Abstract

Southeast Asia was once located within the eastern Tethys close to Gondwanaland, rotated anticlockwise about 60 deg. from its present orientation, and with Sumatra adjacent to the Sahul Shelf. The regional fault trends of Southeast Asia continued into northwest Australia. Emergence of much of Southeast Asia and fragmentation away from Gondwanaland was then initiated in the Ladinian by crustal updoming and formation of three-armed rifts over hotspots that have remained stationary, or approximately so, with respect to Antarctica. The Myitkyina valley of Burma, with its central basic-ultramafic belt, represents a failed rift formed over the Amsterdam-St.Paul hotspot. As Southeast Asia rifted towards Laurasia, the Kalaw and Lashio basins of Burma were formed as flanking grabens. In the early Tertiary, as India moved northwards away from Antarctica towards Laurasia and Southeast Asia, which had now joined along the Red River suture, the west coast of India passed over the Rodriguez hotspot. Outpourings from this hotspot may have formed the Deccan Traps. The trace of the Kerguelen and Amsterdam-St. Paul hotspots as the Indian Plate moved north coincides with the Ninetyeast Ridge, and outpourings from these hotspots may be related to its formation or elevation. Validity of the reconstructions can probably be checked by study of the magnetic anomalies of the Indian Ocean.