75-13 Geology and Geochemistry of Miocene Teton Pass Rhyolites, Jackson Hole volcanic field, Wyoming (U.S.A.)

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)

Presenting Author:

Authors:

Abstract:

Cenozoic volcanism distinct from the Yellowstone Plateau volcanic field in northwestern Wyoming (U.S.A.) occurred in two different episodes. The youngest episode, from ~4.8 Ma to ~480 ka, is focused in the upper Wind River Basin. The oldest episode, from ~9 to 7 Ma, is characterized by basaltic andesite to rhyolite eruptions of the Jackson Hole volcanics (JHV), including rhyolite magmatism in the Teton Pass (WY) area.  JHV eruptions overlapped with deposition of the ~16-6 Ma Teewinot formation, a package of tuffaceous sandstones, fresh-water limestones, and tephras and local extensional basin formation.  Our goal is to describe the petrographic and geochemical characteristics of the Teton Pass Rhyolites to characterize these rocks in the context of their tectonic environment.​ Field relations indicate that most of what we sampled were locally emplaced lavas and dikes, not “welded tuff”, as suggested by prior mapping. Significantly, these locally emplaced units include a 7.6 Ma, eroded obsidian dome used as an obsidian source by native Americans (e.g., Teton Pass obsidian). Rhyolite petrography shows a mineral assemblage dominated by sanidine, plagioclase, and quartz phenocrysts, within a predominantly glassy groundmass. The rhyolites exhibit pronounced flow banding, reflecting dynamic variations in viscosity and eruption behavior during emplacement. Teton Pass rhyolite bulk rock major and trace element geochemistry via XRF and ICP-MS, shows that the rocks are peraluminous and high-Si (e.g., SiO₂> 75 wt%). Trace element data suggests many of the sampled rhyolites, including the obsidian, are related via fractional crystallization of zircon and plagioclase and reflect one magmatic system.  Conversely, a sampled rhyolite air-fall tuff is geochemically distinct and resembles Snake River plain rhyolites; we suggest that it was sourced from a Snake River plain caldera (e.g., Picabo or Twin Falls eruptive centers). We interpret Teton Pass rhyolite peraluminous geochemistry to reflect a cogenetic relationship between melting of mica-rich Archaean basement and Miocene extension in Jackson Hole, which provided conduits for the magmas to ascend and erupt along a pull-apart basin and fault step-over.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.