............................................................................................................................... iii ACKNOWLEDGEMENTS ......................................................................................................... iv LIST OF FIGURES .................................................................................................................... vii LIST OF TABLES ..................................................................................................................... viii CHAPTER 1 INRODUCTION.................................................................................................... 1 1.1 Previous Work ................................................................................................................... 3 CHAPTER 2 GEOLOGIC SETTING .......................................................................................... 5 2.1 The Long Valley Caldera and Volcanic Field ................................................................... 5 2.2 The Resurgent Dome Rhyolite............................................................................................ 6 2.3 The Moat Rhyolites............................................................................................................. 7 2.4 The Hot Creek Flow Rhyolite ............................................................................................. 8 2.5 The Deer Mountain Rhyolite .............................................................................................. 8 CHAPTER 3 METHODS AND ANALYTICAL TECHNIQUES .............................................. 9 3.1 Sampling Techniques .......................................................................................................... 9 3.2 Sample Preparation .......................................................................................................... 10 3.3 Ar/Ar Geochronology .................................................................................................. 10 3.4 Petrography ...................................................................................................................... 13 3.5 EPMA ............................................................................................................................... 14 CHAPTER 4 RESULTS ............................................................................................................. 16 4.1 Ar/Ar Geochronology Results ..................................................................................... 16 4.1.1 LV-RD-005 Plagioclase ............................................................................................ 16 4.1.2 LV-RD-008 Plagioclase ............................................................................................ 16 4.1.3 LV-RD-009 Plagioclase ............................................................................................ 16 4.1.4 LV-RD-005, LV-RD-008, LV-RD-009 Combined Plagioclase ............................... 17 4.1.5 LV-MR-008 Sanidine ............................................................................................... 18 4.1.6 LV-MR-005 Sanidine .............................................................................................. 18 4.1.7 LV-HCF-002 Sanidine .............................................................................................. 19 4.1.8 LV-HCF-005 Sanidine .............................................................................................. 20 4.1.9 LV-HCF-006 Sanidine .............................................................................................. 21 4.1.10 LV-MR-004 Sanidine ............................................................................................. 22 4.1.11 LV-MR-001 Sanidine ............................................................................................. 23 4.1.12 LV-DM-001-1 Sanidine .......................................................................................... 24 4.2 Petrography Results .......................................................................................................... 25 4.2.1 Petrography of the Resurgent Dome Rhyolite .......................................................... 25 4.2.2 Petrography of the Moat Rhyolite............................................................................. 26 4.2.3 Petrography of the Hot Creek Flow Rhyolite ........................................................... 29 4.2.4 Petrography of the Deer Mountain Rhyolite ............................................................. 30 4.3 Electron Probe Micro-Analysis Results ........................................................................... 35 4.3.1 EPMA of the Resurgent Dome Rhyolite ................................................................. 35 4.3.2 EPMA of the Moat Rhyolites .................................................................................. 36 4.3.3 EPMA of the Hot Creek Flow Rhyolite ................................................................... 44 4.3.4 EPMA of the Deer Mountain Rhyolite .................................................................... 46 CHAPTER 5 DISCUSSION ...................................................................................................... 47