Oroclines of the southern New England Orogen, eastern Australia

Abstract

A series of tight bends (oroclines) are recognised in the late Paleozoic-early Mesozoic southern New England Orogen between Brisbane and Newcastle, but their exact geometry and tectonic evolution are still debated. This contribution provides an outline of the different tectonic elements within the orogen and the relationships of these elements with the oroclinal structure. Pre-oroclinal tectonic elements were derived from a Devonian-Carboniferous subduction zone, and include forearc basin terranes and accretionary wedge rocks that are separated from each other by a narrow belt of serpentinites and high-pressure rocks. Rocks are predominantly steeply dipping and their map-view pattern delineates three bends: the Z-shaped Texas and Coifs Harbour oroclines in the north and the U-shaped Manning Orocline in the south. During the early Permian (298-288 Ma), the area was affected by widespread, mostly S-type, magmatism that heralded a period of crustal extension accompanied by the formation of sedimentary rift basins. The spatial distribution of early Permian granitoids mimics the shape of the oroclines, which further defines a fourth bend, the Nambucca Orocline. Whether these curvatures formed by bending of a quasi-linear belt, or as primary early Permian arcuate features, is an unresolved question that warrants further paleomagnetic, geochronological and structural investigations.