THE ROLE OF THE CRUST IN THE MAGMATIC EVOLUTION OF THE ISLAND OF LIPARI (AEOLIAN ISLANDS, ITALY)

Volcanic rocks on the island of Lipari show the entire range of Sr, Nd, Pb isotopic compositions displayed by other islands in the Aeolian archipelago. The rapid isotopic evolution of subaerial volcanic rocks on Lipari towards crustal values together with the appropriate isotopic composition of the neighbouring Calabrian crust (Serre) indicate that many geochemical characteristics observed in the lavas can be attributed to contamination and mixing with crustal materials and melts. Interpretation of the data is complicated by the fact that under-plating onto the crust-mantle boundary and the specific lithologies present in the crustal section differ underneath each individual sector of the island. In the central and northern parts of the island, metapelitic rocks were incorporated to provide the more radiogenic Sr isotopic compositions of some lavas. The products from M. Guardia in the southern part of Lipari, where activity is restricted to the last 30-40 ka, bear geochemical similarities to the island of Vulcano, where it is proposed that considerable remobilization of the crust took place in the presence of mafic mantle-derived melts. On Lipari, the petrogenetic processes of magma mixing and assimilation dominate over fractional crystallization, and the observed increase of K2O over Na2O can be correlated with contributions from metapelitic crustal lithologies. It is suggested that the variability in isotopic composition and the budget of alkalis (Na2O versus K2O) in the lavas can be explained by invoking a heat source from an intruding asthenospheric MORB-type mantle into a cooler lithospheric crust/mantle during the opening of the Tyrrhenian basin.