Cenozoic Tilting of the Australian Continent due to Dynamic Topography

We investigate the possibility of a mantle-dynamic origin to account for the observed pattern of inundation of the Australian continent in the Cenozoic. Since the Paleocene, the Australian continent has experienced a series of regional marine incursions and regressions, which are inconsistent with the expected flooding history due to changes in eustatic sea level alone. During this time, the Australian continent has undergone no major episodes of mountain building or rifting which might account for these patterns of inundation. Since the Eocene, the Australian plate underwent rapid northward motion as the spreading rate at the South East Indian Ridge increased. As it moved northwards, the Australian plate moved away from a dynamic topography low caused by the sinking Gondwanaland slab beneath the South East Indian Ridge, and towards a dynamic topography low caused by subducted slab material in South East Asia. It is thought that these dynamic topography features at the southern and northern extremes of the Australian plate produce an underlying static and long wavelength dynamic feature over which the Australian plate has migrated through the Cenozoic. This dynamic feature should be expressed by an increase in the latitudinal asymmetry of the Australian dynamic signal. Estimates of the dynamic motion of the Australian plate since the Paleocene are made by matching observed patterns of marine incursion with models of marine inundation. Models of inundation are created by backstripping sediment from present-day topography and dynamic motion is quantified by the displacement needed to approximate the observed flooding according to eustatic sea level. We explore the trend of these displacements according to their paleo-position. Preliminary analysis suggests that the continent is influenced by a dynamic feature that is both temporally and spatially varying. We attempt to interpret the evolving dynamic topography field of Australia in the context of kinematic and 3-D dynamic models of the Australian region which provide an integrated explanation for the patterns of marine inundation in the Cenozoic.