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Zircon Hf isotopic features of TTG gneisses and formation environment of Precambrian Sushui complex in Zhongtiao mountains.

GUO LiShuang LIU ShuWen LIU YuLin TIAN Wei YU ShengQiang LI QiuGen L(?) YongJun Key Laboratory of Orogenic Belt and Crustal Evolution Ministry of Education,Peking University,Beijing 100871,China  
The Precambrian Sushui Complex in Zhongtiao Mountain is composed principally of Xiyao and Zhaizi TTG gneisses, Henglingguan and Beiyu calc-alkaline granitoids.SHRIMP zircon U-Pb dating for Xiyao TTG gneiss yield the weighted mean ~(207)Pb/~(206)pb age of 2536±8Ma,revealing that it was formed in the Neoarchean.In-situ zircon Lu-Hf isotopic analyses of Xiyao and Zhaizi TTG gneisses and Henglingguan-Beiyu calc-alkaline granitoids show that the magmatic zircons have positiveε_(Hf)(t) values,and theseε_(Hf)(t) values are plotted within the revolution areas of the 2600~3100Ma old continental crust in the age vs.ε_(Hf)(t) diagrams. The analytical spots of three inherited zircon cores from the Beiyu calc-alkaline granitoid yield a weighted mean ~(207)Pb/~(206)pb age of 2633±84Ma,and theε_(Hf)(t) values of these inherited cores of magmatic zircon grains are,-2.0~+5.6.The characteristics of zircon SHRIMP U-Pb ages and Hf isotope compositions of these TTG gneisses and calc-alkaline granitoids from the Precambrian Sushui Complex indicate that they were possibly formed in the Neoarchean to Paleoproterozoic tectonic settings of Andes-type continent margin, and the magmas could be derived from the partial mehing of juvenile crust materials from the depleted mantle and more older continental crust materials.
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