Zircon U-Pb ages of Yanzihe gneiss from Northern Dabie, China: evidence for Jurassic metamorphism.

U-Pb ages of zircons from Yanzihe gneiss of Northern Dabie have been determined by single-grain TIMS method. There are two types of zircon: one is the magmatic zircon from protolith which had undergone different degree of Pb loss, and the another is metamorphic zircon. Five points give a good concordia line with lower intercept at 228±13Ma and upper intercept at 880±110Ma ( MSWD = 1.1). The upper intercept point represents the protolith age and the lower intercept point represents the metamorphic age. One metamorphic zircon gives concordant U-Pb age of 238Ma, which is similar to the lower intercept age. The result demonstrates that the Northern Dabie gneiss also underwent Jurassic metamorphic event. The suture of North China Block and Yangtze Block should be north of the North Dabie.