Seminari di Scienze della Terra
Universita’ di Genova
30 Gennaio 2007

 Multidisciplinar Approach to Natural Triggers of Lithosphere Evolution

The volcanic products of the island of Linosa (1.06-0.53 Ma) are mainly of sodic alkaline to slightly transitional character and are mainly represented by basalts and hawaiites; more evolved lithologies (mugearites, benmoreites, trachytes) have also been found. Trace element abundances suggest a within-plate tectonic setting, with bell-shaped patterns in primitive mantle-normalized multi-elemental diagrams, peaking at Nb with relatively low LILE abundances, within the HIMU-OIB compositional field. Sr-Nd-Pb isotopic ratios range as follows: 87Sr/86Sr from 0.7030 to 0.7031, 143Nd/144Nd from 0.51298 to 0.51295, 206Pb/204Pb from 19.28 to 19.43, 207Pb/204Pb from 15.60 to 15.62, 208Pb/204Pb from 38.89 to 39.02. The magmatism of Pantelleria, as well as that of Mt. Etna, has been alternatively related to the activity of a mantle plume or to a petrogenetic model in which lithospheric mantle sources, enriched and metasomatized by asthenospheric partial melts, undergo partial melting in an extensional tectonic regime without any mantle plume involvement. Geochemical data on the Sicily Channel seamounts (e.g., Graham and Nameless Banks, Tetide, Anfitrite, Galatea and Cimotoe seamounts, plus other minor volcanic centers) are limited. Rock types range from hawaiites to alkali basalts, basanites, mugearites and tholeiitic basalts, in order of abundance. Volcanic rocks from Graham and Nameless Banks have similar geochemical characteristics, broadly resembling HIMU-OIB. As a whole the Sicily Channel seamounts have 87Sr/86Sr ranging from 0.70308 to 0.70478, 143Nd/144Nd from 0.51312 to 0.51295, 206Pb/204Pb from 19.15 to 19.81, 207Pb/204Pb from 15.66 to 15.70, 208Pb/204Pb from 38.95 to 39.62. A model involving the presence of a fossil plume head beneath the Sicily Channel, Mt. Etna, the Hyblean Mts., Ustica Island and the westernmost island of the Aeolian Archipelago (Alicudi) has been proposed. This model is based on the relatively homogeneous EAR-like major and trace element and Sr-Nd-Pb isotopic characteristics of the magmatic rocks. USTICA: The island of Ustica is made up of Quaternary volcanic rocks with Na-alkaline affinity which range in composition from alkali basalts to rarer trachytes. Ustica lavas have a small range in 87Sr/86Sr (0.7030-0.7033) and 143Nd/144Nd (0.51300-0.51290) and a slightly wider range of compositions for 206Pb/204Pb (18.84-19.56), 208Pb/204Pb (38.61-39.19). On the basis of trace element and Sr-Nd isotopic compositions, a mantle source slightly contaminated by a component of slab origin has been proposed.

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