Bending and slicing of eastern Gondwana's continental margin: late Paleozoic to early Mesozoic reconstruction

The SW Pacific is a classic example of "ribbon tectonics" whereby continental fragments were either accreted to the continental margins by subduction processes or separated from it by backarc extension. While the more recent tectonic processes (e.g. the latest Mesozoic and Cenozoic opening of the Tasman Sea), are relatively well constrained, the earlier tectonic history of eastern Gondwana is poorly understood. Here we present results from onshore study in eastern Australia, showing that bending and fragmentation of eastern Gondwana's continental margin in a backarc extensional environment commenced at ~300 Ma, giving rise to large vertical-axis block rotations and oroclinal bending. The subduction zone has subsequently migrated eastward, in a series of episodes of trench rollback and backarc extension, alternating with episodes of contractional and transpressional tectonism. We attribute this behavior to switches between trench rollback and trench advance, controlled by the heterogeneous nature of the subducted oceanic lithosphere.