HR: 0830h
AN: T11C-0403    [PDF]
TI: Effects of Aluminum on the Compressibility of Silicate Perovskite
AU: Daniel, I
EM: isabelle.daniel@univ-lyon1.fr
AF: Laboratoire de Sciences de la Terre, UMR 5570 CNRS-ENSL-Universite Claude Bernard Lyon 1, Bat Geode, 43 bd du 11 Novembre, Villeurbanne, 69622 France
AU: * Bass, J
EM: jaybas@uiuc.edu
AF: Geology Department, University of Illinois, 1301 W Green St., Urbana, IL 61801 United States
AU: Fiquet, G
EM: Guillaume.Fiquet@lmcp.jussieu.fr
AF: Laboratoire de Min‚ralogie - Cristallographie, UMR 7590 CNRS-Universit‚ Paris VI, 4 place Jussieu, Paris, 75252 France
AU: Cardon, H
EM: Herve.Cardon@ens-lyon.fr
AF: Laboratoire de Sciences de la Terre, UMR 5570 CNRS-ENSL-Universite Claude Bernard Lyon 1, Bat Geode, 43 bd du 11 Novembre, Villeurbanne, 69622 France
AU: Hanfland, M
EM: hanfland@esrf.fr
AF: European Synchrotron Radiation Facility, BP 220, Grenoble, 38043 France
AB: Among the elements present in all mantle compositional models, aluminium oxide (Al$_{2}$O$_{3}$) is estimated to amount 4 to 5 mole %. While aluminium is incorporated in specific minerals such as garnet and majorite in the upper mantle, it is believed to be incorporated into (Mg,Fe)SiO$_{3}$-perovskite under the pressure and temperature conditions of the lower mantle. However, the effect of Al on the elastic parameters of perovskite has received less attention. It was considered to be insignificant, until Zhang and Weidner [1] presented for an Al-bearing silicate perovskite a bulk modulus 10% smaller than that of the end-member MgSiO$_{3}$-perovskite. Since then, numerous experimental studies have been devoted to understanding and confirming that issue. We present here two sets of volume measurements up to 40 GPa, for two Mg-perovskite with respectively 5 and 7.7 mol % aluminum. Samples were either synthesized in a multi-anvil apparatus or in a diamond anvil cell by laser heating a 20 micron thin glass plate of the relevant composition. Samples were studied in a diamond anvil cell with neon as a hydrostatic pressure transmitting medium and were annealed with a YAG laser within their pressure stability filed. Angle dispersive diffraction patterns were collected upon compression to the peak pressure, at the ID9 dedicated high-pressure beamline of the ESRF. From the two data sets fitted to a Birch-Murnaghan equation of state, we deduce that the dependance of the bulk modulus of silicate perovskite is not simply linearly dependent on the aluminum content. Whereas 5 mol % aluminum has very little effect on the compressibility of silicate perovskite, 7.7 mol % aluminum strongly decreases the bulk modulus. These results might be related to the substitution mechanism of Al into perovskite, suggesting that the coupled substitution mechanism might be efficient at low Al content, but is then replaced an oxygen vacancy mechanism at higher Al content. This indicates that the investigations of the chemical and petrological compositions of the lower mantle and heterogenities should definitely take into account the effect of Al on the thermoelastic properties of perovskite. Morover, taking into account the elastic effects of Al in perovskite is thus necessary for assessing the Si/Mg ratio of the lower mantle, and thus the large scale stratification of the Earth. [1] Zhang, J., and D.J. Weidner,{\it Science},{\it 284}, 782, 1999.
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Tectonophysics [T]
MN: 2003 Fall Meeting