Northern margin of the Indian Plate—some litho-tectonic constraints

Abstract

The Indus-Tsangpo Suture Zone represents crustal expression of a subduction zone in the Himalaya. All along its extension in Kohistan, Ladakh and Tibet, the suture zone from south to north is constituted of litho-tectonic assemblages referable to trench zone, fore-arc basin, island arc and back-arc basin. These assemblages lie between the platform sediments deposited at the northern margin of Indian and southern margin of Tibet. The trench assemblage consisting of ophiolitic assemblages exhibits high pressure glaucophanitic metamorphism. The flysch sequence of the Indus Group represents fore-arc sediments deposited in front of the Ladakh magmatic arc comprising Dras volcanics, the Ladakh plutonic complex and the Khardung volcanics. To the north of the magmatic arc, the back-arc basin assemblage represented by the Shyok Group consists of acid and basic volcanics and volcanoclastics intruded by granitic plutons. The rocks of the arc and back-arc region exhibit low pressure, high temperature metamorphism. The high pressure and low pressure metamorphic belts lying to the south and north respectively of the magmatic arc constitute paired metamorphic belts. Detailed analysis of tectonic and lithological characters of various litho-tectonic units indicate that these developed at the northern margin of the Indian Plate during the Mesozoic and Early Tertiary. The Miocene-Pliocene molassic rocks overlying various litho-units unconformably were deposited after the collision of the Indian and Tibetan plates.