Abstract

Chromitites in ophiolites are frequently used as a marker of sub-arc mantle magmatism. This has, however, rarely been verified by modern sub-arc mantle materials. Chromitite xenoliths from Takashima, southwest Japan, derived from the current sub-arc mantle, are here described with comparison to ophiolitic chromitites. The chromitite xenoliths from Takashima from the southwest Japan arc show various textures, including nodular, anti-nodular, and layered varieties. Laurite is commonly found as minute (<5 μm diameter) solitary grains of euhedral shape in Cr-rich spinel. Very fine (around 1 μm) grains of Co-bearing pentlandite are associated with silicate inclusions (mainly pyroxenes) in Cr-rich spinel. The chondrite-normalized PGE pattern of Takashima chromitites shows a slightly negative slope from Ru to Pt. The Takashima chromitite is very similar in its PGE chemistry, spinel chemistry, and textural variations to some discordant chromitites from the Oman ophiolite, a typical podiform chromitite interpreted to have formed in an arc setting, indicating a possible sub-arc origin for the latter. The characteristics of the Takashima chromitite xenoliths indicate that the Oman discordant podiform chromitites were formed in a supra-subduction mantle setting before ophiolite obduction.

You do not currently have access to this article.