HR: 10:35h
AN: T21F-02    [PDF]
TI: Inversions for lower mantle composition and temperature from elasticity parameters and thermodynamic modeling
AU: * Mattern, E
EM: estelle.mattern@ens-lyon.fr
AF: ENS Lyon, LST CNRS, 46 allee d'Italie, Lyon, 69007 France
AU: Matas, J
EM: jan.matas@ens-lyon.fr
AF: ENS Lyon, LST CNRS, 46 allee d'Italie, Lyon, 69007 France
AU: Bass, J
EM: jaybass@uiuc.edu
AF: Department of Geology, UIUC, 1301 W Green Street, Urbana, IL 61801 United States
AU: Ricard, Y
EM: yanick.ricard@ens-lyon.fr
AF: ENS Lyon, LST CNRS, 46 allee d'Italie, Lyon, 69007 France
AU: Jackson, J
EM: jmjackso@students.uiuc.edu
AF: Department of Geology, UIUC, 1301 W Green Street, Urbana, IL 61801 United States
AB: Most constraints on lower mantle composition come from comparison of seismic profiles with their equivalents deduced from mineral physics. For seismologists, the parameters of primary interest are the velocities $V_P$ and $V_S$ and their lateral variations, whereas the most readily determined properties experimentally are $K_S$ and $\rho$. Therefore, the two sets of results cannot be directly compared. Additional data analysis and thermodynamic modeling are then necessary. In this study, we apply a generalized inverse method and recent and highest quality experimental and seismological observations to compute the lower mantle composition and corresponding temperature profile. This method calculates the parameters (composition and temperature) which minimize a misfit function (density and bulk sound velocity) to best match global 1-D seismological profiles. We demonstrate that the Fe/Si and Mg/Si (molar) ratios are well constrained, and that there is a degree of covariance between the Ca/Si ratio and the Mg/Si ratio. The Al/Si ratio is only poorly constrained. The physical properties we have chosen yield a lower mantle model which is chemically homogeneous from 800 to 2700 km. Our method also gives the a posteriori uncertainties on the inverted parameters and, therefore, allows us to precisely evaluate how the experimental uncertainties on elastic parameters affect the composition and temperature. We show that if the bulk modulus of Mg-perovskite is 246 GPa instead of 261 GPa (5% difference), the resulting perovskite fraction is increased by 30%. Finally, if the temperature profile and composition are not simultaneously inverted, then the resulting lower mantle composition is highly dependent of the choice of the thermal regime.
DE: 3655 Major element composition
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3939 Physical thermodynamics
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting