The higher-grade region of the Sanbagawa metamorphic belt in Shikoku and the Kii peninsula contains metagabbro, peridotite, and serpentinite. These rocks occur exclusively in the garnet, albite-biotite, and oligoclase-biotite zones, and tend to have equilibrium mineral assemblages stable with respect to the mineral zones where they occur. Thermal histories of previous equilibrium stages can be discerned through not only the mineralogy of relics, but also the texture, megascopic structure, and bulk composition of the rocks. The protoliths were layered gabbro, cumulate and residual peridotites, and garnet clinopyroxenite. Some of these rocks were in the eclogite facies before emplacement into the Sanbagawa schists and others were in the granulite facies. They were emplaced into the metamorphic regime by solid intrusion during a later stage of the schistosity formation, that is, emplacement was syntectonic. Some peridotites were serpentinized before attaining equilibrium assemblages of the Sanbagawa metamorphism; their emplacement was during an earlier stage of the metamorphism, but not at the sedimentary stage. The source region of those exotic blocks may have been a lower crust-upper mantle region of an island arc.