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A study of relation between undifferentiated and differentiated meteorites based on noble gas elemental and isotopic compositions

基于稀有气体元素和同位素组成的未分化陨石与分化陨石关系研究

基本信息

批准号：
15540464
负责人：
MIURA Yayoi
金额：
$ 2.18万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15540464/
关键词：
Noble gases Meteorite Differentiated meteorite Aubrite Chondrite Formation age Cosmic-ray exposure age

项目摘要

Differentiated bodies (differentiated meteorites and planets) are thought to have been formed from materials like primitive meteorites (=chondrites). However, details about relation between them and differentiation processes are still questions. In this research project, we tried to have better understanding them based on noble gas isotope studies. For this, noble gas elemental and isotopic compositions in several classes of differentiated meteorites (aubrites, angrite, brachinite and lunar meteorites) and chondrites have been determined with a mass spectrometer. Remarkable results we obtained are as follows.(1)Origin of aubrites : Aubrites are only achondrites that have a chondrite-pair for oxygen isotopic compositions. Therefore, it is interesting to study relation of aubrites with the chondrites (enstatite chondrites) and to clear the process of aubrite evolution. We have measured nine aubrites for noble gases and five aubrites for oxygen isotopes, from which we concluded that (i)so … More me of the measured aubrites contain chondritic primordial noble gases, but it is likely originated from chondritic clasts and not a indigenous signature. (ii)^<244>Pu-derived fission Xe has been observed in some aubrites. The Pu/U ratios range in those observed in chondrites and other achondrites, which indicates that aubrites were formed within several hundreds m.y.after the solar system formation. (iii)The distribution of comic-ray exposure ages for aubrites is different from that for enstatite chondrites, implying that orbits of these parent asteroids are probably different.(2)Primordial noble gases in chondrites : Although the majority of primordial noble gases in chondrites are often believed to be "Q" type noble gases, we found another component that is the major component in some (or most) unequilibrated ordinary chondrites. It shows some characteristic features ; enrichments in lighter elements (Ar/Xe and Kr/Xe ratios are higher than those of Q), low release temperatures (〜1100℃ compared with〜1300℃ for Q) and trap in a HCl soluble phase.A mini-oven system for extracting noble gases from mg or sub-mg samples has been designed and constructed. It enables to melt a sample on a Pt-wire with small power (e.g., 〜30W with φ0.6mm Pt-wire). Less

分化的天体（分化的陨石和行星）被认为是由原始陨石（=陨石）等物质形成的。然而，它们之间的关系和分化过程的细节仍然是问题。在本研究项目中，我们试图在惰性气体同位素研究的基础上更好地了解它们。为此，稀有气体元素和同位素组成的几个类别的分化陨石（Aubrites，angrite，brachinite和月球陨石）和陨石已确定与质谱仪。我们取得的显着成果如下。（1）奥辉岩的成因：奥辉岩是唯一一种氧同位素组成为一对无球粒陨石的无球粒陨石。因此，研究奥辉橄榄岩与顽火辉石的关系，弄清奥辉橄榄岩的演化过程，具有重要意义。我们测量了九种稀有气体的奥布利特和五种氧同位素的奥布利特，由此得出结论： ...更多信息大多数被测的Aubrites含有南极原始惰性气体，但它可能来自南极碎屑，而不是本地签名。(ii)^<244>在一些Aubrites中观察到了钚衍生的裂变产物。Pu/U的比值范围在陨石和其他无球粒陨石中观察到的范围内，这表明Aubrites在太阳系形成后的数百万年内形成。（三）Aubrites的漫画射线暴露年龄的分布是不同的顽火辉石的陨石，这意味着这些母小行星的轨道可能是不同的。（2）原生惰性气体：虽然大多数原生惰性气体通常被认为是“Q”型惰性气体，但我们发现另一种成分是某些（或大多数）非平衡的普通惰性气体的主要成分。它具有轻元素富集（Ar/Ar和Kr/Ar）、释放温度低（Q为1100 ℃，Q为1300℃）和捕获于HCl可溶相等特点。它能够以小功率熔化Pt丝上的样品（例如，φ0.6mm铂丝30 W）。少