Abstract
Three biotite K-Ar ages were determined for the Miocene Takatsuki-yama and Miuchi plutons, southwestern Shikoku, Japan. These plutons belong to the Outer Zone Acidic Rocks in the Southwest Japan (OZARSWJ). The obtained ages from the two granodioritic samples in the Takatsuki-yama pluton give a good coincidence; 13.9±0.2 Ma and 14.0±0.2 Ma. The granite sample of the Miuchi pluton gives slightly younger age (13.4±0.2 Ma) than those of the Takatsuki-yama pluton. Though these two plutons were considered as the different exposures of a single batholith, the different ages suggest that these two exposures might belong to the different intrusive blocks with short interval. The obtained ages for the both pultons are within the range of 13-15 Ma, which corresponds to the time interval of the other OZARSWJ granitic rocks.
