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Petrogenesis of the Greenwater Range: Comparison to the Crater Flat Volcanic Field and Implications for Hazard Assessment

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Petrogenesis of the Greenwater Range: Comparison to the Crater Flat Volcanic Field and Implications for Hazard Assessment UNLV Theses, Dissertations, Professional Papers, and Capstones 5-2010 Petrogenesis of the Greenwater Range: Comparison to the Crater Flat volcanic field and implications for hazard assessment Ashley Kaye Tibbetts University of Nevada Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/thesesdissertations Part of the Geochemistry Commons, Geology Commons, and the Volcanology Commons Repository Citation Tibbetts, Ashley Kaye, "Petrogenesis of the Greenwater Range: Comparison to the Crater Flat volcanic field and implications for hazard assessment" (2010). UNLV Theses, Dissertations, Professional Papers, and Capstones. 186. http://dx.doi.org/10.34917/1436699 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 Theses, Dissertations, Professional Papers, and Capstones by an authorized administrator of Digital Scholarship@UNLV. For more information, please contact [email protected]. PETROGENESIS OF THE GREENWATER RANGE: COMPARISON TO THE CRATER FLAT VOLCANIC FIELD AND IMPLICATIONS FOR HAZARD ASSESSEMENT Ashley Kaye Tibbetts Bachelor of Science Boston University 2007 A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geoscience Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas May 2010 Copyright by Ashley K Tibbetts 2010 All Rights Reserved THE GRADUATE COLLEGE We recommend that the thesis prepared under our supervision by Ashley K. Tibbetts entitled Petrogenesis of the Greenwater Range: Comparison to the Crater Flat Volcanic Field and Implications for Hazard Assessment be accepted in partial fulfillment of the requirements for the degree of Master of Science Geoscience Eugene Smith, Committee Chair Adam Simon, Committee Member Pamela Burnley, Committee Member Diane Pyper-Smith, Graduate Faculty Representative Ronald Smith, Ph. D., Vice President for Research and Graduate Studies and Dean of the Graduate College May 2010 ii ABSTRACT Petrogenesis of the Greenwater Range: Comparison to the Crater Flat Volcanic Field and Implications for Hazard Assessment Ashley Kaye Tibbetts Dr. Eugene I. Smith, Examination Committee Chair Professor of Geoscience University of Nevada, Las Vegas Pliocene basalts of the Greenwater Range, California erupted from 24 volcanic vents now represented by volcanic plugs, craters and scoria mounds. Basaltic magmas originated in the asthenospheric mantle, but show evidence of a lithospheric component. Depths and temperatures of melting calculated using a silica activity geobarometer are 54.3–89.6 km and 1367-1435oC, placing melting in the asthenosphere. The preferred petrogenetic model involves melting of lithospheric mantle thermally and mechanically, but not chemically, converted to asthenospheric mantle. Melting depths correspond to low velocity zones in the mantle as revealed in seismic profiles. Chemical and lithologic similarities between basalt in the Greenwater Range and basalt in Crater Flat, Nevada near the proposed nuclear waste repository at Yucca Mountain suggest that both are part of the same volcanic field. These factors result in an increase in the area and number of vents used to calculate volcanic hazard and accordingly an increased risk to the proposed repository. iii TABLE OF CONTENTS ABSTRACT.....................................................................................................................iii TABLE OF CONTENTS.................................................................................................iv LIST OF FIGURES .........................................................................................................vi ACKNOWLEDGEMENTS...........................................................................................viii CHAPTER 1 INTRODUCTION .................................................................................... 1 Geologic Background ........................................................................................... 2 Previous work .......................................................................................................5 CHAPTER 2 GEOLOGY OF THE GREENWATER RANGE.................................... 14 Description of centers ......................................................................................... 14 CHAPTER 3 GEOCHEMISTRY OF THE GREENWATER RANGE....................... 30 Field and Instrumental Techniques..................................................................... 30 Data..................................................................................................................... 32 CHAPTER 4 DEPTH OF MELTING CALCULATIONS........................................... 45 Silica Barometer Method .................................................................................... 45 Results................................................................................................................. 46 CHAPTER 5 PETROGENESIS OF GREENWATER RANGE BASALTS............... 48 Geochemical Observations ................................................................................. 48 The Source of Greenwater Basalt ....................................................................... 50 Origin of Evolved Magmas................................................................................. 55 Summary............................................................................................................. 56 CHAPTER 6 MELTING MECHANISM.................................................................... 66 Edge-Driven Convection .................................................................................... 66 CHAPTER 7 COMPARISON BETWEEN GREENWATER AND CRATER FLAT VOLCANIC FIELDS ............................................................................. 71 Summary............................................................................................................. 73 CHAPTER 8 SUMMARY AND CONCLUSIONS..................................................... 83 REFERENCES ............................................................................................................... 85 APPENDIX A THIN SECTION DESCRIPTIONS ....................................................... 90 APPENDIX B SAMPLE LOCATIONS......................................................................... 96 iv APPENDIX C MAJOR ELEMENT DATA (IN WT. %) ............................................ 100 APPENDIX D TRACE ELEMENT DATA (IN PPM) ................................................ 108 APPENDIX E REE DATA (IN PPM).......................................................................... 115 APPENDIX F ISOTOPIC DATA ................................................................................ 121 APPENDIX G ASSESSMENT OF PREVIOUSLY PROPOSED MODELS FOR DEATH VALLEY AND SURROUNDING REGIONS...................... 122 APPENDIX H FIELD PICTURES............................................................................... 130 VITA............................................................................................................................. 141 v LIST OF FIGURES Figure 1 Map depicting Greenwater Range volcanic centers and Crater Flat and surrounding volcanics ................................................................................ 7 Figure 2 Location and age of 10 Ma-present basalts in the Lunar Crater-Crater Field .......................................................................................................... 8 Figure 3 Map of the Great Basin showing locations of 5 Ma to present mafic ....... volcanic rocks ........................................................................................... 9 Figure 4 Location of the 87Sr/86Sr = 0.706 line in relation to the Death Valley ... 10 Figure 5 Pure shear vs. simple shear model for delamination of Sierran Lithosphere ............................................................................................. 11 Figure 6 Model of crust-mantle structure below the Greenwater Range.............. 12 Figure 7 Locations of faults bordering the Greenwater Range............................. 13 Figure 8 Greenwater Range young basalt center locations................................... 27 Figure 9 Map showing locations and names of Greenwater Range young basalt centers, and young rhyolite..................................................................... 28 Figure 10 Stratigraphic column for Greenwater Range.......................................... 29 Figure 11 Greenwater Range sample locations ...................................................... 35 Figure 12 LeBas et al. (1986) rock classification diagram of the Greenwater Range basalts and basaltic andesites................................................................. 36 Figure 13 Alkaline vs. Subalkaline discrimination diagram for the Greenwater Range basalts and basaltic andesites...................................................... 36 Figure 14 Potassic vs. Sodic classification diagram for alkaline Greenwater Range basalts and basaltic andesites.................................................................
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