HR: 16:15h
AN: T14A-02 INVITED     [Abstracts]
TI: The Predicted Distribution of Post-Perovskite in the Lowermost Mantle: Relationship to Chemical Heterogeneity and Further Constraints on Core-Mantle Boundary Heat Flow
AU: * Hernlund, J
EM: hernlund@ess.ucla.edu
AF: Earth and Space Sciences, UCLA, 3806 Geology Building, Box 951567, Los Angeles, CA 90095 United States
AU: McNamara, A K
EM: Allen.McNamara@asu.edu
AF: Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287-1404 United States
AU: Labrosse, S
EM: labrosse@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4, Place Jussieu, Paris, CA 75252 France
AU: Tackley, P J
EM: ptackley@ucla.edu
AF: Earth and Space Sciences, UCLA, 3806 Geology Building, Box 951567, Los Angeles, CA 90095 United States
AB: We use three-dimensional spherical shell mantle convection models (McNamara, 2005) with plate motion history over the past several hundred million years as a surface boundary condition to study the predicted distribution of post-perovskite in Earth's lowermost mantle, both with and without large-scale chemical heterogeneity. Chemical heterogeneity in the form of "super-piles" induces a strongly bimodal pattern of temperatures in the D" region, and predicts a distribution of post-perovskite that is in good agreement with seismic observations of a discontinuity on top of D". In these cases, post-perovskite is confined to cooler regions associated with downwellings and large scale mantle circulation, whereas the chemically dense piles are hot because they reside just above the core-mantle boundary (CMB) and do not participate in the larger scale mantle circulation. By varying the parameters defining the post-perovskite phase boundary, and applying the double-crossing model of Hernlund et al. (2005), an upper bound for the CMB heat flow can be more confidently estimated. However, significant trade-offs still exist with respect to other uncertain physical parameters, especially thermal conductivity. Our preferred model also predicts that a D" discontinuity should be present beneath Antarctica, a region that has thus far eluded the necessary seismic coverage.
UR: http://geodyn.ess.ucla.edu/~hernlund
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3660 Metamorphic petrology
DE: 8020 Mechanics, theory, and modeling
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: Fall Meeting 2005