HR: 0830h
AN: S51C-0058    [PDF]
TI: Comparison of S-Wave Velocity Structure Beneath the Kaapvaal Craton From Surface-Wave Inversion With Predictions From Mantle Xenoliths
AU: * Larson, A M
EM: alarson@vt.edu
AF: Dept. of Geological Sciences, Virginia Tech 4044 Derring (0420), Blacksburg, VA 24061 United States
AU: Snoke, J A
AF: Dept. of Geological Sciences, Virginia Tech 4044 Derring (0420), Blacksburg, VA 24061 United States
AU: James, D E
AF: Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 United States
AU: Gore, J
AF: Dept. of Physics, University of Zimbabwe, Harare, MP167 Zimbabwe
AU: Nguuri, T
AF: CTBTO, Vienna International Centre, Vienna, 1400-1250 Austria
AB: Results from two-station surface-wave inversions across the Kaapvaal craton of southern Africa are compared with seismic velocities and densities estimated from approximately 100 mantle xenoliths brought to the surface in kimberlite pipes. These cratonic xenoliths from the southern Kaapvaal, all less than 100 Ma in age, have been analyzed thermobarometrically to obtain the equilibrium P-T conditions of the cratonic mantle to about 200 km depth. Seismic velocity-depth and density-depth profiles calculated on the basis of these P-T data and the mineral modes of the xenoliths (James {\it et al}., {\it G-cubed}, in press, 2003) are used to produce theoretical surface-wave dispersion curves and to generate starting models for inverting the observed surface-wave dispersion. Preliminary results obtained as part of this study and from previous surface-wave inversions in Ph.D. theses (in preparation) by Nguuri and Gore are broadly consistent with the predicted velocity-depth curves from xenolith studies that show uppermost mantle S-wave velocities of $\sim$4.7 km/s, decreasing slightly to about 4.65 km/s at 180--190 km. The current research extends the work of Gore and Nguuri by including additional events and a direct-search inversion scheme (Neighbourhood Algorithm) that allows direct comparison with results from the xenolith studies. Finally, preliminary results from surface-wave inversions are presented that contrast mantle velocity-depth profiles off-craton with those on-craton. The implications of results are discussed in terms of the thermal state and recent thermal history of the mantle beneath southern Africa.
DE: 1010 Chemical evolution
DE: 5134 Thermal properties
DE: 7218 Lithosphere and upper mantle
DE: 7255 Surface waves and free oscillations
DE: 8159 Rheology--crust and lithosphere
SC: Seismology [S]
MN: 2003 Fall Meeting