A Multiscale Numerical Modeling Investigation on the Significance of Flow Partitioning for the Development of Quartz c-Axis Fabrics

摘要

Quartz c-axis fabrics in natural mylonites can vary to such an extent that they apparently give opposite senses of shear in a single thin section. Many hypotheses have been invoked to explain this. Here, we couple our self-consistent multiscale approach for flow partitioning with the viscoplastic self-consistent model for c-axis fabric simulation to investigate quartz c-axis fabric development. Quartz aggregates are regarded as microscale Eshelby inhomogeneities embedded in a macroscale medium whose effective rheology is represented by a hypothetical homogeneous equivalent medium which is assumed to be rheologically isotropic or has a planar anisotropy. We reproduced the observed quartz c-axis fabrics. We found that although the microscale flow fields are distinct from one another and from the macroscale flow, the microscale vorticity in every inhomogeneity has the same sense as the macroscale vorticity. This implies that one can use the average of the microscale vorticity axes determined through the crystallographic vorticity axis analysis to obtain the macroscale vorticity axis. However, quartz c-axis fabrics cannot be used to determine the vorticity number where flow partitioning is significant.