Development of anisotropic microstructures by dynamic recrystallization in the crust and mantle

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Dynamic recrystallization (DRX) is characterized by cyclic events nucleation and grain growth during plastic deformation. The evolution of grain size distribution in dynamic recrystallization was investigated by a stochastic model of nucleation-and-growth. Scaling relations representing characteristic grain size and recrystallization cycle were derived from nucleation rate and growth rate. The grain size evolve from an initial distribution to a steady-state one that is approximated by a lognormal distribution. A universal relation between deformation conditions (i.e., stress and temperature) and the steady-state grain size were formulated for recovery creep of minerals. The influence of DRX on texture (or lattice preferred orientation, LPO) development is an important issue in considering seismic anisotropy in the Earth mantle. Since a grain with 'favorable' orientation (soft grain) has larger dislocation energy than that with 'unfavorable' orientation (hard grain), soft grains are replaced with hard grains by grain boundary migration. Therefore, the LPO produced by crystalline slip becomes weak or diminished by grain growth. On the contrary, strain-free nuclei have nearly the same orientation as their host grains, hence nucleation would enhance the LPO dominated by soft grains. Textures between the above two end-members are possible for DRX