Post-collisional and intraplate Cenozoic volcanism in the rifted Apennines/Adriatic domain

The distinctive tectono-magmatic characteristics of rift volcanism in the Apennines/Adria domains are discussed focussing attention on the nature of mantle sources, stress regimes, and conditions of magma generation. Post-collisional intensive lithospheric rifting and tectonic collapse of the Apennines generate large amounts of Pliocene– Quaternary orogenic magmas which overlie a nearly vertical subducted slab along the peri-Tyrrhenian border. This magmatism includes the Roman Magmatic Province sensu lato (RMP-s.l.) and the Internal Apennines Volcanism (IAV), and consists of high-K calcalkaline, potassic (shoshonitic) and ultrapotassic (leucitites, leucite basanite and minor lamproites and kamafugites) products. Integrated petrological and geochemical studies of these rocks (and associated mantle xenoliths) indicate that most of them could have been generated by a restricted partial melting range (F≤5–10%) of extremely inhomogeneous phlogopite-veined lithospheric mantle sources, resulting from subduction related K-metasomatic processes. Moreover, the presence of both intermediate anorogenic and subduction related geochemical features in Mt. Vulture magmas support the existence of a slab window beneath the central-southern Apennines, which could have allowed inflow of subduction components to intraplate mantle sources. This slab discontinuity may mark the transition between the already collisioned Adriatic and the still subducting Ionian lithospheric slabs. By contrast, the Paleogene intraplate magmatism of the Adriatic foreland (i.e., the Veneto Province (VVP) and the minor Mt. Queglia and Pietre Nere magmatic bodies) is characterized by small volumes of basic magmas, varying from tholeiitic to strongly Na-alkaline in composition. This magmatism appears to be related to a limited extensional regime typical of the low volcanicity rifts. Petrogenetic modelling of the intraplate Adriatic foreland magmas indicates that their composition is remarkably depthdependent, with generation of tholeiites to nephelinites/alkaline lamprophyres by decreasing degrees of partial melting (F=25 to ≤5%) of lherzolite lithospheric sources at progressively increasing depths (ca. 40 to 100 km). Moreover, geochemical features of these anorogenic magmas testify that their mantle sources are remarkable homogeneous, as also confirmed by lack of veining in the VVP mantle xenoliths. This homogeneity suggests that Na-metasomatic agents pervasively affected the overlying Adriatic lithospheric mantle by porous flow mechanisms without causing significant inhomogeneities at a regional scale.