Study on the formation process of differentiated meteorites based on platinum group element abundances

铂族元素(以下简称PGE)在宇宙化学上归类为难熔元素。它们在地球化学上被归类为亲铁元素，集中在地球类行星的核心，其相对丰度类似于太阳系的丰度。另一方面，以地幔和地壳为代表的硅酸盐地层具有极低的PGE含量，其相对丰度变化很大。本研究的目的是精确测定不同类型陨石的硅酸盐组分的PGE，并根据它们的相对和绝对丰度来考虑这些陨石的形成过程。采用电感耦合等离子体质谱测定前列腺素E。此外，利用中子和光子进行的活化分析也被用来测定常量和微量元素。在2004年进行的研究之后，真陨石作为一组具有代表性的分异陨石，于2005年被列为研究对象。除了真铁矿外，2005年还研究了中菱铁矿的硅酸盐相。结果表明，中铁铁矿硅酸盐部分的PGE与铁陨石有成因联系。结果表明，中铁铁矿硅酸盐部分中的金属颗粒是以金属-硫化物熔体的形式引入的，它是由固体铁部分熔融而成的。这进一步表明，中铁陨石是由铁陨石撞击硅酸盐目标形成的。通过这些研究，准确和准确地测定了包括CI球粒陨石在内的碳质球粒陨石的PGE丰度，从而可以可靠地计算出各种陨石物质中PGE的相对丰度。

Platinum group elements (hereafter, PGE) are cosmochemically grouped in to refractory elements. They are geochemically grouped into siderophile elements, being concentrated into core in earth-type planets with relative abundances similar to solar system abundances. On the other hand, silicate layers represented by earth mantle and crust have extremely low concentrations of PGE with a large variation in their relative abundances. In this study, it was aimed that PGE were precisely determined for silicate fractions of various differentiated meteorites and that the formation processes of these meteorites were considered based on their relative and absolute abundances of PGE. For determining PGE, inductively-coupled plasma mass spectrometry was applied. In addition, activation analyses using neutrons and photons were also used for the determination of major and trace elements. As a representative group of differentiated meteorites, eucrites were targeted in 2005, following researches conducted in 2004. In addition to eucrites, silicate phases of mesosiderites also were studies in 2005. As a result, PGE in silicate portions of mesosiderites were observed to have genetic relation with iron meteorites. It is implied that metal grains present in silicate portions of mesosiderites were introduced as metal-sulfide melt, which was produced by partly melting of solid irons. This further suggests that mesosiderites formed by impact of iron meteorites onto the silicate target. Along these studies, PGE abundances were precisely and accurately determined for carbonaceous chondrites including CI chondrites so that relative abundances of PGE in various materials of meteorites can be figured reliably.