MANTLE HETEROGENEITY AND MELTING CONDITIONS IN THE STRAIT OF SICILY RIFT ZONE

The Strait of Sicily Rift Zone (SSRZ) is a northwest-southeast trending transtensional rift system situated on the Pelagian Block, the northern promontory of the African plate that represents the foreland domain of the Sicilian Apenninic-Maghrebian orogeny. The SSRZ consists of three basins: the Pantelleria Trough, the Linosa Trough, and the Malta Trough. Volcanoes are present in or adjacent to all except the Malta Trough, and include two islands (Pantelleria and Linosa) and several seamounts. Volcanism in the SSRZ is dominated by continental OIB-like (C-OIB) Na-alkaline mafic lavas and tuffs. Although petrographically similar, there are significant differences in the major-element, trace-element, and isotopic compositions of the rocks distributed throughout this region that cannot be explained by fractional crystallization or degree of partial melting alone. Prior investigators have documented the Sr-Nd-Pb isotope geochemistry of these mafic lavas, and have shown that the Pantelleria suite has a stronger HIMU-like signature than the Linosa suite which suggests a greater role for recycled oceanic material (eclogite/pyroxenite) in the mantle source for these rocks. There are also significant differences in the major- and trace-element geochemistries of these suites. For a given value of MgO, the Pantelleria samples are lower in SiO2, Al2O3, Na2O, and K2O, and higher in CaO, TiO2, and FeO, a major-element signature that suggests a more pyroxenitic mantle source for the Pantelleria suite. Pantelleria and Linosa are also characterized by different incompatible trace-element and rare earth element ratios. This study uses multiple modelling techniques, including inverse modelling of REE ratios, pMELTS, and comparison with experimental data to constrain the relative roles of mantle source composition and melting conditions in the generation of magma beneath the Pantelleria and Linosa troughs. Preliminary results confirm that the differences between the two islands cannot be related solely to different degrees of partial melting and must require a more fertile mantle below Pantelleria