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.

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A model of the structure in the Martian interior was presented on the basis of the high pressure and temperature experiments on the homogeneous Martian mantle model composition of Morgan and Anders (1979). The sequence of phase assemblages with increasing depth in the Martian interior is summarized as follows: olivine+pyroxene+plagioclase (+minor phases) in the mantle at the depths shallower than 230km; olivine+pyroxene+garnet from 230 to 1, 280km; garnet+β-spinel and/or γ-spinel ((Mg, Fe)₂, SiO₄, )+magnesiowustite in the Martian transition zone from 1, 280 to 1, 800km; garnet+Mg-perovskite+Ca-perovskite+magnesiowustite in the Martian lower mantle from 1, 800 to 2, 020km. The core-mantle boundary is calculated on the basis of the total mass of Mars and the density profile of the mantle and core. This model satisfies the observed geophysical data of the mean radius and mean density. The moment of inertia factor of this model (0.363) is close to the observed value (0.365).
Using the Martian basic data, such as the mean density, the total mass, and the density profile of Mars estimated on the basis of the results of the high pressure and temperature experiments, the realistic value of the total iron content and the moment of inertia factor have been estimated. The iron content of Mars which satisfies the mean density and the radius of Mars ranges from 19 wt. % to 27 wt. % with the temperature ambiguities of±200°C. This value is smaller than that of the bulk Earth. The moment of inertia factor of the Mars, which satisfies the mineralogical constraints of the high pressure phase transitions together with the observed data on the mean density and the radius of Mars, ranges from 0.353 to 0.38.

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retaceous Okushiri granodioritic body occurred in Okushiri Island, southwest Hokkaido was studied its geochemical characteristics. This body consists mainly of hornblende biotite granodiorite with small amount of granite and aplite, and contains gabbroic xenoliths. The body shows characteristics of volcanic arc type granite based on Nb-Y and Rb-(Y+Nb) diagrams. Seven samples of granodiorite give a defined Rb-Sr whole rock isochron age of 104±16 Ma and initial Sr isotopic ratio of 0.70536±0.00033 (2σ) and two samples have negative initial εNd values.
Obtained new data and previous reports suggest that Okushiri granodioritic body has geochemical and petrological characteristics of plutonic rocks from both belts of Kitakami and Abukuma.
From trace and isotopic data it may be inferred that source magma of the Okushiri body was caused by partial melting of lower crust, or that derived from upper mantle or lower crust were affected by crustal materials.

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