CONSTRAINING LATE QUATERNARY OFFSET RATES ALONG THE TETON FAULT, WYOMING USING COSMOGENIC 10BE DATING OF ALLUVIAL LANDFORMS

The Teton Range in northwestern Wyoming is one of the most tectonically active regions in the interior western United States due to the presence of the Teton normal fault, which extends ~70 km along the eastern front of the range. Estimates of Pleistocene-Holocene Teton fault slip rates range from ~1.0 to 2.0 m ka^-1, but recent work suggests that slip rates may have been both temporally and spatially variable. Here, we take advantage of fault-offset alluvial and glacial deposits to evaluate spatial trends in Teton fault motion across the eastern range front. We present new in situ cosmogenic ¹⁰Be measurements from alluvial fan boulders (n=4) and water-scoured bedrock (n=1) to constrain the timing of fan abandonment to ~15.6 ka. These ages are broadly similar to previously published ¹⁰Be ages from fault-offset glacial landforms (e.g., recessional moraines), which were abandoned at ~14.7 ka. However, despite the relatively close correspondence in age, the magnitude of landform offset varies considerably along the fault trace; thus, open-ended offset rates derived from alluvial fans differ from those derived from glacial landforms. We discuss potential controls on this apparent variation in past fault motion, including isostatic unloading that accompanied deglaciation of the Yellowstone Plateau ice cap and regional uplift/subsidence cycles related to Yellowstone hotspot activity. We also outline plans for an upcoming field campaign to date other alluvial fans cut by the Teton fault. Additional ¹⁰Be ages from these landforms should further constrain offset rates along the fault, and will contribute to a more comprehensive understanding of regional seismic hazards.