Deep crustal seismic observations from northwest Australia demonstrate that the Cuvier margin is a volcanic passive margin that formed as Greater India rifted away from Australia in the Early Cretaceous. Formation of the Cuvier Basin and initial sea-floor spreading resulted in the emplacement of exceptionally thick oceanic crust, while contemporaneous spreading off the adjacent Exmouth Plateau formed normal-thickness oceanic crust. Rapid rifting of the Cuvier margin created strong lateral temperature gradients in the subjacent upper mantle at the time of breakup. This induced small-scale convection in the upper mantle that increased the rate of upwelling and, thus, the volume of melt generated by decompression partial melting. In turn, this resulted in a larger volume of magma at the initiation of sea-floor spreading, and thicker oceanic crust was initially emplaced. -from Authors