Marine Geochemistry of Lithium Isotopes

由美国国家科学基金会资助的一项初步研究开发了一种测量地质材料中锂同位素比率的新方法。质谱学技术涉及四硼酸锂的热电离，能够产生6Li/7Li比值，不确定度为1.3 0/00(1个标准偏差)。初步调查结果表明，海洋环境中Li的同位素组成发生了重要的变化，证明了Li同位素比值作为海洋物质交换示踪剂的有效性。该提案总结了初步研究的结果，并要求支持对锂的海洋同位素地球化学进行全面调查。将努力确定海洋中锂的源和汇的同位素组成以及与质量转移过程有关的同位素分馏。重点介绍了锂同位素系统学在认识(1)对海水锂同位素组成的控制，(2)海水-玄武岩相互作用过程中锂的迁移方向和大小，以及(3)锂在海洋沉积物中的富集化过程中的应用。这些考虑解决了锂在海洋中的质量平衡问题，并对表征锂的地球化学循环具有重要意义。

A new method has been developed for the measurement of lithium isotope ratios in geological material, as a result of an initial study funded by NSF. The mass spectrometric technique involves the thermal ionization of lithium tetraborate and is capable of producing 6Li/7Li ratios with an uncertainty of 1.3 0/00 (one standard deviation). The results of a preliminary survey indicate important variation of th eisotope composition of Li in the marine environment and demonstrate the usefulness of Li isotope ratio as a tracer for mass exchange in the ocean. This proposal summarizes the findings of the initial research and requests support for a comprehensive investigation of the marine isotope geochemistry of lithium. Efforts will be directed at determining the isotopic composition of the sources and sinks of Li in the ocean and the isotopic fractionation associated with the mass transfer processes. The main emphasis is on the utilization of Li isotope systematics in the understanding of (1) the control on the Li isotopic composition of seawater, (2) the direction and magnitude of Li transfer during seawater-basalt interaction and (3) the process by which Li is enriched in marine sediments. These considerations address the problem of mass balance of Li in the ocean and is of fundamental importance in the characterization of the geochemical cycle of Li.