HR: 16:15h
AN: MR14A-02 INVITED     [Abstracts]
TI: Sound velocities of aluminous perovskite and ferropericlase at high-pressure: Implications for Earth's deep interior
AU: * Jackson, J M
EM: jmjackso@uiuc.edu
AF: Dept. of Geology, University of Illinois, 245 NHB 1301 W. Green St., Urbana, IL 61801 United States
AU: Zhang, J
EM: jzhang@lanl.gov
AF: Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 United States
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: Dept. of Geology, University of Illinois, 245 NHB 1301 W. Green St., Urbana, IL 61801 United States
AB: Accurate determinations of the sound velocities of deep Earth material under the relevant pressures and temperatures are essential for understanding seismic observations in this region. Aluminum-bearing magnesium silicate perovskite and (Mg,Fe)O ferropericlase have been proposed to be the most abundant minerals in Earth's lower mantle, with aluminous perovskite occupying roughly half of Earth's volume. Despite its major role in the deep Earth, the sound velocities of aluminous perovskite at high-pressure have not been measured. Furthermore, some experimental and theoretical studies have indicated that the properties of magnesium silicate perovskite may be significantly altered by the presence of Al$^{3+}$, depending on how this ion is incorporated into the perovskite structure. This complexity adds an additional element of uncertainty to the properties of the actual aluminous perovskite in the lower mantle. Here we present the first high-pressure Brillouin scattering measurements on silicate perovskite. The experiments were performed on a polycrystalline aluminum-bearing MgSiO$_{3}$ perovskite sample (containing 5 wt.% Al$_{2}$O$_{3}$, as described in Jackson {\it et al.} 2004) in a diamond anvil cell, using methanol-ethanol-water as a pressure transmitting medium. The pressure-dependence of the aggregate compressional (V$_{P}$) and shear (V$_{S}$) wave velocities, as well as, the adiabatic bulk (K$_{0S}$) and shear ($\mu $) moduli were obtained. We combine these results with our recent high-pressure Brillouin data on single-crystal (Mg$_{0.94}$Fe$_{0.06}$)O ferropericlase and discuss the importance of shear properties for understanding Earth's lower mantle. Reference: Jackson, J.M., J. Zhang, and J.D. Bass (2004), {\it Geophys. Res. Lett.}, {\bf 31}, L10614, 2004GL019918R.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting