Intraplate deformation in central Australia, the link between subsidence and fault reactivation

Central Australia has experienced two intraplate orogenic events involving significant north-south shortening: the late Neoproterozoic to Early Cambri an Petermann Orogeny and the Devonian to Carboniferous Alice Springs Orogen y. In each event pre-existing structures inherited from Mesoproterozoic ter rain amalgamation were reactivated and basement rocks exhumed from beneath thick sedimentary successions accumulated in the Centralian Superbasin. The pattern of fault reactivation during these events shows a striking similar ity to the pattern of subsidence in the overlying basin. Immediately prior to the Petermann Orogeny, the Centralian Superbasin was thickest in the vic inity of the Musgrave Block, the region in which deformation was subsequent ly localised. At the same time crustal scale faults elsewhere in central Au stralia that were covered by a relatively thin sheet of sediment remained i nactive despite being favourably oriented to accommodate the north-south sh ortening. Between the Petermann and Alice Springs Orogenies, subsidence pat terns shifted, such that fault systems in the Arunta Block and also those i n the southern Musgrave Block were buried by significant thicknesses of sed iment, whereas the major structures that were exhumed during the Petermann Orogeny were not significantly buried. During the Alice Springs Orogeny rea ctivation once again occurred along the most deeply buried faults, even in the instances where those faults had remained inactive during the earlier P etermann Orogeny. Importantly the major Petermann-aged structures that were not buried during renewed subsidence remained inactive during the Alice Sp rings Orogeny. The record of reactivation implies that the presence of pre- existing crustal-scale faults alone was insufficient to localise deformatio n. Rather, fault reactivation appears to have required a priming process th at modulated the strength of the lithosphere on a regional scale. The corre spondence between the distribution of basement fault reactivation and subsi dence patterns during both the Petermann and Alice Springs Orogenies implie s a link between relatively thick sedimentation and long-term lithospheric weakening. We show that this Link is compatible with the thermal effects of a thick sedimentary blanket. In the context of central Australia the mecha nical impact of basin formation is likely to be enhanced by the presence of regionally elevated heat production in the Proterozoic basement. (C) 1999 Elsevier Science B.V. All rights reserved.