Mechanical stability of the Redbank Thrust Zone, central Australia: Dynamic and rheological implications

Deep seismic reflection profiling and other studies indicate that the Moho has been significantly displaced by intracratonic deformation on the Redbank Thrust Zone in central Australia. A two-dimensional finite-element model of the thick-skinned crustal structure of the Redbank Thrust Zone shows that the gravitational stresses generated by the distribution of crustal masses are in agreement with the tectonic and seismic quiescence of the area. Rock failure is concentrated in the downthrusted, and therefore rheologically weakened, crustal segments. Conversely, the upthrusted slices of lower crust and upper mantle undergo little deformation and no failure and thus constitute a mechanically strong whole-crustal core. The presence of north-south oriented intraplate stresses derived from far-field plate boundary forces does not contribute to the inferred mechanical equilibrium of the crust in central Australia. The results may have implications for the mechanical stability of intracratonic thick-skinned crustal structures elsewhere, and for the long-term strength of continental lithosphere in general. The models, however, do predict the possibility. of intraplate seismicity in response to small changes in tectonic stress, since parts of the crust are already at or close to the failure limit.