Initiation timing of Cenozoic compression deformation of the southern Tianshan mountains: Implications from growth strata in the Kuqa Depression

Abstract

Influenced by the far‐field effect of the India–Eurasia collision during the Cenozoic, the Palaeozoic orogenic belt of the southern Tianshan mountains underwent tectonic activation. This resulted in the transmission of intense compressive deformation to the northern margin of the Tarim Basin, Kuqa Depression, where multiple east–west trending fold–thrust belts are formed. Exactly when the Cenozoic compressive deformation in the southern Tianshan orogenic belt was initiated is controversial. Growth strata are sediments of the syn‐tectonic events, and the age of the bottom boundary of the growth strata effectively constrains the initiation timing of the structural deformation. The Kuqa Depression currently receives sediments from the southern Tianshan mountains, and it is natural to use these Cenozoic strata to decipher the southern Tianshan's uplift history. Based on the detailed structural mapping and structural profile survey of the Kuqa Depression area, the Palaeogene Kumugelimu Formation growth strata in the Kuqa Depression were identified. Based on the magnetic stratigraphic sequence of the Cenozoic established by predecessors, the age of the bottom boundary of the Palaeogene Kumgelimu Formation is assumed to be 42–60.5 Ma. Combined with the analysis of the apatite fission‐track ages of the Mesozoic–Cenozoic clastic sediments in the Kuqa Depression by previous workers, there was an evident uplift and cooling event (~50 Ma) during the Palaeogene in the Kuqa Depression. The Cenozoic compression deformation in the south Tianshan and Kuqa Depression was then concluded to be initiated at approximately 50 Ma.