Keywords: field geology, geochronology, tectonics, orogenesis

Abstract: Constraining the age of collision between the Kohistan-Ladakh arc (KLA), an intra-oceanic arc remnant, and Eurasia along the Shyok suture zone is critical to understand the development of the India-Eurasia orogenic system. Estimates of the timing of KLA-Eurasia collision span 100 – 40 Ma, permitting conflicting tectonic scenarios in which the KLA either collided first with Eurasia or first with India. Each of these scenarios has very different implications for how India-Eurasia convergence was accomodated and the linkages between Himalayan orogenesis and global climate change in the Cenozoic. In this talk I will present field observations, structural analyses, and U/Pb zircon ages that constrain the tectonostratigraphy and structural development of the Shyok suture zone in Ladakh, NW India. These results support multi-stage arc-continent accretion models for the India-Eurasia collision because they show that KLA-Karakoram collision likely occurred in the Eocene after the collision between the KLA and India. The final India-Eurasia collision therefore occurred along the Shyok-Tsangpo suture zone, not the Indus-Tsangpo suture zone as was previously thought.