Significance of Ophiolite Emplacement in the Development of Ninetyeast Ridge, South Andaman Island, Indian Ocean

Burmese Arc evolved since late Mesozoic in consequence to eastward subduction of Indian lithosphere at the continental margin of Southeast Asia. Burmese Arc, together with Andaman Arc further south, acts as an important transitional link between the collisional phase of Himalaya on the north and Sunda Arc (a typical consumptive margin) to the south, the latter is in direct tectonic continuation with the western Pacific Arc System. With the advent of Plate Tectonics this arc has been the site of renewed geoscientific studies since the region provides an excellent scope to test various geologic models owing to its transitional tectonic set up between a truly collisional phase (of Himalaya) and a typical consumptive margin (Sunda Arc), where, surface geology, Aerial Photographs and interpretation of Satellite Imageries put important constraints for any tectonic model chosen. Andaman-Nicobar islands in the north eastern Indian Ocean, forms an arcuate chain, which lies at the intersection of Indian and Pacific lithospheric plates. Recent geological investigations reveal that an almost continuous marine sequence of late Mesozoic to Pleistocene age except the Ophiolite Suite occurs on these islands. Ophiolites are an assemblage of mafic and ultramafic lavas and hypabyssal rocks found in association with sedimentary rocks like Greywackes and Cherts. The Ophiolite complex constitutes the Peridotite and their Serpentinised equivalent and basic to intermediate volcanic rocks. These rocks reflect a phase of ultrabasic and basic intrusions which continued till the Eocene and may represent igneous activity connected most probably with Deccan Trap activity (70.45 mya). The significance and origin of ophiolites is a matter of interest to geologists. Many investigators interpret ophiolites as slices of oceanic crust which have been technically emplaced in orogenic belts. Serpentinization of Peridotite may explain the origin of Ninetyeast ridge and presence of Low Velocity Zone (LVZ) in the upper most mantle beneath the ninetyeast ridge. In the present article, a review study is presented in relation particularly to serpentinisation below the Burmese Arc, stress pattern etc. The results are next interpreted to study emplacement of Serpentinites and related tectonics of the region.