北大别片麻岩中锆石U—Pb年龄离子探针初步测定

对北大别鹿吐石和道士冲二个片麻岩中锆石进行了离子探针Ｕ－Ｐｂ年龄测定。二个样品１３个颗粒的２０个有效测定点的年龄表明，鹿吐石片麻岩主要分布在２３３￣３９４Ｍ道士冲片麻岩在３０７￣７１８Ｍａ之间。道十冲片麻岩年龄的一致性程度要高于鹿叶石，两个样品均无低于２２０Ｍａ的年龄信息。由于存在年龄的不一致性，这些年龄可能代表了由古老岩浆锆石和三叠纪的超高压变质锆石或者早白垩纪岩浆锆石所代表的混合、增生锆石。Ｈ

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(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.