Correlation between pumiceous tuff beds of the Morozaki Group and the Mizunami Group

Abstract

Early Miocene sedimentary sequences in the Chubu region of central Japan contain numerous tuff beds, and comparisons and correlations of these beds between sedimentary basins are expected to lead to a better understanding of the stratigraphic architecture of the sequences. In this study, we discuss the correlation of pumiceous tuff beds between the Himaka and lower Yamami Formations of the Morozaki Group in Aichi Prefecture and the Hazama Member of the Akeyo Formation of the Mizunami Group in Gifu Prefecture. We obtained zircon U-Pb ages of 17.87±0.75 Ma and 17.36±0.40 Ma for pumiceous tuff beds from the Himaka and lower Yamami Formations, respectively, and these ages are consistent with the published U-Pb age for the Hazama Member. Paleomagnetic analyses reveal reverse polarity magnetizations in the Himaka and lower Yamami Formations and the Hazama Member. These results suggest that these three units correspond to Chron C5Dr of the paleomagnetic chronology. Chemical analyses of volcanic glasses from pumiceous tuffs in the lower Yamami Formation and the Hazama Member display a single trend in chemical variation diagrams. Plagioclase compositions of pumiceous tuffs in the three units are also consistent. These chemical characteristics indicate that the volcanic glasses and plagioclase of the three units were generated from the same magma plumbing system. The volcaniclastic products of the Morozaki Group examined in this study are considered to have been supplied from the Hazama Member.