COLORADO PLATEAU CRUST AND UPPER MANTLE STRUCTURE AND IMPLICATIONS FOR UPLIFT MECHANISMS

We present preliminary images of the crust and upper mantle seismic structure beneath a complete NW-SE transect of the Colorado Plateau (CP). We use teleseismic data from the ongoing (summer 2004-summer 2006) RISTRA 1.5 experiment which extends northwest from the center of the CP to a point 100 km into the Great Basin, together with data from the LA RISTRA passive seismic array deployed from July 1999 to May 2001, which extends southeast from the center of the CP to the Rio Grande rift and beyond. By combining these two data sets, we construct an image of the crust and upper mantle seismic structure that completely transects the CP. Preliminary images show crustal thickness that ranges from approximately 45 to 50 km thick in the center of the CP, thinning to 35 km thick at the Rio Grande rift, and to less than 30 km thick in the Great Basin. Joint body wave and surface wave tomography results indicate relatively low velocities at 150-300 km depth beneath the CP. These low velocities may indicate elevated temperatures and possibly lower relative densities at depth. These low densities at depth, along with the relatively thick CP crust, may help to buoy the CP to its present high elevation. Ongoing receiver function and body wave tomography work will facilitate a better understanding of lithospheric deformational styles, processes related to late Cenozoic volcanism, mantle convection, and will provide further insight toward understanding the mechanisms supporting the high CP elevation. This research funded by the Los Alamos National Laboratory Institute for Geophysics and Planetary Physics.