Abstract
The Kashio Tectonic Belt in the Ichinose region consists of mylonite and Awasawa metamorphic rocks, which is situated between the Ryoke Belt and the Sanbagawa Metamorphic Belt. The geology of the Ichinose region is elucidated through the studies on litbology, grain size of quartz aggregates and metamorphic minerals. The mylonite belt is divided into zones F, M and C with increasing quartz grain size. Epidote recrystallizes in zones M and F. K-feldspar in pelitic rocks is rare in zone F, but is common in zone C. Phengite contents of muscovite crystals tend to increase from zone C to zone F. These petrological features suggest a decrease in metamorphic temperature from zone C to zone F. In the northern part of the Ichinose region, mylonite foliation strikes N 30°-50°E except for the southernmost region where the foliation strikes N 15 E. Mylonite foliation in the southern part of the Ichinose region strikes N 30°E which is parallel to compositional layering and the boundaries between zones C, M and F. The complex internal structure of the Kashio Tectonic Belt is evidence of a conspicuous deformation of the Kashio Tectonic Belt after the formation of mylonites in the Cretaceous time. This deformation took place during the formation of the Median Tectonic Line (MTL) in the Ichinose region, judging from the widespread occurrence of weakly metamorphosed rocks near the faults in the Kashio Tectonic Belt and the MTL. The deformation of the Kashio Tectonic Belt can be explained in terms of the rotation and northward horizontal shift of the Akaishi Mountains at about 16-15 Ma.
