31-11 RECENT GEOLOGIC MAPPING OF THE STEWART SPRING AND ADJACENT QUADRANGLES ENCOMPASSING THE STEWART VALLEY, NEVADA

Session: Best Student Geologic Map Competition (Posters)

Presenting Author:

Authors:

Abstract:

The entirety of Nevada’s Stewart Spring quadrangle and portions of the Gabbs Mountain, Granny Goose Well, Goldyke, Sunrise Flat, and Simon quadrangles were mapped to cover the central part of the Stewart Valley. Mapping at a 1:24,000 scale was completed using GPS, GIS, and traditional field observations. In addition, thin section analysis and compositional analysis using a handheld XRF were used to confirm relationships among and between various volcanic units. A geologic map of the entire Stewart Valley or Stewart Spring quadrangle has never been published at a 24k scale. Unlike traditional Basin and Range valleys, the Stewart Valley is not bound by a major normal fault. The Stewart Valley is characterized by Miocene and Quaternary strata comprising pyroclastic and lacustrine sediments, as well as intermediate volcanism. The Miocene stratigraphy has been exposed via minor Quaternary faulting, folding, and subsequent fluvial incision, allowing for a detailed description of the sedimentary sequences. However, existing geologic maps and graduate theses are inconsistent in the distribution and naming of volcanic and sedimentary units within the valley, making the stratigraphic relationships between the volcanic rocks and the sedimentary facies dubious and unclear. Our new mapping, in conjunction with petrographic and igneous geochemical analysis, suggests two distinct volcanic units: an older porphyritic andesite and a younger dacite interbedded with block and ash flows, previously undescribed in the Stewart Valley, separated by a period of lacustrine and near-shore sedimentary deposition. Continued mapping and data collection, as well as the addition of new Ar/Ar geochronology from the volcanic units and ashes deposited in the sedimentary units, will allow for spatiotemporal correlation between the regional geologic units and assemble a concrete interpretation for the timing and processes involved in the valley’s formation. The publication will be publicly available through the Nevada Bureau of Mines and Geology.

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

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