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Implications for plastic flow in the deep mantle from modelling dislocations in MgSiO3 minerals

机译：MgSiO3矿物位错模拟对深层地幔塑性流动的影响

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摘要

The dynamics of the Earth's interior is largely controlled by mantle convection, which transports radiogenic and primordial heat towards the surface. Slow stirring of the deep mantle is achieved in the solid state through high-temperature creep of rocks, which are dominated by the mineral MgSiO3 perovskite. Transformation of MgSiO3 to a 'post-perovskite' phase(1-3) may explain the peculiarities of the lowermost mantle, such as the observed seismic anisotropy(4), but the mechanical properties of these mineralogical phases are largely unknown(5-7). Plastic flow of solids involves the motion of a large number of crystal defects, named dislocations(8). A quantitative description of flow in the Earth's mantle requires information about dislocations in high-pressure minerals and their behaviour under stress. This property is currently out of reach of direct atomistic simulations using either empirical interatomic potentials or ab initio calculations. Here we report an alternative to direct atomistic simulations based on the framework of the Peierls - Nabarro model(9,10). Dislocation core models are proposed for MgSiO3 perovskite ( at 100 GPa) and post-perovskite ( at 120 GPa). We show that in perovskite, plastic deformation is strongly influenced by the orthorhombic distortions of the unit cell. In silicate post-perovskite, large dislocations are relaxed through core dissociation, with implications for the mechanical properties and seismic anisotropy of the lowermost mantle.
机译：地球内部的动力学很大程度上受地幔对流的控制，地幔对流将辐射热和原始热传导到地表。通过岩石的高温蠕变，可以在固态下实现深层地幔的缓慢搅拌，而岩石的蠕变主要由矿物MgSiO3钙钛矿形成。 MgSiO3转变为钙钛矿后相（1-3）可能解释了最下层地幔的特殊性，如观察到的地震各向异性（4），但这些矿物相的力学性质尚不清楚（5-7） ）。固体的塑性流动涉及大量晶体缺陷（称为位错）的运动（8）。定量描述地幔中的流动需要有关高压矿物中的位错及其在应力下的行为的信息。目前，使用经验性原子间电势或从头算计算无法直接进行原子模拟。在这里，我们报告了基于Peierls-Nabarro模型（9,10）的框架直接原子模拟的替代方法。提出了MgSiO3钙钛矿（100 GPa）和后钙钛矿（120 GPa）的位错核心模型。我们表明，在钙钛矿中，塑性变形受晶胞的正交畸变强烈影响。在钙钛矿后的硅酸盐中，大位错通过岩心解离而缓和，这影响了最下层地幔的力学性质和地震各向异性。

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