An evaluation of zircon U-Pb dating for metamorphic rocks and comments on zircon ages of Dabie orogen.

Zircon is the most widely used mineral for U-Pb age determinations, and sho ws particular importance to a complicated geological history of a metamorph ic terrain, like Dabie Shan collision orogen. Zircon from metamorphic rocks may suffer from Pb diffusion loss, metamictization caused by lattice radia tion damage, overgrowth-mixing and recrystallization. All of these processe s would affect the accuracy and validity of zircon ages to some extent. In order to get geological meaningful ages, one must pay particular attention to mineral genesis and texture of zircons, and decide firmly zircon genetic process through internal structure observation, especially CL and BSE imag e before zircon U-Pb dating. The selection of reasonable common Pb correcti on, reasonable measured Pb-204 value and simple genetic zircon is preferred for TIMS dating. Here, we emphasize the advantage of SIMS dating technolog y in Dabie orogen research.