Abstract
Fission track dating was carried out for 52 samples from the Muro Pyroclastic Flow Deposit, the Sekibutsu Tuff and the Furudera Tuff in the northern region of the Kii Peninsula, and from fine-grained granitic bodies of the Omine Granitic Rocks (the Dorogawa, Shirakura, Kose, Asahi, Tenguyama, and Shiratani bodies) and various rock facies of the Kumano Acidic Rocks (the Konogi Rhyolite, the Owase-Shirahama Pyroclastic Rocks, the Kumano Granite Porphyry, and the Kozagawa Dike) in the central to southeastern region of the Kii Peninsula. The resulting ages of all these samples and previously reported ages of the Tamateyama Tuff, the Nakaoku Tuffite Dike and the Shionomisaki Igneous Complex in the peninsula were clustering at 15 Ma. Most of the above igneous bodies contain a mixture of reddish and colorless zircons. Characteristic of the mixed zircons from the Muro Pyroclastic Flow Deposit, Sekibutsu Tuff, Tamateyama Tuff and the north and south units of the Kumano Granite Porphyry is similar in terms of a ratio of reddish and colorless zircons being 2 : 3, and dominant crystal planes {100} for reddish and {110} for colorless. Based on the simultaneity and similarity of the mixed zircons, it is strongly suggested that the Muro Pyroclastic Flow Deposit and the adjacent tuffs in the northern Kii Peninsula are correlated with each other as a large-scale pyroclastic flow deposit at 15 Ma, and that its possible source is the Kumano Acidic Rocks in the southeastern Kii Peninsula.
