HR: 14:40h
AN: S33D-05    [Abstracts]
TI: Thermochemical structure of deep slabs beneath America derived from P and S wave tomography.
AU: * Stutzmann, E
EM: stutz@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: Matas, J
EM: Jan.Matas@ens-lyon.fr
AF: Ecole normale superieure de Lyon, 46, Allee d'Italie, Lyon, 07 69364 France
AU: Ren, Y
EM: ren@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75005 France
AU: van der Hilst, R
EM: hilst@mit.edu
AF: Massachusset Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 01239 United States
AB: Slab structure in the deep mantle is investigated from tomographically inferred P- and S-wave velocity anomalies. We have used a waveform cross-correlation technique on broadband data to measure P1-P2 and S1-S2 differential travel times between 2 stations for a given event and PcP-P and ScS-S for given earthquake-station couple. In order to achieve path coverage as similar as possible for both wave types, we have only kept source-receiver configurations for which we could make both P-wave and S-wave differential measurements. Earthquakes and receivers are located along a great circle path from Alaska to South America. We invert the 20,000 P and S wave differential travel times simultaneously to estimate P- and S-wave speeds in 2° x 2° x 200km constant velocity blocks. The lateral variations of seismic velocities in the deep mantle are interpreted in terms of perturbations of temperature and bulk chemical composition with respect to an average pyrolitic mantle. We consider lower mantle bulk chemistry models composed of five compounding oxides: MgO, FeO, Al2O3, CaO, and SiO2. We use the seismic sensitivities (i.e. the partial derivatives of V_p and V_s with respect to temperature and chemical composition) computed from a recent compilation of elastic parameters for lower mantle minerals. We show that seismic features observed in the deep mantle are consistent with cold anomalies and with a bulk composition of harzburgitic type, thus indicating that a signature of recycled lithospheric fragments can be identified in the deep mantle beneath America. We also discuss the effect of uncertainties associated with extrapolation of the elastic data.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8180 Tomography (6982, 7270)
SC: Seismology [S]
MN: Fall Meeting 2005