Geotectonic boundary between the Sanbagawa and Chichibu Belts in central Shikoku, Southwest Japan

Abstract

The Mesozoic accretionary complex in the Tosayama area, central Shikoku, consists of two distinct geologic units, the Akaragi and Takakawa units. These two units are bounded by the Sasagatani fault that strikes E-W and dips southward. On the basis of microfossil ages and K-Ar ages, the Akaragi unit is correlated to the Sanbagawa high-P/T metamorphic rocks, on the other hand, the Takakawa unit is correlated to the Jurassic accretionary complex of the Chichibu belt. There is a remarkable break in metamorphic age and paragenesis along the Sasagatani fault between these two units. The new results refute the previous geological understanding that the Sanbagawa metamorphic rocks tectonically overlie all units of the Chichibu belt in Southwest Japan. -from English summary