Petrochemical and magmatological characteristics of the Aeolian Arc volcanoes, southern Tyrrhenian Sea, Italy: inferences on shallow level processes and magma source variations

The Aeolian volcanic arc, constituted by seven islands and several seamounts, is emplaced on continental lithosphere. The islands are mainly formed by lava flows, domes and pyroclastic deposits, and emerged from the sea in a short time span, from around 200 ka ago at Filicudi, Lipari and Stromboli (Strombolicchio neck), to about 100 ka at Alicudi and Stromboli. At Panarea, an intense fumarolic activity is still present, the last eruptions at Lipari took place on 580 A.D., whereas Vulcano and Stromboli are still active. The rock compositions belong to different magmatic series and show a large silica range (48-76 wt%). Calc-alkaline (CA) and high-K calc-alkaline (HKCA) volcanics are present in all the islands, except for CA rocks at Vulcano. Shoshonitic (SHO) products are only lacking at Alicudi, Filicudi and Salina. Potassic (KS) volcanics have been erupted at Vulcano and Stromboli. Basalts are not found at Lipari, whereas a large amount of rhyolites are present in the central arc islands (Lipari, Vulcano, Salina, Panarea), having different petrochemical characteristics. Sr-87/Sr-86 increases from the western to the eastern sectors of the arc (0.70342-0.70757), whereas Nd-143/Nd-144 decreases (0.51289-0.51243). Pb isotope ratios show a large similar range in the western and central arc islands, but decrease at Panarea and Stromboli (e.g., Pb-206/Pb-204, 18.93-19.77). Among CA and HKCA rocks, incompatible trace element contents and ratios change passing from the central part of the arc to the external sectors. The isotopic and geochemical compositions of SHO and KS volcanics from Stromboli and Vulcano are distinct, with the Vulcano compositional characteristics resembling those of the CA and HKCA magmas from the central arc. Significant rock compositional variations are also observed within the single volcanoes. Aeolian magmas underwent multiple differentiation processes during the ascent to the surface from their mantle source. Fractional crystallisation is often associated to crustal contamination which affected at higher extent either the most evolved magmas at Vulcano, Salina and Lipari or the most mafic magmas at Alicudi, Filicudi and Stromboli. Multiple mixing also played an important role often associated with the other differentiation processes. These evolutionary processes occurred at polybaric conditions, with higher crystallisation pressure for Filicudi and Salina. The different parental magmas were originated in an heterogeneous mantle wedge, metasomatised by subduction-related components at increasing extent, going from west to east (= variation of Sr and Nd isotope ratios). It is also suggested that the mantle source of CA and HKCA magmas from central arc (Salina, Lipari and CA Panarea) is a MORB-like asthenospheric source, contaminated by aqueous fluids released by subducted oceanic crust + pelagic sediments. The same type of source can be envisaged for Volcano SHO and KS parental magmas. In the external sectors of the arc, mass transfer from the subducted slab to mantle seems to be occurred by higher melt/fluid proportions. At west (Alicudi and Filicudi), the other components involved in the magma genesis remain similar to those proposed for the central arc source. On the contrary, the compositional characteristics of eastern magmas (HKCA Panarea and Stromboli) suggest a different pre-contamination mantle source (continental lithosphere?) and/or a different crustal contaminant (with low Pb isotopes) of the mantle wedge. A decreasing partial melting degree of distinct mantle sources is considered to generate magmas with an increasing potassic character at Vulcano and Stromboli.