DYNAMIC TOPOGRAPHY IN THE COLORADO PLATEAU ROCKY MOUNTAIN REGION: GEOLOGIC CONSTRAINTS FOR GEODYNAMIC MODELS AND VICE VERSA

Our hypothesis is that the Colorado Plateau-Rocky Mountain region has been uplifted in the last 10 Ma by mantle processes that have caused long wavelength differential uplift, faulting, sweeps of magmatism, and changes in fluvial systems. Uplift data are anchored at sea level by the Colorado River and Rio Grande systems that were both integrated to near sea level by 5 Ma such that differential uplift amounts accumulate to total surface uplift across the region. In the last 5-10 Ma, western edge of Colorado Plateau has gone up about 600 m relative to sea level based on differential incision of the Colorado and Virgin rivers; southern edge of the Colorado Plateau has gone up about 500 m based on data from the Salt River; western edge of the Rockies has uplifted ~ 800 m relative to the Colorado Plateau; eastern edge of Rockies has gone up ~ 650 m relative to adjacent Great Plains; Taos Plateau has gone up several hundred meters relative to sea level; uplift across the Jemez lineament has been ~ 400 m over 4 Ma; Green River/ Yampa got integrated with Colorado in last 8 Ma. We are constructing data-oriented geodynamic models to determine surface response to mantle flow based on high-resolution seismic tomography and the kinematics of past subduction since 20 Ma. We explore a range of temperature, viscosity and densities that best predict uplift data, volcanic history, and geophysical constraints such as seismic anisotropy. One set of dynamic topography models is based on a simple backward integration of mantle flow by reversing the sign of gravity and imposing plate velocities consistent with Farallon plate subduction; these show predicted scales of differential uplift of several hundred m to a km across several hundred-km-wide zones above mantle velocity gradients, both compatible with geologic data. A second set of models is based on an iterative adjoint solver that better deals with the effect of thermal diffusion and more accurately reproduces the subduction process. These models show patterns of dynamic topography that predict the first-order physiographic provinces in the western U.S. The combined geologic- geodynamic modeling approach will help refine parameters that control dynamic topography and provide a physical understanding for observed surface processes.