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 intra-plate reactions to the Alpine collisional events. The lavas, mostly basic in composition, encompass a wide range of serial affinities from (mela)-nephelinites to quartz-normative 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 ( 87 Sr/ 86 Sr 0.70315–0.70386; 143 Nd/ 144 Nd 0.51279–0.51298; 206 Pb/ 204 Pb 18.8–19.8), share geochemical characteristics with other magmatic occurrences of Adria–North Africa domains, and they show a clear affinity with intraplate sodic lavas, particularly HIMU (high U/Pb = high µ) and, to a lesser extent, enriched-mantle–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 spinel-peridotite lithospheric mantle, from progressively deeper sources (30–100 km) and with a concomitant decrease in the degrees of partial melting (25%–3%) from quartz-normative 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 identified: 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.

Silica-undersaturated magmas intruded stable continental crust in southern Texas throughout Late Cretaceous time, forming at least 200 small volcanic centers and intrusive bodies in a shallow, epicontinental sea. Rock types, in order of decreasing abundance in outcrop, are melilite-olivine nephelinite, olivine nephelinite, alkali basalt, phonolite, and nepheline basanite. Melilite-olivine nephelinite, olivine nephelinite, and nepheline basanite contain xenoliths of spinel lherzolite, dunite, and harzburgite. On the basis of Mg/(Mg + Fe) and Ni contents, some but not all analyzed samples of melilite-olivine nephelinite, olivine nephelinite, nepheline basanite, and alkali basalt could have crystallized from primitive mantle-derived liquids that underwent little fractionation. Preliminary trace-element data suggest that the four mafic types could all have formed from the same parent through extraction of varying amounts of liquid. Phonolites are strongly fractionated and peralkaline, and probably formed from olivine nephelinite magma, and possibly from the other mafic types, by removal of kaersutitic amphibole, olivine, and clinopyroxene at high pressure. The bimodal Balcones suite resembles others in which mafic rocks and phonolites are associated, but it may be unique in the absence of coeval silica-oversaturated magmas and in the subordinance of alkali basalt.