Cenozoic Velocity and Topography Change of the Australian Plate Linked to Fossil New Guinea Slab Below Lake Eyre and the Murray-Darling Basin

Abstract

The causes for absolute velocity changes of tectonics plates and changes in continental dynamic topography are challenging because of the interdependence of large-scale geodynamic processes that might drive such change. Here, we unravel a clear spatio-temporal relation between latest Cretaceous-Early Cenozoic subduction at the northern edge of the Australian plate, Early Cenozoic Australian plate motion changes and Cenozoic topography evolution of the Australian continent. We present geological and geophysical evidence for a ~4000 km wide subduction zone, which culminated in ophiolite emplacement and arc-continent collision in the New Guinea-Pocklington Trough region during subduction termination. This coincided with cessation of spreading in the Coral Sea, a ~5 cm/yr decrease in northward Australian plate velocity, and slab detachment. Renewed northward motion of the Australian plate caused it to override the sinking subduction remnant, which we detect with seismic tomography models at 800–1200 km depth in the lower mantle under central-southeast Australia at a position predicted by our absolute plate reconstructions. With a numerical model of slab sinking and mantle flow we predict a long-wavelength negative dynamic topography migrating southward from ~50 Ma to present, explaining Eocene-Oligocene subsidence of the Queensland Plateau, ~330 m of late Eocene-early Oligocene subsidence in the Gulf of Carpentaria, Oligocene-Miocene subsidence of the Marion Plateau, and providing a first-order fit to the present-day, ~200 m deep, topographic depression of the Lake Eyre basin and Murray-Darling basin. We propose that dynamic topography evolution provides an independent means to couple geological processes at the surface to a deep mantle reference frame. This is complementary to, and can be integrated with, other approaches such as hotspot and slab reference frames.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015