HR: 0800h
AN: S31B-04    [Abstracts]
TI: Post-perovskite Lens and Heat Flux at the CMB Under the Cocos Plate
AU: * Lay, T
EM: thorne@pmc.ucsc.edu
AF: University of California, Santa Cruz, Earth and Planetary Sciences Department, Santa Cruz, CA 95064, United States
AB: Investigations of structure in the lowermost mantle have revealed evidence for one or more velocity discontinuities in the lowermost mantle. The existence of a lower mantle velocity discontinuity can be interpreted as evidence for a phase change, with the most commonly discussed possibility being the transformation from perovskite to post- perovskite in relatively low temperature regions of the boundary layer. Subduction of Farallon Plate may account for low mantle temperatures in the deep mantle under the Caribbean and, if material has displaced westward above the core-mantle boundary, under the Cocos plate. But, even in a cooled region, the temperature at the core- mantle boundary will be the same as elsewhere, so a very steep thermal gradient is expected in the very regions where post-perovskite may exist, creating favorable conditions for a second intersection of the phase boundary and conversion back to perovskite. This would form a lens of post-perovskite bounded by velocity discontinuities above and below, of opposite sign and equal magnitude. Such paired discontinuities are being sought, as they can intrinsically provide two P-T points in a given region that allow the thermal gradient to be determined, and with assumption of a thermal conductivity, the heat flux can be estimated. The evidence for such structures is considered and the implications for heat flux in the putatively low temperature region near the core-mantle boundary below the Cocos plate is discussed.
DE: 7203 Body waves
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8121 Dynamics: convection currents, and mantle plumes
SC: Seismology [S]
MN: 2007 Joint Assembly