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

分化天体（分化陨石和行星）被认为是由原始陨石（=球粒陨石）等物质形成的，但是，在这个研究项目中，它们之间的关系和分化过程的细节仍然是个问题。基于稀有气体同位素研究，已对几类不同的陨石（奥氏陨石、红陨石、碳陨石和月球陨石）和球粒陨石中的稀有气体元素和同位素组成进行了研究。我们得到的显着结果如下。(1)奥氏体的起源：奥氏体是唯一具有氧同位素组成的球粒陨石对的球粒陨石，因此，研究奥氏体与球粒陨石的关系是很有趣的。顽火辉石球粒陨石）并阐明了赤铁矿的演化过程，我们测量了九种赤铁矿的稀有气体和五种赤铁矿。对于氧同位素，我们得出的结论是（i）所测量的赤铁矿中含有球粒状原始惰性气体，但它很可能源自球粒状碎屑，而不是源自本地特征（ii）^<244>Pu。在一些赤铁矿中观察到了裂变 Xe，Pu/U 比率范围在球粒陨石和其他无球粒陨石中观察到的范围，这表明赤铁矿中存在裂变。 (iii)奥辉石球粒陨石的漫画射线暴露年龄分布与顽火辉石球粒陨石不同，这意味着这些母小行星的轨道可能不同。(2)原始惰性气体。球粒陨石中：虽然球粒陨石中的大多数原始稀有气体通常被认为是“Q”型稀有气体，但我们发现了另一种成分，它是主要成分在一些（或大多数）不平衡的普通球粒陨石中表现出一些特征； Q) 并捕获在 HCl 可溶相中。设计并构建了一种用于从毫克或亚毫克样品中提取稀有气体的微型烤箱系统，它能够熔化铂丝上的样品。小功率（例如，约 30W，使用 φ0.6mm 铂丝）。