华南典型砖红壤风化剖面Si和U同位素组成及其分馏机制研究

砖红壤的风化和成土过程是元素表生地球化学循环的关键环节之一。针对砖红壤中硅（Si）和铀（U）同位素的垂向组成和分馏机理尚不清楚的问题，本项目以湛江玄武质砖红壤剖面为研究对象，综合采用全剖面全岩同位素组成测定、原生矿物溶解实验、土壤分相提取实验，以及质量平衡模型计算的方法，将主量元素Si和氧化还原敏感性元素U耦合起来，研究砖红壤Si和U同位素组成垂向分布特征，分析同位素分馏机理，确定玄武岩强风化过程对水圈元素和同位素组成的净输出。项目预期将建立高精度U稳定同位素测试方法，阐明砖红壤风化剖面Si和U的同位素组成和分馏机制，实现对玄武岩强风化过程中元素迁移和同位素组成净输出的定量估算。项目研究成果对理解Si和U的表生地球化学循环具有重要意义，也为国内今后开展U稳定同位素研究带来便利。

The weathering and pedogenic processes of latosol is one of the key components of element biogeochemical cycle in Earth surface. Currently the vertical compositions and fractionation mechanisms of Silicon (Si) and Uranium (U) isotopes in latosol profile are poorly understand. In view of this, this project takes basaltic latosol profile in Zhanjiang city as research object, and comprehensively determine the Si and U isotope signatures of bulk soil, dissolved primary minerals and sequential extracted fractions of this profile. In this project, major element Si and redox sensitive element U are coupled to study vertical distribution characteristics and fractionation mechanisms of Si and U isotopes in latosol profile. Mass balance model calculation will be adopted to estimate the net elements and isotopes exportation to Hydrosphere during intense weathering of basalt. This project is expected to establish a high precision U stable isotope measurement method, and clarify the isotopic compositions and fractionation mechanisms of Si and U in latosol profile. It will also quantitatively estimate the net element migration and isotopic output during intense weathering of basalt. Research results of this project are of great significance for understanding the biogeochemical cycle of Si and U in Earth surface, and make it more convenient for future research on U stable isotope in China.