Sedimentary thickness variations and deformation intensity during basin inversion in the Flinders Ranges, South Australia

The central and northern parts of the Adelaide fold belt in the Flinders Ra nges, South Australia, consist of a sequence of Neo-Proterozoic-Cambrian se diments overlying a Meso-Proterozoic basement complex. both of which were m ildly deformed in an intracratonic setting during the similar to 500 Ma Del amerian orogeny. The fold belt lies within a prominent heat Bow anomaly (av erage heat flows of similar to 90 mWm(-2)) reflecting extraordinary enrichm ents in heat producing elements in the Meso-Proterozoic basement, suggestin g that anomalous thermal regimes may have been significant in localising De lamerian deformation. However, spatial variations in deformation intensity correlate more closely with variations in the thickness of the sedimentary sequence than with observed variations in heat Bow. suggesting that the thi ckness of the sedimentary blanket plays a crucial role in localising Delame rian deformation during basin inversion. We use simple numerical models of lithospheric strength to investigate the potential role of sedimentary thic kness variations on the distribution and style of deformation, focussing on the impact of a variable thickness sediment pile deposited above a 'radioa ctive' basement. We show that for thermal parameters appropriate to the Fli nders Ranges, Moho temperatures may vary by similar to 25-30 degrees C for every additional kilometre of sediment. For a 'Brace-Goetze` lithospheric r heology, controlled by a combination of temperature-dependent creep process es and frictional sliding, the observed variations in thickness of the sedi mentary pile are sufficient to cause dramatic reductions in the vertically- integrated strength of the lithosphere (by many orders of magnitude), there by providing a plausible explanation for observed correlation between sedim ent thickness and deformation intensity during basin inversion. (C) 1998 El sevier Science Ltd. All rights reserved.