中性子放射化分析値に基づく小惑星天体中でのパラサイトいん石の化学進化に関する研究

概要

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Pallasite meteorites, which are classified into stony-iron meteorites, have a unique structure that olivine grains are included in iron-nickel metal. They have been considered to be formed by the mixing of olivine mantle and metallic core at the core-mantle boundary in a differentiated asteroid. A study of such small planetary bodies gives us information of early formation and differentiation processes of rock-type planets, like Mars or Earth. The purpose of this study was to present the detailed formation process of the pallasite parent body based on trace elemental abundances in pallasite meteorites. For rare earth elements (REEs) and platinum group elements (PGEs), an analytical technique based on neutron activation analysis with extraction chromatography was developed. This new method enables the quantitative determination at the ppt level for REEs (La, Ce, Nd, Sm, Eu, Gd, Tb and Lu) in only 100 mg samples. REE data of this work in olivines from six pallasites, classified in main group pallasite, indicate that primordial REE patterns for pallasites are not so-called "V-shaped", but linear light REE-depleted patterns. The formation scenario expected from trace elemental data is that a pallasite parent body experiences partial melting and subsequent large-scale melting. This scenario is consistent with the core-mantle mixing model for the formation of pallasite meteorites.
社団法人日本分析化学会の論文
2005-02-05