Preliminary U-Pb ion probe age determination of zircons from gneisses, Northern Dabie Terrain
北大别片麻岩中锆石U—Pb年龄离子探针初步测定

Two zircon ages were determined for U-Pb ion probe analyses from Lutushi(LTS) and Daoshicong(DSC) gneisses, Northern Dabie Terrain(NDT). Twenty U-Pb ages from thirteen zircon grains indicated that the ages for LTS gneiss are mainly ranged between 233~394Ma and DSC gneiss between 307~718Ma. The degree of concordance for DSC gneiss is better than that of LTS gneiss. Both gneisses show no age information below 220Ma. Since there were exits of discordances, these zircon ages probably represented mixing and overgrowth of ancient magmatic zircons with Triassic ultra-high pressure metamorphic and Cretaceous magmatic zircons. Those which were treated by Harker et al. as typical gneisses occurred in NDT may also be complex zircons which are formed in Precambrian magmatic zircons with late Cretaceous metamorphic zircons. Therefore, according to their U-Pb ages and distribution of zircons, one cannot conclude that all the gneisses from NDT were formed at Cretaceous. There may be two different age gneisses in NDT.