Extension of Tian Shan along a nascent shear zone.

Our understanding of the dynamics of mountain belt growth is hampered by the lack of high-resolution kinematic observations spanning entire orogenic belts. This is particularly the case for the structurally complex and nascent Tian Shan plateau. Here we use 8 years of Sentinel-1 data across 2 million square kilometres of the Tian Shan to show that the mountain range is extending along its strike, predominantly by rotating along a northeast-trending distributed shear zone. This zone is conjugate to the range strike but aligned with fast axes of shear-wave splitting measurements and a band of strike-slip earthquakes. We interpret this broad zone of shear as resulting from the clockwise rotation of the indenting Tarim Basin, which drives the northeast-to-east motion of the part of the Tian Shan southeast of the cryptic shear zone. Conjugate strike-slip components on numerous basin-bounding faults within the Tian Shan likely facilitate this escape. The present-day vertical deformation of Tian Shan results from a mix of tectonic, climatic, and anthropogenic forcings, with uplift of the highest peak facilitated by thrust along a south-dipping Nalati fault that could be promoted by deglaciation.