A Lithospheric Drip Triggered Green and Colorado River Integration

Abstract

The integration of the Green and Colorado Rivers shifted the continental drainage divide of North America, marking a key event in the hydrological and biogeographical evolution of the continent. Sedimentological and stratigraphic evidence shows that for integration to occur, the Green River likely cut through the Uinta Mountains between 8 and 1.5 Ma, long after the range formed more than 50 Ma. Though the Uinta Mountains have not been subject to active compressional tectonics since 50 Ma, the geomorphology of the range hints at some post-orogenic process influencing the topography of the range. The river networks draining the range preserve relict topography, which may form due to base-level fall or an increase in the rock uplift rate. By using a 2-D topographic inversion, we quantify the elevation change the relict topography has experienced relative to past base level. Based on the inferred pattern of elevation change to base level, we suggest the relict topography was most likely created by a rock uplift rate increase. Seismic tomographic images evidence a lithospheric drip beneath the range as the most likely driver of enhanced rock uplift. An estimate of the drip's velocity, and its imaged depth suggest that the drip detached between 2.3–4.7 Ma, matching the response time of the relict river network (2.1–4.6 Ma). Importantly, this fits existing age constraints for Green River incision through the Uinta Mountains, providing a mechanism for crustal deformation that could explain this event. Our findings demonstrate the profound impacts of geodynamic processes on topography, surface hydrology, and biogeography.