Hf-Nd-Sr-Pb isotopic evidence for the presence of pelagic sediments in the source of Italian poptassic volcanic rocks

Abstract Sr, Nd, Pb and Hf isotopes were analyzed in 36 primitive Plio-Pleistocene volcanic rocks from central and southern Italy (Radicofani, Cimini, Vico, Vulsini, Sabatini, Ernici, Vesuvius, Aeolian Islands, Etna-Iblean Basin, Tyrrhenian Basin). The sample collection comprises basanites, basalts, trachybasalts, shoshonites and phonotephrites. The samples display two distinct geografical trends: the south- to –north Etna, Iblean-Tuscan Magmatic Province at east, with 87Sr/86Sr = 0.70285-0.715647, Nd = +8.23 to –11.37, Hf = +8.78 to –11.53, 206Pb/204Pb = 19.908 to 18.714, 207Pb/204Pb = 15.679 to 15.617 and 208Pb/204Pb = 39.917 to 39.621, and the west- to -east Tyrrhenian basalts (sites 655, 651, Vavilov Basin) trend at west, including samples with 87Sr/86Sr = 0.70372-0.70733, Nd = +9.21 to +5.89, Hf = +15.38 to +7.10, 206Pb/204Pb = 18.698 to 18.919, 207Pb/204Pb = 15.573 to 15.677 and 208Pb/204Pb = 38.666 to 39.183. Whereas the two trends cannot be distinguished in the Sr-Nd isotope space, they are clearly resolved in the Pb-Hf, Nd-Pb and Sr-Pb isotope spaces. In a Nd-Hf isotope plot the compositions of the central Italy volcanics (e.g. Tuscan and Roman Magmatic Provinces, and Vesuvius) plot between the field of Mn-nodules and the Hf-Nd isotopic mantle-crust array, within the field of pelagic sediments. Their Hf-Nd isotopic properties therefore signal a significant contribution of clay/pelagic material to the source of these magmas. Combined with the heavy oxygen isotope compositions of these lavas, which requires that the mantle source has incorporated a very substantial fraction of material that went through the exogenic cycle, we suggest that the central-southern Italy volcanics formed by remelting of a crustal component that can be identified by radiogenic and stable isotopes, as well as trace elements. Origin of central-southern Italy magmas by melting of mantle that had incorporated slivers of “dirty” lithosphere stands as the best interpretation of the present isotopic data. The Quaternary Italian volcanics (Tuscan and Roman Magmatic Provinces, Vesuvius, Aeolian Arc, Etna, and Iblean Basin) appear to be the result of various interaction of an OIB mantle source (HIMU-type) with different proportions and/or heterogeneous slivers of crust and clay/pelagic sediments. According to these data it is suggested the involvement of at least two mantle reservoirs in the central-southern Italy: an OIB type (Etna-Iblean Basin and Sardinia), and a MORB-type in the Tyrrhenian Basin (Vavilov). Nevertheless we suggest that the Tyrrhenian (Vavilov) upper mantle material is not melted together with the recycled component in the magma source of the RMP and TMP volcanics.