Fission track ages of some granitic rocks in the outer zone of Kyushu, Japan

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 +- 0.8 m.y., 13.3 +- 0.8 m.y., 13.6 +- 1.1 m.y., 13.7 +- 1.1 m.y., 13.9 +- 1.1 m.y., 14.0 +- 1.1 m.y.,; Takakumayama granite, 12.9 +- 1.0 m.y.: Ichifusayama granite, 12.0 +- 0.9 m.y.; and Shibisan granite , 12.3 +- 1.0 m.y. and 12.7 +- 1.2 m.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 +- 2.6 m.y. is almost the same as zircon fission-track age, showing that the Osumi granite cooled rapidly around 12 m.y. ago. (author)