Southwestern Tian Shan: 1. Deformation of Cenozoic Intra‐Montane Basins and Intervening Basement Ranges in Front of the Indian Mantle Indenter

Abstract A structural analysis of intra‐montane basins establishes the deformation field of the southwestern Tian Shan, that part of the Tian Shan that faces the Pamir and thus the deformation that the Indian mantle‐lithosphere indenter beneath the Pamir imposes—northward indentation and westward crustal collapse. Tight‐isoclinal footwall synclines in the basins accompany major ∼E‐striking Cenozoic reverse faults that reactivate Paleozoic ones, separate basement blocks, and accommodated ∼N‒S shortening and dextral strike‐slip faulting. They connect with ∼WNW‐striking dextral strike‐slip faults, and ∼ENE‐striking thrusts; the latter are confined to the western southwestern Tian Shan. The deformation field resembles that of the Afghan‐Tajik Basin fold‐thrust belt and mimics in shape the geometry of the intermediate‐depth earthquake zone beneath the Pamir that traces the lithospheric delamination zone separating the Indian mantle indenter from Asian lithosphere. The basement‐rooted Cenozoic faults require a detachment underlying the southwestern Tian Shan, likely along the brittle‐ductile transition, consistent with the regular spacing of the intra‐montane basins. This mid‐crustal detachment and the shallow evaporite detachment below the Afghan‐Tajik Basin may root in a common deeper one, likely along the Moho. As the southwestern Tian Shan is involved in the northward motion and westward collapse of the Pamir, the deep detachment must root in the lithospheric delamination zone of the Pamir. The deep structure of the eastern Tian Shan is different; thus, the detachment underlying the southwestern Tian Shan and Afghan‐Tajik Basin must terminate along the eastern margin of the Pamir delamination zone, that is, along the western margin of the Tarim craton.