Two late Palaeozoic collisions produced the ancestral Tien Shan Range. Extension following the younger collision, preceded a phase of thermal subsidence associated with fluvial and lacustrine sedimentation throughout the Jurassic, Cretaceous and early Tertiary. This thermal subsidence was interrupted by renewed movement on Palaeozoic reverse faults, caused by the Mesozoic collisions at the southern margin of Asia. The India/Asia collision in the early Tertiary has produced widespread thrusting in the Tien Shan, which in turn is responsible for the formation of active foreland basins at the southern and northern margins of the range and similar basins within the range itself. This compression produced uplift and relief, and consequent erosion gave rise to alluvial fans, braidplains and ephemeral lakes in an extremely arid environment.