The Colorado Plateau and its Role in the Laramide Orogeny

The Colorado Plateau is a relatively undeformed region bordered on the south and west by the highly extended Basin and Range province and on the north and east by the towering Laramide uplifts of the Rocky Mountains. Tectonically, the Plateau is a part of the Laramide orogen and contains basement-cored uplifts similar in style to those of the Rocky Mountains but with lower structural and topographic relief. Together, these observations have led some workers to hypothesize that the Plateau is anomalously strong and behaved as a rigid microplate during the Laramide orogeny. Evidence for a fundamental difference between the Plateau and the Rocky Mountains is largely circumstantial however, and is not supported by structural, topographic, geophysical or crustal assemblage data. The gradation in deformational intensity is better explained as the product of northeastward-increasing tectonic force, which is a predictable result of coupling between the North American crust and the flat, northeastward-subducting Farallon slab. Assuming that coupling-related stress and crustal strength are approximately constant, net force (and hence deformational intensity) grow with distance over which the coupling is active resulting in low tectonic force/minor deformation in the hinterland and high force/intense deformation in the foreland just before the subducting slab loses contact with the overriding plate. Minimal deformation of the Colorado Plateau is thus a logical result of its location in the hinterland of the Laramide orogen. Interpreted northeastward translation and clockwise rotation of the Plateau are consistent with a normal along-strike "bow and arrow" orogenic shortening profile and require no special explanation.