UNLV Retrospective Theses & Dissertations 1-1-2000 The geology and geochemistry of volcanic rocks in the Lava Mountains, California: Implications for Miocene development of the Garlock Fault Deborah L Keenan University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Keenan, Deborah L, "The geology and geochemistry of volcanic rocks in the Lava Mountains, California: Implications for Miocene development of the Garlock Fault" (2000). UNLV Retrospective Theses & Dissertations. 1209. http://dx.doi.org/10.25669/86xt-tu2t 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. 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Further reproduction prohibited without permission. NOTE TO USERS Page(s) not included in the original manuscript and are unavailable from the author or university. The manuscript was microfilmed as received. 8 This reproduction is the best copy available. UMI ® Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. THE GEOLOGY AND GEOCHEMISTRY OF VOLCANIC ROCKS IN THE LAVA MOUNTAINS, CALIFORNIA: IMPLICATIONS FOR MIOCENE DEVELOPMENT OF THE GARLOCK FAULT by Deborah L. Keenan Bachelor of Science Old Dominion University 1996 A thesis submitted in partial fulfillment of the requirement for the Master of Science Degree Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas December 2000 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 1403082 UMI UMI Microform 1403082 Copyright 2001 by Bell & Howell Information and Learning Company. All rights reserved. This microform edition is protectesd against unauthorized copying under Title 17, United States Code. Bell & Howell Information and Learning Companny 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 UNIV The Graduate College University of Nevada, Las Vegas November 5 .20 00 The Thesis prepared by Deborah L. Keenan Entitled The Geology and Geochemistry of Volcanic Rocks in the Lava Mountains, California : Implications for Miocene Development of the Garlock Fault________________________ is approved in partial fulfillment of the requirements for the degree of Master of Science in Geology Examinatiob Committee Chair Dean of the Graduate College Examination Committee Member Examination CommitteelMember Graduate College Faculty Representative PR/1017-53/1-00 U Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT The Geology and Geochemistry of Volcanic Rocks in the Lava Mountains, California: Implications for Miocene Development of the Garlock Fault by Deborah L. Keenan Dr. Eugene I. Smith, Examination Committee Chair Professor of Geology University of Nevada, Las Vegas The Lava Mountains are located in the Mojave Desert, southern California along the Garlock Fault, a major continental strike-slip fault that separates the southwestern Basin and Range to the north from the Mojave block to the south. Chemical similar dacitic lava and pyroclastic flows erupted from the 9-km diameter Western Lava Mountains volcano. Dacites with limited chemical variability reflect interaction of mantle derived basalt with both metabasalt and graywacke of the Mesozoic Rand Schist and Cretaceous “Atolia-type” granitoids. Geophysical data suggests a low angle contact between these lithologies at a depth of about 20 km. This boundary may have served as a density barrier to rising magma. Magma trapped at this barrier could not ascend until it evolved by fractional crystallization and assimilation to a density less than that of the host rock. This density was achieved as soon as SiOz evolved to values greater than about 63 wt. %; the resulting magma corresponds to the composition of Lava Mountains dacite. Both geochemistry and stratigraphy were used to develop correlations of volcanic units across the Garlock Fault between the Lava Mountains to the south and the El Paso iii Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Mountains to the north of the fault This work demonstrated a total o f32-40 km movement of the fault since 10.3 Ma, which indicates a displacement rate of 3.1-3.8 mm/yr. IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT.......................................................................................................................iv TABLE OF CONTENTS.................................................................................................. vi LIST OF FIGURES......................................................................................................... vüi ACKNOWLEDGMENTS................................................................................................. ix CHAPTER 1 INTRODUCTION.......................................................................................1 CHAPTER 2 STRATIGRAPHY...................................................................................... 4 Lava Mountains................................................................................................................4 Episode 1.......................................................................................................................5 Episode 2.......................................................................................................................5 Episode 3.......................................................................................................................8 Summary .......................................................................................................................9 CHAPTER 3 THE WESTERN LAVA MOUNTAINS VOLCANO..............................18 Introduction.................................................................................................................... 18 The Central Vent A rea...................................................................................................19 Stratigraphy and Origin of Moat Units.......................................................................... 21 Gravity Survey and Geology ......................................................................................... 26 Structural Control of the Western Lava Mountains Volcano.........................................27 Evolution of the WLMV............................................................................................... 27 CHAPTER 4 GEOCHEMISTRY................................................................................... 35 Geochemical Techniques.............................................................................................. 35 Results............................................................................................................................36 Nature of Lithosphere.................................................................................................... 38 Petrogenetic M odel....................................................................................................... 40 CHAPTER 5 CORRELATION ACROSS THE GARLOCK FAULT.........................