Amplitude of Sdiff across Asia: effects of velocity gradient and Qs in the D region and the asphericity of the mantle

Mafic to ultramafic dykes and sills in South China, dated as 828±7 Ma old, are identical in age to the 827±6 Ma Gairdner Dyke Swarm in Australia, thought to be of mantle plume origin. These intrusive rocks, accompanied by widespread granite intrusions and rapid unroofing at a lateral extent of ca. 1000 km, and followed by continental rifting, are interpreted to indicate the arrival of a plume head centred beneath South China. This interpretation supports the idea that South China lay between Australia and Laurentia in the Rodinia supercontinent, and suggests that Rodinia breakup may have started with a mantle plume which initiated continental rifting at about 820 Ma ago.