Dating the India–Eurasia collision through arc magmatic records

The Himalayan orogeny, a result of the collision of India and Eurasia, provides direct evidence of strain accommodation and large-scale rheological behavior of the continental lithosphere. Knowledge of the timing of the India–Eurasia collision is essential to understand the physical processes involved in collisional systems. Here we present a geochronological and multi-isotopic study on rocks from the upper crust of the Kohistan Paleo-Island Arc that formed in the equatorial part of the Neo-Tethys Ocean. In situ U–Pb geochronology and Hf isotopes in zircon, and whole-rock Nd and Sr isotopic data of plutonic rocks from the Kohistan-Ladakh Batholith, are used to construct a continuous record of the isotopic evolution of the source region of these granitoids that are related to both the subduction of the oceanic lithosphere and subsequent arc–continent collisions. We demonstrate that profound changes in the source region of these rocks correspond to collisional events. Our dataset constrains that the Kohistan–Ladakh Island Arc initially collided along the Indus suture zone with India at 50.2±1.5 Ma, an age generally attributed to the final India–Eurasia collision for the entire Himalayan belt. In the western Himalaya, the final collision between the assembled India/Arc and Eurasia however, occurred ∼10 Ma later at 40.4±1.3 Ma along the so-called Shyok suture zone. We present evidence indicating that a similar dual collision scenario can be extended to the east and conclude that a final India/Arc–Eurasia collision at ∼40 Ma integrates crucial aspects of the magmatic, tectonic, and sedimentary record of the whole Himalayan mountain belt.