Oxide-coated silicate droplets record three immiscible melts in sulfide-silicate emulsions

Abstract Emulsion textures between sulfide and silicate minerals provide insight into the complex mingling behaviors between immiscible sulfide and silicate melts. The Sora gabbroic intrusion in eastern Germany not only hosts exceptionally well-preserved emulsion textures but also displays previously undescribed spherical silicate droplets within a sulfide matrix. These droplets are completely enclosed by thin coats of partly skeletal magnetite, ilmenite, apatite and/or biotite. The mineral assemblage and crystal morphologies of these coats suggest the involvement of a third immiscible Fe-Ti-P-rich melt (besides silicate and sulfide melts) during the formation of the emulsion textures. Supporting evidence includes the absence of reaction textures at the droplet interfaces, the independence of the composition of hosting sulfides and the enrichment of V and Cr in magnetite and Mn in ilmenite, hence of elements that are generally incompatible in both sulfide and silicate melts. This dense, rapidly crystallized Fe-Ti-P melt enclosing silicate droplets could have acted as geological emulsifier, increasing the effective density of the coated silicate melt and preventing its ascent through the hosting denser sulfide melt. This prevention of coalescence could have likely contributed to the exceptionally well preserved emulsion textures at the Sora intrusion. This study provides new evidence for three-liquid immiscibility involving silicate, sulfide, and Fe-Ti-P melts in a natural example and highlights how their interaction can preserve complex multi-melt processes in magmatic systems.