Did rifting on Australia’s Southern Margin result from tectonic uplift?

Subsidence analyses from Australia’s southern margin are used to investigate the idea that rifting on the margin was caused by an extensional lithospheric stress field induced by a hot thermal plume impinging on the base of the lithosphere from beneath. The continental lithosphere is modelled as a thin sheet with depth‐dependent rheology; the model does not explicitly include elastic, flexural, or thermal stresses. The excess buoyancy of a thermal plume pushes the lithosphere upward by as much as 1 km, thereby increasing its potential energy. If the horizontal components of lithospheric stress are fixed at some distant plate boundary (the lithosphere is a stress guide), the lithospheric stress field above the plume will produce horizontal extension that may ultimately be followed by continental separation and seafloor spreading. The uplift is modelled by a time‐dependent function which increases smoothly from zero to its peak value and then decreases back to zero. Using a plausible mantle rheology, the amount of extension inferred at well sites on the margin (typically 20% to 30% extension) is explained by uplift of the lithosphere to approximately 900 m, with a subsequent decay of the uplift over a period of approximately 60 m.y. The rise time of the uplift function is poorly constrained. In the uplift model, extension occurs in the subaerial environment during the late Jurassic ‐ early Cretaceous. The initial stage of rapid subsidence observed at most well sites on the margin is due in large part to decrease of the vertical stress anomaly caused by the decay of the thermal plume (or by the lithosphere moving away from above it). The rapid subsidence is followed by very gradual continued subsidence attributed to cooling of the extended lithosphere, as in previous studies.