Petrologic and Isotopic characteristics of potassic and ultrapotassic alkalic magmatism in Central-Southern Italy: inferences on its genesis and on the nature of its mantle source

Miocene to Quaternary magmatic rocks, found along the Tyrrhenian border of peninsular Italy, mostly belong to potassic and ultrapotassic suites. They can be divided into three different petrographic provinces, where magmatism is confined in terms of space, time and petrographic characteristics. The Tuscan Magmatic Province is the northernmost province, in which mantle-derived potassic and ultrapotassic, leucite-free volcanic rocks occur, prevailing over high potassium calcalkaline rocks, and covering a time span of activity between 14.2 and 0.19 Ma. These rocks are silicasaturated to silica-oversaturated and range from high-potassium calc-alkaline to ultrapotassic lamproite, through potassic and ultrapotassic shoshonitic series. The Roman Magmatic Province extends from Northern Latium to the Umbrian and Campanian areas, arranged in a volcanic belt along the Tyrrhenian border of the Apennine chain. It is made up of rare shoshonitic rocks (KS) and leucite-bearing rocks (HKS). Some HKS may contain melilite, and therefore belong to the kamafugitic group (KAM). Minor high potassium calc-alkaline rocks are also found in the Pontine archipelago and in drill in the Campanian plain. Volcanism has been active from 0.7 Ma to 0.1 Ma in the northern districts of the Latian area (i.e., Vulsinian, Vico, Sabatinian, Alban, Hernican, Auruncan) whereas in the southernmost portion of the province, the Neapolitan district, shoshonitic and ultrapotassic magmatism are consistently younger than the Latian ones, ranging from 0.3 Ma to present. Historical eruptions in the Neapolitan district are indeed recorded at Phlegrean Fields, Procida, Ischia and Vesuvius volcanoes. The Lucanian Magmatic Province is the easternmost volcanic region characterized by rocks rich in both Na and K. Most of the rocks are haüyneand leucite-bearing, and were erupted at Monte Vulture volcano between 0.6 and 0.1 Ma. Carbonatites have been described in the last phase of activity. Minor amounts of K-rich rocks are also found in the Aeolian Arc, in the southern Tyrrhenian Sea. These rocks are intimately associated with calcalkaline rocks at Vulcano, Vulcanello, and Stromboli. Enrichment in K2O and related incompatible trace elements is accompanied by strong to mildly fractionation of high field strength elements with respect to large ion lithophile elements. This can be attributed to the input of a crustal component into the mantle source of the magma prior to partial melting. Variations in trace element enrichment and isotope characteristics of the three magmatic provinces are thought to be the result of different metasomatic events and complex processes of partial melting of the mantle sources. Peculiar geochemical and isotopic characteristics of the Lucanian and Neapolitan regions are the result of different channelling of withinplate material through lateral inflow from foreland, during the roll-back of the Ionian subduction. Metasomatism affected lithospheric mantle sources characterised by variable degrees of depletion. The peculiar petrologic, geochemical and isotopic features of the mafic magmas are consistent with a post-orogenic subduction-related geodynamic setting for the production of their parental magmas.