Apatite fission track thermochronology evidence for the Mid-Cretaceous tectonic event in the Qiangtang Basin, Tibet
西藏羌塘盆地白垩纪中期构造事件的磷灰石裂变径迹证据

Collision and orogenesis between Lhasa and Qiangtang terrane in Early-Middle Cretaceous have significant impact on the thermal regime and tectonic evolution of the proto-Qiangtang Basin. Apatite fission track dating was applied to analyze the sandstone samples of the Xiali Formation from Longe'ni area in southern Qiangtang Basin and of the Xueshan Formation from Tuonamu area in northern Qiangtang Basin. The results show single population grain ages with a single mean age and associated central ages mainly ranging from 120Ma to 80Ma and indicate that there would be a tectonic event in middle Cretaceous. The ages coincide well with the ages of magmatism in the Early Cretaceous, main deformation occurred in the Late Cretaceous, and angular unconformity indicated by the Xueshan and Abushan formations. Therefore, the Mid-Cretaceous tectonic event is the result of collision between Lhasa and Qiangtang terrane. Thermal history modeling suggests a different thermal evolution of southern and northern Qiangtang Basin during the Middle Cretaceous Period. The results indicated that cooling rate in southern Qiangtang Basin with 1500m uplift-denudation is lower than the cooling rate in northern Qiangtang Basin with 4000m uplift-denudation. The different uplift-denudation may be related to flexuring in the Qiangtang terrane caused by tectonic loading of Lhasa terrane during southward subduction of the Bangong-Nujiang Ocean seafloor.