STRUCTURE OF THE WESTERN ALBANY MOBILE BELT (SOUTHWESTERN AUSTRALIA) - EVIDENCE FOR OVERPRINTING BY NEOPROTEROZOIC SHEAR ZONES OF THE DARLING MOBILE BELT

The Albany Mobile Belt is dominated by ductile fabrics and regional structures formed during progressive dextral transpression at similar to 1190 Ma (D-1) resulting from NW-SE to NNW-SSE shortening and represents the oblique convergence between the West Australian and East Antarctic shields. Deformation was accompanied by metamorphism up to granulite facies and granitoid intrusion. Neoproterozoic extension and progressive deformation within a sinistral transcurrent to transtensional shear zone in the Leeuwin Complex of the southern Darling Mobile Belt may be contemporaneous with transpressional shearing along the Donnybrook-Nannup Shear Zone on the western Yilgam Craton margin, During this Neoproterozoic event, E-W Mesoproterozoic trends in the western Albany Mobile Belt have been rotated into a N-S orientation. Ductile reactivation and overprinting of Mesoproterozoic structures is accompanied by retrogression of granulite facies assemblages to amphibolite facies, migmatisation and pegmatite and granitoid intrusion. In demonstrating that the N-S orientation of the western Albany Mobile Belt results from a younger event, a continuation of this mobile belt is expected in northeast India, whilst a continuation of the Darling Mobile Belt may exist in the Mirnyy area of East Antarctica. Folding and the formation of conjugate brittle-ductile shear zones during NE-SW shortening and Early Cambrian conjugate faulting and jointing resulting from ESE-WNW shortening is common io both the western Albany Mobile Belt and Leeuwin Complex.