Thermo‐Tectonic History of the Qilian Shan and Adjacent Areas: New Insights From Apatite U‐Pb and Fission Track Thermochronology

Abstract The Qilian Shan is situated along the northeastern margin of the Tibetan Plateau, and has undergone multiple episodes of tectonic deformation since the Paleozoic. Strikingly, tectonic deformation in the Qilian Shan and adjacent areas encompasses newly formed and inherited lithospheric and crustal structures. This study presents the Mesozoic‐Cenozoic post‐orogenic thermo‐tectonic histories of these active tectonic units utilizing an integrated approach combining apatite U‐Pb and fission track thermochronometers. The apatite U‐Pb dates are dominantly Paleozoic, mainly recording post‐magmatic cooling of the sampled granitoid rocks. The apatite fission track data record Late Triassic to Cretaceous cooling ages (central ages between ∼223 and ∼88 Ma), and most of the measured mean track lengths are between ∼13 and ∼12 μm. The apatite fission track results and thermal history models revealed that the Qilian Shan, Longshou Shan and Beida Shan experienced various moderate to rapid basement cooling episodes during the Late Triassic to Early Cretaceous, which we interpret as a far‐field response to a series of distant tectonic events including the Paleo‐Asian Ocean's closure, Qiangtang collision, Tethys‐deformation and Lhasa collision. During this period, these fault‐bounded tectonic units displayed different exhumation patterns, with the North Qilian Shan exhibiting a late Early Cretaceous rapid denudation while others preserved uplifted apatite partial annealing zones.