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Structural analysis of silicic lava flow margins at Obsidian Dome, California
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 breakout 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 and lithological data from the northwest margin of Obsidian Dome constrain the margins of discreet break-out lobes that flowed independently in slightly different directions. The combination of lithology, flow-banding and stretching vesicle directions support simple models of break-out lobe structure, and disagree with the predicted structure of non-lobate margins. This interpretation challenges common assumptions about silicic lava emplacement, and supports observations made at Cordon Caulle, Chile.
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