The microstructural anatomy of a major thrust zone on Fleurieu Peninsula, South Australia

Abstract

Microstructures from a traverse through Early Proterozoic gneiss and Adelaidean and Cambrian metasediments on southern Fleurieu Peninsula, South Australia, show strong mylonitic textures in their common shallowly east‐dipping foliation. The intensity and style of mylonite development is strongly linked to rock type: quartz‐biotite schist has undergone crystal plastic deformation including twinning, deformation banding, intragranular creep, subgrain formation and dynamic recrystallization. Grain boundary sliding and slip on basal planes of cleavage forming micas are dominant in metapelite. Gneiss in the Early Proterozoic inlier shows plastic deformation of quartz augen, brittle deformation of feldspar porphyroclasts and basal slip on phyllosilicates. The Adelaidean calc‐silicate rocks structurally beneath the Early Proterozoic inlier are the weakest unit on the traverse and accommodate the biggest displacement. The sense of shear has been derived statistically from porphyroclast asymmetries, S‐C planes and...