Intraplate lithospheric and sublithospheric components in the Adriatic domain: Nephelinite to tholeiite magma generation in the Paleogene Veneto volcanic province, southern Alps

We investigated the petrogenetic characteristics of the Paleogene Veneto volcanic province and compared them with other intraplate magmatic occurrences of the Adria–North Africa plate since Late Cretaceous time. Veneto volcanic province magmas were erupted through a transtensional rift system that resulted from intraplate reactions to the Alpine collisional events. The lavas, mostly basic in composition, encompass a wide range of serial affi nities from (mela)-nephelinites to quartznormative tholeiites. Nephelinites and basanites often carry spinel-peridotite mantle xenoliths that have rheologic and thermobarometric characteristics that indicate an origin from the mechanical boundary layer at depths not exceeding 50–60 km. Incompatible element patterns of the most primitive Veneto magmas, together with their isotopic signature (87Sr/86Sr 0.70315–0.70386; 143Nd/144Nd 0.51279–0.51298; 206Pb/204Pb 18.8–19.8), share geochemical characteristics with other magmatic occurrences of Adria–North Africa domains, and they show a clear affi nity with intraplate sodic lavas, particularly HIMU (high U/Pb = high μ) and, to a lesser extent, enrichedmantle –ocean-island basalt (EM2-OIB) magmas. An integrated petrogenetic model, generally applicable for Adria–North Africa domains, suggests that most of the magmas were generated within the spinelperidotite lithospheric mantle, from progressively deeper sources (30–100 km) and with a concomitant decrease in the degrees of partial melting (25%–3%) from quartznormative tholeiites to nephelinites. The modeled magma sources invariably require enrichments in incompatible elements and metasomatic phases comparable (or equivalent) to those observed in some mantle xenoliths associated with the Veneto volcanic province lavas. Two kinds of mantle sources were identifi ed: lherzolites bearing amphibole ± phlogopite for tholeiites to basanites, and lherzolites bearing amphibole ± phlogopite plus carbonatitic components for nephelinites. The elemental and isotopic characteristics of these mantle sources correspond to variable mixing of HIMU and, to a lesser extent, EM2 metasomatic components with a pristine depleted-mantle (DM) lithosphere. The HIMU metasomatizing agents may possibly be related to the mantle plume that is thought to extend from the eastern Atlantic to Europe and the Mediterranean, including Adria–North Africa domains, since the Late Cretaceous. These components more effectively accumulated in the lower lithospheric portion, i.e., the thermal boundary layer, whereas older metasomatic EM2 components may have been better preserved in the upper, more rigid, mechanical boundary layer.