摘要：

We have used the geodynamic modelling software CitcomS 3.0 to model the surface evolution of Australia since 140Ma and constrain the location of the Cretaceous aged subduction zone that paralleled its eastern margin. Australia's paleogeography is known to have been profoundly affected by mantle convection processes. Eastward passage of the Australian plate over subducted slab material induced negative dynamic topography in eastern Australia, causing widespread time-dependent subsidence and formation of a vast epeiric sea during a eustatic sea-level low. Although there is a considerable amount of geological evidence for active convergence between Australia and the paleo-Pacific at this time, the exact location of the subduction zone has remained elusive. To constrain the location of subduction we tested two end-member models, one with the subduction zone directly east of Australia's reconstructed continental margin, and an alternative model with subduction translated 23° east. Our forward geodynamic models incorporate a rheological model for the mantle and crust, plate motions since 140Ma and evolving plate boundaries, implemented in the GPlates software. While mantle rheology affects the magnitude of surface vertical motions, the timing of surface uplift and subsidence depends critically on plate kinematic reconstructions and plate boundary geometries. Simulations with subduction proximal to the coast resulted in accelerated basin subsidence delayed by 20Myr compared with tectonic subsidence from well data. However this timing offset was reconciled when subduction was shifted eastward. Comparisons between whole mantle seismic tomography images and equivalent model temperature cross-sections validate our proposed eastward shift in subduction. Finally an absence of subduction zone volcanism along Australia's east coast in the Early Cretaceous supports our conclusion that a back-arc basin existed east of Australia during the Cretaceous.

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