レター
北海道南西部，羊蹄火山東麓に分布する緑色凝灰岩層のジルコンU-Pb年代
キーワード:
zircon U-Pb age,
greenish tuff,
Miocene,
Japan sea opening,
Yotei Volcano,
southwest Hokkaido
2020 年 126 巻 10 号 p. 589-595
詳細
2020 年 126 巻 10 号 p. 589-595
In this study, we carried out zircon U-Pb dating of greenish tuff deposits from the eastern base of Yotei Volcano, southwest Hokkaido, Japan, to investigate the Miocene ignimbrite volcanism associated with the opening of the Japan Sea. This tuff may be correlated with the Pepenai-gawa green tuff member of the Wakikata Formation. Zircon grains from the tuff yield an eruption age of 5.7±0.2 and 5.6±0.2 Ma based on the youngest five zircon grains from a total of twenty analyses and using a weighted mean value and the Tera-Wasserburg method, respectively. The tuff also includes zircon grains with ages of 8-25 Ma. These zircons may represent xenocrysts that formed in the crust beneath Hokkaido due to intermittent heat flux during opening of the Japan Sea.
