Thermochronological Study on the Elk and West Elk Mountain Ranges and Interpretations of Exhumation Processes in Western Colorado.

Riccio, Edward J

Undergraduate Honors Thesis

Thermochronological Study on the Elk and West Elk Mountain Ranges and Interpretations of Exhumation Processes in Western Colorado. Público Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/sn00b002c

Abstract

This research report asks the question: What is the exhumation history on Crested Butte and Snodgrass Mountain in Crested Butte, CO? This area of Western Colorado is of particular interest due to a ‘bull's-eye’ region of exhumation discovered in the Elk and West Elk mountains through the application of low temperature thermochronology. This technique yields ages when rocks were at shallow depths in the Earth's crust (1.5-2 km). Previous work on Gothic Mountain completed a 700m vertical transect where all samples were 12-10 Ma. However sample HC19-1, located about 500m below and east of the summit of Gothic Mountain, yielded a much older date than the peak. This elevation-date inversion led to the hypothesis that a paleo-river was causing the observed data anomaly. To test this hypothesis, I determined that Snodgrass Mountain and Crested Butte would be great candidates because they’re located south-southeast of Gothic Mountain and exhibit a geomorphology that could favor a paleo-river valley traveling between the two mountains. By collecting rock samples from the region, I then conducted mineral separation methods to obtain apatite crystals which I then analyzed at the CU thermochronology lab. The transect completed on Crested Butte exhibits typical behavior of younger ages with lower elevations. My data yielded an age of ~18 Ma at the summit of Crested Butte (3707m) and an older age of ~25 Ma at the peak of Snodgrass Mountain (3396m). Since Snodgrass is lower in elevation than Crested Butte, I can infer that the paleo-river hypothesis remains viable. Hence my results add to an ongoing database that tells a story about the exhumation rates and erosional processes occuring in this area.

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