Study On The Deformation Features And Themetamorphic-deformation Stage Of The Jinshajiang In The Western Segment Of Yidun Island Arc

The Jinshajiang ductile shear zone with width of60-80km has the component ofstrike-slip, located between the Yidun Arc and Qiangtang Block, at the northwestern Yunnanand western Sichuan provinces, SW China. This ductile shear zone along the SN-strikingJingshajiang Suture was produced by the closing of the Paleotethys Ocean in Late Permianto Triassic. Based on field investigation and indoor analysis, the conclusions are as follows:(1) The Jinshajiang ductile shear zone experienced3major deformational andmetamorphic events: D1and M1are penetrative foliation and bearing of staurolite-kyanite-almandine, which indicate the crustal thickening of subduction and collision duringthe Variscan; D2are crenulation cleavage and sheath fold, M2are sillimanite, whichindicates the crustal thinning during the Indosinian; D3and M3are brittle fault and regionalretrograde metamorphism, which were produced by the collision of the Indian and Tibetplateau.(2) P-T clockwise path show trend of cooling from staurolite and kyanite to almandine.The path represent process of the medium temperature and high pressure metamorphismproduced by the crustal thickening to the medium temperature and low pressuremetamorphism due to the crustal thinning, which is attributed to the collapse of the orogen.(3) The kinematics vorticity (Wk) is0.78to0.97, which shows Jinshajiang ductileshear zone are general shear with major component of simple shear.(4) The kinematics vorticity (Wk) based on the EBSD of quartz indicates theJinshajiang ductile shear experienced the shearing process of median to low temperature. Allsamples experiende the low temperature process is consistent with the retrogrademetamorphism observed in the microscope. The preferred orientation of the quartz C-axisare have the characteristics of median temperature obviously, which was overprinted by thelow temperature metamorphism.