广西姑婆山花岗岩单颗粒锆石LA-ICP-MS U-Pb定年及全岩Sr-Nd同位素研究  

Study on Zircon LA-ICP-MS U-Pb Dating and Sr-Nd Isotope of the Guposhan Granite in Guangxi

作　　者：顾晟彦[1] 华仁民[1] 戚华文[1,2] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学花岗岩火山岩及成矿理论研究所 [2]中国科学院地球化学研究所,贵阳550002

出　　处：《地质学报》2006年第4期543-553,共11页Acta Geologica Sinica

基　　金：国家自然科学基金重点项目(编号40132010);国家重点基础研究发展规划项目(编号1999CB403209)资助成果。

摘　　要：LA-ICP-MS锆石U-Pb同位素年龄测定表明,组成广西姑婆山花岗岩的东、西岩体和里松岩体的年龄分别为160.8±1.6Ma、165.0±1.9Ma、163.0±1.3Ma,在误差范围内基本一致,说明整个姑婆山岩体是同一时代的产物,是燕山中期第一阶段华南大规模陆壳重熔型花岗岩浆活动的产物。姑婆山花岗岩中的各个岩体虽然形成于同一时代,但它们之间在岩石学、地球化学特征方面有一定的差异。除了主微量元素、稀土元素特征有所不同外,Rb-Sr、Sm-Nd同位素特征研究表明姑婆山西岩体的粗粒花岗岩、东岩体、里松岩体及其包体的平均(87Sr/86Sr)i=0.7064、εNd(t)平均为-3.03,反映它们的源区有较多地幔物质组分参与;而姑婆山西岩体的细粒花岗岩的(87Sr/86Sr)i=0.7173、εNd(t)平均为-5.00,具强烈的Eu亏损、高Rb/Sr值等特征,它的源区可能是由一个相对古老地壳组分和年轻地幔组分组成的混合源区。此外,姑婆山东岩体(GP-1)中发现的继承锆石的206Pb/238U年龄为806.4Ma,与杭州—诸广山—花山花岗岩带(HZH)上的赣北九岭堇青石花岗岩、广西英桥混合花岗岩的年龄相似,为HZH带新元古代的岩浆活动提供了锆石年代学方面的依据。Zircon U-Pb dating with the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite, among which the east Guposhan unit is 160. 8±1.6 Ma, the west Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. It is worth noticing that the ages of the three units are very similar to each other within the analytical error. It thus proves that the whole Guposhan granite was formed in the same age. They are products of large-scale magmatism of crust-remelting granitoids in the first stage of the middle Yanshanian Period in South China. Though forming in the same age, the three units have differences in petrological and geochemical characteristics. Besides the differences in major, trace and rare earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The east unit, Lisong unit and its enclaves have a similar （^87Sr/^86Sr）i value of 0. 70643 and average εNd （t） （-3.03）, indicating that more mantle materials participated in the magma derivation; whereas the west unit has higher （^87Sr/^86Sr）i （0. 7173）, lower εNd （t） （-5. 00）, and is characterized by strong negative Eu anomalies and a higher Rb/Sr ratio, which may suggest that its source was composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the east Guposhan unit （GP-1） yielded a ^206Pb/^238U age of 806.4 Ma, which is similar to those of the Jiulin cordierite granite in northern Jiangxi and the Yinqiao migmatic granite in Guangxi in the HZH granite zone. The discovery thus provides new evidence for late-Proterozoic magmatism in the HZH granite zone.

关 键 词：姑婆山花岗岩 锆石U-Pb年龄 Rb—Sr Sr—Nd同位素 

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