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Zircon U-Pb Age and Geochemical Characteristics of Peraluminous Fine-Grained Granite in Western Part of the Fucheng Pluton, Jiangxi Province
详细信息   
摘要
In this paper,fine-grained granite in western part of the Fucheng pluton in Huichang county,Jiangxi Province,was selected for a detailed geochronological,whole-rock geochemical,and Hf isotopic geochemical study in order to elucidate its petrogenesis.LA-ICP-MS U-Pb zircon dating of the studied fine-grained granites yields ages of 219.1-221.5 Ma,with an mean value of 220 Ma,indicating that this pluton was generated during Indosinian stage.Chemically,this pluton is peraluminous(A/CNK=1.11-1.26) and shows high contents of silica(SiO 2 =71.7%-78.2%) and alkalis(K 2 O+Na 2 O=7.16%-8.13%,K 2 O/Na 2 O=2.00~3.53),low abundance of calcium,and magnesium.The rocks display low total REE contents(ΣREE=72.9× 10-6 ~203.0×10-6) with strongly negative Eu anomalies,and are enriched in LILEs such as Rb,Cs,K,Pb,and HFSEs such as Th,U,Ta,Zr,and depeted in Ba,Sr,P,Ti.Overall,the mineralogical and geochemical features suggest that the Fucheng fine-grained granite can be genetically grouped into S-type granite.LA-ICP-MS U-Pb zircon ages for the main coarse-grained granite of the Fucheng pluton are 227 Ma,indicating that this pluton was also generated during Indosinian stage.Chemically,the coarse-grained granites are weakly peraluminous to strong pereluminous(A/CNK=0.9~1.14) and show high contents of silica(SiO 2 =75.1%~76.3%) and alkalis(K 2 O+Na 2 O=7.392%~8.72%,K 2 O/Na 2 O=1.79~2.60),low abundance of calcium,magnesium.The rocks display low total REE contents(ΣREE=125.5×10-6 ~160.2×10-6) with strongly negative Eu anomalies,and enriched in LILEs such as Rb,Cs,K,Pb,and HFSEs such as Th,U,Ta,Zr and depeted in Ba,Sr,P,Ti.According to the petrographic and geochemical characteristics,the coarse-grained granite is also S-type.The zircon Hf isotopic compositions of the fine-grained granites show large variations,with ε Hf(t) values ranging from-2.3 to-10.8(mean value of-7.5),and two stage model ages between 1.4 and 1.96Ga.The zircon Hf isotopes of the main coarse-grained granite also show large variations,with ε Hf(t) values varying between-5.0 and-19.8(average of-8.8),and two stage model age between 1.59 and 2.51 Ga.In summary,the granite was formed from the magma generated by partial melting of metamorphic rocks of mainly pelite,and the magma then suffered fractional crystallization under a syn-collisional setting.

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