International Geologiical Congress - Oslo 2008


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MPN-12 Sederholm symposium on high-grade metamorphism, crustal melting, migmatites and granites


Geochemical evidences of the petrogenesis of a mixed mantle-crustal source and evolution at tiquiushan eclogite in the northern Jiangsu province


Li Huiming, Center of Modern Analysis (China)
Wang Yinxi, Center of Modern Analysis (China)
Chen Daogong, Department of Earth and Space Sciences (China)
Li Jianhua, No.5 Geological Party (China)


Introdution: Geological scientists have paild much attention to the suture zones formed by collision between the Sino-Korean and Yangtze blocks because of the discovery of the ultrahigh pressue metamorphic(UHPM) rocks from northern Jiangsu Province(Su), china.. Elogite from Tiquiushan lie in tectonics of the Xinyi-Donghai Regions, Jiangsu Province and is one of the ultrahigh pressue metamorphic rock. The chemistical composition of elogits: SiO2(45.03-45.89%),Fe2O3(1.54-1.65%),FeO(7.10-7.27%),Al2O3(20.05-20.69%),CaO(11.18-11.48%),MgO(9.57-9.61%),K2O(0.21-0.24%),Na2O(0.94-0.96%),P2O5(0.0862-0.0867),MnO(0.24-0.25%),TiO2(0.28-0.29%),H2o(0.56-0.61). Although the age of 200-240 Ma is probably the best estimation for UHPM metamorphism in the Dabie Mountains, the primary intrusive and metamorphic ages of the complex from northern Jiangsu province have not determined before. Using the Sm-Nd and Rb-Sr isotopic dating methods, our study is aimed at dating the UHPM metamorphic event of northern Jiangsu Province and its geochemical evidences of the eclogite petrogenesis.
Dicusion of Result and Conclusions: Sm-Nd dating on the three eclogite bodies in the northern Jiangsu yields the following new results: 213, 217 and 222 Ma, respectively. For three eclogites and six mineral samples, the age is 217±4.6 Ma (MSWD=0.68) ,εNd(T)=-2.90. Rb-Sr age of the eclogite body at the Tiqiushan is 200.4 Ma. Sm- Nd age of 217 Ma is adopted as the age of Tiqiushan eclogite body formed by ultrahigh pressure metamorphism. The Rb-Sr age reflects the age of this intrusion after the distribution of the subsequent geological processes. The model age of eclogite is about 1900 Ma and provides a close estimate of the average age of the basement. The pathogenesis and evolution of the eclogues show a mantle origin and a small amount of lower crystal contamination. The evidences show that Su and Lu blocks used to be a part of Qinling-Dabie fold zone. The collision period between the Sino-Korean and Yangtze blocks occurred about 217 Ma. The chemistical composition of elogits, Rb-Sr and Sm-Nd isotopic characteristic reflect crustal source from collision period of blocks.
Reference: Zheng Y F, Fu B, Gong B and Li Shuguang 1995. Unusually light oxygen in eclogite from Qinglingshan in the Su-Lu terrane. Chinese Science Bulletin Vol.40(Supplement)129-130.


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