Deformation of granitic rocks within Derbugan Fault belt, Erguna Massif, Northeast China: Implication of the subduction of Mongol‐Okhotsk oceanic plate

Abstract

The NE–SW striking Derbugan Fault has been comprehensively accepted as a Mesozoic strike‐slip fault in Erguna Massif rather than a suture belt of Erguna and Xing'an massifs. The rocks exposed within the fault belt, which consist of Jiageda Formation and intrusions which have been multiply deformed and metamorphosed. These deformed rocks provide an ideal opportunity to understand the geodynamics of the uplift history and tectonic evolution of Derbugan Fault in Mongol‐Okhotsk regime and influence of the circum‐Pacific tectonic regime, particularly during the later stages of the Mongol‐Okhotsk Ocean collision. In this study, we report kinematics, meso‐microstructures, quartz EBSD analysis and geochronology data of the Jiageda Formation exposed within the Derbugan Fault belt in Cuogang area, Erguna Massif. The Jiageda Formation and granitic rocks have experienced regional metamorphism and deformation, and is mainly characterised by simple‐shear dominated general shearing with LS tectonites. Our new zircon U‐Pb data of mylonitic rocks from Cuogang area yielded ages between 381 to 401 Ma which was produced as a result of the subduction of the Paleo‐Asian Ocean. Deformed granitic intrusive formed in the Early Triassic (244.8 ± 5.6 Ma) was related to the southward subduction of the Mongol‐Okhotsk oceanic plate beneath the Erguna Massif. The Derbugan Fault represents a ductile to brittle deformation at decreasing crustal level due to the dominant oblique (subhorizontal) slip. The early sinistral strike‐slip deformation with a medium temperature between 450 and 550°C developed at a deep ductile regime resulted from NW–SE extension. The subsequent deformation was essentially brittle that corresponded to a low‐temperature deformation corresponded to a greenschist metamorphic facies. Crystallographic textures indicate a restricted recrystallisation of quartz mainly via dislocation creep through activation prismatic <a> slip and rhomb <a> slip system, with a later activation of basal <a> slip system. The Early Cretaceous extensional environment may consist with the main medium temperature deformation stage of Derbugan Fault, which was related to either delamination or upwelling of the thickened lithosphere of the Mongol‐Okhotsk tectonic regime, and rollback of the Paleo‐Pacific Plate.