EVALUATION OF EROSION VARIABILITY AND DRAINAGE BASIN RELIEF USING DETRITAL APATITE THERMOCHRONOLOGY IN THE TETON RANGE, WYOMING

Alpine topography is created by variable erosion resulting from differences in rock strength, competition between geomorphic processes and climate conditions that fluctuate with altitudinal domain. This study evaluates individual mechanisms shaping the landscape using detrital thermochronology and cosmogenic radionuclides to understand the spatial and temporal progression of dynamic erosion processes in the Teton Range, WY. Modern fluvial and glacial moraine sediments, as well as 5 bedrock samples, were dated with apatite (U-Th)/He thermochronometry in Garnet Canyon. This catchment exhibits complex interactions between glacial, mass wasting, and fluvial processes and drains the highest elevations in the range, including the Grand Teton. To test erosion variability, we created a model probability density function (PDF) based on the age-elevation relationship determined from apatite (U-Th)/He ages of bedrock samples and basin elevation hypsometry. Inspection of grain quality in two different bedrock lithologies led to corrections on the model PDF based on bedrock area and apatite yield. Comparison of glacial and fluvial sediment PDFs to the model PDF yields higher than predicted concentrations of older ages for both sediment age spectra. Individual apatite grains were also observed with scanning electron microscope (SEM) and cathodoluminescence (CL) to test if element zonation and inclusions caused overestimation of apatite ages. Inclusions appeared less frequently in sediments than in bedrock samples, lessening the possibility that they influenced sediment age distributions. Measurements of ¹⁰Be cosmogenic radionuclide concentrations in quartz from bedrock and sediments were used to calculate denudation rates in and around Garnet Canyon and preliminary results indicate slow surface erosion rates, particularly along ridges.