Geochronology of the Plio-Pleistocene Hyblean volcanism (SE Sicily): new 40Ar/39 data

The first results of an ongoing geochronological study on the Plio-Pleistocene Hyblean volcanic rocks are presented and discussed. 40Ar-39Ar age determinations are reported for separated groundmass and plagioclase fractions from alkaline and tholeiitic products. 40Ar-39Ar age spectra on analysed groundmasses vary from almost ideal to slightly discordant. Obtained ages, even if do not give an exhaustive geochronological picture, reveal that the Plio-Pleistocene volcanic rocks within the Hyblean Plateau are younger going from South (2.4 Ma, Torrente Risicone) to North (1.4 Ma, Vallone del Loddiero). These chronological data, in Agreement with the geological observations, let us exclude a possible link of the Hyblean volcanism with a "mantle plume". The Hyblean Plateau is a stable segment of the African plate; taking into account the NW movement of this plate, a mantle plume would produce a younger volcanism from North to South in this area. It is more likely that litospheric faults, set out on the Hyblean Plateau following the Africa-Eurasia interaction, have favoured and controlled the volcanism in this Mediterranean Sector since Late Cretaceous.