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 granitoi d plutons in the Dongshan area, southeast China. Microstructures in th e granitoids range from undeformed to solid state lineations and folia tion. Migmatitic textures are common in some units. Microprobe analysi s of total Al has been carried out on hornblende rims in four samples of gneiss from various points across the shear zone. Confining pressur es calculated fall into range of: 4.2-4.9 kb. The average pressure (si milar to 4.5 kb) suggests that the shear zone may have reached at leas t 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 intrusiv e relations between the various granitic phases and their relative deg rees of deformation suggest that emplacement of the different magma ph ases may be closely related in time and to movement along the Changle- Nanao shear zone. Zircon from one deformed pluton yielded a crystalliz ation U-Pb age of 121.5 +/- 2.8 Ma. Field and microstructural data sug gest the dated pluton is syntectonic, which constrains the upper age o f high temperature deformation in the orthogneiss along the Changle-Na nao shear zone at that locality.