演題概要

オーラルセッション

第2日　6月23日（木）　10:20～10:40　C会場（411，412）

2C-O1-1020　　PDF

完新世試料年代分析のためのレーザーアブレーションICPトリプル四重極型質量分析法を用いたウラン系列放射非平衡年代測定法の開発

(¹東大地殻化学・ ²京都フィッショントラック)
^o仁木創太¹・ 小杉周平¹・ 岩野英樹^1,2・ 檀原徹²・ 平田岳史¹

U-series disequilibrium dating methods are conducted for Quaternary samples, especially volcanic rocks and minerals to derive chronological information of magmatic processes including volcanic eruptions, restorage/mixing of magma, and melt generation. To understand the multiplicated magmatic processes, statistical treatments of chronological data are effective, and rapid and in situ analytical techniques for U-series disequilibrium dating are highly desired.
Faced with this problem, we have developed an in situ ²³⁸U-²³⁰Th dating method using an ICP-triple quadrupole-mass spectrometer coupled with a multiple-spot femtosecond laser ablation sampling technique (msfsLA-ICP-QQQ-MS). With a kinetic energy discrimination (KED) technique applied by the QQQ system, the polyatomic interferences can be effectively eliminated while the loss of the ion transmission through the KED was only 30%. Moreover, owing to the msfs LA system with the repetition rate of 60 kHz, laser sampling from 1×1 mm² area can be carried out with short time durations (e.g., < 1 s), resulting in the better signal-to-noise ratios (SNRs) of the analytes and the higher analysis throughput. For age determinations on Holocene samples, the ²³⁰Th-²²⁶Ra disequilibria are also important, and the present msfsLA-ICP-QQQ-MS technique was applied for the in situ measurements of ²²⁶Ra from standard zircon and standard rock materials. Analytical capability of the present system for the ²³⁸U-²³⁰Th-²²⁶Ra dating method onto Holocene volcanic samples will be discussed in this talk.