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 visco-plastic self-consistent model for crystallographic 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 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.