HR: 09:15h
AN: MR21A-06    [Abstracts]
TI: The interaction between a thermo-chemical boundary layer and the post perovskite phase change near the core-mantle boundary
AU: Tackley, P J
EM: ptackley@ess.ucla.edu
AF: Department of Earth and Space Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 3806 Geology Building, Box951567, Los Angeles, CA 90095-1567 United States
AU: * Nakagawa, T
EM: takashi@eps.s.u-tokyo.ac.p
AF: Department of Earth and Planetary Sciences, University of Tokyo, Bldg #1, Grad. School of Sci., 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033 Japan
AB: Two- and three-dimensional numerical simulations of compressible, thermo-chemical mantle convection including plate-like behavior are used to investigate the effects of the perovskite to post-perovskite phase transition at around 2700 km depth on the dynamics and observational (seismological) signatures of thermochemical mantle convection. Both cases with, and without a compositionally-dense layer of subducted oceanic crust, are considered. For purely thermal convection the exothermic post-perovskite phase change destabilizes the lower thermal boundary layer, increasing the heat flow, increasing interior mantle temperature, and increasing the number and time-dependence of upwelling plumes. The resulting weak, highly time-dependent upwellings also have a smaller horizontal spacing than the plumes that occur in the absence of the phase transition [Nakagawa and Tackley, 2004 published in GRL]. In the present study, we progress to a more realistic model that includes plate-like behavior of the upper boundary layer, which may alter the character of the downwellings reaching the D'' region, and the possibility of a layer of segregated subducted crust above the CMB, which, due to its different perovskite fraction, may result in interesting interactions as may occur in the 660-720 km depth region. Our analysis focuses on seismological observables, including topography of the discontinuity, the possibility of a second crossing of the discontinuity at greater depth [Hernlund et al., 2004], the temperature gradient in the lower 40 km which might be linked to ULVZ presence of absence, and horizontal wavelengths and planform. Also studied is the effect on heat transfer across the CMB, which is important for understanding core evolution.
DE: 8121 Dynamics, convection currents and mantle plumes
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 1212 Earth's interior--composition and state (8105)
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting