Tectonic strain in some volcanic, sedimentary, and intrusive rocks near Canberra, Australia: A comparative study of deformation fabrics

Abstract

A study of several strain features (including grain shape, texture, and crystallographic orientation) in a series of deformed sedimentary, volcanic, and intrusive rocks near Canberra indicates that intracrystalline and intergranular movements took place during deformation. The relative importance of these two types of movement in each rock type was dependent on the relative values of intergranular cohesion and yield strengths of individual grains. The shape of strain markers indicates the directions of rock flowage, but can only be used to determine the amount of rock flowage if the yield strength of these markers was the same as that for the rock as a whole, and if there was no differential movement between marker and matrix. Several features of the fabrics of these rocks were used to determine whether or not differential movement had occurred between the groundmass and the grains chosen as strain markers. This facilitated a comparison between different strain markers in each rock type and aided in determining the relative importance of intergranular and intracrystalline movements.