浙西双溪口花岗岩锆石U-Pb定年、Hf同位素组成和地球化学特征:对Sn成矿作用的制约

浙西地区地处下扬子陆块东南缘,区内中生代岩浆侵入活动强烈,与成矿作用关系密切。与锡成矿作用有关的双溪口花岗岩锆石LA-ICP-MS U-Pb定年结果显示,成岩年龄为130.4±1.1 Ma。岩石具有富SiO_2,高Ga、Zr、Nb和Y,贫Al_2O_3、Sr、Ba、Ti和P,Eu强烈负异常(δ_(Eu)=0.08~0.42)的地球化学特征,Zr饱和温度为848~887℃,属铝质A型花岗岩。锆石Hf同位素ε_(Hf)(t)变化范围集中在-4.66~-2.50之间,二阶段模式年龄t_(DM2)变化于1192~1311 Ma之间,暗示其源区物质主要来自中元古代地壳。结合区域地质矿产资料综合分析,认为浙西地区与锡相关的成矿事件发生于132~127 Ma之间,受控于早白垩世伸展环境下壳幔岩浆的相互混合作用。

Zircon U-Pb Age,Hf Isotope and Geochemistry of the Shuangxikou Granite in Western Zhejiang: Constraints on the Tin Mineralization

The Mesozoic magmatism in the western Zhejiang province,i.e.,the southeastern margin of the Yangtze Block,is widespread and commonly associated with ore mineralization.LA-ICP-MS zircon U-Pb dating of the Shuangxikou granite yielded an age of 130.4±1.1 Ma.The granite intrusion is characterized by metaluminous,showing features of high-K calc-alkalic series.The granites have low A12O3,Sr,Ba,Ti,P contents,obvious negative Eu anomalies (6Eu=0.08-0.42),and high contents of SiO2,Ga,Zr,Nb,and Y.The crystallization temperature estimated by "Zr saturation temperature" is 848-887 °C,reflecting the character of A-type aluminous granite.Zircon Hf isotopic compositions (εHf(t) of-4.66--2.50,and tDM2 of 1.19-1.31 Ga) indicate that the source of the Shuangxikou granite was dominated by the Mesoproterozoic crust material.On the basis of an integrated study of geological survey and mineral exploration in the western Zhejiang,we conclude that the tin mineralization occurred in 132-127 Ma controlled by the crust-mantle interaction in the extensional environment in the Early Cretaceous.