We report helium isotope data for 0.03–1？Ma olivine-bearing basaltic hawaiites from three volcanoes of the southern Italy magmatic province (Ustica, Pantelleria, and Linosa Islands). Homogenous 3 H e / 4 H e ratios (range: 7.3–7.6？ R a ) for the three islands, and their similarity with the ratio of modern volcanic gases on Pantelleria, indicate a common magmatic end-member. In particular, Ustica ( 7 . 6 ± 0 . 2 ？ R a ) clearly differs from the nearby Aeolian Islands Arc volcanism, despite its location on the Tyrrhenian side of the plate boundary. Although limited in size, our data set complements the large existing database for helium isotope in southern Italy and adds further constraints upon the spatial extent of intraplate alkaline volcanism in southern Mediterranea. As already discussed by others, the He-Pb isotopic signature of this magmatic province indicates a derivation from a mantle diapir of a OIB-type that is partially diluted by the depleted upper mantle (MORB mantle) at its periphery. 1. Introduction Plio-Quaternary volcanism in the Italian Peninsula has developed in the complex tectonic environment of African-European continental plate collision and Adriatic-Ionian slab subduction under the expanding Tyrrhenian Sea back-arc basin ([1] and references therein). This complexity is reflected in the wide compositional diversity of erupted magmas, which range from ultrapotassic and potassium-rich in Tuscany and the Roman-Napolitean province, to calc-alkaline in the Aeolian Island arc, and to OIB-type Na-alkaline basaltic in southern Sardinia and Sicily. This magmatic diversity is also accompanied by spectacular regional gradations in the trace-element and isotope geochemistry of volcanic products. In particular, the progressive south to north trend of 87Sr/86Sr and 18O/16O in magmas, and 13C/12C and 3He/4He in emitted gases [2–6] indicates a northward increase in contamination of magma sources by crustal material from the subducting Adriatic and Ionian plates. Na-alkaline mafic magmatism currently active at or close to the collision plate boundary in southern Italy displays minor imprint of these subduction processes and thus provides the “cleanest” signature of the mantle beneath the region. This basaltic magmatism has developed on tensional tectonic faults cutting the African plate margin and over both a thinner crust and lithosphere (60–100？km). This basalt displays trace-element patterns typical of Ocean Island Basalts (OIB), relatively radiogenic 87Sr/86Sr and 206Pb/204Pb isotopic signatures [7–11], and has been recognized to represent a
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