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《Earth Science》 2018-07
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Indosinian Metamorphism and Anatexis in Yunkai Massif:Evidences from Zircon Geochronology and Hf Isotopes of Migmatites and Gneisses

Ke Xianzhong;Zhou Dai;Long Wenguo;Wang Jing;Xu Deming;Tian Yang;Jin Wei;Wuhan Center of China Geological Survey;  
The Mesozoic tectonic evolution in Yunkai massif has always been one of hot topics in South China.Zircons from five metamorphic rocks including migmatite and gneiss and one granite from the metamorphic basement in Yunkai massif were measured by the LA-ICP-MS U-Pb dating method,yielding 7 metamorphic(anatectic)or magmatic ages(440.3±3.3 Ma,230.2±2.9 Ma,230.7±1.3 Ma,459.5±2.7 Ma,431.5±4.3 Ma,229.2±5.4 Ma,229.7±2.7 Ma)and 2 groups of detrital ages.Both the detrital zircons showed Archaean-Neoproterozoic age range with ~1.0 Ga age peaks,which were similar with those of the Tiantangshan Group and the Yunkai Group.Together with the regional data,it was concluded that the Tiantangshan Group and the Yunkai Group,which were analogous in provenance and formed in Early Palaeozoic-Neoproterozoic,were broadly overprinted by the Indosinian metamorphism(anatexis)-deformation-fluid activities after the Caledonian tectonic-thermal events,resulting in differences in metamorphic grade and appearance.In situ zircon Lu-Hf isotopic analysis from four samples show that both the isotopic compositions of Caledonian metamorphic and anatectic zircons were similar with each other,which was ascribed to inheriting the com-positions of provenance rocks,whereas the different isotopic compositions of Indosinian metamorphic and anatectic zircons could have been caused by individual mechanism of metamorphic and anatectic processes.It was inferred that the dominant Paleo-Mesoproterozoic crustal material played important role in the metamorphism and anatexis processes in Caledonian and Indosinian,and a few mantlederived material was added in the anatectic processes in Caledonian and Indosinian with relatively remarkable contribution of mantlederived material in Indosinian.
【Fund】: 中国地质调查局项目(Nos.DD20160031 DD20160035 12120114039201 12120113066400)
【CateGory Index】: P588.3
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