Mineralogy, petrology, and isotope geochemistry of magmatic rocks from the Western Alps, Ernici and Roccamonfina, Italy: Constraints on mantle enrichment processes

Mineralogical and geochemical data from lamprophyres from the Western Alps, northern Italy, and volcanic rocks from Roccamonfina and Ernici, central-southern Italy, are used to investigate mantle enrichment processes. The lamprophyres are classified as minettes, spessartites, and kersantites, whereas the volcanic rocks from Roccamonfina and Ernici include a potassic series (KS) and an ultrapotassic series (HKS). The lamprophyres and the KS and HKS rocks have high concentrations of LREE and strongly fractionated LREE/HREE and LILE/HFSE ratios similar to many subduction-related rocks. Incompatible trace element ratios and Sr, Nd, and Pb isotopic data support metasomatism by a slab-derived fluid in the Alpine mantle, and by a carbonate-rich melt beneath the Apennines. High B contents in rocks from Roccamonfina and Ernici constrain subduction-related metasomatism to the past 5 Ma in central-southern Italy.; Isotopic data from rocks from the Western Alps, Roccamonfina, and Ernici fall on a previously-defined, two-component mixing line between a depleted, mantle end-member and an enriched, crust-like end-member. The lamprophyres from the Western Alps best represent the enriched end-member, while rocks from Roccamonfina and Ernici have moderately enriched signatures that lie between those of the Roman and Campanian Provinces. The geodynamic model favoured for the origin of the two isotopic end-members involves a widespread, isotopically-depleted asthenosphere variably contaminated by pelagic sediments subducted during closure of the Tethyan Ocean. Incompatible trace element and K2O contents of rocks from Roccamonfina and Ernici are attributed to source enrichment during Apennine subduction.