東北地方南部，会津駒ヶ岳と月山火山で発見された完新世中期の十和田中掫テフラ

摘要

We analyzed the major element chemical composition of volcanic glass shards in Azuma tephra on Mount Aizu-komagatake and the Gassan volcano in northern Japan by means of electron probe X-ray microanalysis. This analysis confirmed that the two samples of Azuma tephra obtained from those mountains can be identified as the same tephra. We also examined three members of Towada Chuseri tephra (i.e., Chuseri pumice layer, Kanegasawa pumice layer, and Utarube volcanic ash layer) whose age is ca. 6.0 cal ka BP in the proximal area of the Towada volcano in northern Japan for comparison with the Azuma tephra on Aizu-komagatake and Gassan. It was found that Azuma tephra originates primarily from Kanegasawa pumice. Azuma tephras found on Aizu-komagatake and Gassan were composed of widespread fine particles derived from the plinian eruption that produced the Kanegasawa pumice layer. Fallout Towada Chuseri tephra is expected to be discovered in the more southern area of Mount Aizu-komagatake, ca. 400 km from the Towada volcano.%福島県会津駒ヶ岳と山形県月山火山の山岳土壌に挟まれる完新世中期のガラス質テフラ（吾妻火山灰）について.主要元素組成分析を行った.その結果，両者は同一のテフラであることが確認された.また.十和田火山東麓において十和田中掫テフラ（6.0cal ka BP)を構成する3部層（中掫軽石.金ヶ沢軽石，宇樽部火山灰）を対象に主要元素組成分析を行い.会津駒ヶ岳および月山火山の吾妻火山灰と比較した.その結果，会津駒ヶ岳と身山火山の吾妻火山灰は十和田中揮テフラに由来し，特に金ヶ沢軽石に対比されるテフラ粒子を主な起源とすることが判明した.現時点で十和田中掫テフラの分布は会津駒ヶ岳が南限となるが,さらに南へ展開するのは確実である.