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Structural Analysis of Silicic Lava Flow Margins at Obsidian Dome, California

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Structural Analysis of Silicic Lava Flow Margins at Obsidian Dome, California Structural Analysis of Silicic Lava Flow Margins at Obsidian Dome, California by Abigail Martens, B.S. A Thesis Submitted to the Department of Geological Sciences California State University Bakersfield In Partial Fulfillment for the Degree of Masters of Geology Spring 2017 ii Copyright By Abigail Elizabeth Martens 2017 i Structural Analysis of Silicic Lava Flow Margins at Obsidian Dome, California by Abigail Martens, B.S. This thesis or project has been accepted on behalf of the Department of Geological Sciences by their supervisory committee: Dr. William C. Krugh Assistant Professor of Geology, California State University, Bakersfield Committee Chair Dr. Anthony Rathburn Professor of Geology, California State University, Bakersfield Committee Member Dr. Graham Douglas Michael Andrews Assistant Professor of Geology, West Virginia University Committee Member 111 Contents List of Tables .................................................................................................................................. v List of Figures ................................................................................................................................ vi Abstract ........................................................................................................................................... 1 1 Introduction .................................................................................................................................. 2 1.1 Models of Silicic Lava Emplacement ................................................................................... 2 1.1.1 Competing models of silicic lava growth and advance ................................................. 2 1.1.2 Structural components in silicic lavas............................................................................ 4 1.1.3 The 2011-2013 eruption of Cordón Caulle and prolonged silicic lava emplacement ... 5 1.1.4 Hypothesis...................................................................................................................... 6 1.2 Obsidian Dome, eastern California ....................................................................................... 7 1.2.1 Long Valley caldera and Mono-Inyo volcanic chain ..................................................... 7 1.2.2 Obsidian Dome ............................................................................................................ 10 2 Methodology .............................................................................................................................. 13 2.1 Data Collection ................................................................................................................... 13 2.2 Analysis of Structural Data ................................................................................................. 15 3 Results ........................................................................................................................................ 16 3.1 Lithofacies and fabrics ........................................................................................................ 16 3.1.1 Unit 1A......................................................................................................................... 16 3.1.2 Unit 1B ......................................................................................................................... 16 3.1.3 Unit 1C ......................................................................................................................... 16 3.1.4 Unit 2A......................................................................................................................... 16 3.1.5 Unit 2B ......................................................................................................................... 17 3.2 Structural Data .................................................................................................................... 24 3.2.1 Gully 1 ......................................................................................................................... 24 iv 3.2.2 Gully 2 ......................................................................................................................... 24 3.2.3 Gully 3 ......................................................................................................................... 25 3.2.4 Gully 4 ......................................................................................................................... 25 3.2.5 Gully 5 ......................................................................................................................... 26 3.2.6 Gully 6 ......................................................................................................................... 26 3.2.7 Gully 7 ......................................................................................................................... 27 3.2.8 Gully 8 ......................................................................................................................... 28 3.2.9 Gully 9 ......................................................................................................................... 28 3.2.10 Gully 10 ..................................................................................................................... 29 3.2.11 Gully 11 ..................................................................................................................... 29 3.2.12 Gully 12 ..................................................................................................................... 30 4 Discussion .................................................................................................................................. 54 4.1 Lithological Architecture .................................................................................................... 54 4.2 Structural Analysis .............................................................................................................. 54 4.2.1 Structural Comparisons Between Gullies .................................................................... 54 4.2.2 Structural Similarities Between Different Sides of the Same Gully ............................ 57 4.2.3 Structural Evidence of Break-Out Lobes ..................................................................... 57 4.3 The Origins of Gullies Incising the Flow Margins at Obsidian Dome ............................... 57 5 Summary .................................................................................................................................... 59 6 References .................................................................................................................................. 60 List of Tables Table 1 - GPS coordinates of study sites at Obsidian Dome 22 Table 2 - Summary of foliation data at erosional and localized gullies 65 v List of Figures Figure 1 - Conceptual diagrams of exogenous and endogenous growth for a silicic lava 3 Figure 2 - Foliation patterns typical of silicic lavas 5 Figure 3 - Map of the Long Valley region 8 Figure 4 -V olcanic activity in the Mono-Inyo Craters volcanic chain over the last 5,000 years 10 Figure 5 - An aerial photo and surface illustration of Obsidian Dome, North and South Glass Creek Dome 11 Figure 6 - Schematic representation of the lithological layering within Obsidian Dome as discerned from fieldwork and drilling 12 Figure 7 - The idealized lithostratigraphy of textural units within an obsidian lava based on studies of outcrops and scientific drilling 12 Figure 8 - Google Earth image of each measured gully 15 Figure 9 - Examples of unit 1A lithofacies and ductile deformation textures 17 Figure 9 (continued) - Examples of unit 1A lithofacies and brittle deformation textures 18 Figure 10 - Examples of unit 1B lithofacies deformation textures 19 Figure 11 - Examples of unit 1C lithofacies textures and brittle-ductile deformation 20 Figure 12 - Examples of unit 2A lithofacies textures and ductile deformation 21 Figure 12 (continued) - Examples of unit 2A lithofacies textures and brittle-ductile deformation 22 Figure 13 - Examples of unit 2B lithofacies textures and brittle-ductile deformation 23 Figure 14 - Gully 1 (E) 31 Figure 15 - Gully 1 (W) 32 Figure 16 - Gully 2 (E) 33 Figure 17 - Gully 2 (W) 34 Figure 18 - Gully 3 (E) 35 Figure 19 - Gully 3 (W) 36 Figure 20 - Gully 4 (S) 37 Figure 21 - Gully 4 (NE) 38 Figure 22 - Gully 5 (S) 39 vi Figure 23 - Gully 5 (NE) 40 Figure 24 - Gully 6 (N) 41 Figure 25 - Gully 6 (S) 42 Figure 26 - Gully 7 (N) 43 Figure 27 - Gully 7 (S) 44 Figure 28 - Gully 8 (E) 45 Figure 29 - Gully 8 (W) 46 Figure 30 - Gully 9 (NW) 47 Figure 31 - Gully 9 (SE) 48 Figure 32 - Gully 10 (NW) 49 Figure 33 - Gully 10 (SE) 50 Figure 34 - Gully 11 (SE) 51 Figure 35 - Gully 12 (NE) 52 Figure 36 - Gully 12 (SW) 53 Figure 37 - Conceptual diagram based on observations at Obsidian Dome. 58 vii Abstract The emplacement of silicic lavas is a rarely observed phenomenon and most of what is known about the processes is interpreted from ancient lavas. Recent lava emplacements in Chile have challenged existing models of lava emplacement and suggest that silicic lavas are emplaced via internal flow, similar to basaltic lavas, and that the margin advances by breeches know as break- out lobes. Obsidian Dome in eastern California is an ideal natural laboratory to test emplacement models by looking for break-out lobes and the characteristic structures and lithological architectures that they produce. Structural
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