Abstract
Ten zircon fission-track ages from four granitic bodies in the Outer Zone of Kyushu have been determined by the external detector method. The ages are as follows: Osumi granite, 13.1±0.8m.y., 13.3±0.8m.y., 13.6±1.1m.y., 13.7±1.1m.y., 13.9±1.1m.y., and 14.0±1.1m.y.; Takakuma. yama granite, 12.9±1.0m.y.: Ichifusayama granite, 12.0±0.9m.y.; and Shibisan granite, 12.3±1.0m.y. and 12.7±1.2m.y. These fission-track ages indicate that the four granitic bodies cooled at virtually the same time.
One apatite fission-track age of the Osumi granite has also been determined here, using a population method. The apatite age of 12.0±2.6m.y. is almost the same as zircon fission-track age, showing that the Osumi granite cooled rapidly around 12m.y. ago.
