Microfabric of Tectonites from the Wyangala Dam Area, New South Wales, Australia
The microfabric of tectonites from the Wyangala Dam area, New South Wales, is characterized by the presence of linear fabric domains in which the quartz grains possess a similar orientation of [0001]. In folded rocks, there is a close relationship between the position of a certain domain and heterogeneities in the deformation. Thus, whether the fabric domains are relict primary grains (which have been replaced by an aggregate of smaller grains) or are features totally imposed by the deformation, they appear to occupy sites of heterogeneity in the deformation. It is argued that the fabric has been produced by movements which were heterogeneous but such that deformation of a certain kind was restricted to flat, rod-shaped regions. The movement picture in each of these regions possessed a unique symmetry plane and it is suggested that the amount of strain may have differed from one type of domain to another. The microstructure of the rocks studied is consistent with adjustment of grain boundaries under the influence of interfacial tension. In particular, it is possible that the dimensional orientation of quartz in these rocks may be due to anisotropic inhibition of grain boundary migration by a dispersed phase of white mica with a preferred orientation of {001}.