Abstract
K-Ar ages of five hornblendes were determined for the Matsugadaira-Motai Metamorphics. They are dated as 479-524 Ma for three hornblendes and 225-239 Ma for two. The dated hornblendes from the Matsugadaira and Yamagami epidotea-mphibolites are barroisitic indicating high pressure type, and one hornblende of the Ohachimori amphibolites from the Motai Metamorphics retains igneous nature in its core. The values of the 479-524 Ma of two Ohachimori amphibolites and one of Matsugadaira epidote-amphibolite suggest the age of metamorphism, and are in harmony with the stratigraphic evidence. The 225-239 Ma ages of the Yamagami epidoteamphibolites suggest the effect of the Cretaceous granites or some other events. The results of ca. 500 Ma age may constrain consideration of the tectonic regime of the Southern Kitakami Belt in pre-Silurian time.
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