Spinel compositional variation in the crustal and mantle lithologies of the Othris ophiolite

Spinels from cumulus and non-cumulus members of the Othris ophiolite display a considerable variation in composition. Cumulus picrites and gabbros contain either a primary chromite and/or a reaction spinel formed by reaction with co-existing silicates (Cr-Al varia tion) or intercumulus liquid (Cr-Fe variation). Non-cumulus peridotites contain spinels which vary along a Cr-Al trend. Harzburgites contain a Cr-spinel and lherzolites a more aluminous spinel. The occurence of gabbroic segregations within the host lherzolite appears to affect the spinel chemistry. Spinels adjacent to these plagioclase—diopside veinlets are richer in aluminium than the spinels scattered within the depleted lherzolite surrounding the veinlet. [Protoclastic harzburgites contain a highly aluminous spinel phase either as an exsolution phase within pyroxenes or as a groundmass spinel.] The Cr-Al variation of the peridotites is believed to have resulted from interaction with interstitial aluminous liquid—in situ basaltic melt from a fused peridotite?