The numerical simulation of microstructure

This review discusses the attempts that have been made by geologists to numerically simulate the evolution of microstructures in rocks. The strengths and weaknesses of the differing techniques are compared and equivalent materials science results are included. In particular we focus on the application of techniques that have been used to predict texture development, grain boundary geometries, deformation in one and two-phase systems and crystal growth. Jessell & Bons, Numerical simulation of microstructure page 3 The role of deformation in modifying structures can be seen at all scales, from the formation and movement of dislocations in single grains to changes in the structure of the whole Earth (Hobbs et al. 1976; Poirier 1985; Passchier & Trouw 1996). Attempts to simulate the evolution of these structures at each scale have been undertaken, from molecular dynamics at the atomic scale (Schiøtz et al. 1998; Yamakov et al. 2001), through to simulations of mantle convection (Houseman 1988; Moresi & Solomatov 1995). At the grain scale an understanding of the coupling of deformation processes, mechanical properties and microstructural evolution underpins our ability to correctly interpret natural microstructures in terms of rock history and to develop relevant geodynamic models. The numerical simulation of microstructures in geological materials has progressed in parallel with techniques developed in the wider materials science community (see Raabe 1998 for a comprehensive bibliography). In recent years there has been an upsurge in interest in this field due to the easy access to powerful computers. Equally important has been the introduction of new measurement techniques such as Orientation Imaging Microscopy (OIM) and Electron Backscattered Diffraction (EBSD) (Lloyd and Freeman 1991; Panozzo-Heilbronner & Pauli 1993; Fueten 1997; Leiss et al. 2000). These techniques allow us to systematically characterize the grain boundary topologies and textures of rocks with relative ease and in much more detail (Trimby et al. 1998), thus provoking us to rethink what microstructural parameters we should use as indicators of specific processes. It is beyond the scope of this review to describe in detail the numerous numerical techniques that have been developed to simulate microstructure evolution. Instead we will focus on their application to the simulation and prediction of some geologically important microstructures, Jessell & Bons, Numerical simulation of microstructure page 4 namely: texture (lattice preferred orientation) development; grain boundary geometries; deformation in two-phase systems and crystal growth. Numerical simulation of microstructures