Modelling dislocation cores in Mg2SiO4 wadsleyite at 15 GPa: Comparison with TEM observations
Abstract
Wadsleyite (Mg,Fe)2SiO4 is considered as a major constituent of the transition zone of the mantle (between ca. 410 km and 520 km depth). The rheology of this mineral is thus of primary importance for the dynamics of this important layer of the mantle and for matter exchanges between the upper and the lower mantle. A series of deformation experiments followed by detailed dislocation characterizations at the transmission electron microscope (TEM) have led to a first description of the possible dislocation microstructures in this mineral (see Thurel et al's publications below). The aim of this work is to study numerically the dislocation core structures of Wadsleyite at 15GPa. We use the Peierls-Nabarro (PN) model combined with finite elements methods. Generalized Stacking Faults (GSF) calculated at the atomic scale with the GULP code are used as an input for the PN model. We have considered five slip planes in Wadsleyite: (100), (010), (001), (011) and (101). The PN model is used to determine the core structures of dislocations with [100], [010], [001] and [101] Burgers vectors in the appropriate glide planes. Our numerical results are in good agreement with previous TEM study of Thurel et al.. In particular, we show that [100] glide is the easiest. We also reproduce the dissociation of the [010] dislocation into four partial dislocations and the dissociation of the [101](010) dislocations. E. Thurel and P. Cordier (2003) Plastic deformation of wadsleyite: I High-pressure deformation in compression. Physics and Chemistry of Minerals, 30(5), 256-266. E. Thurel, P. Cordier, D. Frost and S.-I; Karato (2003) Plastic deformation of wadsleyite: II High-pressure deformation in shear. Physics and Chemistry of Minerals, 30(5), 267-270. E. Thurel, J. Douin and P. Cordier (2003) Plastic deformation of wadsleyite: III. Interpretation of dislocations and slip systems. Physics and Chemistry of Minerals, 30(5), 271-279.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMMR21B1794M
- Keywords:
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- 3900 MINERAL PHYSICS;
- 3902 Creep and deformation;
- 3904 Defects