Origin of the New England Oroclines, eastern Australia

During most of the Paleozoic, the Australian continent has occupied a tectonic position between the Tethys Ocean in its northern boundary and the Circum-Pacific (Panthalassan) subduction zones in the east. The latter has been subjected to alternating episodes of trench advance and trench retreat, as expressed, in the Australian Tasmanides, by changes from accretionary processes to rifting and S-type magmatism. Geological observations from the easternmost and youngest component of the Tasmanides, the New England Orogen, show that this orogenic belt forms a strongly contorted ear-shaped structure, delineated by a number of early Paleozoic to early Permian tectonic elements. Bending and fragmentation of the continental margin commenced in the early Permian, at ~300 Ma, and was associated with the development of extensional sedimentary basins, large vertical-axis block rotations and oroclinal bending. In this work, we constrain the geometry and kinematics of the New England Oroclines by providing new structural, geochronological and paleomagnetic data from key localities along the bent system. We show that the process of oroclinal bending was intimately linked to the development of backarc sedimentary basins, suggesting that extensional tectonics may have played a major role in the formation of the oroclines. This may indicate that the process of oroclinal bending in eastern Australia was controlled by trench retreat and slab segmentation, similarly to the modern tectonics of the SW Pacific and Mediterranean regions. In the context of Paleozoic Australia, it is possible that such complex plate boundary processes originated from the kinematic interaction between the Tethyan and circum-Pacific systems.