Kinematics Analysis and Formation Mechanism of Qidashan Ductile Shear Zone,Eastern Anshan,Liaoning Province,NE China
Liu Xinyue;Li Jing;Liu Yongjiang;Li Weimin;Wen Quanbo;Liang Chenyue;Chang Ruihong;College of Earth Sciences,Jilin University;Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Land and Resources;
The controversy over the Archean tectonic regimes has lasted several decades focused on the horizontal and vertical tectonics,the two classical tectonic models for Archean.Thus,more studies of the early crustal tectonic evolution are requisite for better understanding geodynamic regimes in the early Precambrian.In this study,detailed structural analysis of Qidashan down-slip ductile shear zones which developed in the eastern Anshan area was carried out and an example for revealing Neoarchean vertical tectonics is provided.The ribbon structures formed by intensely elongated felsic minerals are widespread in the deformed gneisses.The quartz C-axis fabric patterns obtained by electron backscatter diffraction technique imply low to middle temperature non-coaxial deformation with active rhomb a slip and basala slip.Deformation behaviors of minerals and quartz crystallographic preferred orientations demonstrate that the rocks underwent mylonitization at a temperature of 400-500℃ under greenschist facies metamorphic conditions.Dislocation creep is the main rock deformation mechanism within the shear zones.Finite strain measurement results suggest that toward the iron ore belt,the tectonites change from L=S-to LS-type and the strain intensity exhibits an enhanced trend across the shear zones.Kinematic vorticity values(0.75)indicate that the deformed rocks in ductile shearzones were produced by steady-state simple-shear dominated general shear.Compared to the Baijiafen ductile shear zone to the west,the Qidashan and Baijiafen ductile shear zones both have mutually down-slip kinematic characteristics,indicating that the Neoarchean crust growth and tectonic evolution in Anshan area is dominated by vertical tectonics.
【Fund】： 国家自然科学基金重点项目(No.41230206);国家自然科学基金资助项目(No.41672185);; 国家重点研发计划项目(No.2016YFC0600108-02)
【CateGory Index】： P542
【CateGory Index】： P542