Late Mesozoic compressional to extensional tectonics in the Yiwulüshan massif, NE China and its bearing on the evolution of the Yinshan–Yanshan orogenic belt: Part I: Structural analyses and geochronological constraints

With a cratonic nucleus, the North China Craton (NCC) experienced a complex tectonic evolution with multiphase compressional and extensional events during Mesozoic times. Along the northern part of the NCC, the Yinshan–Yanshan fold and thrust belt was a typical intraplate orogen. Jurassic and Cretaceous continental sedimentation, magmatism, widespread intraplate characterize the Yinshan–Yanshan orogenic belt. The geodynamic significance of these tectonic events is still in dispute. In the western part of the Liaoning province, the Yiwulüshan massif crops out at the eastern end of the Yinshan–Yanshan orogenic belt. The Yiwulüshan massif presents an elliptical domal shape with a NE–SW striking long axis. The structural evolution of this massif brings new insights for the understanding of the Mesozoic plutonic–tectonic history of the NCC. A multidisciplinary study involving structural geology, geochronology, Anisotropy of Magnetic Susceptibility (AMS) and gravity modeling have been carried out. The presentation of the new results splits into two parts. Part I (this paper) deals with field and laboratory structural observations, and presents the main geochronological results. The AMS, gravity modeling data will be provided in a companion paper (Part II). The early compressional deformation (D1) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulüshan massif. A detailed structural analysis allows us to distinguish several deformation events (D2, D3, and D4). The Cretaceous extensional structures, such as syntectonic plutons bounded by ductile normal faults, metamorphic core complexes, and half-graben basins are recognized in many places in East Asia. These new data from the Yiwulüshan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region.