Modes of occurrence and chemical compositions of garnets from the Seba pelitic schists in the Sambagawa metamorphic belt, central Shikoku, Japan

The Seba area is situated in the central part of the Besshi district of central Shikoku, and is composed of the Sebadani metagabbro mass and surrounding Seba basic schists.Eclogitic assemblages are sporadically preserved in both the Sebadani metagabbro and the Seba basic schists.The Sebadani metagabbro mass is surrounded by the Seba basic schists and a thin layers of pelitic schists and siliceous schists intercalated elsewhere within the Seba eclogitic basic schists.Pelitic schists consist mainly of garnet, omphacite, phengite, chlorite, and quartz, along with small amounts of epidote, amphiboles (sodic, sodic-calcic and calcic-amphibole), albite, biotite and carbonaceous matter.Rutile, titanite, calcite, chloritoid, K-feldspar, tourmaline apatite and zircon are occasionally present as accessory minerals.The garnets in the Seba pelitic schists exhibit three modes of occurrence.Garnet 1 (Grt 1) occurs as porphyroblasts in the matrix, garnet 2 (Grt 2) showing composite zoning occurs adjacent to the Sebadani metagabbro contact, and garnet 3 (Grt 3) is found as fine grains in the matrix.The mineral assemblage of inclusions in the cores and rims of the Grt 1 garnets suggests a prograde path of eclogitic metamorphism from the epidote blueschist facies, through the epidote amphibolite facies, to the eclogite facies.The cores of the composite zoned garnets (Grt 2) underwent the same eclogite facies metamorphism with the Grt 1 garnets, which is correlated with the second high-pressure metamorphic event of the Onodani eclogite.The rims of the Grt 2 garnets probably underwent another eclogite facies metamorphism.Fine-grained garnets in the matrix (Grt 3) probably record similar P-T histories as the rims of the Grt 2 garnets.