Abstract
Tectonics of mid-Cretaceous metamorphic belts, the Ryoke, Higo, Abukuma, Sanbagawa and Kamuikotan Belts, are reviewed on the basis of geochronological and geological data. The Higo metamorphic rocks and klippes of mid-Cretaceous metamorphic and granitic rocks exposed in the Sanbagawa Belt are considered to belong to the southern extension of the Abukuma Belt. The Ryoke-Higo-Abukuma Belt and Sanbagawa-Kamuikotan Belt are paired metamorphic belts which were formed simultaneously with the juxtaposition of Jurassic-Lower Cretaceous accretionary complexes of Northeast Japan and the Inner Zone of Southwest Japan. During the period of 130-95 Ma, Izanagi Plate subducted beneath eastern Asia. Its rapid plate motion caused a northward drift of Northeast Japan and the Outer Zone of Southwest Japan. The Sanbagawa-Kamuikotan Belt was formed in the eastern margin of the drifting landmass, while the Higo-Abukuma Belt was formed in its western portion. The Ryoke Belt was formed in the eastern part of the Inner Zone of Southwest Japan which was not displaced significantly. The mid-Cretaceous tectonics were completed at approximately 95 Ma when the subducting plate was changed from Izanagi Plate to Kula Plate. New accretion tectonics and subduction-related magmatism took place in the Shimanto Belt and the Inner Zone of Southwest Japan, respectively.
