Fabric domains in quartz mylonites: localized three dimensional analysis of microstructure and texture

Abstract

Fabric domains of a quartz vein deformed under greenschist facies conditions are analysed with domainal X-ray texture goniometry, optical microscopy, computer integrated polarization microscopy (CIP) and shape analysis in two mutually perpendicular sections. The analysed domains consist of large non-recrystallized deformed clast fragments, prolate non-recrystallized ribbon grains and prolate recrystallized domains. In terms of texture, monomaximal and polymaximal domains have been distinguished. Pronounced partitioning of deformation is observed between these domains. This strain partitioning asks for caution when making kinematic inferences for fault zones based on a study of domainal fabrics. Domains persist as fabric elements up to high strains. This emphasizes the often neglected role of a non-random initial fabric. Neighbouring domains with alternating c-axis orientations and grain boundary preferred orientations, indicating opposing senses of shear, occur in both sections.The bulk texture is controlled by clast and ribbon domains, rather than being strictly deformation-induced. We infer that prolate elongation of clasts and ribbons is achieved mainly by combined prism and basal slip. Recrystallized domains are characterized by different textures. They are deformed by intracrystalline slip, combined with grain boundary migration and sliding. Inclined preferred grain boundary orientations are continuously maintained by grain boundary migration.