ABSTRACT

A technique for noble gas mass spectrometry was applied to the K-Ar dating of very young volcanic rocks to examine the reproducibility in Ar analysis. For two selected samples TE1 (trachyandesite) and NE2 (obsidian) with relatively low atmospheric Ar and high K concentrations, five and seven analyses were performed, respectively, using small sample size (0.5 g), and they gave highly reproducible K-Ar ages. The mean ages for TE1 and NE2 were 13.0 ± 1.6(1σ) and 17.0 ± 1.4(1σ) ka, respectively. Six repeated analyses of the Quaternary reference material YZ1 of Yamagata University showed a mean age of 218 ± 11 ka, which agrees well with the reported values. These results imply the possibility that volcanic rocks as young as ten thousand years can be dated by the K-Ar method with the condition that the samples satisfy the required conditions for K-Ar dating.