Two contrasting garnet zonings found in a hand specimen of a metasediment from the Sanbagawa metamorphic belt

Abstract

Two contrasting garnet zonings, type1 with Mn-rich core and type2 with Mn-poor one, are found in a hand specimen of a metasediment from the Besshi district, the Sanbagawa belt. Both type show rounded cores and surrounding euhedral rim of discontinuous compositions, suggesting they suffered resorption and fluid infiltration during prograde metamorphism. The distributions of two types of garnet are separated by a thin layer of very Mn-rich garnet, which is concordant to the main schistosity, though the main constituent minerals are similar in composition within the two parts. The different zonings should be derived from the inhomogeneity of the protolith.