HR: 17:00h
AN: MR34A-05 INVITED    [Abstracts]
TI: First-Principles Study of Mg-Perovskite Deformation Mechanisms Under Lower Mantle Conditions
AU: * Carrez, P
EM: philippe.carrez@univ-lille1.fr
AF: Lab. de Structure et Proprietes de l Etat Solide CNRS-UMR 8008, Universite de Lille 1, Villeneuve d'Ascq, F-59655, France
AU: Ferre, D
EM: denise.ferre@univ-lille1.fr
AF: Lab. de Structure et Proprietes de l Etat Solide CNRS-UMR 8008, Universite de Lille 1, Villeneuve d'Ascq, F-59655, France
AU: Cordier, P
EM: patrick.cordier@univ-lille1.fr
AF: Lab. de Structure et Proprietes de l Etat Solide CNRS-UMR 8008, Universite de Lille 1, Villeneuve d'Ascq, F-59655, France
AU: Mainprice, D
EM: david.mainprice@gm.univ-montp2.fr
AF: Geosciences Montpellier CNRS-UMR 5243, Universite Montpellier II, Montpellier, F-34095, France
AU: Tommasi, A
EM: andrea.tommasi@gm.univ-montp2.fr
AF: Geosciences Montpellier CNRS-UMR 5243, Universite Montpellier II, Montpellier, F-34095, France
AB: It is widely accepted that MgSiO₃ Perovskite is one of the most abundant minerals of the Earth's mantle. Therefore, the convective flow and the seismic properties of the Earth's deep mantle should depend strongly on the mechanical and physical properties of this mineral. Global studies of seismic anisotropy of the lower mantle suggest that the lower mantle is essentially isotropic. These results are commonly interpreted as indicating that diffusion creep dominates in the lower mantle. However, recent studies on olivine at high-pressure have shown that isotropic seismic properties do not necessarily imply the absence of Crystal Preferred Orientation (CPO) and should not be considered as a strong evidence for diffusion creep (Mainprice et al. Nature 2005). To evaluate the role of plastic deformation and lattice preferred orientation in the development of seismic anisotropy, it is important to have a good understanding of the deformation behavior of minerals at conditions of the Earth's deep mantle. Whereas, this information is generally difficult to obtain through experiments, atomic scale modeling of dislocation properties in minerals have recently shown that relative activities of slip systems in minerals can be predicted (Carrez et al. Nature 2007, Ferre et al. PEPI 2007). In this study, we propose a theoretical modeling of dislocation glide systems in MgSiO₃ Perovskite based on ab initio calculation and the Peierls-Nabarro model. These results are used as an input for a polycrystalline Visco-Plastic Self-Consistent (VPSC) models of CPO development. Our results show that clear CPO can develop. The plastic anisotropy of perovskite and the texture development remain fairly similar in the pressure range 30- 100 GPa with a dominant [010](100) slip system. Our results are in good agreement with recent experimental results of Wenk et al. (EPSL 2004). The seismic anisotropy of MgSiO₃ Perovskite aggregates is calculated using the CPO predicted from the ab initio/VPSC model for a given shear strain and single crystal elastic constants at lower mantle pressures and temperatures (ranging from P=30 to 100 GPa and T=1500 and 3500 K). At the top of the lower mantle, we predict a relatively weak anisotropy for P and S waves, with higher values for P waves (2.9% for P waves and 1.6% for S waves at 1500K ). The weak nature of the predicted seismic anisotropy is in general agreement with global seismology observations, without the need to involve mechanisms that do not produce CPO.
DE: 0545 Modeling (4255)
DE: 3902 Creep and deformation
DE: 3904 Defects
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting