Modeled flexural response to erosion in the Colorado Plateau: Implications for Laramide and post-Laramide rock uplift processes

In the landscape of the western United States, the Colorado Plateau features as a large physiographic province whose rock and surface uplift remain enigmatic. While the debate over the timing and distribution of uplift of the Colorado Plateau is ongoing, the goal of this study is to quantify and sum the expected contributions from known processes: Laramide shortening and Cenozoic erosion. The present-day reconstructed elevations of Late Cretaceous marine sediments are used to infer an average of 2400 meters of net Cenozoic rock uplift of the Colorado Plateau. In order to test the hypotheses for rock uplift, we generate quantitative models to determine the contribution of isostatic response to erosion to total rock uplift. The results of this study show that the flexural isostatic response to net Cenozoic erosion contributes 405 to 328 meters of mean rock uplift across the plateau depending upon the effective elastic thickness modeled, with rebound notably higher towards the center of the plateau and approaching zero at its edges. By subtracting the rock uplift due to erosion from the total rock uplift, the resultant residual surface is inferred to represent the amount of tectonically-driven uplift since Late Cretaceous time. The residual rock uplift pattern shows a regional background of ~2100 m of rock uplift, with local variations (±1 to 1.5 km) around the background corresponding to Laramide shortening structures. The amplitude of the residual epeirogenic rock uplift (~2.1 km) is larger than can be explained by Laramide crustal shortening processes, and its regional uniformity precludes thickening by eastward lower crustal flow away from the Sevier orogenic wedge. We suggest that regionally/spatially uniform geophysical processes must be responsible for the majority of epeirogenic rock uplift of the Colorado Plateau.