andrew Hanson, Examination Committee Chair Associate Professor of Geology University of Nevada, Las Vegas Deer Canyon, Redondo Creek, and Del Medio rhyolites were erupted in the Valles Caldera within 54 ka following caldera collapse. Postcollapse rhyolites and Bandelier Tuff magmas are compositionally distinct, and Deer Canyon is heterogeneous between individual flows. ^^*U/^°^Pb zircon dating shows that Redondo Creek zircons were derived from the residual Bandelier Tuff crystal mush system whereas Deer Canyon zircons were derived from remelting of a pluton at depth. Electron microprobe analyses of feldspars reveal complex zonation caused by interactions between mafic magmas and silicic melts of residual crystal mush as well as between distinct melts from the crystal mush. Each postcollapse rhyolite was produced by independent melting events in the residual Bandelier Tuff crystal mush, interactions between these melts and heat-providing mafic magmas, and magma arriving from deeper in the crust. They are not comagmatic with each other, nor with the preceeding Bandelier Tuff magmas. in Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT.........................................................................................................................................iii LIST OF TABLES............................................................................................................................ vii LIST OF FIGURES.........................................................................................................................viii ACKNOWLEDGEMENTS...............................................................................................................x CHAPTER I INTRODUCTION ..............................................................................................1 The Geologic Problem ..................................................................................................................1 The Valles Caldera........................................................................................................................ 2 Research Objectives......................................................................................................................6 CHAPTER 2 GEOLOGIC SETTING .................................................................................... 9 The Valles Caldera...................................................................................................................... 12 Post Collapse Volcanism ...........................................................................................................13 CHAPTER 3 PREVIOUS WORK......................................................................................... 17 Upper Bandelier Tuff ..................................................................................................................19 Deer Canyon, Redondo Creek and Del M edio .................................................................... 20 CHAPTER 4 SAMPLE STRATEGY AND ANALYTICAL METHODS..................23 Sample Collection .......................................................................................................................23 Sample Preparation .....................................................................................................................23 Petrography .................................................................................................................................. 25 EMPA ............................................................................................................................................25 LOI Calculations ......................................................................................................................... 26 XRF/ICPMS Analysis ................................................................................................................ 27 238u/206pb Zircon A nalysis .......................................................................................................27 Zircon Imaging .............................................................................................................................28 CHAPTER 5 PETROGRAPHY ............................................................................................ 29 Petrography of the Deer Canyon Rhyolite ........................................................................... 29 Petrography of the Redondo Creek Rhyolite ........................................................................33 Petrography of the Del Medio Rhyolite .................................................................................38 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6 EMPA MINERAL CHEMISTRY ................................................................45 Feldspar .................................................................................................................................. 47 Biotite ...................................................................................................................................... 54 P yroxene ................................................................................................................................ 55 CHAPTER 7 GEOCHEMISTRY .......................................................................................... 58 Major Element Chemistry .................................................................................................. 58 Trace Elements Chemistry ................................................................................................. 61 Ratios of Incompatible Trace Elements .......................................................................... 67 REE Chondrite Diagrams .................................................................................................. 69 CHAPTER 8 2^*U/^°^Pb ZIRCON ANALYSES .....................................................
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