Mid‐Mesozoicto Cenozoic multiphase deformation in the Bayanwula Tectonic Belt, northern China

Abstract

The Bayanwula Tectonic Belt (BTB) is located between the Alxa Massif and the Ordos Basin in the northwestern North China Craton (NCC). The Mid‐Mesozoic to Cenozoic deformation characteristics of the BTB is crucial for understanding the tectonic processes of eastern Asia during that time. Together with the regional geology, our field observation and structural analysis reveal that the BTB has undergone three phases of deformation since the Late Jurassic. The first phase of deformation (D1) is represented by NE–SW‐striking thrust faults involved in the Jurassic strata, indicating a phase of NW–SE shortening deformation. Based on the combination of angular unconformity between the Upper Jurassic and Lower Cretaceous strata, the timing of D1is constrained at the end of Jurassic and dynamically related to the westward subduction of the Palaeo‐Pacific Plate during the end of the Jurassic. The second one (D2) is characterized by the ~NE–SW‐striking normal faults and Lower Cretaceous syn‐sedimentary strata on both sides of the BTB, which show that a phase of ~NW–SE extension deformation occurred in the Early Cretaceous, dynamically related to the rollback of the Palaeo‐Pacific Plate in the Early Cretaceous. The third stage of deformation (D3) is represented by the NW–SE‐striking folds that involved the Pliocene strata, as well as dextral strike‐slipping of the East Bayanwula Fault and the West Helanshan Fault, indicating a phase of NE–SW shortening at the end of the Pliocene. Dynamically, the D3is related to the outward expansion of the Tibetan Plateau.