Late Mesozoic compressional to extensional tectonics in the Yiwulushan 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 multi-phase 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 Yiwulushan massif crops out at the eastern end of the Yinshan-Yanshan orogenic belt. The Yiwulushan 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 (D-1) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulushan massif. A detailed structural analysis allows us to distinguish several deformation events (D-2, D-3, and D-4). 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 Yiwulushan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW-SE extensional Mesozoic tectonics occurred throughout the entire region. (c) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.