Deformation of granitoid plutons in the Dongshan area, southeast China: Constraints on the physical conditions and timing of movement along the Changle-Nanao shear zone

The NE-trending Changle-Nanao shear zone has affected several granitoid plutons in the Dongshan area, southeast China. Microstructures in the granitoids range from undeformed to solid state lineations and foliation. Migmatitic textures are common in some units. Microprobe analysis of total Al has been carried out on hornblende rims in four samples of gneiss from various points across the shear zone. Confining pressures calculated fall into range of: 4.2-4.9 kb. The average pressure (similar to 4.5 kb) suggests that the shear zone may have reached at least 16 km depth. Fluid inclusion studies referred from the correspondent P-T isochores indicate that the temperature of ductile deformation in the shear zone was similar to 740 degrees C. Observations on intrusive relations between the various granitic phases and their relative degrees of deformation suggest that emplacement of the different magma phases may be closely related in time and to movement along the Changle-Nanao shear zone. Zircon from one deformed pluton yielded a crystallization U-Pb age of 121.5 +/- 2.8 Ma. Field and microstructural data suggest the dated pluton is syntectonic, which constrains the upper age of high temperature deformation in the orthogneiss along the Changle-Nanao shear zone at that locality.