THE LONGEST JOURNEY: MANTLE PLUME, CONTINENTAL RIFTING, COLLISION TECTONICS AND EVOLUTION OF THE INDIAN PLATE

The tectonic evolution of Indian plate, which started in Early Jurassic (~180 Ma) with the separation of Gondwana from Laurasia, provides an excellent and complex case history against which various models of plate tectonics like continental breakup, sea-floor spreading, birth of ocean, flood basalt volcanism, hotspot trails, transform faults, subduction, obduction, continental collision, accretion, and mountain building can be tested. A series of plate tectonic maps are presented here illustrating the repeated rifting and morphing of the Indian plate from its Gondwana home, its northward journey, its collision first with the Kohistan-Ladakh arc in its NW corner, and then with Tibet at the Indus-Tsangpo Suture, its final accretion to Asia, and the rise of Himalaya and Tibet plateau by crustal shortening. The relationships between flood basalts and the recurrent consequential breakup of Indian plate from Gondwana are reviewed and a mixed scenario of ‘active/passive’ rifting model is presented. The break up Gondwana and the opening of the Indian Ocean is thought to have been caused by heating of the lithosphere from below by the large Bouvet plume, whose relicts are short-lasting swarm of plumes including Rajmahal-Kerguelen, Marion, Somnath, and Deccan-Reunion; and a 4,500 Km long hotspot trail along the Ninety East Ridge. On the other hand, plate-boundary forces mediated the collision of Kohistan-Ladakh arc with present day Indian plate in the north-west, and the closure of the Neotethys, resulting the northward motion of the Indian plate since the Late Cretaceous. The obduction at Kohistan-Ladakh arc might have triggered the acceleration of the Indian plate (18-20 cm/yr) from Late Cretaceous (~85 Ma) to Paleocene (~55 Ma) and then slowed down to (5 cm/yr) after the continental Indian plate collided with continental Asia in Early Eocene (~50 Ma).