Australia's buoyancy inherited from Gondwanaland

In company with the other components and continental successors of the Neoproterozoic to Mesozoic Gondwanaland supercontinent, Phanerozoic Australia has a buoyant cratonic platform characterised by non-marine facies, in contrast to the marine facies of the components of depressed Laurasia. As a supercontinent, Gondwanaland lasted much longer than Laurasia, and was therefore hotter from its more effective insulation of internal heat. Moreover, the Pan-African orogenic cycle, confined to Gondwanaland, augmented the heat supply, and I postulate that Pan-African heat generated a permanently buoyant lower crust by mafic underplating. A crustal layer in the Australian Proterozoic shield with subhorizontal reflectors and velocity (V_p) 7.5 km s^-1 is interpreted as the product of mafic underplating beneath latest Neoproterozoic flood basalt. The Pan-African terrane in East Africa also contains evidence of mafic underplating, and most of Gondwanaland (but not Laurasia) was affected by terminal Pan-African (0.5 Ga) uplift and cooling. In equivalent Late Cretaceous and Late Ordovician stages of the 400 m.y. Pangean supercycle, the Australian (and possibly the South American) platform deviated from the global norm by rising faster than eustatic sea level. In Australia, plate boundary events -- steeper subduction, mafic underplating of a lower plate along a divergent backs-arc boundary -- explain uplift in the east, but not that in the west, which relaxed to its natural buoyant state.