Abstract
Knowledge of the deformation mechanisms of (Mg,Fe)2SiO4 olivine is important for the understanding of flow and seismic anisotropy in the Earth’s upper mantle. We report here a numerical modelling at the atomic scale of dislocation structures and slip system properties in Mg2SiO4 forsterite. Our study focuses on screw dislocations of [100] and [001] Burgers vectors. Computations are performed using the so-called THB1 empirical potential set for Mg2SiO4. Results of dislocation core structures highlight the primary importance of the (010) plane for [100] slip dislocations. For [001] dislocations, we confirm the occurrence of a stable narrow core that evolves into transient planar configurations to glide in (100) and (010). Such configurations suggest a locking–unlocking mechanism.
Highlights
It is nowadays well accepted that convection in the upper mantle is constrained by the plastic behaviour of olivine (Mg,Fe)2SiO4, one of its main constituents
Based on neighbours’ cations analysis, the core of the [100] screw dislocation shows a clear tendency of spreading in (010) with a core centre located between SiO4 tetrahedra at the M2 site
Molecular static calculations relying on the THB1 potential have been undertaken to study dislocation core structures and slip in Mg2SiO4 forsterite
Summary
It is nowadays well accepted that convection in the upper mantle is constrained by the plastic behaviour of olivine (Mg,Fe)2SiO4, one of its main constituents Seismological observations, such as seismic anisotropy, can be related to the development of lattice-preferred orientations, and inform us about flow in the mantle The dislocations with [001] Burgers vectors usually exhibit straight screw segments (Phakey et al 1972, Durham et al 1977, Evans and Goetze 1979, Darot and Gueguen 1981, Gaboriaud et al 1981, Wang et al 1988). For temperature above 1200 °C, transmission electron microscope (TEM) investigations (Durham et al 1977, Gueguen and Darot 1982) show that, in (010), [100] dislocations exhibit long straight edge segments while the screw components appear to be much shorter and curved
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