127 Mineralogy, Geochemistry, Petrology, and Volcanology Student Session

GSA’s MGPV student representatives invite the division’s student population to present their research (oral or poster). We encourage abstracts from any subdiscipline within our respective fields with hopes of stimulating a multi-disciplinary, early career researcher (ECR) community within MGPV.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 216AB

The Dacite Lava Domes of Wildcat Hills, UT: Using Optical Mineralogy to Characterize a Lunar Silicic Analog

Paper number: 127-5
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

Granitic fragments found within rocks returned by Apollo missions and silicic domes identified from orbit are evidence that silicic magmatism occurred on the Moon. Which geologic processes led to these evolved compositions are still uncertain. The Lunar-VISE (Lunar Vulkan Imaging and Spectroscopy Explorer) payload will land at Mons Gruithuisen Gamma (a lunar silicic dome) to investigate these mysteries. To prepare for the first in situ exploration of a lunar silicic dome, fieldwork was conducted at Wildcat Hills (WH), a terrestrial analog site in Utah that is compositionally, morphologically, and tectonically similar to the Gruithuisen domes. The petrologic origin of this lunar analog will be used to provide constraints on the origin of lunar silicic magma.

Fieldwork at the WH occurred in June 2025 and included sampling numerous sites across the rhyolite and dacite domes. Thin sections were made from all sampled rocks. Presented here are petrographic analyses of two rocks sampled from the dacite dome. Our first sample, a vitrophyric dacite, is a dark gray porphyritic rock with a glassy matrix. In thin section, flow banding is visible and a high concentration of microlites can be discerned in individual layers. Phenocrysts and larger xenocrysts of plagioclase with resorption features are present. Small equant pyroxenes are also present, along with large, heavily fractured, euhedral orthopyroxene. Pyroxene and plagioclase glomerocrysts are found to disrupt the flow bands. Our second sample, a dacite flow breccia was collected west of the vitrophyric dacite. The flow breccia is a textbook autobreccia. Clasts are black, glassy, and are angular to sub-rounded in shape. In thin section the clasts are brown volcanic glass with perlitic fracturing and microlites. The clasts have two distinct colored bands around their edges (interior is yellow, exterior is red), both ~40 µm thick. This disequilibrium texture likely formed when the clasts became entrained in the oxidized matrix. The matrix is red orange in color and glassy, filled with microlites that cluster together and create dark, cloudy regions in thin section.

These preliminary results reveal different characteristics of the dacite flow and will be used as a basis for selection of representative samples for bulk rock geochemical analyses.

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

doi: 10.1130/abs/2025AM-413744

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