The geochemistry of leucite-bearing lavas from early stages of the Somma-Vesuvius volcanic complex. Feeder systems and mantle enrichment processes in the Neapolitan district of the Roman Magmatic Province

The lavas of the Monte Somma activity (early stage of the Somma-Vesuvius volcanic complex) are mildly differentiated plagioclase-clinopyroxene-olivine- ± leucite-bearing lavas (leucite tephrites, leucite-bearing shoshonites, latites), low in MgO, Cr and Ni, with a Sr-Nd-isotope range (87Sr/86Sr = 0.706865-0.707861; 143Nd/144Nd = 0.51244-0.51258) overlapping that of the Vesuvian lavas late after 1638 CE (late stage of the Somma-Vesuvius volcanic complex). The differentiation is dominated by fractional crystallization of clinopyroxene, calcic plagioclase, olivine and leucite, with limited interaction with crustal rocks. Oxygen isotopes on clinopyroxene and olivine phenocrysts (δ18O = 6.5-7.9 ‰) are higher than typical uncontaminated mantle magmas. However, these values are also not fully consistent with the sole opensystem assimilation+fractional crystallization of a mantle-derived ultrapotassic magma. A contribution from a recycled crustal component in the mantle source is required, likely dominated by sediment-derived fluids and melts. The Somma lavas are characterized by distinctly different geochemical features compared to the mafic products of the neighboring volcanic areas (i.e., Phlegrean Fields, Procida and Ischia volcanoes), where the recycled crustal component is less pronounced.