Abstract
The Karasaki mylonite unit crops out as a series of isolated klippes on the Sambagawa Belt, along its northern margin in western Shikoku. It mainly consists of strongly deformed amphibolites and subsidiary of pelitic and quartzo-feldspathic metamorphic rocks. This tectonic unit is distinguished on the basis of field occurrence, difference in metamorphic grade and in shear sence with respect to the underlying Sambagawa metamorphic rocks.The chemical composition of garnet and hornblende suggests that the protolith of the Karasaki mylonite is amphibolite facies metamorphic rocks, that have been devoid of Sambagawa metamorphism. Hornblendes from amphibolitic mylonites yield the K-Ar ages of 104±5 Ma, 119±6 Ma and 122±6 Ma. Accordingly, the Karasaki mylonite is possibly correlative to the Higo, Oshima, Yorii, Nishidohira and Takanuki metamorphic rocks of the latest Early Cretaceous age, which are considered to constitute the Paleo-Ryoke Belt interleaved between the Ryoke and Sambagawa Belts.
