Evolution of pressure-temperature paths and fluid compositions during the Sanbagawa prograde metamorphism was reviewed on the basis of chemical characteristics and zonal structures of sodic pyroxene, amphibole, garnet and phengite. Zonal structures of sodic pyroxene, garnet and phengite imply that (1) dP/dT of prograde P-T paths of individual rocks decreased with increasing metamorphic grade and (2) dP/dT just before metamorphic climax might have been negative in some high-grade rocks. Changes of amphibole composition indicate that the prograde P-T path recorded in the higher-grade rocks was situated on the higher-temperature side of that of the lower-grade rocks and on the lower-pressure side of the metamorphic field gradient (1.4-1.8kbar/100°C). The systematic change of prograde P-T path implies an increasing dP/dT during continuous subduction by continuous cooling of the surrounding mantle. These features can be interpreted as documenting prograde metamorphism within a young subduction zone that has a non-steady-state geotherm. X_co2 [=CO₂/(CO₂+H₂O)] value of metamorphic fluid seems to increase with increasing metamorphic grade, and reaches>0.2 in some higher-grade rocks. The increasing X_co2 might have been promoted by oxidation of carbonaceous material caused by mechanical mixing of metapelites and Fe₂O₃-rich metabasites. Differences in petrological and age data between the Sanbagawa high-grade rocks and pebbles of high-grade in the Eocene Kuma Group in central Shikoku were also briefly reviewed to discuss evolution of subduction zone in the southwest Japan of Jurassic-Cretaceous age.

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The chemical composition and compositional zoning of garnets from seven Sanbagawa basic schists were studied. The samples were collected from the albite-biotite and oligoclase-biotite zones in the Besshi and Asemi River areas, Central Shikoku. All the examined garnets from the Asemi River area show Mn-bell shaped normal zoning. Mn-content in the core of garnets (up to 30 wt% of MnO) varies from a rock to another, reflecting their bulk composition. In the Besshi area, very Mg-rich garnets as compared with those in the Sanbagawa schist and in the literature were found from basic schists near the epidote-amphibolite masses. Further, reversely zoned garnet in regard to Mn distribution occurs, along with normaly zoned garnets, in two basic schists near the Tonaru epidote-amphibolite mass. These facts imply that higher temperatures than the other Sanbagawa schist were attained at the Besshi area. Disequilibrium crystallization was noticed in the garnet near the amphibolite mass, probably correlating to the emplacement of the amphibolite masses.

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The mode of occurrence and mineralogical properties of wairakites from Haga, Hyôgo Prefecture were described.
Wairakite occurs as a narrow vein (about 1 mm width) only in Palaeogene sedimentary formation (shale or siltstone) around intrusive granodiorite. From X-ray powder diffraction studies, wairakites found in above collecting sites have disordered tetragonal or pseudo-tetragonal structures. They are considered to have been formed at higher temperature than ordered ones (typical monoclinic wairakites).

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