Palaeozoic and Mesozoic tectonic evolution and biogeography of SE Asia-Australasia

Southeast Asia comprises a complex assembly of continental fragments (terranes), bounded by suture zones that represent former ocean basins. In the Early Palaeozoic (545–410 Ma), all the principal Southeast Asian continental terranes were located on the Himalayan-Australian Gondwanaland margin, where they formed part of a “Greater Gondwanaland”. Multidisciplinary studies suggest that the Asian terranes rifted and separated from NW Australian Gondwanaland as three continental slivers around 350, 270, and 200–140 Ma. During the separation of these continental slivers, three ocean basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys, opened between each successive sliver and Gondwanaland. The first sliver, interpreted to have separated at 350 Ma, included North China, South China, Tarim, and Indochina. By 325 Ma, these terranes had no Gondwanaland faunas and floras, and palaeomagnetic data indicate that they were separated from the parent craton. Clockwise rotation of Gondwanaland around 320–300 Ma sent Australia into high southern latitudes, and glaciation affected much of Gondwanaland from 320 to 270 Ma. During this time, glacial ice reached the marine environment and glacial-marine sediments were deposited on the Sibumasu, Qiangtang, and Lhasa terranes now located in South and Southeast Asia. Gondwanaland cold-climate faunas and floras and cold water oxygen isotopic signatures are also found in Lower Permian rocks of these terranes. Rifting, starting at about 300 Ma, led to separation of the Sibumasu and Qiangtang terranes from Gondwanaland at approximately 270 Ma. These Cimmerian terranes drifted rapidly northwards between 270 and 250 Ma and significant changes in both brachiopod and tusulinid biogeographic provinces on these between 300 and 250 Ma are interpreted as being primarily due to the separation and northwards drift of the Cimmerian continental terranes, coupled with climatic amelioration following retreat of the Gondwanaland glaciation. Rifting and separation of a third continental sliver from Gondwanaland began 230 million years ago with the separation of the Lhasa block and progressed eastwards with separation of West Burma and possibly the small Sikuleh terrane of SW Sumatra and other small microcontinental fragments now located in Borneo and West Sulawesi around 160 Ma. Amalgamation and accretion of Gond-wanaland-derived Asian terranes occurred progressively between the Late Devonian and Cretaceous.