Zircon U–Pb ages and whole–rock geochemistry from the Hida granites: implications for the geotectonic history and the origin of Mesozoic granites in the Hida belt, Japan

抄録

The Hida granites, classified into the pre–Jurassic and Jurassic plutons in this study, are important components of the Hida belt, which is a Paleozoic–Mesozoic basement of the Japan arc and underwent Permian to Triassic metamorphism during the collision between the North and South China blocks. This study performed zircon U–Pb dating and whole–rock geochemical analyses for the Hida granites from the major plutonic bodies to reveal the geotectonic history and the origin of the Hida belt. Obtained ²³⁸U–²⁰⁶Pb weighted mean ages exhibit 239.1–238.3 Ma for the Katakaigawa body (augen granite) and 200.5–180.9 Ma for the other bodies (non–deformed granitoids), and these ages can be correlated to the pre–Jurassic and Jurassic plutons, respectively. Geochronological results suggest that the mylonitization forming augen granites of the pre–Jurassic plutons occurred during its intrusion and indicate that the Jurassic plutons are distributed widely in the Japan Sea side of the Hida belt. Meanwhile, geochemical characteristics of whole–rock major and trace element compositions indicate that the pre–Jurassic and Jurassic plutons seem difficult to distinguished geochemically and suggest that both of them are adakitic and non–adakitic granites generated in subduction zone.