Determination Of The Ductile Shear Zone In Kalaqin Core Complex Of Chifeng And Its Tectonic Implictions

Kalaqin Core Complex is a typical example of extensional structural styles in thesouth of Chifeng which is located at the northern margin of the south China Block.Due to its unusaul tectonic setting and complicatied tectonic development, KalaqinCore complex becomes a key place for understanding not only the mechanism of theintra plate orogenic, but also the formation of the North China. Therefore, it has beenone of the hotspots among geologists all over the world. There are several differentkinds of high-strain shear zones scattered on this island which provides a good naturallaboratory for understanding the mechanism of the conversion.Based on field observations and microstructural analysis, combining with thedevelopment of its lineation foliation in metamorphic core complex, there are threetypes of ductile shear zones in the South of Kalaqin Core Complex: Reshui ductileshear zone is NNE-trending, with the sinistral shear; Qijia ductile shear zone isNEE-trending, with the dextral shear; Maojingba ductile shear zone is NNE-trending,with the dextral shear.Two common methods of kinematic vorticity measurement have been explored forthe above shear zones: the polar Mohr diagram and the extentional crenulation(i.e C’).Quantitative vorticity analyses in deformed rocks from Qijia shear zones lead totwo-stage deformation. For the early stage,the Qijia shear zone, the kinematicvorticity values(Wk) for S-C fabrics range from0.75-0.86; Wk of C’in the shear zoneis0.17-0.24.These results of kinematic vorticity values suggest that shear zones aregeneral shear, with simple shear as a dominate in the early stage. With thedevelopment of the extensional crenulation, the pure shear component increased. Inthe Maojingba shear zone, the kinematic vorticity values(Wk) range from0.71-0.93.Itsuggest that Maojingba shear zone are general shear with simple shear as a dominate.In the vertical section, kinematic vorticity of Qijia showed that the strength is moreweaken the Wk is less. In Maojingba shear zone, the kinematic vorticity valuedecreases from middle to the sides.Combined with regional tectonic evolution, it indicate that the world began in thelate Permian massive area of compression and shortening, thickening lithospherebegan, culminating in the Cretaceous entered the extension phase.According to quartz EBSD fabric analysis and microstructural analysis: rock inQijia regions experienced a high temperature deformation, the temperature is about500℃; Reshui regions experienced the high temperature deformation, temperaturearound550℃; while Maojingba region belongs to low temperature shear zone,temperature less than400℃.The U-Pb zircon data set a time limit of the occurrence of sinistral strike-sliptectonic era. The Qijia shear zone formed before271Ma.