广东湛江湖光岩地区玄武岩风化壳Fe同位素研究

Iron Isotope Study of Basalt Weathering Crust from the Huguangyan District,Zhanjiang,Guangdong Province

本文对广东湛江湖光岩地区厚度分别为4m和7m的两个不同喷发时代玄武岩形成的风化壳样品进行Fe同位素分析,分析结果显示：厚度4m风化壳样品Fe同位素组成δ~57 Fe范围为0.17‰~0.57‰;厚度7m风化壳样品Fe同位素组成δ~57Fe范围为0.20‰~0.68‰,相对于标准物质IRMM-014,不同深度风化壳样品均显示Fe的重同位素富集。两风化壳剖面自下而上,随风化程度增大,风化壳样品中Fe同位素分馏程度也呈现逐渐增大的趋势,表明风化壳样品中Fe的重同位素富集趋势与风化壳的发育程度正相关,风化壳土壤中Fe同位素组成是反映土壤风化程度的指标。另一方面,风化过程可将地球外部圈层（岩石圈、水圈、生物圈）有机结合起来,风化壳土壤Fe同位素组成变化是表生植物和水淋滤共同作用的结果,对化学风化过程中Fe同位素研究,将会极大地补充表生过程中同位素地球化学的知识,同时Fe同位素可作为表生过程中物质的循环、环境的变化等过程中有力的示踪/指示技术手段加以应用。

We measured weathering crust iron isotope composition of depth profile 1 （4 m） and depth profile 2 （7 m） from Huguangyan district in Zhanjiang city, Guangdong province. The result shows that the distribution range of 57Fe in depth profile1 is 0.17‰~0.57‰, and is 0.20‰-0.68‰ in depth profile 2. Both depth profiles have heavy iron isotope composition. Iron isotope composition become increasing heavier from bottom to top in both depth profiles, and the positive correlation between heavy iron isotope enrichment and degree of weathering happened. It implied iron isotope composition of weathering crust can be the index of the degree of weathering. On the other hand, lithosphere, hydrosphere and biosphere can be linked by weathering process because iron isotope composition of weathering crust affected by plants and leaching. Iron isotope study on weathering will greatly complement supergene geochemistry udnerstanding and iron isotope can be used as powerful tracer to be applied.