Highly reproducible 13 and 17ka K-Ar ages of two volcanic rocks.

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 TE 1 and NE2 were 13 .0 1.6(1 a) and 17.0 1.4(l a) 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 .