Mesozoic-Cenozoic multistage tectonic deformation of the qilian shan constrained by detrital apatite fission track and zircon UPb geochronology in the Yumu Shan area

Abstract The Qilian Shan on the northeastern edge of the Tibetan Plateau contains structural, sedimentary and tectonothermal records of plateau formation and growth in response to the Indian-Asian continental collision. In this study, we reveal the tectonic deformation evolution of the Qilian Shan by detrital apatite fission track (AFT) thermochronology and provenance analysis of a sedimentary section on the northern flank of the Qilian Shan based on paleocurrent measurements and detrital zircon U Pb geochronology. The unannealed detrital AFT peak ages span ~154–10 Ma, and the zircon U Pb ages range between ~3260 Ma and ~ 178 Ma. Detrital AFT ages showing that the initial exhumation occurs ca. 154–135 Ma and ca. 105–81 Ma and abundant ages of ca. 61–24 Ma indicate the prominent exhumation of the sedimentary provenance from the Qilian Shan at those times. Zircon U Pb analysis suggests that the sediments were generally sourced from the Qilian Shan to the south, with moderate provenance changes at ~10 Ma and 5.1 Ma. These geochronological datasets imply that the Qilian Shan experienced multistage deformation during the Mesozoic-Cenozoic, i.e., late Jurassic-early Cretaceous (153.6–135.2 Ma), late Cretaceous (104.5–80.9 Ma), late Paleocene-Oligocene (61–43.1 Ma;38.2–24.6 Ma), mid-late Miocene (10 ± 4 Ma) and Pliocene (5.1–3.6 Ma). During the Cenozoic, the deformation initiated in the late Paleocene reflects the synchronous far-field response of the northeastern Tibetan Plateau margin to the Indian-Asian plate collision.