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.

► We present a temporal isotopic record for the Kohistan-Ladakh Arc granitoids. ► Granitoids >50 Ma show characteristics of the intra-oceanic history of the Arc. ► At 50.2±1.5 Ma India collided with the intra-oceanic arc. ► At 40.4±1.3 Ma the India/Arc assembly collided with Karakoram in western Himalaya. ► Final India-Eurasia collision occurred at ∼40 Ma.