UNRAVELING THE DRIVER FOR RECENT TOPOGRAPHIC REJUVENATION OF THE COLORADO ROCKY MOUNTAINS

The cause of recent topographic rejuvenation in the Colorado Rocky Mountains (CRM), as evident by long-wavelength tilting and a sustained increase in sediment flux in the last 5 Ma, is under ongoing debate. To date, two main hypotheses have been proposed to explain it: (1) mantle dynamics and active tectonics linked to the Rio Grande Rift system; (2) increased erosional efficiency due to glacial-interglacial changes in the Quaternary. One of the main reasons for this ongoing controversy is that most of the studies seeking to test these hypotheses focus on the CRM foreland basin and its relatively soft sedimentary basement, where interpretations from geomorphic patterns that record recent changes in boundary conditions (i.e., tectonics, climate) are ambiguous. Here, we aim to overcome this challenge by conducting a regional geomorphic analysis in the crystalline-dominated basement of the Colorado Rockies, upstream from the CRM foreland basin, where geomorphic patterns are more easily interpretable in the context of the two prevailing hypotheses. Using analysis of channel steepness below fluvial knickpoints, cosmogenic nuclide-derived basin-averaged erosion rates, and fluvial terrace-derived channel incision rates, we find a systematic increase in all these metrics from north to south over a ~350 km region across the Colorado Rockies drainage network. These findings imply a southward increase in rock uplift rate, consistent with a geodynamic impact of the Rio Grande Rift system in the last 5 Ma, suggesting tectonics and geodynamics primary drivers of recent rejuvenation in the CRM.