Crustal growth and two-stage India-Eurasia collision in Ladakh

Abstract

The post-Palaeozoic history of crustal growth between India and the Karakoram-Lhasa accreted southern margin of Asia begins with the creation of the oceanic crust during the northward drift of the Karakoram-Lhasa block, away from the northern margin of India, after Permo-Triassic rifting. Data suggest initiation of northward subduction and the development of the island arc close to the southern margin of Asia sometime in Upper Jurassic (160 m.y.). The northward retreat of the overriding Eurasian Plate due to movements along transform faults, which subsequently changed into transcurrent faults, resulted in the opening of the Shyok back-arc basin in the Kohistan-Ladakh region during pre-Upper Cretaceous time. The mature and thickened tholeiitic island arc lying between the subducting Indian Plate and the spreading Shyok back-arc basin suffered compression, deformation, emplacement of ophiolitic melanges and metamorphism during the Upper Cretaceous (80 m.y.). The intrusion of the calc-alkaline magma into the deformed rocks of the island arc and the back-arc basin during the Paleocene-Eocene (60-40 m.y.) was followed by explosive calc-alkaline volcanism (40-25 m.y.) resulting in further crustal growth in this part of the Trans-Himalaya. The collision of the Dras island arc with the approaching margins of the Indian and Eurasian plates took place in two stages. In the first stage it collided with the northern margin of India during the Paleocene along the Indus Suture. The final collision of the island arc-accreted northern margin of India with the Eurasian Plate took place along the Shyok Suture during the Early Oligocene (30 m.y.).