HR: 12:05h
AN: MR22A-08    [Abstracts]
TI: Plastic deformation of MgGeO3 post-perovskite beyond 100 GPa
AU: * Merkel, S
EM: smerkel@berkeley.edu
AF: Dept of Earth and Planet. Sc., UC Berkeley, Berkeley, CA 94720 United States
AU: Kubo, A
EM: akubo@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08544 United States
AU: Speziale, S
EM: speziale@uclink.berkeley.edu
AF: Dept of Earth and Planet. Sc., UC Berkeley, Berkeley, CA 94720 United States
AU: Miyagi, L
EM: miyagi@eps.berkeley.edu
AF: Dept of Earth and Planet. Sc., UC Berkeley, Berkeley, CA 94720 United States
AU: Wenk, R
EM: wenk@seismo.berkeley.edu
AF: Dept of Earth and Planet. Sc., UC Berkeley, Berkeley, CA 94720 United States
AU: Duffy, T
EM: duffy@princeton.edu
AF: Department of Geosciences, Princeton University, Princeton, NJ 08544 United States
AU: Mao, H
EM: mao@gl.ciw.edu
AF: Geophysical Lab, Carnegie Institution 5251 Broad Branch Road, NW, Washington, DC 20015 United States
AB: Strong seismic anisotropy and regional variations have been reported in the D" layer and it has been a longstanding issue. Therefore, the recent discovery of a new phase of MgSiO₃, stable at pressure and temperature conditions of the D" layer attracted considerable interest. It has been suggested that post-perovskite (p-Pv) may exhibit significant anisotropies for both compressibilities and elastic moduli. Moreover, the p-Pv structure has silicate layers parallel to {010} and it was therefore suggested that this material could develop strong preferred orientation when plastically deformed. In a first attempt to investigate the plastic behavior of post-perovskite under the pressures of the deep mantle, we deformed MgGeO₃ post-perovskite in a diamond anvil cell at 100-125 GPa pressure and room temperature at APS (HPCAT, beamline ID-16-B). Germanates are known to be low pressure analogues of silicates for many properties, such as the sequence of pressure induced phase transitions, including a transition towards a post-perovskite phase. In addition, as for MgSiO₃-pPv, GeSiO₃-pPv also displays a strong anisotropy in compressibilities. Images obtained in radial diffraction geometry exhibit elastic and plastic deformation, the latter expressed in intensity variations along Debye rings. The images were analyzed to obtain the orientation distribution function, both with fitting individual peak intensities and with the Rietveld method MAUD. With both methods and for several samples we document a strong preferred orientation pattern with [100] direction parallel to the compression direction. Those pattern formed most likely by dislocation glide in the {100} plane. The LPO measured in MgGeO₃-pPv deformed in axial compression at megabar pressures indicate that deformation mechanisms are more complex than previously thought. But these first experimental results on a MgSiO₃ analogue suggest that post-perovskite could indeed develop significant preferred orientation and seismic anisotropy during deformation in D".
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8162 Rheology: mantle (8033)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005