Apatite fission-track data indicate that Mesozoic strata exposed on the northern flank of the Chinese Tian Shan underwent ∼4-5 km of late Cenozoic unroofing, beginning at ∼24 Ma. This age apparently dates initial reactivation of the northern Tian Shan in response to the India-Asia collision, which continues to raise the mountain range today. Numerous studies of the Himalaya and Tibet suggest that a major shift from extrusion-dominated to crustal thickening-dominated tectonics occurred in latest Oligocene-early Miocene time, approximately coincident with the start of unroofing in the Tian Shan. This suggests that Tian Shan unroofing was a distant effect of that shift within the collision zone.

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