The recognition of curved orogenic belts (oroclines) in modern and ancient tectonic environments provides crucial information for tectonic reconstructions. Using examples from the Mediterranean Sea, it can be shown that the fundamental control on the development of oroclines is the migration of convergent plate boundaries through the processes of indentation, trench retreat, and subduction segmentation (tearing). This conclusion is in contrast to common explanations for the origin of oroclines, which assume that originally linear belts were subjected to buckling in response to orogen-parallel forces. Importantly, if oroclines formed by migrating plate boundaries, then we can enhance the resolution of plate tectonic reconstructions by carefully examine spatio-temporal relationships associated with oroclinal structures.
In this talk I will explore this topic in the Tasmanides of eastern Australia. Previous studies in the Tasmanides have mainly focused on individual “orogens” and “orogenies”, and relatively little attempt has been done to describe spatio-temporal relationships across the whole system. To address this issue, I subdivide the Tasmanides into approximately 75 “building blocks”, each represents an igneous province or a sedimentary basin. Spatio-temporal patterns of these building blocks, combined with information on the timing and extent of contractional and extensional deformation, unravel key features with regards to the evolution of the convergent plate boundary. In particular, it is recognised that the northern and southern parts of the Tasmanides are separated by major crustal-scale structures, which likely represent an original segmentation of the plate boundary. This segmentation likely played a fundamental role in controlling the origin of oroclines during periods of trench retreat and overriding-plate extension.