Geological significance of the Takada Granodiorite in the San'in batholith, Southwest Japan

Abstract

This study investigates the geological significance of the metaluminous Takada granodiorite in the San’in batholith, Southwest Japan. The lithology of the granodiorite varies from medium- to coarse-grained hornblende–biotite tonalite to porphyritic hornblende-bearing biotite granodiorite and porphyritic biotite granite. The tonalite facies shows evidence of mingling with the fine-grained Ogi quartz diorite. The whole-rock chemical composition of the Takada granodiorite is variable, and U–Pb zircon dating yields ages of ~65 to 60 Ma. These geochemical and chronological variations suggest that the granodiorite suite experienced multiple magmatic events during its formation. Peak magmatic activity occurred around 61 Ma, representing the initial stage of intrusion of the granitic suites in the San’in region during the late Inbi period (68–53 Ma). Thus, the metaluminous Takada granodiorite is significant because it represents the first stage of igneous activity during the main period of formation of the San’in batholith.