HR: 0800h
AN: U41A-0708    [Abstracts]
TI: Effects of Aluminium on the compressibility of silicate perovskite
AU: * Daniel, I
EM: Isabelle.Daniel@univ-lyon1.fr
AF: Universite Lyon1, Lab. de Sciences de la Terre UMR 5570 43 bd du 11 novembre 1918, Villeurbanne, 69622 France
AU: Bass, J D
EM: jaybass@uiuc.edu
AF: University of Illinois, Dpt of Geology 1301 W. Green St., Urbana, IL 61801 United States
AU: Fiquet, G
EM: Guillaume.Fiquet@lmcp.jussieu.fr
AF: Laboratoire de Mineralogie, Laboratoire de Mineralogie - Cristallographie UMR 7590 Campus Boucicaut 140 rue de Lourmel, Paris, 75015 France
AU: Cardon, H
EM: Herve.Cardon@ens-lyon.fr
AF: Universite Lyon1, Lab. de Sciences de la Terre UMR 5570 43 bd du 11 novembre 1918, Villeurbanne, 69622 France
AU: Hanfland, M
EM: hanfland@esrf.fr
AF: ESRF, 6 rue Jules Horowitz, 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. Recently, the effect of Al on the elastic parameters of perovskite has received extreme attention, since 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. However, the bulk moduli obtained afterwards at various alumina content were highly scattered. We present here a series of volume measurements up to 40 GPa, for Mg-perovskites with respectively 5, 7.7 and 20 mol % aluminium. Samples were either synthesized in a multi-anvil apparatus or in a diamond anvil cell by laser heating a 20 $\m$um thin glass slide 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 and during decompression, at the ID9 dedicated high-pressure beamline of the ESRF. From the various data sets fitted to a Birch-Murnaghan equation of state, we deduce that the the relationship between the bulk modulus of perovskite and the Al content is not a linear decrease. Whereas 5 mol % aluminium has no noticeable effect on the compressibility of silicate perovskite, increasing slightly the aluminium content of perovskite strongly decreases its bulk modulus. Moreover, as the aluminium is added into perovskite, the compression/decompression behaviour of the samples displays different regimes. These results can be related to the substitution mechanism of Al into perovskite, suggesting that the coupled substitution mechanism is probably efficient at low aluminium content, but might then replaced by the oxygen vacancy one at higher aluminium content. This indicates that the investigations of the chemical and petrological compositions of the uppermost lower mantle and of heterogeneities should definitely take into account the effect of Al on the thermoelastic properties of perovskite. This also suggests that the partitioning behaviour of some trace elements between perovskite and the other lower mantle phases might be different in deep subducted lithospheric plates than in the `mean' lower mantle. [1] Zhang, J., and D.J. Weidner,{\it Science},{\it 284}, 782, 1999.
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 1025 Composition of the mantle
SC: Union [U]
MN: 2004 AGU Fall Meeting