Post-Orogenic Cooling History of Eastern South Australia from Apatite FT Thermochronology

Abstract

An apatite fission track (FT) study of shallow borehole and outcrop samples from the Cambrian Arrowie Basin and Late Proterozoic Flinders Ranges sedimentary rocks, and the underlying Early to Mid Proterozoic basement rocks of the Curnamona Craton of eastern South Australia, yields ages of 200–350 Ma and mean track lengths of 11–14 μm. Forward modelling of the data suggests at least two periods of significant cooling subsequent to the extensive Early Palaeozoic Delamerian Orogeny. Regionally, these represent cooling since ~400 Ma from temperatures >110°C via an estimated minimum of ~2.5 km denudation, although local denudation may have attained 4–5 kms. Although the time-temperature cooling paths of individual samples may be poorly constrained and variations in the quality of data set exists, some regional coherence is apparent. Late Palaeozoic cooling, probably related to the Alice Springs Orogeny, is preserved ubiquitously throughout the region. The cooling affects of denudation related to this episode have not been reported in southern Australia and were previously believed to have been predominantly confined to central Australia and eastern Australia, where it is known as the Kanimblan Orogeny. A second, less well constrained period of regional cooling is suggested for the mid Cretaceous to Tertiary, probably in response to kilometre scale denudation. This cooling is of smaller magnitude and less well constrained in its timing, and as such is difficult to resolve in detail. This episode is believed to be associated with intraplate stresses related to the reconfiguration of the Australian plate and its margins during this time.