Mineralogy of spinel peridotite inclusions of alkali basalts from Sardinia

Alkali basalts of Pliocene-Quaternary age from Sardinia contain inclusions of spinel peridotites: Iherzolite, harzburgite-Iherzolite, wehrlite, and pyroxenite. Although the minerals of the basalts have distinctive chemical compositions, there are remarkable similarities in the compositions of olivine, orthopyroxene, and clinopyroxene of the inclusions. Chromian spinels show large variations in composition, although their Al contents show a good correlation with those of the coexisting orthopyroxene and clinopyroxene. The minerals of the inclusions are generally not zoned. However, the clinopyroxene of Iherzolites is zoned: the rims are higher in Mg and Ca and lower in Al and Na than the cores. Glass unrelated to the host basalt occurs in several specimens.

The mineralogy of the inclusions, the chemistry of the minerals, and the composition of the glasses are consistent with the hypothesis that these spinel peridotite inclusions were originated by different degrees of partial melting of mantle material and were possibly re-equilibrated at different mantle depths.