The age and nature of Mesozoic-Tertiary magmatism across the Indus Suture Zone in Kashmir and Ladakh (N. W. India and Pakistan)

We report the following new40Ar/39Ar ages: 130–150 and 90–100 Ma from monzodiorite and tremolite-actinolite schist of the Kohistan Complex; 44±0.5, 39.7±0.2 Ma from dikes cutting the Ladakh-Deosai Batholith Complex; 130–145 Ma from a diorite in the Shyok melange; and 7.8±0.1 Ma from a late stage monzogranite of the Kärakorum Batholith. A 261±13 Ma age from gneiss of the Karakorum Batholith is of uncertain significance.These dates, previously published ones which we summarize here, and some Sr isotope data suggest the following, (due to subduction switching between the Indian and Asian margins during closing of the Tethys ocean):Late Cretaceous emplacement of the Dras-Kohistan Cretaceous Island arc, followed by rapid cooling between abut 85 and 45 Ma.A quiet phase tectonically on the northern Indian plate during the Palaeocene to early Eocene, when subduction was occurring on the Asian margin.Further southward thrusting of the Indian continental margin associated with the development of an Andean-type arc (the Ladakh-Desosai Batholiths) on the northern Indian margin during the Eocene.An Oligocene Andean arc (the Karakorum Batholiths) on the Asian margin, followed by Miocene collision of the two continents and intrusion of ‘true’ granites derived from partial melting of continental crust.