Sulfide inclusions in phenocrysts from basanite lithic clasts and mafic phonolite lapilli from the Upper Laacher See Tephra (Germany): Evolution of an immiscible sulfide liquid

Sulfide inclusions in phenocrysts from phonolite pumice lapilli from the Upper Laacher See Tephra (ca. 13 ka) along with basanite lithic clasts were analyzed in situ for major- and trace-element compositions using SEM and LA-ICP-MS techniques. For the first time, we trace the compositional evolution of trace elements in the Laacher See immiscible sulfide liquids that exsolved from the basanite and mafic phonolite melts at various stages of differentiation. Sulfide inclusions represent former immiscible sulfide liquids that exsolved from both basanite parent magma and evolved daughter phonolite melts. After their incorporation into host minerals, the inclusions in basanitic mafic phenocrysts evolved during ascent and cooling in dikes and/or lava flows. The resultant sulfide inclusions are always polymineralic and composed of Fe-, Cu-, and Ni-rich phases (mainly pyrrhotite, chalcopyrite, pentlandite). In contrast, sulfide inclusions in mafic and felsic phenocrysts in phonolite pumice lapilli are almost pure, homogeneous pyrrhotite (Cu-Ni-poor phase) and have low content of Ni, Co, and Cu, but elevated concentrations of Cd, Pb, Te and Zn. Our data thus document a sequence of sulfide liquid exsolution that occurred along the differentiation path from basanite to phonolite magma.