HR: 1340h
AN: V33A-1158    [Abstracts]
TI: Thermal and compositional contributions to mantle heterogeneity
AU: * Simmons, N A
EM: simmons27@llnl.gov
AF: Lawrence Livermore National Laboratory, L-206 7000 East Ave, Livermore, CA 94551, United States
AU: Grand, S P
EM: steveg@geo.utexas.edu
AF: University of Texas at Austin, Geol Sci Dept 1 University Station C1100, Austin, TX 78712, United States
AU: Forte, A M
EM: forte.alessandro@uqam.ca
AF: University of Quebec at Montreal, GEOTOP-Dept Sci. Terre & Atmos. C.P. 8888 Succ. Centre-Ville, Montreal, QC H3C 3P8, Canada
AB: We have integrated seismic, geodynamic and mineral physics constraints to obtain models of mantle heterogeneity. The seismic constraints primarily consist of teleseismic shear body wave travel times and the geodynamic constraints include the global free-air gravity field, tectonic plate divergences, dynamic surface topography and the excess ellipticity of the core-mantle boundary. The geodynamic observations are interpreted with viscous flow response kernels and velocity-to-density scaling relationships for thermally-varying mantle material. Considering the viscosity model from Mitrovica & Forte (2004) and an optimal thermal density-velocity scaling relationship, we have found a single velocity/density model capable of satisfying the combined dataset to high degrees. The implication is that thermal variations dominate and compositional contributions are secondary throughout most of the non-cratonic mantle (Simmons et al. 2007). This modeling approach inherently minimizes potential non-thermal contributions to the density field and thus establishes a minimal estimate of the influence of composition needed to reconcile the observations. This is due to the fact that we use optimal viscosity and density-velocity scaling relationships to model the data with the initial assumption that all heterogeneity is generated by thermal variations. Therefore, we test other possibilities including simplified viscosity profiles and alternative thermal density-velocity relationships in order to evaluate how these input parameters increase the level of compositional influence required to satisfy the combined dataset. We also demonstrate the potential downfall of scaling a purely seismically-derived shear velocity model to obtain density heterogeneity in the mantle. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. UCRL-ABS-233968
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7270 Tomography (6982, 8180)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8180 Tomography (6982, 7270)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting