UNIFORMITY OF DRAINAGE BASIN EROSION AND RELIEF BASED ON DETRITAL THERMOCHRONOMETRY AND LANDSCAPE ANALYSIS OF THE TETON RANGE, WYOMING

Mountain landscapes evolve as climate patterns shift and erosional processes alternate between glacial and fluvial regimes. The Teton Range, Wyoming, exemplifies a landscape experiencing a complex balance between glacial, fluvial, and mass wasting processes. Alpine glaciations since ~3 Ma likely focused erosion on valley floors rather than summits, thereby increasing overall relief as observed in other Laramide ranges (Small and Anderson, 1998). However, the spatial variation of specific denudational mechanisms in mountain drainage basins is not yet quantified. We use detrital (U-Th)/He thermochronology and landscape analysis to track the spatial variation of erosion and its potential effects on basin relief evolution. To quantify the enhanced incision by glaciers, we compare detrital apatite age spectra from glacial moraines to age probability density functions predicted for uniform basin erosion based on basin hypsometry and bedrock age-elevation gradients. The age spectra from modern river sediments additionally test whether basin erosion is more uniform under fluvial conditions. Field observations suggest modern river sediment may be dominated by high-altitude particles based on the prevalence of thick talus that buries the formerly glaciated valley bottom. We hypothesize that frost wedging, rock shattering, and other periglacial processes enhance interglacial erosion on bedrock interfluves. Angular quartz grains sampled from high altitude surfaces and talus suggest microfracturing associated with mechanical weathering and rapid sediment transport and support the hypothesis. This postulated interglacial erosion of interfluves may be due to the extreme relief of the Tetons. While other Laramide peaks flatten near their summits, rugged ridges and peaks characterize the Teton Mountains. Valley spacing, pre-glacial topographic expression or recent uplift related to Yellowstone Hotspot migration may cause the greater ruggedness. Topographic analysis of a projected Cambrian unconformity verifies deep incision of the Teton Range. Quantifying spatial distribution of erosion during glacial and post-glacial conditions is thus revealing about the dynamics of landscape evolution in the Teton Range.