New constraints on the neotectonic stress pattern of the Flinders and Mount Lofty Ranges, South Australia

Abstract

The majority of published in-situ stress information in the Australian continent is confined to petroleum provinces where industry technologies facilitate the capture of contemporary crustal stress information. In contrast, the stress pattern of non-petroleum regions such as the Flinders and Mount Lofty Ranges in South Australia, where intraplate deformation is localised, has not been investigated comprehensively so far. The ongoing activities of the mining industry in South Australia has enabled us to access recently drilled boreholes for image logging techniques that have typically been under-utilised by the mineral sector. Herein, we conduct stress analysis by analysing borehole image logs from 16 boreholes in the basement rocks of South Australia as well as two geothermal wells and one coal seam gas well in South Australia’s northern Flinders Ranges, the Gawler Craton and the Eyre Peninsula. The resulting dataset of stress orientations is further accomplished by including recent seismological observations, which provide crustal stress information derived from focal mechanism solutions. The results of this study suggest a regional E–W orientation of the maximum horizontal compressive stress that is consistent with numerous observed neotectonic structures in this region. The focal mechanism solutions in this study suggest that the majority of events occur in a thrust faulting stress regime, which is consistent with the observed Quaternary fault scarps. However, our data compilation also indicates the presence of strike-slip and normal faulting stress regimes in the region, which has not been suggested extensively before this study.