Tectonic and Geodynamic Evolution of the Northern Australian Margin and New Guinea

Abstract

Rapid convergence between the Indo-Australian, Southeast Asian, and Pacific plates in the Cenozoic has resulted in a complex tectonic evolution of Australia’s northern margin. A lack of available geologic data leads to large uncertainties, such as the timing of the Sepik collision with the New Guinea margin, currently constrained to sometime between 50 and 30 Ma. Previous work suggested a link between the Sepik collision and a voluminous fast seismic anomaly presently in the mantle beneath Lake Eyre. Following from previous work, this study uses coupled plate reconstruction and numerical geodynamic models to test 50 Ma and 30 Ma collision timings of the Sepik terrane, along with an upper extent back-arc basin, to further refine our understanding of the origin and trajectory of the slab beneath Lake Eyre and address uncertainties in the plate reconstructions. The results of mantle flow models indicate that the Eocene collision timing (~50 Ma) is more likely than an Oligocene collision (~30 Ma). In addition, dynamic topography results support previous suggestions that dynamic subsidence relating to the down-going Sepik slab has influenced the evolution of the Eyre Basin, with up to ~100 m of dynamic subsidence since ~20 Ma. However, further work is required to address numerical issues relating to rapid thermal diffusion of slab material, and to investigate reasonable trench retreat velocities for intermediate (~3000 km) subduction zone lengths. This work highlights the role of numerical experiments in understanding transient plate-mantle processes and their effect on basin evolution.