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滇西地区沿金沙江-哀牢山断裂带广泛发育新生代富碱斑岩,其中六合富碱斑岩中发现了与镁铁-超镁铁质深源包体紧密共生的花岗岩包体。本文对花岗岩包体中锆石进行了阴极发光图像、LA-ICP-MS微量元素分析和U-Pb定年研究。研究表明,该花岗岩包体中锆石可分为岩浆锆石、老核新壳的复合岩浆锆石和变质交代成因锆石;复合岩浆锆石的新壳206Pb/238U平均加权年龄为39.2±2Ma,代表花岗岩包体的成岩年龄,与寄主富碱斑岩的成岩年龄基本一致;复合岩浆锆石的老核206Pb/238U平均加权年龄为828.1±7.1Ma,代表基底岩石年龄。变质锆石的206Pb/238U平均加权年龄为108.4±4.4Ma,与角闪石化金云石榴透辉岩中角闪石Ar-Ar年龄102.87±1.19Ma基本吻合,代表地幔流体交代矿物的结晶年龄,表明地幔流体交代作用过程可能在白垩纪前后延续一个相当长的时期。结合岩相学研究,认为该花岗岩包体被捕获运移时处于熔融态;花岗质熔浆的形成很可能与地幔流体作用引发的地壳部分熔融与壳幔岩浆混合作用密切相关。
The Cenozoic alkali-rich porphyries are extensively developed along the Jinsha-Ailaoshan fault zone in Western Yunnan. The granite inclusions closely intergrowth with the mafic-ultramafic deep-sourced inclusions are found in the Liuhe alkali-rich porphyry. In this paper, the cathodes luminescence images, LA-ICP-MS trace element analysis and U-Pb dating of zircons in granite inclusions were studied. The results show that the zircons in the granitic inclusions can be divided into magmatic zircons, composite magmatic zircons of the old nuclei and new metamorphic zircons, and 206Pb / 238U zircons of the composite magmatic zircons have an average weighted age of 39.2 ± 2Ma. The diagenetic ages of representative granitic inclusions are basically the same as those of the host alkali-rich porphyries. The average weighted age of the 206Pb / 238U cores of the composite magmatic zircons is 828.1 ± 7.1Ma, which represents the basement rock age. The average weighted 206Pb / 238U age of metamorphic zircon is 108.4 ± 4.4Ma, which is basically consistent with the amphibole Ar-Ar age of 102.87 ± 1.19Ma in the amphibole-petrochemical phlogoid garnet, representing the crystallization age of the mantle fluid metasomatism, It shows that the mantle fluid metasomatic process may extend for a long time before and after the Cretaceous. Based on the study of petrography, the granite inclusions are believed to be in a molten state when they are captured and transported. The formation of granitic magma is probably closely related to the crustal mantle magma mixing caused by the mantle fluid interaction.