组构数值模拟的原理及其在地学中的应用

Numerical Modeling of Textures in Polycrystals:Theory and Applications in Geosciences

组构是指由岩石塑性变形导致多晶体的结晶学优势取向现象。组构的存在会增加岩石的各向异性,进而可能影响到岩石的后续变形。岩石组构包含了变形类型、运动学、变形环境、流变学特征等信息,因而成为显微构造学的重要内容。组构数值模拟是近年来得到重视的一种组构研究方法,它以晶体塑性理论为基础,利用计算机技术定量地模拟多晶岩石中组构的形成和演化。在晶体塑性理论中,晶体的塑性变形是由滑移系的剪切滑动导致的,由单晶塑性本构关系表征。多晶均匀化模型包括Sachs模型、Taylor模型、自洽模型和有限元模型,它们从不同角度描述了由单晶变形组成的多晶体变形。极图、反极图和取向分布函数被用来显示多晶体中各晶粒的空间取向。目前组构数值模拟在地学中的应用主要体现在各种单相和多相岩石的组构形成、重结晶作用下的组构形成、组构对地幔和地核地震波波速各向异性的影响等方面。

Texture is referred to as the crystallographic lattice preferred orientation （CPO） produced in polycrystalline rock by plastic deformation. The presence of texture would enhance the anisotropy of rock, and most likely influence subsequent deformation, if it happens. A single goal of microstructural analysis is to determine from the texture observed in rock deformation type, kinematics, environment, rheology, and so on. Based on the crystal plasticity theory, numerical modeling is efficient and powerful in calculating the formation and evolution of texture in polycrystalline rocks. Plastic deformation is therein accomplished by an infinite number of slips occurring in the slip systems of each individual crystal. The averaging scheme, such as the Sachs model, the Taylor model, the self-consistent model, and the finite element model, accounts for the response of crystal aggregate to the plastic deformation of each crystal in it. CPO is expressed either graphically in pole figure or inverse pole figure, or quantitatively using the orientation distribution functions. Numerical modeling of textures has been applied to geosciences for decades, for example, in the development of monophase and polyphase rock textures and of textures formed due to dynamic recrystallization, and in the influence of textures in the seismic anisotropy of the upper mantle and the inner core.