HR: 0800h
AN: DI41A-1258    [Abstracts]
TI: Pressure Sensitivity of Olivine Deformation Mechanisms and Implications for Seismic Anisotropy of Deep Upper Mantle
AU: * Couvy, H
EM: helene.couvy@sunysb.edu
AF: Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794 United States
AU: Cordier, P
EM: patrick.cordier@univ-lille1.fr
AF: Laboratoire Structure et Proprietes de l'Etat Solide, Universite de Lille, Villeneuve d'Ascq, 59000 France
AU: Frost, D J
EM: dan.frost@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, 95447 Germany
AU: Heidelbach, F
EM: florian.heidelbach@uni-bayreuth.de
AF: Bayerisches Geoinstitut, Universitaet Bayreuth, Bayreuth, 95447 Germany
AU: Mainprice, D
EM: David.Mainprice@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, Universite de Montpellier II, Montpellier, 34095 France
AU: Tommasi, A
EM: Andrea.Tommasi@dstu.univ-montp2.fr
AF: Laboratoire de Tectonophysique, Universite de Montpellier II, Montpellier, 34095 France
AB: The mechanical behaviour of the Earth's upper mantle and many physical properties such as seismic anisotropy and viscosity are strongly coupled to the rheological properties of olivine, the dominant phase in this region. Until recently, experiments at high temperature and moderate pressure and extensive data on naturally deformed mantle rocks lead to the conclusion that olivine deforms essentially by dislocation creep with dominant slip on the [100](010) system. The predominance of this slip system and the crystallographic preferred orientation (CPO) it produces have been extensively used to explain the strong seismic anisotropy occurring down to 250 km depth. Below this depth, pressure extrapolation was thus necessary to infer mantle rheology. We have carried out a series of high-pressure deformation experiments on polycrystalline samples of olivine at 1300-1400°C and mantle pressures - ranging from 2 to 11 GPa - using the multianvil apparatus and the deformation-DIA. Microstructural investigations show an important pressure-induced change in intracrystalline slip system. At high pressure and high temperature, deformation of olivine is dominated by the [001]{hk0} slip system. We show that [001] slip produces CPOs resulting in extremely low seismic anisotropy, consistent with a fast decrease of seismic anisotropy observed below 250 km. These results raise new questions about the mechanical state of the lower part of the upper mantle and its coupling with layers above and below.
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Study of Earth's Deep Interior [DI]
MN: Fall Meeting 2005