Zircon U–Pb dating using LA-ICP-MS: Quaternary tephras in Yakushima Island, Japan

Abstract

Zircon U–Pb dating using LA-ICP-MS was applied to three Quaternary tephras in Yakushima Island, southern Japan: the Anbo Tephra, the Koseda pyroclastic flow deposit (Ksd), and the Kikai-Tozurahara (K-Tz) Tephra. The obtained U–Pb ages were 0.73±0.04Ma (error shown as 95% confidence level) for the Anbo, 0.63±0.04Ma for the Ksd, and 0.17±0.05Ma for the K-Tz. These ages are consistent with or slightly older than those reported previously, which demonstrates the applicability of the U–Pb method to date zircons as young as ~0.1Ma. The K-Tz contains ~0.7–0.6Ma zircons, assumed to be derived from the Anbo and Ksd tephras. Because the K-Tz was originated from the Kikai Caldera, ~30km north of Yakushima Island, both the Anbo and Ksd were likely also derived from the same caldera system. Therefore our data and interpretation will contribute to elucidate the magmatic history of the Kikai Caldera whose latest eruption devastated prehistoric human settlements of southern Kyushu, Japan, and provide an improved chronostratigraphic constraint for Japan.