Joint system in the Osumi granodiorite batholith, southern Kyushu, Southwest Japan

This study analyses the joint system of the Middle Miocene Osumi granodiorite batholith in southern Kyushu, Southwest Japan. The analysis included 916 joints at 96 localities covering the northern, middle, and southern domains of the exposed area of the Osumi granodiorite batholith. Two major sets of steep joints striking NNW and ENE and a minor set of gentle joints are recognized in the northern and the middle domains. Two further sets of steep joints striking NS and EW with a minor set of gentle joints are recognized in the southern domain. Previous paleomagnetic studies indicate counterclockwise rotation of microplates in southeast Kyushu after 2 Ma. When the orientations of the joints are restored according to the rotation angles of the microplates (45° for the northern-middle domains and 30° for the southern domain), the strikes of the steep joints are largely oriented NNE and WNW.