Modelling dislocation cores in Forsterite
Abstract
Olivine (Mg,Fe)2SiO4 is considered as the main constituent of the Earth's upper mantle (down to 410 km deep). The rheology of, and convection in, the upper mantle is therefore controlled by the deformation mechanisms of this mineral. Numerous experimental studies have been undertaken leading to a good description of the deformation mechanisms and rheological properties of this mineral at ambient pressure. However, recent studies have show that [001] glide is enhanced over [100] glide when pressure increases or when trace amounts of water are dissolved in the crystals. These observations have a lot of implications on our understanding of the rheology of the upper mantle and call for a more detailed description of the dislocation cores and dynamics. The Peierls-Nabarro (PN) model including generalized stacking fault energies is a privileged tool to calculate core structures at a remarkably low cost. Moreover, the PN model, which is usually restricted to the description of planar cores, is very adapted to look for the most mobile core configurations. However, dislocation cores may exhibit distinct, low-energy, configurations that are not described by the PN model. We present here new calculations based on full atomistic calculations (using the THB1 potential) and a method coupling Peierls-Nabarro and element-free Galerkin methods. These techniques expand the possibilities of previously reported calculations, in particular in permitting modeling 3D dislocation cores. We show that, [100] dislocations may exhibit non collinear dissociation in the (010) plane following the reaction [100] = 1/6[3 0 1] +1/6[3 0 -1]. We also discuss several possible core structures for [001] screw dislocations, including non-planar core spreadings.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMMR14A..09C
- Keywords:
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- 3902 Creep and deformation;
- 3904 Defects