湘中锡矿山矿区煌斑岩中捕获锆石U-Pb定年及其地质意义  

Zircon U-Pb Dating of the Lamprophyre in the Xikuangshan Mining District, Central Hunan and its Geological Implications

作　　者：彭建堂[1,2] 胡阿香[1] 张龙升[1] 雷文艳 阳杰华[2] 林芳梅[1] 

机构地区：[1]中南大学有色金属成矿预测教育部重点实验室,地球科学与信息物理学院,湖南长沙410083 [2]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵州贵阳550002 [3]广东省有色金属地质局932队,广东韶关512026

出　　处：《大地构造与成矿学》2014年第3期686-693,共8页Geotectonica et Metallogenia

基　　金：国土资源部公益性行业科研专项课题(编号:200911007);国家面上基金项目(批准号:41272096);中国地调局危机矿山项目(编号:20109901)联合资助

摘　　要：利用LA-ICP-MS技术,对湘中锡矿山煌斑岩中的锆石进行U-Pb同位素定年。研究表明,该煌斑岩中的锆石呈半自形或半浑圆状,为捕获锆石。锆石阴极发光图像显示有典型的振荡环带和韵律结构,部分还可见扇形分带,其形貌和地球化学特征均显示为岩浆成因。锆石U-Pb同位素年龄主要集中在830 Ma和800 Ma附近,少量为-730 Ma,与江南古陆前寒武纪浅变质岩的年龄十分吻合,揭示湘中盆地深部确实存在新元古界基底,这为示踪湘中锑矿的成矿物质来源和判别湘中地区大地构造环境提供了新的依据。锡矿山煌斑岩形成于一种拉张伸展的构造环境中,其侵位深度为5 km以上。The giant Xikuangshan deposit, located in the Xiangzhong Basin, Central Hunan, is the largest antimony deposit in the world. In spite of numerous detailed geological investigations and geochemical researches have been carried out, the sources and tectonic background of the giant ore deposit is unclear. The lamprophyre dyke occurring in the eastern part of the mining district probably can shed light on these issues. LA-ICP-MS U-Pb isotopic dating has been conducted on zircon grains collected from the lamprophyre dyke in the Xikuangshan mining district. The zircon grains are usually subhedral or sub-rounded, and exhibit typical oscillatory or sector zoning under cathodoluminescence. Both its the morphology and geochemical signatures（Th/U ratio and REE chondrite-normalized distribution pattern） of these zircon grains reveals that they are predominately of magmatic origin, and were probably captured from the wall rocks during magma ascending. The zircon U-Pb ages mainly vary in the range of 830 Ma to 800 Ma, which coincide well with the ages of the Neoproterozoic Lengjiaxi Group and Banxi Group occurred in the adjacent Xufeng Range, implying the possible existence of underlying Precambrian clastic basement in the Xiangzhong Basin. The inferred Precambrian basement lays foundation for the further understanding for tracing the ore-forming metal of the giant Xikuangshan deposit and determining the tectonic nature of the Xiangzhong Basin. The Neoproterozoic basement underlying in the Xiangzhong Basin might have provided Sb for the giant ore accumulation in the Xikuangshan mining district. Tectonically, the Xiangzhong Basin should belong to the Yangtze Block rather than the Cathaysian Block as was previously considered. The lamprophyre in the Xikuangshan mining district formed under the geodynamic setting of crustal extension, and emplaced at a depth of at least 5 kilometers.

关 键 词：锆石U-PB定年 煌斑岩 锡矿山矿区 湘中地区 

分 类 号：P597[天文地球—地球化学]