Fission track ages on apatite from Miocene igneous rocks in the Kii Peninsula, Japan

This paper reports fission track (FT) ages on apatite from Miocene igneous rocks of the Kii Peninsula. A total of twelve ages was determined, of which nine data passed a statistical test. Ages of around 15 Ma were obtained for the Muro Pyroclastic Flow Deposit, the Sekibutsu Tuff, and the granite porphyry of the Kumano Acidic Rocks, and were indistinguishable from the zircon FT ages we reported previously (Iwano et al., 2007, Jour. Geol. Soc. Japan, 113, 326-339), indicating instantaneous cooling. On the other hand, two plutonic bodies of the Omine Granitic Rocks yielded apatite FT ages of about 13 Ma that were significantly younger than the zircon FT ages (approximately 15 Ma), suggesting relatively slow cooling.