Correlation of tuffs intercalated in the Pliocene Mukaiyama Formation, Sendai area, Japan, based on apatite trace element compositions

Abstract

The Mukaiyama Formation is a Pliocene non-marine sequence exposed widely in the Sendai area of Japan. This formation is thought to provide a detailed record of Pliocene caldera activity in the Tohoku area as it is intercalated with numerous thick felsic tuffs. However, the sources of and correlations between most of the tuffs in the Mukaiyama Formation have not been well studied. We examined the lithostratigraphy of the Mukaiyama Formation in the Sendai area and identified six traceable tuff beds: the Otsutsumizawa, Hirosegawa, Kabasawa, Shishiochizaka I, Shishiochizaka II, and Shionosawa tuffs, in ascending order. These tuffs can be distinguished based on lithology, heavy mineral assemblages, and apatite trace element compositions, and each tuff can be correlated between sections. Our correlation of the tuffs based on apatite trace element compositions suggests that one of the tuffs was derived from the Shiroishi caldera and another from the Nanatsumori caldera. The U-Pb zircon ages of the Hirosegawa and Shionosawa tuffs show that the depositional age of the Mukaiyama Formation is 3.7-3.5 Ma.