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

Mio-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 petrologic characteristics. The Tuscan Magmatic Region is the northernmost province, in which mantle-derived potassic and ultrapotassic leucite-free volcanic rocks occur, covering a time span of activity within 14.2 and 0.19 Ma. These rocks are silica-saturated to silica-oversaturated with variable primary compositional characteristics, and range from high-Potassium calc-alkaline to ultrapotassic lamproite, through potassic and ultrapotassic shoshonitic series. The Roman Magmatic Region extend from Northern Latium to Umbrian and Campanian areas along the Tyrrhenian border of the Apennine chain. It is made up of shoshonitic series (KS), ultrapotassic leucite-bearing series (HKS), some of them bearing also melilite, and therefore belonging to the kamafugitic group (KAM). Volcanism was active from 1.2 Ma to present time. The Lucanian Magmatic Region is the easternmost volcanic province characterized by rocks rich both in Na and K. Most of the rocks are haüyne-bearing, and have been 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 potassium-rich rocks are also found in the Aeolian Arc, in the Southern Tyrrhenian Sea. These rocks are intimately associated to calc-alkaline rocks. Enrichment in K2O and related incompatible trace elements is accompained by strong fractionation of high field strength elements with respect to large ion lithophile elements. This is more confidently due to the input of a crustal component in the mantle source of the magma prior to partial melting. Differential trace element enrichment and isotope characteristics of the three Magmatic Regions are thought to be inherited by different metasomatic events and by complex processes of partial melting of mantle sources. In addition metasomatism interested lithospheric mantle sources at variable degree of residuality. The peculiar petrologic, geochemical and isotopic features of the mafic magmas of the three regions can be reconciled with a post-orogenic geodynamic setting for the production of their parental magmas. Partial melting occurred in an uopper mantle modified by subduction related silica +/- carbonate rich either fluid or melts.