Integrated geophysical appraisal of crustal architecture in the eastern Lachlan Orogen

Abstract

Forward modelling of potential field data, combined with new geological mapping and deep seismic reflection transects acquired by the Australian Geodynamics Cooperative Research Centre (AGCRC), has led to testing of robust crustal architectural models for the eastern Lachlan Orogen of New South Wales. This integrated analysis has led to new subsurface inferences unlikely to be deduced solely from any of the individual datasets used. The overall Palaeozoic history of the eastern Lachlan Orogen implied by the integrated analysis of geophysical and geological datasets, involves: formation of an Ordovician oceanic island arc; early Silurian thin-skinned east-directed overthrusting of a continental backarc basin over the arc; generation of Silurian granites due to crustal thickening; early Silurian to early Devonian rifting, resulting in the dismemberment of the deformed arc-basin complex, and formation of a series of arc fragments with intervening thin basins; tight, asymmetric folding of these basins during the Early to Mid Devonian, with some granite magmatism; extensive Carboniferous thin-skinned thrust stacking involving both east-, and west-directed transport, and slicing of the upper structural level of earlier antiformal stacks, together with granite roof zones; and final granitic arc magmatism during amalgamation with the New England Orogen.