Date of Award

5-2025

Document Type

Thesis

Degree Name

Master of Science in Geology

Department

Geological Sciences

First Reader/Committee Chair

McGill, Sally

Abstract

The Inyo Volcanic Chain (IVC) is a series of rhyolitic lava domes straddling the northwest rim of the Long Valley Caldera (LVC), most recently erupting ~650 years ago, producing the South Deadman, Obsidian, and Glass Creek Domes. For this study, samples were analyzed for geochemistry and petrography at six of the IVC domes. To measure geochemistry, a portable x-ray fluorescence machine (PXRF) was used, in part to test how well it performed on felsic rocks. The PXRF performed poorly with the factory calibration in detecting most elements, though detection of some elements improved with a calibration curve applied. The three oldest domes each derived from their own sources and there was no evolution of those lavas as they were emplaced. Obsidian Dome showed variability in geochemistry with the lava becoming more evolved as it was emplaced. South Deadman and Glass Creek Domes are both composed of two lavas, coarsely porphyritic (CP) lava, and finely porphyritic (FP) lava while Obsidian Dome is composed of the FP lava. Limited sampling of South Deadman and Glass Creek Domes meant that variation within a lava type on those domes could not be determined. Comparing the lavas of the chain indicated that none of them derive from the same magma source. The CP lava could be related to the lava that formed Deer Mountain which is thought to be the youngest eruption of the LVC. The other lavas of the IVC were not related to any external magma source studied.

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