Evolution of Anisotropy in Olivine Polycrystals

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• Neil Ribe (CNRS (Centre national de la recherche scientifique); Université Paris Saclay)
• Friday 15 April 2016, 13:30-14:30
• Seminar Room 1, Newton Institute.

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MIMW02 - From the grain to the continuum: two phase dynamics of a partially molten, polycrystalline aggregate

Progressive deformation of upper mantle rocks via dislocation creep causes their constituent crystals to take on a non-random orientation distribution (crystallographic preferred orientation or CPO ) whose observable signatures include shear-wave splitting and azimuthal dependence of surface wave speeds. Comparison of these signatures with mantle flow models thus allows mantle dynamics to be unraveled on global and regional scales. However, existing self-consistent models of CPO evolution are computationally expensive when used in 3-D and/or time-dependent convection models. We propose a new method, called ANPAR , which is based on an analytical parameterization of the crystallographic spin predicted by the second-order (SO) self-consistent theory. Our parameterization runs ≈2–6\times 10^4 times faster than the SO model and fits its predictions for CPO and crystallographic spin with a variance reduction >99 per cent. We illustrate the ANPAR model predictions fo r the deformation of olivine with three dominant slip systems, (010)[100], (001)[100] and (010)[001], for three uniform deformations (uniaxial compression, pure shear and simple shear) and for a corner-flow model of a spreading mid-ocean ridge.

This talk is part of the Isaac Newton Institute Seminar Series series.

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