Geochemistry of the Othris Ophiolite, Greece: Evidence for refertilization?

The Othris peridotite massif, Greece, shows conflicting evidence for a mid-ocean ridge and supra-subduction zone tectonic setting with the presence of plagioclase peridotite that may represent an area of either incomplete melt extraction, or melt impregnation and accumulation. To address these problems we focus on a 3km continuous section in the Fournos Kaïtsa area, consisting of layers of harzburgite, plagioclase harzburgite and plagioclase lherzolite with accurately known structural and petrographic control. Refractory, Cr-rich spinel compositions and light rare earth element depleted clinopyroxenes in the harzburgites are consistent with ∼15% dry partial melting. Simple batch and fractional melting models are not sufficient to explain the composition of the residual phases and a multistage model with some melting in the garnet stability field is proposed. The pyroxenes from the plagioclase peridotites have higher Ti and rare earth element contents than those from the harzburgites, but similar refractory spinel compositions in both rock types indicate that the plagioclase peridotites may be products of impregnation of harzburgites with a fractionating melt. These observations are in good agreement with previous structural studies and suggest that the moderately depleted Fournos Kaïtsa mantle section most probably originated at a slow-spreading mid-ocean ridge.