| Xiaowulanhua ductile shear zone lies in the area of Baiyinxile in Siziwangqi,middle Inner Mongolia.The north of this ductile shear zone is the north margin of North China plate,and the south of it is North China plate.The geotectonic position of this ductile shear is at the conjunction between the Siberia plate and the North China plate,so it have undergone strong metamorphism and deformation.Xiaowulanhua ductile shear zone is longth of about 15 km and width of 500 to 1000 m and strikes NEE with SE-dipping angle of 40?80°.The whole ductile shear zone shows alternate strong-light deformable zone,and is the type of thrust ductile shear zone form south to north.There are some structural characters in the shear zone,such as folded mylonitic foliation,mineral lineation,S-C fabric,rotational porphyroclast,asymmetrical folds.Based on the observation and analysis of these deformations,the ductile shear zone shows right-lateral shear on macrocosm and microcosm.We account some stress in the shear zone,the orientation of principal stress is NW-SE.And we reckon differential stress by subgrain,which is 46.64Mp,we obtain average strain velocity by creep equation,which is 7.59×10-13 s-1.According to character of deformation and mineral association,we think the ductile that formed 10-15 kilometer the earth's crust,so we conclude this shear zone attribute to low-greenschist facies,it's temperature of formation is less than 400?-500?.According to the analysis of the Ziron isotopic chronology of deformed rock and tectonic melange zone,combined tectogenesis of region,we think this shear zone formed in Late Ordovician-Early Silurian.By researching the Xiaowulanhua ductile shear zone,we discuss the meaning of structure and geology of this shear zone,it is an important boundary of the north margin of North China plate and the North China plate.According to these research,we sum up tectonic evolution history of this study area in Paleozoic,and discussed the model of Palaeo-Asia Ocean subduction. |
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