U-Pb ages and oxygen isotope compositions of zircons from gneiss of Huangtuling, Northern Dabie: old protolith and multi-stage evolution

The internal structure of zircons from gneiss of Huangtuling, Northern Dabie has been investigated by cathodoluminescence imaging, and their U-Pb ages and oxygen isotope compositions have been determined by SIMS (Cameca 1270). Zircons display core-mantle-rim structure, the core is the magmatic domain which preserves oscillatory zoning, the mantle is the metamorphic zone induced by recrystallization, and the rim is the overgrowth domain which was precipitated from partial melt. These three domains have different ages: similar to2800 Ma for the core is the protolith age, similar to2000 Ma for the mantle is the metamorphic age, and similar to110 Ma age for the rim reflects the influence of Cretaceous thermal event. similar to2800 Ma and similar to2000 Ma ages for Huangtuling gneiss and its included granulite and similar to3400 Ma age for relict zircon from Huangtuling granulite are comparable with the ages for Kongling group of Yangtze block, so it is inferred that Northern Dabie was a part of Yangtze block and the suture between Yangtze and North China blocks should be north of Northern Dabie. Oxygen isotope composition of the core, mantle and rim of zircons are different, delta(18)O values of the core are similar to11.7parts per thousand, 11.1parts per thousand similar to18.7parts per thousand for the mantle and 5.5parts per thousand similar to8.2parts per thousand for the rim. From these oxygen isotope data we suggest that the protolith of Huangtuling gneiss was S-type granite and exotic fluid/melt involved in the system during both similar to2000 Ma and similar to110 Ma events.