HR: 11:35h
AN: MR12A-06    [Abstracts]
TI: Multi-Scale Modeling of Post-Perovskite Deformation Processes: From Atomic Scale to Polycrystal Plasticity
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, 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, 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, Villeneuve d'Ascq, F-59655, France
AU: Mainprice, D
EM: david.mainprice@gm.univ-montp2.fr
AF: Geosciences Montpellier CNRS UMR 5243, Universite de Montpellier II, Montpellier, F- 34095,
AU: Tommasi, A
EM: andrea.tommasi@gm.univ-montp2.fr
AF: Geosciences Montpellier CNRS UMR 5243, Universite de Montpellier II, Montpellier, F- 34095,
AB: The D" layer that extends up to several hundred kilometers at the transition between the silicate mantle and the metallic core is an essential feature of the mantle's convecting system. This layer is known to display a strong and heterogeneous seismic anisotropy. At the same time, seismic velocities change laterally, indicating large thermal and chemical variation. It is generally accepted that D" is essentially composed of (Mg,Fe)SiO₃, which can be found in the Perovskite (Pv) structure or in the post perovskite (PPv) structure depending on the temperature of the region of interest. The interpretation of the origin of the anisotropy of D" is still in debate. Essentially, two propositions appear: strain-induced Crystal Preferred Orientation (CPO) of mineral (MgSiO₃ PPv or (Mg,Fe)O₂) and/or shape preferred orientation (SPO) of inclusions. With the last assumption, to produce azimuthal anisotropy, inclusions have to be inclined or strain-induced CPO has to be invoked. To explore the contribution of CPO due to plastic flow of PPv to seismic anisotropy in the D" layer, we use a multi- scale modeling approach that couple atomistic/continuum models of dislocations at D" pressures to polycrystal plasticity simulations (using a viscoplastic self-consistent (VPSC) model). Indeed to model the development of CPO, we need to determine a fundamental parameter that controls the activity of a dislocation glide system: the critical resolved shear stress (CRSS). Nowadays, dislocation core properties can be calculated from first principles calculation through the Peierls- Nabarro model using the generalized stacking faults approach. Dislocation properties such as planar core spreading and Peierls stresses are thus modeled under a pressure of 120 GPa for 10 potential glide systems of the PPv structure. As lattice friction is commonly considered as the major factor in plastic deformation of minerals, we have then chosen to take the CRSS proportional to the Peierls stresses for additional VPSC simulations. VPSC calculations show that CPO development are very sensible to CRSS, here with a strong alignment of [010] in the shear direction and of (001) in the shear plane, reflecting the high activity of [100](010), [110](001) and [110](11̄0) glide systems. Finally, these results also illustrate that, when several slip systems are activated with similar contributions, is not possible to directly determine the dominant glide system from the pole figures.
DE: 0545 Modeling (4255)
DE: 3902 Creep and deformation
DE: 3904 Defects
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting