Deformation in the South Australian Craton: >1 Ga of intraplate activity

Active intraplate seismicity has often been related to either anomalously high heat flow within the crust or pre- existing zones of weakness. Located in the central part of the Australian plate, more than 1000 km from the nearest active plate-boundary, the South Australian Craton has a long history of intraplate deformation from the Neoproterozoic to the Quaternary. Ongoing intraplate deformation occurs in a zone of moderate seismic activity (magnitudes <6.0) that generally follows the trend of the Neoproterozoic Adelaide "Geosyncline". Anomalously high heat flow observations have been used to suggest that seismicity is concentrated where the crust is thermally weakened by high heat producing granites within the buried cratonic basement. Here we use surface geology together with gravity and magnetic data to produce cross-sections that constrain the nature of buried basement structures in this seismically active area. A spatial analysis of earthquakes suggests seismicity is localized on basement structures that juxtapose rocks with significantly different petrophysical properties. Hence seismicity is not solely related to high-heat producing granites in the South Australian Craton. For example, a splay of seismicity along the Kalinjala shear zone suggests that this ~1.7 Ga shear zone remains a zone of crustal weakness that is unrelated to elevated heat flow. Our observations highlight the strong link between the architecture of the basement and intraplate seismicity in cratonic areas.