HR: 1340h
AN: T33A-1144    [Abstracts]
TI: Shear Wave Splitting and Mantle Flow beneath The Colorado Plateau and the Colorado Plateau-Great Basin Transition
AU: * Wang, X
EM: wangxl@nmsu.edu
AF: Department of Physics, MSC 3D, New Mexico State University, Las Cruces, NM 88003, United States
AU: Ni, J
EM: jni@nmsu.edu
AF: Department of Physics, MSC 3D, New Mexico State University, Las Cruces, NM 88003, United States
AU: Aster, R
EM: aster@ees.nmt.edu
AF: Deptartment of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801, United States
AU: Sandvol, E
EM: sandvole@missouri.edu
AF: Department of Geological Sciences, University of Missouri, Columbia, MO 65211, United States
AU: Wilson, D
EM: dwilson@usgs.gov
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, United States
AU: Sine, C
EM: christophersine@bocsi.net
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, United States
AU: Grand, S
EM: steveg@maestro.geo.utexas.edu
AF: Department of Geological Sciences, The University of Texas at Austin, Austin, TX 78712, United States
AU: Baldridge, W S
EM: sbaldridge@lanl.gov
AF: Earth and Environmental Sciences Division, MS D462, Los Alamos National Laboratory, Los Alamos, NM 87545, United States
AB: Shear-wave splitting measurements are determined using data collected from LA RISTRA 1 and 1.5 (Colorado pLAteau RIo Grande Rift/Great Plains Seismic TRAnsect) to study the origin of seismic anisotropy in the mantle beneath the Colorado Plateau and the Colorado Plateau-Great Basin transition. Results show that, on the average, the fast polarization directions are sub-parallel to North American absolute plate motion within the central Rio Grande Rift and Colorado Plateau until it reaches the western rim of the plateau where the fast direction becomes NNE-SSW, then rotated westward to N-S in the transition zone, and then to NNW-SSE along stations in western Great Basin. The location of the onset of change of SKS splitting fast direction corresponds exactly to the position where the S-wave velocity perturbations change from about -8 percent beneath the Great Basin to 4 percent beneath the western Colorado Plateau. This location coincides approximately with the Proterozoic-Paleozoic lithospheric boundary (Wasatch line) and the eastern edge of the Marysvale volcanic field. The anisotropy beneath the Colorado Plateau and central Rio Grande Rift shows a remarkably consistent pattern with a mean fast direction of about 45 degrees. Delay times average from 1.5 s beneath the central Colorado Plateau to 0.8 s near the transition zone. Delay times for stations beneath the Great Basin are about 1.2 s. For the central Colorado Plateau, we suggest that anisotropy is controlled predominantly by a combination of sub- continental asthenospheric flow and "frozen" lithosphereic fabric. The observed pattern of rotating westward anisotropy from the western Colorado Plateau through the Colorado Plateau-Great Basin transition and into the Great Basin can be explained by asthenospheric flow around and deflected by a lithospheric keel beneath the Colorado Plateau or by the combined effect of North America plate motion and the edge driven small-scale convection.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7299 General or miscellaneous
DE: 8103 Continental cratons
SC: Tectonophysics [T]
MN: 2007 Fall Meeting