FORMATION AND EVOLUTION OF HIMALAYAN FOREDEEP AND BENGAL BAY BASIN

The formation and evolution of the Himalayan foredeep and Bengal Bay Basin are carefully studied in this paper based on a comprehensive review of regional geology, geophysics, plate reconstruction and their geodynamic background. The Himalayan foredeep and the Bengal Bay Basin are separated by a high named the Shillong plateau. The former is located to the north of the plateau, with its basement dominated by the pre-Cretaceous Lhasa block.From Late Cretaceous to Early Eocene, it was a fore-arc and a back-arc basin resulted from subduction of the Neo-Tethys to the intra-ocean island arc and the Lhasa block.During the period from Middle Eocence to Early Miocene, the neo-Tethys subducted progressively and destructed finally, and the collision between the Indian plate and the Lhasa block was intensified gradually, and as the result, a foreland basin was formed.Since Middle Miocene, as the collision between the Indian plate and the Eurasian plate intensified, the Himalayan foreland basin experienced uplifting and denudation, and left behind a foredeep of the former foreland basin at last. The Bengal Bay Basin is located to the south of the Shillong plateau, the basement of its northwestern part is dominated by the pre-Cambrian of the Indian plate. From Carboniferous to Permian, it was a rift basin, and then denuded during Triassic.Volcanism dominated the Jurassic to Early Cretaceous.From Late Cretaceous to Early Eocene, it became a basin of passive continental margin.Since Middle Eocene, as the Indian plate intensively subducted under the Lhasa block and the Indian Ocean plate subducted under the Burma continent, the Bengal Bay Basin evolved into a residual ocean basin in which terrigenous clastic supply gradually increased. The basement of the southeastern part of the Bengal Bay Basin is dominated by pre-Paleogene oceanic crust, and the thick filling sequences of the residual oceanic basin has been formed since Eocene in the southeastern part of the basin.