Zircon U–Pb ages of the granitic rocks in Kunisaki district, northeastern Kyushu, Southwest Japan

Abstract

The Kunisaki district in the eastern part of northern Kyushu is interpreted to be the western extension of the Ryoke belt. Zircon U–Pb ages of 8 granitoid samples from the district were obtained. Granite samples from the western part of the district are 96–100 Ma in U–Pb age and are attributed to the Ryoke belt. Granitoid samples from the eastern part of the district show relatively older ages than the western part, 108–110 Ma which is consistent with the Higo belt rather than the Ryoke belt. The granitoids in the district broadly become younger towards the northwest, from the oceanic side to continental side as well as the western side of central to northern Kyushu. Although the extension of the Ryoke belt was confirmed in the eastern side of Kyushu in this paper, the western extension of the Ryoke belt remains unclear.