Keywords:Kikai Caldera, U-Pb dating, elemental analysis
The Kikai Caldera, situated ~50 km south of the Kyushu Island, experienced a gigantic eruption at ~7300 years ago (or 7.3 ka). In order to understand the next gigantic eruption it is now under an intensive investigation using a research vessel (Tatsumi et al., 2018), receiving a great deal of attention from researchers and the public. Meanwhile, we performed zircon U-Pb dating of three widespread tephras (Anbo, Ksd, K-Tz) from the Yakushima Island, ~30 km south of the Kikai Caldera, and found ~0.7 Ma and ~0.6 Ma zircons in the ~0.1 Ma K-Tz tephra of the Kikai Caldera origin. Therefore we speculated that the Kikai Caldera may have experienced at least 3 gigantic eruptions before the 7.3 ka eruption (Ito et al., 2017). In order to verify this hypothesis, we collected volcanic products from the Tanegashima Island and the Kikai Caldera (Satsuma-Iwojima and Takeshima Islands), and performed zircon U-Pb dating and elemental analysis of zircon and volcanic glass. So far, zircon U-Pb dating ascertained that the Ksd is also distributed in the Tanegashima Island and revealed that the age of the Akazaki lava in the Takeshima Island is ~0.2 Ma. Through these investigations, we propose a new history of gigantic eruptions in the Kikai Caldera.
Ito, H., Uesawa, S., Nanayama, F., and Nakagawa, S., 2017. Zircon U–Pb dating using LA-ICP-MS: Quaternary tephras in Yakushima Island, Japan. J. Volcanol. Geotherm. Res., 338, 92–100.
Tatsumi, Y. et al., 2018. Giant rhyolite lava dome formation after 7.3 ka supereruption at Kikai caldera, SW Japan. Sci. Rep. 8, 2753; DOI:10.1038/s41598-018-21066-w.