The heterogeneous nature of the Southern Tyrrhenian mantle: Evidence from olivine-hosted melt inclusions from back-arc magmas of the Marsili seamount

The olivine-hosted melt inclusions with a composition different to that of the host rock reveal two further distinct geochemical signatures. One signature resembles that of the OIB-like lavas from the nearby Ustica Island, and is also alike to that of the few OIB-like lavas so far recovered from the Marsili volcano. However, the Marsili OIB-like melt inclusions are richer in SiO2, TiO2, Na2O, Zr, Y and HREE and depleted in CaO relative to these OIB-like lavas, suggesting an origin by melting of trachyandesitic bodies in the lower lithospheric mantle, which are themselves formed by high pressure fractional crystallization of parental OIB-like melts. The other detected signature is similar to that of the MORB lavas recording the early ocean-formation stage of the Southern Tyrrhenian back-arc basin. Nevertheless, the high CaO contents of these melts suggest that they probably resulted from melting of clinopyroxene-rich veins related to this early ocean-forming stage.