Constraining the Timing of River Incision in the Upper Colorado Drainage Basin Using Apatite (U-Th)/He Thermochronology in the Elk Mountains, Western Colorado
Abstract
This study utilizes apatite (U-Th)/He, or AHe, to produce a vertical transect of cooling histories along the height of the partially exhumed Crystal Pluton in the Elk Mountains of west/central Colorado. These cooling histories are interpreted to reflect exhumation controlled by the incision of the Crystal River – a tributary of the Colorado River. A period of rapid exhumation is observed from 8 – 11 Ma, likely beginning earlier, that is consistent with previous AHe data taken from nearby exhumed plutons in the Elk and northern West Elk Mountains. This period of exhumation predates the incision of a low relief surface that developed in northwestern Colorado by ca. 10 Ma, and is therefore not believed to have been controlled by the incision of the Colorado River. A review of previously noted incision constraints suggests that post-10 Ma Colorado River incision has become more rapid in the last 1 – 3 Ma, suggesting that climate change, rather than epeirogenic uplift, is the major driver for recent river incision.
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