The earliest stage of mantle-melt evolution during subduction initiation: Evidence from the Neo-Tethyan Mirdita Ophiolite, Albania

Mantle-melt evolution processes in the earliest stage of subduction initiation (SI) are still ambiguous. Here, we report systematic petrogeochemical and physical records SI demonstrated by Gomsiqe massif, Mirdita ophiolite. The ultramafic body consists basal lherzolites, upper harzburgites containing lentoid dunites disseminated chromitites, displaying transition petrological (Cr# spinels range from 12.7 to 47.1) geochemical signatures. Clinopyroxene trace element modeling indicates that lherzolites have undergone variable garnet-facies melting prior spinel-facies melting. Harzburgites encountered higher degrees compared with those (∼ 8–10% vs. ∼ 3–5%), late-stage MORB melt metasomatism. Lherzolites escaped chromitites formed interactions between harzburgitic lithosphere MORB-like transitional magmas continued, but limited hydrous fluid involvement during subduction. characteristics metasomatic composition condition (i.e., oxygen fugacity [fo2]) different lithologies consistent corresponding archive Izu-Bonin-Mariana forearc. comparable fo2 abyssal peridotites. apparently more oxidized associated further supporting a hypothesis sulfur-saturated melts were responsible for formation reduced Cr# chromitite spinels. Thermometry showed preserved equilibration temperatures than harzburgites. Both experienced later lower-temperature re-equilibration process. Thus, ophiolite preserves multi-stage mantle-melt processes, which comprehensive physicochemical responses SI.