Dynamic Topography of the Australian Continent and its Margins

Mantle convection generates transient vertical motion at the surface, which is referred to as dynamic topography. The bulk of topography and bathymetry is isostatically supported by variations in the thickness and density of both the crust and the lithosphere which means that dynamic topography generated by sub-plate density anomalies needs to be isolated from these dominant isostatic signals. Australia’s isolation from plate boundaries and its rapid northwards translation suggest that long-wavelength dynamic topography is primarily controlled by the interplay between plate motion and sub-plate convection. Along the eastern seaboard of Australia, the coincidence of elevated topography, positive long-wavelength free-air gravity anomalies and Cenozoic basaltic magmatism imply that a combination of asthenospheric temperature anomalies and thinned lithosphere generate and maintain regional topography. Distributions of onshore and offshore intraplate magmatism reflect both plate motion and convective instabilities. Compilations of deep seismic reflection profiles, wide-angle surveys and receiver function analyses are used to determine crustal velocity structure across Australia. Residual (i.e. dynamic) topographic signals are isolated by isostatically correcting local crustal structure with respect to a reference column that sits at sea level. The resultant pattern of dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia. Significant positive dynamic topography occurs along the eastern seaboard and in southwest Australia (e.g. Yilgarn Craton). These signals are corroborated by independent geologic evidence for regional uplift.