A SUMMARY OF IDEAS ON THE TIMING AND DISTRIBUTION OF ROCK AND SURFACE UPLIFT ACROSS THE COLORADO PLATEAU

During and following the Laramide orogeny, the Colorado Plateau has behaved as a tectonically coherent, relatively undeformed block within the active western North America deformation zone. This presentation gives an overview of current thinking on the mechanisms of rock and surface uplift of the Colorado Plateau integrating available geologic, geomorphic, and geophysical data. The widespread occurrence of shallow marine rocks of late Cretaceous age across the plateau suggests that the average elevation of the Colorado Plateau was at or below sea level in late Cretaceous time, thus constraining the net Tertiary rock and surface uplift. Ideas regarding the uplift of the Colorado Plateau are based on the timing of elevation change from near sea level in late Cretaceous time to average elevations ~1.9 km at present. Geodynamic models of the uplift of the Colorado Plateau can be divided into those that attribute much of the elevation change to rock and surface uplift due to crust or mantle modification during: (a) Laramide-related lower crustal shortening with little upper crustal deformation (b) partial removal and/or modification of a significant portion of mantle lithosphere during Laramide flat-slab subduction and accompanying surface uplift upon removal of the Farallon slab in middle Cenozoic time, and (c) late Cenozoic (ongoing?) epeirogenic uplift. The role of the subducted Farallon slab beneath the Colorado Plateau is controversial, though there is general agreement that the slab would have modified the overriding plate by cooling and hydrating it and subsequent slab removal preceded or coincided with the timing of the voluminous late Eocene-Oligocene caldera-complexes (the “ignimbrite flare-up”) in the western US.

One of the key assumptions of previous work on the plateau is that rock and surface uplift of the Colorado Plateau must be thought of as the result of a common geodynamic process that affected the whole plateau. This presentation will challenge this assumption and explore the idea that geodynamic processes generating rock and surface uplift of the Colorado Plateau may have been heterogeneous. In particular, we will focus on processes that may have distinctly affected the edges of the plateau vs. its center, leading to the observed heterogeneity in rock and surface uplift of the plateau.