Triangulating from the cairns…
This research aims to clarify the timing and mechanics behind a sixty kilometer- wide Bull’s Eye of exhumation in Colorado’s Elk and West Elk mountains that took place about 15-8 million years ago (Ma). To do this, I use the apatite (U-Th)/He low temperature thermochronology (AHe) technique to study the burial history and exhumation rates of granite outcrops that I collected along two vertical transects. My objective is to constrain the eastern perimeter of the Bull’s eye of exhumation and to compare erosion rates from the center towards the edge along a six-kilometer long, 1.2 km high vertical transect that connects from Taylor Peak A’s summit at 4,095m (Figure 1) to a site in Castle Creek at 2,891m with already analyzed AHe data. My data suggest that the eastern edge of the Bull’s Eye is a few kilometers east of the summit of Taylor Peak A, near the Grizzly Peak Caldera, and that the White Rock granodiorite at the summit was emplaced at about 500m depth 34 million years ago. AHe dates at four sample sites along an eastern vertical transect agree with White Rock Pluton emplacement age (33.9Ma +/- 1Ma Obradovich, 1969), implying shallow burial (1.5km or less) of the entire eastern side of Taylor Peak A at that time. Furthermore, comparison to data collected 12km west of my site atop White Rock Mountain suggests that the White Rock Pluton was emplaced along a gradient that rose at least a kilometer from there to the summit of Taylor Peak A.
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