U-Pb Zircon Ages of the Eclogite and Tonalitic Gneiss from the Northern Dabie Mountains, China and Multi-Overgrowths of Metamorphic Zircons

The U?Pb zircon ages of the eclogite and tonalitic gneiss from the Northern Dabie Mountains were presented. The data suggest that: (1) the peak metamorphic age of the eclogite facies from the Raobazhai eclogite is 226～230 Ma; (2) the tonalitic gneiss near Ta'erhe underwent a Triassic metamorphic event; (3) zircon U?Pb ages of 226～230 Ma for the high?or ultrahigh pressure rocks from the Northern Dabie Mountains are similar to those from the Southern UHP metamorphic belt, implying that most of eclogites or tonalitic gneiss here should be a part of Yangtze subducted continental crust and underwent a Triassic HP or UHP metamorphism; (4) the protolith ages of both eclogite and tonalitic gneiss are Late Proterozoic Era; (5) they are both affected strongly by Early Cretaceous thermal event; (6) the zircons from eclogite and gneiss have experienced two episodes of overgrowths on the margin of old zircons during the Triassic HP or UHP metamorphism and the Early Cretaceous thermal metamorphism. The overgrowth model of zircon under multi?metamorphism is very helpful to interpret the U? Pb zircon data from the high?grade metamorphic rocks.