抄録
This paper describes advances in isotopic measurements that have been made with an inductively coupled plasma mass spectrometry (ICP-MS) and presents results of new experiments aimed at further progress of the isotope geochemistry. I begin with a direct measurement of in-situ Os isotopes in solid geochemical samples by laser microprobe-MC-ICPMS technique. In this study, possible isotopic variation in 187Os/188Os ratios have been measured with a laser pit size of 15μm. Although no significant isotopic variations could be detected from iridosmine samples, it was well demonstrated that the laser microprobe-MC-ICPMS has the potential to become a new analytical technique for the in-situ Re-Os age determinations of solid samples. I follow with a discussion of the Ge isotopes in metallic materials of meteorites. Although an abundance of data on Ge have been widely used for the classification of the iron meteorites, there still remains an enigma or a kind of gap between the simple theoretical model and the cosmochemical sequences of the iron meteorites drawn by the abundance of Ge data. In this study, I measured the Ge isotopic ratios of iron meteorites in order to discuss further the detailed formation mechanisms of the iron meteorites. The isotopic ratios for Ge were found to have small but significant variation mainly due to fractional evaporation. The data obtained here demonstrate clearly that Ge isotopes can provide us a useful information on the iron meteorite formation. This was followed by topics on zircon U-Pb chronology using a laser microprobe-ICPMS. Based on the data presented here, a realistic conclusion is that the laser microprobe-ICPMS technique has the strong potential as a reconnaissance analytical method and given increasing improvement in this instrument will in the future produce data comparable to ion probe techniques such as SHRIMP. Finally, I will report on the preliminary results of the new ion detector for ICP magnetic sector multiple collector mass spectrometer. The ion detector developed here enables us to detect several isotopic signals at the same time with an enhanced sensitivity compared with conventional Faraday collector. Principles of the new detector and its wide versatility will be described in this paper.
