Zircon U-Pb dates from Lower Miocene rhyolitic welded tuffs in the Hokuriku region, central Japan: Implications for silicic volcanism prior to the opening of the Sea of Japan

Abstract

To constrain the timing of 24-22 Ma silicic volcanism prior to the opening of the Sea of Japan in 21-15 Ma, zircon U-Pb dating was conducted on rhyolitic welded tuffs from the Nishitani Formation and the Goroku-Kamiwazumi-Matsunagi formations around the Toyama Basin. We obtained weighted mean ²⁰⁶Pb/²³⁸U dates of 21.8 ± 0.2 and 22.6 ± 0.2 Ma of from the Nishitani Formation and the Goroku-Kamiwazumi-Matsunagi formations, respectively. This suggests that 24-22 Ma silicic volcanism occurred or that rhyolitic pyroclastic density currents reached the Noto Peninsula in addition to the Toyama Basin. Additionally, spatial variation in zircon U-Pb dates reported in this and previous studies suggest the possibility that eruptive vents shifted from northeast to southwest during the 24-22 Ma interval. The results of this study constrain both the timing and temporospatial evolution of the 24-22 Ma silicic volcanism in and around the Toyama Basin.