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
Abstract：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 Neo-archean 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 basal <a> slip.Deformation behaviors of minerals and quartz crystallographic preferred orientations demonstrate that the rocks underwent mylonitization at a temperature of 400-500 ℃ un-der 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 shear zones 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.
Keywords：ductile shear zoneArchean gneissfabric analysissag ductionvertical tectonicNorth China cratontectonics
Publication Date：2017-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：17( 2129-2145 )