Meteorite research based on microanalysis of oxygen isotopes using SIMS

我改进了使用二次离子质谱仪(SIMS)进行氧同位素微量分析的技术。对10μm光斑的氧17/16和18/16比值的分析精度约为±2‰，与世界上其他实验室相比是很好的。利用这项技术，深入研究了不同类型球粒陨石中包裹体和球粒陨石的氧同位素微观分布。众所周知，难熔夹杂物(CAI)在0-16时有4-5%的过剩，这项研究的一个重要目的是了解它们的来源。在研究过程中，我和桥本博士发现了富含橄榄石的包裹体，其中也有与在CAIS中发现的类似的大量氧同位素异常，并将结果发表在《科学》杂志上。这一结果对于思考氧同位素异常的来源非常重要，因为橄榄石是一种比CaI矿物更难熔的矿物，并且富含球粒陨石。我们还发现，不同碳质球粒陨石群中的各种包裹体具有非常相似的氧同位素异常。这表明这些包裹体的形成有共同的来源或共同的过程。这项研究的结果表明，早期太阳系中的某种化学过程可能是观测到的氧同位素异常的原因。一些包裹体的镁、钾同位素组成也得到了一些重要的结果。本研究取得的大部分成果在国际会议和国内会议上都有介绍。

I have improved the technique of microanalysis of oxygen isotopes using SIMS (secondary ion mass spectrometry). Precision of the analysis for the oxygen 17/16 and 18/16 ratios for a 10 μm spot is about ±2‰, which is excellent when compared with other laboratories in the world. Using this technique, micro-distribution of oxygen isotopes were intensively studied for inclusions and chondrules in different types of chondrites. It has been well known that refractory inclusions, or CAIs, have 4-5% excess in 0-16, and an important aim of this study was to understand their origin. During the course of the study, I and Dr. Hashimoto discovered olivine-rich inclusions which also have large O-isotopic anomalies similar to those found in CAIs, and the results were published in Science The results are very important in considering the origin of the O-isotopic anomalies, because olivine is a mineral less refractory than CAI-minerals and much abundant in chondrites. We also found that various types of inclusions in different carbonaceous chondrite groups have very similar O-isotopic anomalies. This suggests a common source or a common process for the formation of these inclusions. The results of this study suggests a possibility that some kind of chemical processes in the early solar system may be responsible for the observed O-isotopic anomalies. Also some important results were obtained for Mg and K isotopic compositions in some selected inclusions. Most of the results obtained in the present study were presented at international conferences as well as domestic ones.