The simulation of fabric development in plastic deformation and its application to quartzite: The model

Abstract

The Taylor-Bishop-Hill model for polycrystalline deformation has been applied as the basis of a computer program for simulating the development of preferred crystallographic orientations in deforming rocks in which the predominant mode of deformation is dislocation glide within the grains. The model assumes homogeneous deformation on the scale of the grains and rigid-plastic flow obeying Schmid's critical resolved shear stress law for the glide systems. The input data for the simulation are the initial orientation distribution, the set of possible glide systems and their relative critical shear stresses, and the details of the deformation including its path, which can involve non-coaxial deformation histories in the general case. The analysis is applied to model quartzites in which four possible choices of glide systems and their critical resolved shear stresses are considered, for three different deformations. Some of the simulated fabrics bear close similarity to observed fabrics, suggesting that fabric development as a result of rotation of crystal axes during dislocation glide is potentially an important geological process, and that the Taylor-Bishop-Hill model is suitable for analyzing it. From the profound influence of deformation history on the simulated fabric and the sensitivity of the fabric to the choice of glide systems and their relative critical shear stresses, important possibilities are suggested for gaining information about geological environment and deformation history from the analysis of natural deformation fabrics.