Abstract
The Tanakura Basin was formed by strike-slip movement of the Tanakura Fault during the opening of the Sea of Japan in the early to middle Miocene. In this study, we conducted U–Pb and fission-track (FT) double-dating of pyroclastic rocks from two stratigraphic units in the Tanakura Basin. Using these ages, we constructed a detailed chronostratigraphy and discuss the evolution of the Tanakura Basin with respect to regional tectonics and the opening of the Sea of Japan. We obtained new ages of 17.1 ± 0.6 Ma for the middle part of the Asakawa Formation and 17.4 ± 0.9 Ma for the lower part of the Nawashiroda Formation. Based on a comparison of the ages from this study and previously published data, we clarify the ages of each formation of the Miocene basin fill. We suggest that the Tanakura Basin was formed by sinistral movement on the Tanakura Fault between 17.2 and 16.7 Ma, followed by the development of lakes and the deposition of alluvial fans within the basin. Rapid tectonic subsidence and submarine dacite volcanism occurred just prior to 16.7 Ma. The basin then began to uplift due to dextral strike-slip movement on the Tanakura Fault at ca. 15.7–15.3 Ma.
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