We found discordant dunites from the mantle section of the Lizard ophiolite. They are strongly serpentinized, but we could find rare relic olivine only in some dunites. Two-phase(black and dark green portions) spinel grains are ubiquitous in the dunites. The black portion is rich in Fe3+ and Ti, and the dark green portion is low in Cr#, Fe3+, and Ti. The Fo content(82 to 85) of olivine in the discordant dunites is lower than that of mantle peridotites(89 to 92). The discordant dunites were formed by interaction between the mantle peridotite, and a melt rich in Fe, Ti and olivine components such as ferropicrite. The interaction enhanced the Ti and Fe3+ contents of the magma to precipitate the Ti- and Fe3+-rich spinels that have been decomposed into two phases on cooling.
