A unique lower mantle source for Southern Italy volcanics

The Southern Italy volcanism is characterized by the unusual occurrence of volcanic rocks with ocean-island basalt (OIB)-like characteristics, in particular at Etna and Iblean Mts in Sicily. The geochemical properties of the source of the Italian magmatism are usually explained by a north-south binary mixing between a mantle- and a crustally-derived end-members. The nature of the mantle end-member is, however, not agreed upon. One type of interpretation invokes a mixture of depleted mantle (DMM) and high U/Pb (HIMU) end-members [Gasperini, D., Blichert-Toft, J., Bosch, D., Del Moro, A., Macera, P., Albarède, F., 2002. Upwelling of deep mantle material through a plate window: Evidence from the geochemistry of Italian basaltic volcanics, J. Geophys. Res. 107, 2367-2386], whereas an alternative view holds that the mantle end-member is unique and homogeneous, and similar to the FOZO- or C-type end-member identified in oceanic basalts [Bell, K., Castorina, F., Lavecchia, G., Rosatelli, G., Stoppa, F., 2004. Is there a mantle plume below Italy? EOS 85, 541-547]. Because mixing does not produce linear relationships between the isotopic compositions of different elements, we applied Principal Component Analysis (PCA) to the Pb isotope compositions of the Italian volcanics inclusive 36 of Sicily volcanoes. We demonstrate that HIMU cannot be an end-member of the Italian volcanics, but rather that the common component C (∼FOZO), which we interpret as reflecting the lower mantle, best represents the mantle source of the Italian magmatism. Our PCA calculation shows that the first principal component alone, which we take to be a mixture of two geochemical end-members, C and a crustally-derived component, explains 99.4% of the whole data variability. In contrast, the DMM end-member (the second principal component) is only present in the volcanics from the Tyrrhenian Sea floor. The C-like end-member, well represented by the Etna and Iblean Mts (Sicily), has relatively low 3He/4He ratios suggesting upwellings of lower mantle material from the 670 km transition zone. A slab detachment beneath the central-Southern Italy and probably the Sicily could account for the particular character of Italian magmatism.