2017 Volume 123 Issue 9 Pages 765-776
The Towada Ofudo and Hachinohe tephras distributed in the northern part of Tohoku district are petrographically similar. Major element compositions of volcanic glass shards of both tephras are also similar. Only a difference in the trace element zirconium content in volcanic glass shards has been observed; however, both tephras are mainly identified by the presence of green hornblende. The content of the green hornblende in the Hachinohe tephra is generally higher than Ofudo tephra. The Ofudo tephra contain a small amount of green hornblende. In addition, a low content unit of green hornblende is also included in the Hachinohe tephra. For this reason, the two tephras cannot be identified only by this content.
In this study, several Ofudo and Hachinohe tephras were sampled from a wide area, and the content of amphibole, major elements of volcanic glass, trace elements of volcanic glass were analyzed by EDX and laser ablation (LA)-ICP-MS. As a result, it is clear that the both tephras cannot be clearly identified by the green hornblende content, and major element chemical composition of volcanic glass shards. Trace element contents of both tephras closely resemble, but there is a clear difference in the Pb content. The two tephras can be discriminated by the Pb content.
