VOLCANOLOGICAL AND PETROLOGICAL EVOLUTION OF VULCANO-ISLAND (AEOLIAN ARC, SOUTHERN TYRRHENIAN SEA)

Petrological and geochemical data are reported for volcanic rocks from Vulcano island. The subaerial volcanism (120 ka to present) built up a NW-SE elongated composite structure, affected by two intersecting mu ltistage calderas. Volcanics older than 20 ka consist mostly of high-K calc-alkaline (HKCA) to shoshonitic (SHO) mafic rocks. These magmas i nteracted significantly with the continental crust, which generated va riable Sr isotopic ratios (0.70412-0.70520). However, a major role was also played by input of parental liquids into the magma chamber, whic h prevented further evolution of the magmas. HKCA, SHO, and potassic ( KS) racks formed from 20 to 8 ka, display a much larger range of SiO2 (from shoshonites to rhyolites) and higher concentrations of incompati ble elements with respect to the previous stage. Sr isotopic ratios sh ow small variations (0.70448-0.70486). Mixing of silicic and mafic liq uids and fractional crystallization processes (FC) were the main evolu tionary processes during this stage. Volcanics younger than 8 ka consi st of SHO and leucite-bearing KS mafic rocks, with abundant intermedia te and silicic products. Mafic and intermediate rocks display similar incompatible element abundances and Sr isotopic ratios as the previous stage volcanics, whereas higher Sr-87/Sr-86 (0.70494-0.70583) are obs erved in some rhyolites. These products originated from a complex inte rplay of FC, crustal assimilation, and magma mixing processes. The mos t mafic rocks show increasing incompatible element abundances, Rb/Sr, Rb/Ba, Mg/Al, Mg/Ca, and a decrease in large ion lithophile to high fi eld strength element ratios, passing from older HKCA-SHO to the younge r SHO-KS volcanics. These variations suggest a shifting of magma sourc es from a slightly metasomatized asthenosphere (fertile peridotite) to a more strongly metasomatized lithospheric mantle (residual peridotit e). Time-related petrological and geochemical variations have been use d to develop a model for the evolution of the Vulcano plumbing system.