Formation history and protolith characteristics of granulite facies metamorphic rock in Central Cathaysia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

The petrochemical as well as zircon U-Pb andLu-Hf isotopic studies of granulite facies metamorphic rockfrom the Taoxi Group in eastern Nanling Range, CentralCathaysia indicate that its protolith is the sedimentary rockwith low maturation index. The clastic materials are mostlyfrom middle Neoproterozoic (~736 Ma) granitoid rocks withminor Neoarchaean and Paleoproterozoic rocks. The timingof this Neoproterozoic magmatism is in agreement with thesecond period of magmatism widespread surrounding theYangtze Block. Hf isotopic data indicate that the Neopro-terozoic granitoids resulted from the recycled Paleoprotero-zoic mantle-derived crustal materials. The sedimentary rockwas deposited in Late Neoproterozoic Era, and carried intolow crust in Early Paleozoic. The partial melting of themeta-sedimentary rock took place at about 480 Ma and sub-sequently granulite facies metamorphism occurred at ca. 443Ma. The zircons forming during this time interval (EarlyPaleozoic) show large Hf isotope variations, and their εHf(t)values increase from ?13.2 to +2.36 with decreasing age,suggesting the injection of mantle-derived materials duringpartial melting and metamorphism processes in the EarlyPaleozoic. Calculation results show that this metamorphicrock, if evolved to Mesozoic, has similar isotopic compositionto the nearby Mesozoic high Si peraluminous granites, im-plying that this kind of granulite facies metamorphic rock isprobably the source material of some Mesozoic peralumi-nous granitoids in eastern Nanling Range.