Thermal and tectonic consequences of India underthrusting Tibet

The Tibetan Plateau is the largest orogenic system on Earth, and has been influential in our understanding of how the continental lithosphere deforms. Beneath the plateau are some of the deepest (∼100km) earthquakes observed within the continental lithosphere, which have been pivotal in ongoing debates about the rheology and behaviour of the continents. We present new observations of earthquake depths from the region, and use thermal models to suggest that all of them occur in material at temperatures of ≲600°C. Thermal modelling, combined with experimentally derived flow laws, suggests that if the Indian lower crust is anhydrous it will remain strong beneath the entire southern half of the Tibetan plateau, as is also suggested by dynamic models. In northwest Tibet, the strong underthrust Indian lower crust abuts the rigid Tarim Basin, and may be responsible for both the clockwise rotation of Tarim relative to stable Eurasia and the gradient of shortening along the Tien Shan.

► Earthquakes deeper than 50 km are restricted to two areas of NW and SE Tibet. ► They occur within underthrusting India, which is continuous beneath the plateau. ► They occur within material colder than ∼600°C. ► High-temperature earthquakes and rigid behaviour are consistent with anhydrous Indian lower crust. ► Rotation of Tarim may be driven by its collision with rigid Indian crust at depth.