1993 年 88 巻 9 号 p. 415-431
Geochemical and cosmochemical studies on lithium are reviewed and the potential of lithium isotope systematics as a geological tracer is discussed in this article.
Lithium, the smallest of the alkaline elements, possesses two stable isotopes, 6Li and 7Li. It also displays the following unique physicochemical characteristics: (1) an extremely high cross-section of the lithium isotope 6Li for thermal neutrons; (2) high incompatibility in the mafic silicate minerals in the magmatic processes; (3) high solubility in fluid phases; and (4) large isotopic variations in the 6Li/7Li ratio of natural samples exceeding 30‰. The content and isotopic composition of lithium in meteoritic and terrestrial materials may provide important clues
to understanding nucleosynthesis theories and many geological phenomena including water/rock interactions, metamorphic and magmatic processes.
However, the isotopic behavior of lithium in geologic processes is still not well understood, since only a few reliable isotopic measurements of lithium are available for natural samples due essentially to analytical difficulties; derived from the extremely large mass difference between the two isotopes and no internally-derived correction for the mass fractionation in mass spectrometry. In order to apply lithium isotope systematics for understanding geochemical and water-related processes in the Earth and other planets, the development of a high precision technique for lithium isotope analysis is urgently required so as to accumulate the much needed fundamental data set of natural samples.