Origin and evolution of the Pleistocene magmatism of Linosa Island (Sicily Channel, Italy)

Abstract

Major, trace element and Sr-Nd isotope data are reported for volcanic rocks from Linosa Island (Sicily Channel) with the aim of discussing the genesis and evolution of magmatism at the northern margin of the African plate. The volcanic rocks exposed at Linosa exhibit a transitional to mildly Na-alkaline affinity and are mainly mafic in composition (alkali basalt to hawaiite); benmoreitic to trachytic lithic clasts occur in the lowest exposed pyroclastic deposits. Magmas have been erupted between 1.06 ± 0.10 and 0.53 ± 0.07 Ma during three main cycles of activity: Paleolinosa, Arena Bianca and Monte Bandiera. Major and trace element data indicate a magma evolution by dominant fractional crystallization. However, compatible vs. incompatible element diagrams highlight distinct variation trends, which are interpreted to suggest fractional crystallisation starting from slightly different parental magmas, and separation of distinct mineral assemblages during polybaric evolution. Small variation of Sr and Nd isotope ratios indicate modest interaction with the crust. As other mafic magmas in Eastern Sicily and Sicily Channel (Etna, Iblei, Pantelleria, Sicily Channel seamounts), the most primitive magmas at Linosa are characterised by enrichments in high-field-strength elements (Nb, Ta) and depletion in Rb, Cs and other large ion lithophile elements. Their isotopic signatures fall close to the field of the so-called EAR (European Asthenospheric Reservoir) and FOZO (Focus Zone) mantle compositions. However, there are many significant geochemical and isotopic differences among various volcanoes in Eastern Sicily and Sicily Channel, which suggest variable degrees of melting at different depths of a heterogeneous mantle source. Overall, radiogenic isotope signatures reflect mixtures between EAR-FOZO and DMM (Depleted MORB Mantle) and may be related to mixing of asthenosphere-lithosphere or to variably metasomatised lithospheric mantle.