Timing of the Hong′an Group in Hubei：Constraints from U-Pb dating of metagranitic intrusions

Abstract：The age of the protolith of the Hong′an Group in Hubei has been a controversial issue. Zircon U-Pb dating of different types of granitic intrusions in the Hong′an Group suggests that the Shuangfengjian granite lying unconformably below the Hong′an Group was emplaced at 813±6 Ma, whereas the Gaoge granite was intruded into the Hong′an Group at 638 ±142 Ma and metamorphosed at high pressure at 229±22 Ma. On that basis, combined with a number of Neoproterozoic age data obtained from the Yangtze craton and the Dabie orogen, it is believed that the ages of the sedimentary sequences in the metamorphic complex of the Hong′an Group, which are the product of the break-up of the Yangtze craton in the Neoproterozoic, should be limited in the range of c. 825～630 Ma. These sequences underwent low-temperature and high-pressure blueschist to eclogite facies metamorphism during the Indosinian (c. 230 Ma) collision between the North China and Yangtze cratons.