TEMPORAL EVOLUTION OF A 3 COMPONENT SYSTEM - THE ISLAND OF LIPARI (AEOLIAN ARC, SOUTHERN ITALY)

The volcanic products from Lipari define an evolutionary trend with a high gradient of K-enrichment, similar to the calc-alkaline to potassic volcanism of other islands in the Aeolian arc. Stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages. The first stage, from 223 to 42 ka, consists of six eruptive cycles and is characterized by basalts and basalt-andesites showing progressive increase in both SiO2 and K2O contents with time. The second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products. Fractional crystallization, assimilation and mixing models suggest that the geochemistry of Lipari volcanism evolved with time by a complex interplay between two mantle-derived components, one sub-alkaline and the other alkaline, in addition to crustal melts and/or crustally-derived materials. A petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro- and microscopic features. Melts from the crustal and mantle end-members are almost always present in the system but the relative proportions appear to vary with time. The sub-alkaline mantle component (source of Tyrrhenian tholeiites) is an important contributor to the early evolution of the volcanism in Lipari; input from the alkaline mantle component (source of the Roman Comagmatic Province) increases with time, and the crustal component becomes dominant in the later activity. The preferred petrogenetic model for the temporal evolution of the volcanic system in Lipari involves melting initially caused by an increase in the thermal input related to the opening of the Tyrrhenian Sea and/or to subduction processes. The quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts.