Multi-stage crustal thickening, surface uplift, and collision in the western Himalaya-Karakoram-Tibet orogen revealed by chemical mohometry

The Himalaya-Karakoram-Tibet (HKT) orogen provides an unrivaled opportunity to study the dynamic linkages between deep and surface processes during collisional orogenesis. However, these efforts are hindered by conflicting interpretations on the number and timing of collisional events, and the timing of crustal thickening and associated surface uplift. Here, we resolve this with quantitative paleo-crustal thickness estimates in the northwestern HKT orogen. We show that: (a) the paleo-Asian margin had thick crust (50–60 km) at least 65 Ma prior to terminal collision, consistent with a continental arc setting, (b) crustal thickening to 60 km or more occurred at ca. 60–50 Ma in the Kohistan-Ladakh arc and by 40–25 Ma in the paleo-Asian margin, indicating a multi-stage Himalayan collision, and (c) modern crustal thicknesses in the northwestern HKT have been sustained since ca. 40–25 Ma suggesting an orogenic steady-state in which crustal thickening, crustal flow, and surface uplift have been balanced by erosion.