EARLY PALEOZOIC FORELAND THRUSTING AND BASIN REACTIVATION AT THE PALAEO-PACIFIC MARGIN OF THE SOUTHEASTERN AUSTRALIAN PRECAMBRIAN CRATON - A REAPPRAISAL OF THE STRUCTURAL EVOLUTION OF THE SOUTHERN ADELAIDE FOLD-THRUST BELT

Regional and detailed structural mapping, kinematic analysis and balancing and restoration of cross sections has lead to a re-interpretation of the Adelaide Fold Belt in South Australia. In this belt sedimentary rocks of the Late Proterozoic Adelaidean and Early Cambrian Normanville and Kanmantoo sequences were deposited during at least two episodes of subsidence related to major crustal attenuation. Contraction and crustal thickening accompanied by granitoid intrusions are related to the Cambro-Ordovician Delamerian orogeny. During this event both basins were reactivated (''inverted'') and the sedimentary rocks are now incorporated in a WNW-verging foreland fold and thrust belt at the margin of the Proterozoic southeast Australian craton. Maximal shortening of the orogen was around 55%. Within the Adelaidean basin, shortening is dominantly accommodated by major mylonitic shear zones and reverse faults. In the Cambrian Kanmantoo basin, several thrusts are demonstrably reactivated growth faults, across which thickness changes of Cambrian sedimentary rocks are revealed by balancing and restoration of cross sections. Owing to the steep easterly dips of these faults, in the western part of the Kanmantoo basin lateral shortening of up to 58% is largely accommodated by intense folding and fold axial-planar flattening strain. Further east, strain magnitudes wane and the overall shortening of around 30% is accommodated by both, discrete thrust zones and regional folds. The basin reactivation along the Australian part of Gondwana's palaeo-Pacific craton margin reflects the rapid transition from passive to active tectonism, which possibly is a consequence of the disintegration of the formerly conjugate margins of Gondwana and Laurentia.