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

动态再结晶(DRX)以塑性变形过程中的循环形核和晶粒长大为特征。采用形核长大随机模型，研究了动态再结晶过程中晶粒度分布的演化规律。由形核速率和生长速率推导出表征特征晶粒度和再结晶周期的标度关系式。晶粒度由初始分布演化为符合对数正态分布的稳态分布。建立了矿物回复蠕变的变形条件(即应力和温度)与稳态晶粒度之间的普遍关系。DRX对结构(或晶格择优取向，LPO)发展的影响是考虑地幔地震各向异性的一个重要问题。由于“有利”取向(软晶)的位错能大于“不利”取向(硬晶)的位错能，软晶通过晶界迁移被硬晶取代。因此，晶体滑移产生的LPO随着晶粒的长大而变弱或减弱。相反，无应变晶核与其主晶具有相同的取向，因此成核会增强以软晶为主的LPO。对于DRX，上述两个终端部件之间的纹理是可能的

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