北部フォッサマグナ地域,糸魚川-静岡構造線の西側に分布する中新統山本層安山岩のK-Ar年代

概要

論文の詳細を見る
Andesite rocks of the Yamamoto Formation unconformably overlying pre-Miocene basement rocks in the western part of "the Itoigawa-Shizuoka Tectonic Line" in the Northern Fossa Magna were dated by the K-Ar method. Aphyric andesite of the lower member of the Yamamoto Formation is estimated to be a lava flow erupted at 16.0 Ma on the land surface. Andesite of the upper member is dated at 15.5 Ma, whereas the andesite occasionally occurs as hyaloclastite. These results and geological setting suggest that tectonic movements related to the Itoigawa-Shizuoka Tectonic Line might have continued along at least several hundred meters even after 16 Ma.
2007-03-25