The ophiolites of northeast India — a subduction zone ophiolite complex of the Indo-Burman orogenic belt

摘要: Abstract The ophiolites of northeast India are rootless blocks various dimensions, floating in a matrix which belongs to the upper Cretaceous-Lower Tertiary Disang Group. They consist diverse igneous, sedimentary and metamorphic rocks, ultramafics main component. do not constitute continuous sheet but made up units haphazardly juxtaposed along faults or they lensoid slices interbedded with Group rocks. interpreted as oceanic crust mantle obducted onto Indian continental margin. Associated blue schist is indicative subduction zone tectonics. occurrences showing intrusive contacts presence intermediate — acid volcanics suggest an island arc continent type collision Benioff Zone coincident ophiolite belt. tectonic history Indo-Burman orogenic belt can be tentatively summarised follows: (1) Introduction during Cretaceous times; obduction intermixing deep sediments. (2) Deposition Formation separating basin into eastern western sub-basins. Barail sediments were deposited both basins. formation was accompanied by plutonism volcanism deformation low grade metamorphism lower (3) Gradual shallowing consequent upon easterly subducted plate. (4) Continent-continent rotation down-basin normal angle reverse (thrusts) thrust sheets piled up. frontal areas asymmetrically folded. This followed asymmetrical folding rocks foreland areas. (5) gravity conjugate sets strike-slip orogen structures associated attributed first subducting plate subsequently Burma