Southwestern Tian Shan: 2. Timing of Cenozoic Mountain Building, Intra‐Montane Basin Inversion, and Relation to Lithospheric Mantle Indentation

Abstract Cenozoic reactivation of the Paleozoic thick‐skinned fold‐thrust belt of the southwestern Tian Shan has—as the Afghan‐Tajik Basin inversion—been interpreted to be driven by Indian mantle‐lithosphere indentation beneath the Pamir. Herein, we date the reactivation and explore its temporal and spatial variations. Three structural domains emerged. In the Central Domain (Zeravshan‐Gissar, Vashan), apatite fission‐track (AFT) data—aided by Raman‐spectroscopic chemical‐composition discrimination of detrital apatites and vitrinite‐reflectance paleotemperature estimates—record a 15–10 Ma onset of shortening and >4 km exhumation. The Northern Domain, with the southerly bounding N‐Zeravshan Fault as the major Cenozoic structural divide reactivating the Paleozoic Zirabulak Suture, exhumed from <4 km. Apatite (U‐Th)/He (AHe) ages suggest a similar reactivation history as in the Central Domain. The synchronous structural reactivation implies rapid shortening propagation from the Pamir across the Afghan‐Tajik fold‐thrust belt into the southwestern Tian Shan. In the Southern Domain (Paleozoic Gissar Batholith), 9–7 Ma AFT and ∼4 Ma AHe ages suggest southward shortening propagation from both northern Domains and anew fault formation. In the hanging walls of major thrusts, 7–3 Ma AFT ages record significant and/or long‐lasting exhumation. Zircon (U‐Th)/He data limit exhumation to <6 km. Most of the Southern and Central Domains cooled monotonously but temperature‐time models indicate northward‐decreasing reheating by syn‐orogenic deposition, consistent with stratigraphic data. The refined timing supports the synchroneity between major Cenozoic Tian‐Shan mountain building and India mantle‐lithosphere indentation beneath the Pamir and western Tibet, and the instantaneous transfer of shortening across a >500‐km‐wide foreland, facilitated by structural reactivation.