Seismic evidence for partial lithospheric delamination model of Colorado Plateau uplift

The lithospheric structure beneath the Colorado Plateau and Great Basin of the western United States is investigated using Pn and surface wave data from the Colorado Plateau - Great Basin broadband seismic experiment. Average Pn velocities of 8.0 km/s in the Colorado Plateau and 7.8 km/s in the eastern Great Basin are found. Teleseismic Rayleigh waves are also measured, and eastern Great Basin phase velocities are found to be 3-4% higher than Colorado Plateau phase velocities in the 20-35 s range, but indistinguishable at periods greater than 40 s. The apparent Pn/surface wave discrepancy is resolved with models that include a thicker crust and faster mantle lid for the Colorado Plateau than the eastern Great Basin. Models for both regions require a mantle low velocity zone. The slow mantle deep beneath the Colorado Plateau may suggest a thermal origin of Plateau uplift, which has not yet penetrated the mantle lid.