STRUCTURE OF THE COBAR BASIN, NEW-SOUTH-WALES, BASED ON SEISMIC-REFLECTION PROFILING

The Cobar Basin in central western New South Wales is a mineral-rich E arly Devonian basin typical of those that characterize the Siluro-Devo nian history of the Lachlan Orogen of southeastern Australia. One hund red and seventy kilometres of seismic profiling in three lines across the basin have shown it to be asymmetrical in shape with an east-dippi ng western margin that is steeper than the moderately west-dipping eas tern margin. Maximum basin thickness is around 6 km, but there are sig nificant thickness changes, especially from south to north, which refl ect the effect of synsedimentary faulting. Seismic profiling suggests that the basin deformed by thin-skinned tectonics; postulated strike-s lip effects were not visible on the sections. The seismic profiling ha s, for the first time, imaged the western synrift basin margin which i s generally not exposed. Strain variations during deformation along th is edge were taken up by the formation of a major jog ('dog-leg) which has propagated into the basin as a tear fault. Intrabasinal tears, as well as thrusts, which link into one or more detachments, provide pot ential pathways for mineralizing fluids during basin inversion.