ABSTRACT

Four apatite fission track (AFT) and two zircon fission track ages were determined on the Ryoke granitic rocks, located close to the Median Tectonic Line (MTL), Southwest Japan. The AFT ages range from ∼9.3 to ∼32 Ma, and thus can be correlated to the “young” AFT ages previously found near the MTL; meanwhile, zircon ages are around 65 Ma. Because some of the localities lie in the western portion of the Ryoke Belt that was not studied previously, it is suggested that the region characterized by the “young” AFT ages, probably representing later thermal events along the MTL, may be extensive to the overall Ryoke Belt.