HR: 1340h
AN: T23A-0525    [Abstracts]
TI: Mantle Flow Beneath the Pacific Basin Determined via Shear Wave Splitting
AU: * Garcia, T M
EM: nanite1@ufl.edu
AF: Dept. of Geological Sciences University of Florida, PO Box 112120 241 Williamson Hall, Gainesville, Fl 32611 United States
AU: Russo, R M
EM: russo@geology.ufl.edu
AF: Dept. of Geological Sciences University of Florida, PO Box 112120 241 Williamson Hall, Gainesville, Fl 32611 United States
AB: We analyzed shear wave splitting induced by upper mantle anisotropy to asses the dynamics of coupling between oceanic lithosphere and underlying asthenosphere in the Pacific Basin. Deformation of olivine-dominated upper mantle aggregates produces LPO (lattice preferred orientation) in the aggregate structure. The resulting fast seismic velocities most often parallel the material extension direction, minimum velocities lie orthogonal to the shear plane, and shear wave splitting occurs. If the asthenosphere is sheared beneath moving oceanic lithosphere, the thickness and direction of the resulting anisotropy can be determined by the delay times between the split signals and the fast direction of shear wave propagation. We used shear wave splitting to determine whether lithosphere-asthenosphere interaction in the Pacific Basin produces shearing in the asthenosphere, and, if so, if recrystallization erases evidence for such coupling with increasing plate age. New island GSN stations in the Pacific basin allow this hemispheric-scale study of lithosphere-asthenosphere coupling. We used SKS and SKKS phases recorded at 12 stations spanning the Pacific basin (e.g., MIDW, MSVF, PTCN, PAYG), sited on lithosphere ranging from around 160 Ma (KWAJ) to less than 5 Ma (PAYG, RPN). The records were filtered to enhance signal to noise ratios and analyzed for splitting using the technique of Silver and Chan (1991). To enhance our estimates of splitting parameters, we also used a simultaneous linearization technique applied to groups of split phases at individual stations. Prior results indicate that stations in the south-central Pacific show clear evidence of asthenospheric LPO parallel to the Pacific's motion relative to hotspots. We will present our complete results at the meeting in December.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7218 Lithosphere (1236)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8162 Rheology: mantle (8033)
SC: Tectonophysics [T]
MN: Fall Meeting 2005