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 are closely associated in space and time and display variable degrees of evolution, from nearly primary mafic compositions to strongly evolved rhyolites, trachytes, and phonolites. Scrutiny of major and trace element data allows one to recognize several magmatic provinces, which show distinct composition in terms of major and/or trace elements, and/or radiogenic isotopes. This varied magmatic setting reveals compositionally heterogeneous mantle sources, 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 variable petrological characteristics, from slightly oversaturated lamproites to saturated and strongly undersaturated Roman-type potassic and high-potassium series (KS and HKS) and kamafugites. Incompatible trace element abundances and ratios and radiogenic isotope signatures are also variable and appear 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 sources that were subjected to subduction-related metasomatic modifications. However, data are insufficient to put constraints on the age and, to some extent, 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 compositionally 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 province. Metasomatism in the other districts is probably younger and is suggested to be related to west and north-west dipping subduction zones of the Adriatic 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 mantle sources. These were generated by distinct metasomatic events that acted over petrologically variable premetasomatic mantle rocks.