Late Miocene erosion and evolution of topography along the western slope of the Colorado Rockies Public Deposited

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  • In the Colorado Rocky Mountains, the association of high topography and low seismic velocity in the underlying mantle suggests that recent changes in lithospheric buoyancy may have been associated with surface uplift of the range. This paper examines the relationships among late Cenozoic fluvial incision, channel steepness, and mantle velocity domains along the western slope of the northern Colorado Rockies. New ⁴⁰Ar/³⁹Ar ages on basalts capping the Tertiary Browns Park Formation range from ~11-6 Ma and provide markers from which we reconstruct incision along the White, Yampa and Little Snake Rivers. The magnitude of post-10 Ma incision varies systematically from north to south, increasing from ~500 m along the Little Snake River to ~1500 m along the Colorado River. Spatial variations in the amount of late Cenozoic incision are matched by metrics of channel steepness; the upper Colorado River and its tributaries (e.g. Gunnison and Dolores Rivers) are two to three times greater than the Yampa and White Rivers, and these variations are independent of both discharge and lithologic substrate. The coincidence of steep river profiles with deep incision suggests that the fluvial systems are dynamically adjusting to an external forcing, but is not readily explained by a putative increase in erosivity associated with late Cenozoic climate change. Rather, channel steepness 34 correlates with the position of the channels relative to low velocity mantle. We suggest that the history of late Miocene – present incision and channel adjustment reflects long-wavelength tilting across the western slope of the Rocky Mountains.
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  • Rosenberg, R., Kirby, E., Aslan, A., Karlstrom, K., Heizler, M., & Ouimet, W. (2014). Late Miocene erosion and evolution of topography along the western slope of the Colorado Rockies. Geosphere, 10(4), 641-663. doi:10.1130/GES00989.1
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  • 10
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  • 4
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  • This study was funded by the National Science Foundation–Colorado Rockies Experiment and Seismic Transects (NSF-CREST) project grant EAR-0607808. Additional support provided from grants EAR-0711546 (KEK) and EAR-1119635 (KEK and AA).
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