Development of zircon U-Th disequilibrium dating for determination of the eruption age of Zenikame-Menagawa tephra

Kagami, Saya   ; Yokoyama, Tatsunori   ; Niki, Sota*; Sakata, Shuhei*; Umeda, Koji*; Okada, Rina*; Kondo, Misaki*

Tephras from submarine eruptions are easily affected by secondary deposition and alteration and the constraints on their geochronology may be difficult. In this study, we conducted zircon U-Th disequilibrium dating by LA-ICP-MS for Zenikame-Menagawa tephra (Z-M), which was erupted from Zenakame volcano on the seafloor of the Tsugaru Strait and is a valid age indicator for MIS3. The zircons in the Toya pumice were measured to evaluate the accuracy of the method and their isochron age of 128 ka was obtained. This result is consistent with the previous reported data by the same method used in this study. We measured the zircons from Z-M and found that many of the zircons did not record eruption ages, and that many grains had U-Th disequilibrium model ages of about 100 ka. In the future, we will attempt U-Th disequilibrium dating of each zircon along with understanding its characteristics (shape, chemical composition and so on).