Strain localisation and high-grade metamophism at Broken Hill, Australia: A view from the southern cross area

Abstract

Progressive localisation of strain within Proterozoic high-grade rocks in the Southern Cross area of the Willyama Supergroup, Broken Hill, has resulted in the formation of shear zones of highly strained D2 fabrics separated by less strained D2 zones that preserve pre-tectonic relationships, complex fold interference patterns and abundant pegmatites related to a D1/M1 deformation/metamorphic event. The metamorphic peak (M1) is characterised by biotite-sillimanite-quartz-alkali feldsparplagioclase with garnet or cordierite in metapelites, formed at about 750°C and 400-500 MPa, presumably relatively late in M1, as garnet has overgrown the S1 biotite-sillimanite fabric. The D2 strain is concentr..