Gao et al., Mantle Dynamics Beneath the Rio Grande Rift and Colorado Plateau

We have inverted P and S wave teleseismic delay times recorded by the LA RISTRA (Colorado PLateau, Rio Grande Rift, Great Plains Seismic TRansect) array. The RISTRA array consisted of 57 broad band seismic stations most of which were deployed in a line extending 950 km from Lake Powell, Utah to Pecos, Texas. P, PKP, S, and SKS travel time delays were inverted using the LSQR algorithm to determine lateral variations in seismic velocity to about 600 km depth beneath the line. The small station spacing along the line as well as its great length result in a well resolved image of the mantle beneath the line. Within the upper 200km of the mantle slow seismic anomalies are obvious beneath the Rift with the slowest anomalies beneath Mt Taylor on the west of the Rift and Carrizozo near the east of the rift. The mantle beneath the Great Plains and Colorado Plateau is seismically faster than within the Rift but within each of the other two provinces, there are significant variations. In particular, the eastern edge of the Colorado Plateau has faster seismic wavespeeds than in the center of the Plateau (near the four corners region) and the western edge of the Great Plains shows a narrow (about 75 km wide) fast structure that is faster than the mantle further to the east in the Great Plains. These fast mantle anomalies in the upper 200 km of the mantle at the edges of the Rift may represent lithosphere that has been removed from the Rift region. Alternatively, if the fast mantle anomalies are more ancient, they may provide structural control on where rifting and volcanism have occurred.

For more information on LA RISTRA tomography contact:

Steve Grand steveg@speer.geo.utexas.edu,
Wei Gao gao@speer.geo.utexas.edu,
University of Texas, Austin, Department of Geological Sciences, Austin, TX 78712