Preliminary U-Pb ion probe age determination of zircons from gneisses, Northern Dabie Terrain.

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