云南六合正长斑岩中花岗岩包体锆石U-Pb定年及其地质意义  

Zircon U-Pb Dating of Granite Xenolith from the Liuhe Syenite Porphyry from Yunnan, and Its Geologic Significance

作　　者：赵甫峰[1] 刘显凡[1,2] 卢秋霞[1] 楚亚婷[1] 李春辉[1] 宋祥峰[1] 蔡飞跃[1] 吴冉[1] 肖继雄[1] 

机构地区：[1]成都理工大学地球科学学院,成都610059 [2]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《地质学报》2011年第10期1574-1584,共11页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号40773031;40473027);教育部博士点基金(编号20105122110010);中国地质大学地质过程与矿产资源国家重点实验室开放基金项目(编号GPMR2007;GPMR0509);成都理工大学矿物学岩石学矿床学国家重点(培育)学科建设项目(编号SZD0407)联合资助成果

摘　　要：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 Jinshajiang-Ailaoshan faulting belt in western Yunnan province were found to host the Cenozoic alkali-rich porphyries, of which the Liuhe syenite porphyry contains granite xenolith paragenetically associated with deep mafic and ultramafic xenoliths. CL imaging LA-ICP-MS U-Pb dating and trace element analysis for the zircon from granite xenoliths conducted were conducted in this study. The results show that the zircons in the xenoliths contain three types： magmatic zircons, compound magmatic zircons with old cores and new growth zones, and metamorphic zircons. The new outer zones of compound magmatic zircons have an average weighted age of 39.2±2 Ma, which represents the petrogenic age of granite xenoliths and is consistent with formation age of alkali-rich porphyries. The old core has an average weighted age of 828.1±7.1 Ma, which represents the age of basal rock. The metamorphic zircons have an average weighted 206Pb/238age of 108.4±4.4 Ma, which is consistent with the age （102.87±1.19 Ma） of amphiboled flogopite garnet bistagite and represents the crystallization age of mantle fluid metasoatism. Above analytical data indicate that mantle fluid metasoatism may occur at and last a long period around Cretaceous period. Combined with lithographic research, it is concluded that the granite xenoliths were in a melting state when captured and migraged and granitic melting magma likely formed from partial melting of crust induced by mantle upwelling and contamination of mantle and crust fluid.

关 键 词：富碱斑岩 花岗岩包体 锆石U-PB定年 地幔流体作用 

分 类 号：P597.3[天文地球—地球化学] P588.121[天文地球—地质学]