Pyroclastic deposits around the southern base of Kurikoma volcano, Miyagi prefecture, Japan — stratigraphy, petrology and K-Ar ages of Onoda Formation -

Abstract

There is a caldera cluster around southern base of Kurikoma volcano, and their eruptive products are exposed there. Most of them have been regarded as members of the neogene Onoda Formation. This study shows the stratgraphy, petrology and K-Ar data of two new samples in the Onoda Formation. Onoda Formation contains four tuff members, Yubama, Chijimisawa, Modume, Toshoji tuffs, in stratgraphic order. These four tuffs are composed mainly of pyroclastic flow deposits, and Modume Tuff is accompanied by the lower fall-out deposit. Whole-rock chemical analysis revealed that Toshojisawa Tuff belongs to dacite, and other tuffs belong to rhyolite, according to IUCS classification. K-Ar ages are 1.00±0.06 Ma and 0.87±0.21 Ma for Chijimisawa and Toshoji tuffs, respectively.