天山东段1.4 Ga花岗闪长质片麻岩SHRIMP锆石U-Pb年龄及其地质意义  

1.4 Ga SHRIMP U-Pb age for zircons of granodiorite and its geological significance from the eastern segment of the Tianshan Mountains,Xinjiang,China

作　　者：胡霭琴[1] 韦刚健[1] 邓文峰[1] 张积斌 陈林丽[1] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学和地球化学重点实验室,广东广州510640 [2]新疆有色地质勘查局,新疆乌鲁木齐830000

出　　处：《地球化学》2006年第4期333-345,共13页Geochimica

基　　金：国家重点基础研究发展计划项目(2001CB409805);中国科学院广州地球化学研究所知识创新工程领域前沿项目(GIGCX-04-06)

摘　　要：天山最东段星星峡地区出露的片麻岩、混合岩和斜长角闪岩等,一直被看作是东天山最老的地层星星峡群,实际上是中—新元古代变质杂岩体。用SHRIMP锆石U-Pb定年技术分析了星星峡花岗闪长质片麻岩中19颗锆石,由其中谐和性较好的14个锆石的分析结果得到206Pb/238U和207Pb/206Pb加权平均年龄分别为(1436±13)Ma(2σ)和(1405.2±7.8)Ma(2σ),为天山东段星星峡花岗闪长岩的形成年龄,从而确定了天山造山带中元古代基底岩浆岩形成的时间,与北美及欧洲大陆广泛存在的1.4Ga岩浆活动具有同时性,对进一步思考天山造山带中1.4Ga岩浆活动形成的古陆块在前Rodinia大陆时期的归属有重要意义。主元素和微量元素研究结果显示星星峡1.4Ga花岗闪长岩具有岛弧岩浆岩特征,与北美中部大陆和欧洲大陆Fennoscandia的中元古代非造山作用形成的岩浆岩有所不同。另外,片麻岩中有的锆石具有新的生长边,并给出年轻化和较大的不一致年龄,说明1.4Ga片麻岩不同程度地受到新元古代(0.9～1.1Ga)变质作用和岩浆活动的改造,同时形成一些混合岩和花岗片麻岩。19颗锆石分析数据中有1个锆石的207Pb/206Pb比值年龄为(1845±23)Ma,与该片麻岩的Nd模式年龄相一致,可能代表更古老地壳物质中的残留锆石。The gneisses, migmatites Tianshan Mountains, have long been and amphibolites occurred in Xingxingxia area, the most eastern segment of the regarded as the oldest strata of Xingxingxia Group. However, they are actually a suit of Meso-neoproterozoie metamorphic complex. Nineteen zircons from a Xingxingxia granodioritie gneiss were dated using SHRIMP U-Pb method. The results indicate that 14 of these zircons show concordant ages with a mean ^206Pb/^238U and ^207Pb/^206Pb age of （1 436±13） Ma （2σ） and （1 405.2±7.8） Ma （2σ）, respectively, which represents the crystallization age of this Xingxingxia granodiorite. This age suggests that the Mesoproterozoie magmatism occurred in the Tianshan orogen was coeval with the 1.4 Ga magmatism that was widely observed in Northern America and Europe, and help to understand the ubiety of the Tianshan continental block in the Pre-Rodinia supereontinent in ca. 1.4 Ga. According to the major and trace elements, the 1.4 Ga Xingxingxia granodiorites show geochemical characteristics of island arc magma, which are different from those of Mesoproterozoic anorogenic granites in central continent of North America and Fennoscandia in Europe. Otherwise, some zircons from the granodioritic gneiss have growth margin, and show disconcortant ages with a trend of younging. This indicates that the 1.4 Ga granodioritic gneiss had been suffered from metamorphism and magmatism during Neoproterozoic （0. 9-1.1 Ga） to some extent, resulting in forming some migmatite and granitic gneiss. Among the 19 analyzed zircons only one shows older ^207Pb/^206pb age of （1845 ± 23） Ma. This is consistent with tDM age of Xingxingxia gneisses, suggesting remain zircon from contamination of older continental materials.

关 键 词：花岗闪长质片麻岩 1.4 GA SHRIMP U—Pb年龄 天山东段 

分 类 号：P597[天文地球—地球化学]