The western Iratsu mass, the largest tectonic body in the Sambagawa metamorphic belt, central Shikoku, is mainly composed of epidote amphibolite with minor amounts of eclogite. Systematically, a majority of garnets show bell-shaped chemical zoning of pyrope contents and Mg/(Mg+Fe2+) monotonously increasing outward. The grossular component in zonal garnet increases outwards, maximizes at an intermediate part, and then decreases towards the outermost rim, reflecting a process from increasing to decreasing pressure conditions during the prograde metamorphism. Jadeite contents of omphacite range from 25～20mole% within the cores to 15～10 mole% at the rims, implying a pressure-decreasing process (from 11 × 105 Pa to 8 × 105 Pa). The peak pressure-temperature (P-T) condition of 630～680 ℃ and ca. 15× 105 Pa in the western Iratsu mass is much higher than that of (610±25) ℃ and (10± 1)× 105 Pa of the Sambagawa oligoclase-biotite zone schists. The authors suggest a clockwise P-T-t path for the western Iratsu mass.
