Radiometric ages of the volcanic rocks of the Late Cenozoic in southern Kyushu, Japan

Fission-track dating was carried out on six volcanic materials (one tuff layer, two rhyolitic lavas and three pyroclastic flow deposits) in Southern Kyushu by GBGRE method (Yokoyama, 1983). They are as follows; A tuff layer in the Koriyama Formation 2.6 +- 0.2 Ma: Nagamaki rhyolite (Ichiki acidic volcanic rocks) 2.4 +- 0.5 Ma: A pyroclastic flow deposit in the Nagano Formation 2.4 +- 0.3 Ma: Sasanodan rhyolite (Sanpozukayama acidic volcanic rocks of the Jogudake Formation) 1.2 +- 0.2 Ma: Komiyaji Tuff Member of the Kajiki Formation 0.96 +- 0.17 Ma: Oda Tuff Member of the Kokubu Formation 0.97 +- 0.22 Ma. The K-Ar ages of three andesitic lavas in the investigated area are reported as follows; 1) Shigehirayama pyroxene andesite in the Siake Formation 2.9 +- 0.4 Ma: 2) Akanita lava of the Uranomyo pyroxene andesite 2.1 +- 0.5 Ma: 3) Eboshidake pyroxene andesite 2.3 +- 0.4 Ma. These radiometric ages did not contradict the stratigraphical evidence. (Kubozono, M.)