Geochemistry and petrogenesis of quaternary magmatism in central-southern Italy

Central-southern Italy is characterized by a wide range of Quaternary magma types, from subalkaline to Na- and K-alkaline and ultra-alkaline. These ar e closely associated in space and time and display variable degrees of evol ution, from nearly primary mafic compositions to strongly evolved rhyolites , trachytes, and phonolites. Scrutiny of major and trace element data allow s one to recognize several magmatic provinces, which show distinct composit ion in terms of major and/or trace elements, and/or radiogenic isotopes. Th is varied magmatic setting reveals compositionally heterogeneous mantle sou rces, which originated by a complex geodynamic evolution. Potassic and ultrapotassic magmatism is one of the most striking geological features of the Tyrrhenian side of the Italian peninsula. It extends from Tuscany in the north to the Aeolian are in the south and displays very vari able petrological characteristics, from slightly oversaturated lamproites t o saturated and strongly undersaturated Roman-type potassic and high-potass ium series (KS and HKS) and kamafugites. Incompatible trace element abundan ces and ratios and radiogenic isotope signatures are also variable and appe ar to be related to the regional distribution of rocks. There is a wide, though not unanimous, consensus that the bulk of volcanism from Tuscany to the Aeolian are was generated in a variety of mantle sourc es that were subjected to subduction-related metasomatic modifications. How ever, data are insufficient to put constraints on the age and, to some exte nt, on the nature of metasomatism. Scrutiny of geological and geochemical data suggests that the upper mantle beneath the Italian peninsula was affected by at least three compositionall y distinct metasomatic events; these likely occurred at different times and generated variably metasomatized mantle sources. The oldest event appears to be Alpine in age and affected the upper mantle beneath the Tuscany provi nce. Metasomatism in the other districts is probably younger and is suggest ed to be related to west and north-west dipping subduction zones of the Adr iatic and the Ionian sea plates. The overall picture that unfolds from petrological and geochemical data is that the variety of magmas reflects a mosaic of compositionally distinct ma ntle sources. These were generated by distinct metasomatic events that acte d over petrologically variable premetasomatic mantle rocks.