Orthopyroxene veins in back-arc peridotite xenoliths from the Shiribeshi Seamount, Japan Sea

Abstract

We found rare orthopyroxene veins intruding into an olivine grain in a two-peridotite xenolith from the Shiribeshi Seamount, Japan Sea. The orthopyroxenes in the veins are characterized by low Al₂O₃, CaO and Cr₂O₃ contents, which are similar to secondary orthopyroxenes replacing olivines reported in arc-peridotite xenoliths. REE patterns of the melts in equilibrium with the orthopyroxenes imply that the orthopyroxene veins were derived from garnet-bearing source material. These orthopyroxene veins were possibly produced by the addition of Si-rich melt/fluid released from the subducted slab into the back-arc mantle beneath the Japan Sea.