Study On The Deformation Features Of The Mid-jinshajiang Suture Zone, In The Western Segment Of Yidun Island Arc

The place that studied in this paper is the middle part of the Jinshajiang ductileshear zone which is in the south of Batang and in the north of Suwalong.According tothe thorough analyzing on the structural sections in this place and detailed observingby the microscope,I divided the structural deformations of this place in threestages.The D1stage of the deformation formed the S1foliation.The S1foliationcharacterized with the foliations which formed by the S0foliation’s folding that alongthe rock layers.The S1foliations is filled.The first event D1-M1is recorded by mainschistosity S1in metamorphic rocks and prograde chlorite-to sillimanite-gradeBarrovian metamorphism during subduction of Jinshajiang Ocean Plate andsubsequent crustal thickening and shortening.The second deformation D2is recordedas S2schistosity and ductile shear zone. The retrograde metamorphic stage M2isdeciphered to be coeval with the D2deformational event. The D2-M2event representsregional extension after previous crustal thicken. The third deformation (D3) ischaracterized by brittle fault, S3foliation, and related fault breccias and gauge. Thelast movement of fault is~200-~135ka, indicated by ESR ages.According to the analyzing of the Jinshajiang ductile shear zone on finitestrain,along the river appear the biggest strain intensity.From the river to its bothsides,the strain intensity is gradually reduced.We can divide the place into three strainareas.They are0.7＜εs＜0.9and0.55＜εs＜0.7and0.4＜εs＜0.55areas.The calculating of kinematic vorticity which based on polar circles suggestedthat the value of kinematic vorticity of Jinsha river is between0.87-0.98.It suggestedthat the Jinshajiang ductile shear zone dominated by simply shearing acting.Thekinematic vorticity and the strain intensity are of positive correlations.