Petrogenesis and evolution of the Euganean Magmatic Complex, Veneto Region, North-East Italy

The Euganean magmatic complex consists of basic and differentiated volcanic and subvolcanic rocks, Upper Eocene-Lower Oligocene in age. It is one of the districts in the Veneto Region (North-East Italy) where widespread eruptive activity took place during the Tertiary in relation to tensional tectonics which developed in the Southalpine foreland. On the basis of petrological features, three magmatic series are recognized: alkaline (alkali basalts, trachybasalts, trachyandesites, trachytes), transitional (basalts, trachybasalts, latites, quartz-latites, quartz-trachytes, rhyolites, alkali rhyolites), quartz-tholeiitic (basaltic andesites, dacites). Trace element patterns of the basic rocks are typical of anorogenic within-plate settings, showing significant affinities with ocean island basalts, as also indicated by their isotopic signature (⁸⁷Sr/⁸⁶Sr(t) from 0.70319 to 0.70341; εNd(o) from +4.6 to +5.6). Modelling of partial melting for the parental magmas of the three series requires metasomatized mantle sources, with amphibole involvement and melting at increasing degrees from alkali- to quartz-tholeiitic basalts. Chemical and mineralogical compositional variations suggest that low-pressure fractional crystallization processes played a dominant role in the generation of the differentiated rocks. This has been quantitatively tested in the predominant transitional series by mass balance calculations between phenocrysts and bulk rock composition, and Rayleigh modelling of trace elements. The results are in accordance with the block-faulting tectonics of the area, which may have favoured the fractionation of basic melts in multiple shallow magma chambers. Sr and Nd isotopic data suggest that wall-rock crustal contamination of the rising magmas and rock/seawater interaction may have affected some intermediate (⁸⁷Sr/⁸⁶Sr(t) from 0.70393 to 0.70422; εNd(o) from +2.2 to +4.6) and acidic rocks (⁸⁷Sr/⁸⁶Sr(t) from 0.70462 to 0.70490; εNd(o) from +2.7 to +3.9).