Discovery of datolite in a high–pressure marble from the Sanbagawa metamorphic belt: Indication of B–rich fluid activity

Abstract

Datolite [CaBSiO 4 (OH)] was discovered in an eclogite – facies calcite marble collected from the Eastern Iratsu body in the Sanbagawa metamorphic belt of central Shikoku. The marble was composed of calcite, diopside, and garnet that contained inclusions of omphacite. Enclosed in the marble is a pod composed mainly of quartz, with subordinate calcite, diopside, and garnet that has inclusions of datolite. The formation conditions of the datolite were estimated on the basis of mineral assemblage and the Raman elastic geobarometer to be approximately 400 – 650 °C and 0.8 – 1.3 GPa, which coincide with the conditions of the eclogite juxtaposition with the non – eclogite units in the Besshi district. Our study records the highest pressure – temperature conditions as the metamorphic datolite formation. Our fi ndings provide evidence for the occurrence of B – rich fl uid in fi ltration during the juxtaposition of eclogite unit with the non – eclogite unit in the Besshi district.