湖南丫江桥岩体锆石U-Pb年代学、地球化学及其地质意义  

Zircon U-Pb geochronology,geochemistry and geological significance of the Yajiangqiao granite in Hunan province

作　　者：夏宗强 肖敏[1,2,3] XIA Zongqiang;XIAO Min(National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing,Beijing 100029,China;Beijing Research Institute of Uranium Geology,Beijing 100029,China;CNNC Key Laboratory of Uranium Resources Exploration and Evaluation Technology Beijing Research Institute of Uranium Geology,Beijing 100029,China)

机构地区：[1]铀资源探采与核遥感全国重点实验室,北京100029 [2]核工业北京地质研究院,北京100029 [3]中核集团铀资源勘查与评价技术重点实验室,北京100029

出　　处：《世界核地质科学》2024年第4期665-680,共16页World Nuclear Geoscience

基　　金：中国核工业地质局生产中科研项目(编号:202238-9,202446-3)资助。

摘　　要：丫江桥岩体是湘中铀成矿带中的产铀花岗岩体之一。为了进一步评价花岗岩体的铀成矿潜力,对岩体内不同期次花岗岩开展LA-ICP-MS锆石U-Pb年代学、微量元素地球化学研究,分析花岗岩的成岩时代、岩石成因类型及岩体含铀性。结果表明:丫江桥岩体主体花岗岩锆石年龄为(231.0±2.4)Ma,补体花岗岩锆石年龄为(229.3±1.4)Ma、(221.7±3.2)Ma,岩体形成于晚三叠世,是印支晚期岩浆活动的产物。花岗岩锆石微量元素显示典型的壳源岩浆锆石特征,轻稀土亏损、重稀土极度富集,Ce正异常,Eu强烈负异常。丫江桥岩体是在后碰撞伸展的构造背景下,地壳减薄、压力降低以及地幔物质上涌的共同作用下,中元古界地壳物质部分熔融形成的花岗质岩浆上涌侵位冷却结晶而形成,岩浆演化过程中源区局部有幔源岩浆的参与。丫江桥岩体为印支期S型花岗岩,锆石铀含量高、w(Th)/w(U)比值低,符合产铀花岗岩的特征,但岩体出露面积小,平均铀含量低,不利于形成大型铀矿田。Yajiangqiao granite pluton is a uranium producing granite body in the Central Hunan uranium metallogenic belt.In order to further evaluate the uranium metallogenic potential of granite bodies,LA-ICPMS zircon U-Pb geochronology and trace element geochemistry studies were conducted on the granites of different stages.The diagenetic age and rock genesis type were analyzed,and the uranium ore-forming potential of the granite was further evaluated.The results indicate that the zircon age of the main granite in the Yajiangqiao pluton is(231.0±2.4)Ma,and the zircon ages of the complement granite are(229.3±1.4)Ma and(221.7±3.2)Ma.The pluton was formed in the Late Triassic and is a product of Late Indosinian magmatic activity.The trace elements in granite zircons exhibit typical characteristics of crustal magmatic zircons,with light rare earth elements depleted and heavy rare earth elements extremely enriched,positive Ce anomaly,strongly negative Eu anomaly.Under the tectonic background of post collision extension,by the combined effects of crustal thinning,pressure reduction,and mantle material upwelling occur,the crustal material of the Mesoproterozoic was partially melted to form the granitic magma.After the magma upwelling,emplacement,cooling and crystallization,the Yajiangqiao granite pluton formed.During the process of magma evolution,some parts of the source area were involved in mantle derived magma.The Yajiangqiao pluton is an Indosinian S-type granite with high zircon uranium content and low w(Th)/w(U)ratio,which is consistent with the characteristics of uranium-bearing granite.But the small exposed area of the pluton and low average uranium content are not conducive to the formation of large uranium ore field.

关 键 词：LA-ICP-MS锆石U-PB定年 锆石地球化学 产铀花岗岩 丫江桥岩体 湖南 

分 类 号：P597.3[天文地球—地球化学] P595[天文地球—地质学] P619.14