2018 Volume 124 Issue 7 Pages 533-538
The Hachiya Formation of the Kani Group in southern Gifu Prefecture is the oldest sediment in the eastern part of the Setouchi Geologic Province, and is composed mainly of volcaniclastic rocks deposited in a nonmarine basin. We present the results of new laser ablation-inductively coupled plasma-mass spectrometry U-Pb analyses of zircons separated from a sample of the Tochibora Welded Tuff Member in the lowest horizon of the Hachiya Formation. The analyses yielded a weighted mean 238U-206Pb age of 22.38±0.17 Ma (2σ), which constrains the time of initial sedimentation of the Hachiya Formation. The whole-rock major- and trace-element compositions of the welded tuff sample, analyzed by X-ray fluorescence, are also reported.