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  

作　　者：YU Jinhai ZHOU Xinmin Y. S. O'Reilly ZHAO Lei W. L. Griffin WANG Rucheng WANG Lijuan CHEN Xiaomin 

机构地区：[1]State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210093, China [2]GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, N.S.W. 2109, Australia

出　　处：《Chinese Science Bulletin》2005年第18期2080-2089,共10页

基　　金：funded by the National Natural Science Foundation of China(Grant Nos.40372087 and 40132010);National Innovation Group Foundation of China(Grant No.40221301)

摘　　要：The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic (~736 Ma) granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early Paleozoic) show large Hf isotope variations, and their -Hf(t) values increase from -13.2 to +2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.The petrochemical as well as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Tao＇xi Group in eastern Nanling Range, Central Cathaysia indicate that its protolith is the sedimentary rock with low maturation index. The clastic materials are mostly from middle Neoproterozoic （-736 Ma） granitoid rocks with minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement with the second period of magmatism widespread surrounding the Yangtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recycled Paleoproterozoic mantle-derived crustal materials. The sedimentary rock was deposited in Late Neoproterozoic Era, and carried into low crust in Early Paleozoic. The partial melting of the meta-sedimentary rock took place at about 480 Ma and subsequently granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval （Early Paleozoic） show large Hf isotope variations, and their ZHf（t） values increase from -13.2 to ＋2.36 with decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early Paleozoic. Calculation results show that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby Mesozoic high Si peraluminous granites, implying that this kind of granulite facies metamorphic rock is probably the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

关 键 词：麻粒岩 锆石 同位素 变质结构 沉积岩石 

分 类 号：P588.3[天文地球—岩石学] P597[天文地球—地质学]