Petrogenesis and evolution of the Euganean Magmatic Complex, Veneto Region, North-East Italy
Milani, Lorenzo; Beccaluva, Luigi; Coltorti, Massimo
European Journal of Mineralogy Volume 11 Number 2 (1999), p. 379 - 400
published: Apr 19, 1999
manuscript accepted: Oct 29, 1998
manuscript received: Oct 30, 1997
ArtNo. ESP147051102009, Price: 29.00 €
Abstract 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/86Srt from 0.70319 to 0.70341; ∊Nd0 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/86Srt from 0.70393 to 0.70422; ∊Nd0 from +2.2 to +4.6) and acidic rocks (87Sr/86Srt from 0.70462 to 0.70490; ∊Nd0 from +2.7 to +3.9).