HR: 0800h
AN: U41A-0724    [Abstracts]
TI: Comparing lower mantle compositions and temperatures inverted from different seismic observations
AU: Mattern, E
EM: estelle.mattern@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR CNRS 5570, Ecole Normale Superieure de Lyon, 46 allee d'Italie, Lyon, 69007 France
AU: * Matas, J
EM: jan.matas@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR CNRS 5570, Ecole Normale Superieure de Lyon, 46 allee d'Italie, Lyon, 69007 France
AU: Bass, J
EM: jaybass@uiuc.edu
AF: Department of Geology, University of Illinois-Champaign, 1301 W Green Street , Urbana, IL 61801 United States
AU: Ricard, Y
EM: ricard@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR CNRS 5570, Ecole Normale Superieure de Lyon, 46 allee d'Italie, Lyon, 69007 France
AB: Most constraints on lower mantle composition and temperature come from comparison of seismic profiles with their equivalents deduced from mineral physics. For seismologists, the parameters directly observable are the velocities $V_P$ and $V_S$, whereas the most readily determined properties experimentally are density $\rho$ and bulk modulus $K_S$. In this study, we apply a generalized inverse method and high-quality experimental datasets to infer the lower mantle composition and temperature profile from seismic observations. Inversion from density and bulk sound velocity highlights the following points: (1) equally satisfactory fits to seismic profiles can be obtained either for pyrolite-type composition with a cool geotherm, or for perovskite-rich composition with a hot geotherm, (2) consistent features in all inversions are a total iron content of 0.1 and a subadiabatic temperature gradient, with a peculiar correlated behavior of these two parameters below the 660 km discontinuity (3) the results of inversions are unaffected by the partitioning of iron between perovskite and magnesiow\"ustite (4) the inversion does not constrain the Al$_2$O$_3$ and CaO contents of the lower mantle. Using the compressional and shear velocities as additional constraints decreases the a posteriori uncertainties on the inverted parameter and removes the dependence of the final results on the a priori model. However, the inverted composition and temperature profiles drastically depend on the shear properties of lower mantle minerals, particularly of silicate perovskite. The experimental uncertainties yield a wide range of compositional and thermal profiles ranging from a uniform pyrolite-type lower mantle with closely adiabatic geotherm to a lower mantle whose composition gradually increases from pyrolite at 660 km depth to pure perovskite at the CMB with a strongly superadiabatic profile. A better understanding of lower mantle composition and temperature requires better constraints on shear properties, especially their pressure and temperature dependence.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3655 Major element composition
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3939 Physical thermodynamics
SC: Union [U]
MN: 2004 AGU Fall Meeting