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, mesomicrostructures, 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.

Tectonic evolution of Mohe area, North‐east China: Evidence from the Early Ordovician to Early Cretaceous magmatism and tectonism

“…(a) Schematic tectonic diagrams showing the main subdivisions of central and eastern Asia and the location of the study area (modified from Zhou & Li, 2017); (b) tectonic divisions of North‐east China (modified from Liu et al, 2017; Liang et al, 2019). (c) Geological map of the Mohe Basin showing the distribution of the Emuerhe Group (modified from Z. X. Guo, Yang, Zyabrev, & Hou, 2017)…”

“…B. Wu & Zheng, 2004; W. L. Xu et al, 2013; Zhou & Wilde, 2013; Zhou et al, 2011, 2015, 2018; Zhao et al, 2016). There are still many disputes about the tectonic evolution of the Erguna Block from Early Ordovician to late Early Cretaceous (Fan, Guo, Wang, & Lin, 2003; Liang et al, 2019; Meng, 2003; J. Tang et al, 2015; Q. Zhang et al, 2019; Zhou et al, 2015; Zorin, 1999; Zorin, Zorina, Spiridonov, & Rutshtein, 2001). Some scholars believe that magmatic events in the Erguna Block during the Early Ordovician are mainly related to the collision and collage of Erguna Block and Xing'an Block (Ge, Wu, Zhou, & Rahman, 2005).…”

“…However, others believe that the magmatic event in this period was formed in the tectonic environment of the transition from compression to extension and was related to the closure of the Palaeo‐Asian Ocean between the Erguna Block and the Siberian Craton (G. Wu et al, 2015). For the Mesozoic magmatic events of the Erguna Block, it is generally believed that the Mongol–Okhotsk tectonic domain mainly influenced the Late Permian to Early Cretaceous (Dai et al, 2018; Fan et al, 2003; Liang et al, 2019; Meng, 2003; Q. Zhang et al, 2019; Zorin, 1999; Zorin et al, 2001). The Early Cretaceous may be influenced by the Palaeo‐Pacific Ocean and Mongol–Okhotsk Ocean dual tectonic domains (W. L. Xu et al, 2013).…”

“…The Mohe area is located north‐west (NW) of the Erguna Block and closed to the eastern part of the Mongol–Okhotsk suture zone. It is crucial to study the evolutionary history of the eastern part of the Mongol–Okhotsk Ocean and the western part of the Erguna Block (Liang et al, 2019; Q. Zhang et al, 2019).…”

“…Therefore, identifying rock genesis and the tectonic evolution of magmatic events in the Mohe area is essential in indicating the tectonic events in NE China. However, in recent years, numerous studies have focused on the formation of the sedimentary sequence in the Mohe area (Z. X. Guo et al, 2017; Liang et al, 2019; Wang et al, 2015; Q. Zhang et al, 2019). Nevertheless, it is scarce in the research on the genesis and tectonic background of magmatic events from Palaeozoic to Mesozoic in the Mohe area.…”