Abstract
A granitic enclave, ca. lm in diameter, was found in a basalt/rhyolite composite dike along the Yoshino River at Ifashio in the central part of Nara Prefecture, Southwest Japan. The dike intruded into Mesozoic accretionary complex, and there are no outcrop of granitic rocks in the vicinity. To clarify the origin of the granitic enclave, we carried out whole rock chemical analysis with XRF and U-Pb zircon dating using laser ablation ICP-MS. The whole rock composition of the granitic enclave is within the range of the Ohmine granitic rocks, one of the member of the Middle Miocene granitic rocks of Outer Zone of Southwest Japan. The time of the solidffication of the granitic enclave is estimated to be 13.2 ± 1.0 Ma based on the youngest zircon U-Pb results. These facts suggest the existence of concealed middle Miocene granitic body beneath the Kashio region.
