Palaeomagnetism and terranes in the Lachlan Orogen

Abstract

Recent ideas on the structural development of the Lachlan Orogen have interpreted fold and fault geometry in terms of thrust and strike-slip tectonics, in which steep surface faults shallow with depth to sole into subhorizontal detachments in the upper and middle crust. This concept of thin-skinned tectonics has provided a new framework for the generation of terrane models in the orogen involving translation and possible rotation of crustal blocks. These conceptual models should be tested, with palaeomagnetisrn being potentially the best tool with which to do this. Previous palaeomagnetic work in the Lachlan Orogen has, however, highlighted several barriers to obtaining successful palaeomagnetic results. Problems caused by late Palaeozoic and Mesozoic overprints, multiple deformation, uncertainty about deformation ages, and uncertainty about the Australian Apparent Polar Wander Path all need to be overcome before models of terrane accretion, some of which are described here, can be successfully tested.