Deformation characteristics and geochronology of the Xiajing- Changhanying ductile shear zone in the Shangyi area, northern margin of North China block
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    Abstract:

    The northern margin of North China block experienced multiple tectonic events in the late Paleozoic, with complex and diverse tectonic activities. The Xiajing- changhanying ductile shear zone located in the middle segment of the North China block underwent strong tectonic deformation. The study of the deformation characteristics and formation age of the ductile shear zone is of great significance to further explore the tectonic evolution of the northern margin of the North China block, especially the timing and mechanism of oceanic subduction crust in the late stage of Paleo- Asian Ocean. In view of this, the kinematic and geometric profiles, microstructural analysis and zircon LA- ICP- MS U- Pb geochronology of the ductile shear zone were carried out in order to define the deformation characteristics and time of the ductile shear zone. The protoliths in the shear zone are a set of dioritic- granitic magmatic rocks, which were formed by strike slip shearing in the later stage. The synmorphic potassium feldspar granitic mylonite veins were precipitated by the tectonic deep melting, and were emplaced by the undeformed hornblende diabase veins in the later stage. Thus, three stages i.e. an early stage of the deformation of granitic diorite- granitic mylonite, long with deformation fine vein potassium granitic mylonite, and post deformation undeformed hornblende diabase can be identified. Among them, mylonite foliation is close to E—W or SW—NE trend, inclining to NW—N, with steep dip angle, SW dip direction and gentle dip angle. Macro and micro structures such as tensile lineation, S- C fabric, asymmetric fold, rotary remnant and domino porphyroclastic structure are developed in the zone, indicating that the nature of the shear zone is characterized by left lateral strike slip shear deformation. Zircon LA- ICP- MS U- Pb geochronology of the early, syn- and post- deformation rocks was carried out. The zircon 206Pb / 238U concordant ages of 286.7±4.1 Ma, 280.0±5.5 Ma and 278.8±0.6 Ma were obtained. It is concluded that the age of left strike slip deformation in the Xiajing- Changhanying ductile shear zone is ~ 280 Ma, that is, the late Early Permian. Based on the data of tectonic magmatic age, dynamic background and evolution process in the southern margin of the Central Asian orogenic belt, it is considered that the Xiajing- Changhanying ductile shear zone was formed during the compression of the Xingan subduction accretionary orogenic belt on the southeastern margin of the Central Asian orogenic belt to the post orogenic extensional tectonic transformation along the Solun Xilamulun river line.

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Li Yadong, Liu Yongqing, Jiang Xiaojun, Li Chao, Peng Nan, Yan Qinggao, Wang Zhongqiang, Gan Xi.2022. Deformation characteristics and geochronology of the Xiajing- Changhanying ductile shear zone in the Shangyi area, northern margin of North China block[J]. Acta Geologica Sinica,96(3):863-880

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History
  • Received:July 14,2020
  • Revised:October 13,2020
  • Adopted:January 08,2021
  • Online: February 22,2021
  • Published: