Zircon age determinations for the Ladakh batholith at Chumathang (Northwest India): Implications for the age of the India-Asia collision in the Ladakh Himalaya

The Ladakh batholith is part of the > 2500 km long Trans-himalayan batholith that forms the southern margin of the Asian plate and is unconformably overlain by the post-collision Indus Molasse Group sedimentary rocks. We present new U-Pb ID-TIMS zircon ages from a host hornblende-bearing granodiorite (57.7 ± 0.2 Ma) and a later intrusive leucocratic granite dyke (47.1 ± 0.1 Ma) from the Ladakh batholith at Chumathang in northeast Ladakh, India. Subduction-related granodioritic magmatism in eastern Ladakh is dominantly of late Paleocene-early Eocene age. The age of the Chumathang dyke gives a maximum age constraint on Indus Molasse Group basin formation along the northern margin of the Indus Suture Zone and a minimum age constraint on the India-Asia collision. Together with the age of youngest marine sedimentary rocks in the suture zone (Nummulitic Limestone; 50.5. Ma) we propose that by late Ypresian-early Lutetian (early Eocene) time, the two continents had collided, sedimentation in the suture zone became purely continental and subduction-related igneous intrusions had ceased. © 2010