Abstract
A spatial variation in chemical and isotopical composition is observed between the volcanoes belonging to the Campanian Comagmatic Province. At a given MgO content, magmas from volcanic islands (Procida and Ischia) are enriched in Ti, Na, depleted in La, Ba, Rb, Sr, Th, K contents, and shows lower LREE/HFSE (e.g., La/Nb = = 1-2), lower Sr-Pb isotopic ratios and higher Nd isotopic ratios with respect to magmas from volcanoes locat- ed inland (Campi Flegrei and Somma-Vesuvius). The observed compositional variations are explained involving two different mantle sources in the genesis of the magmas erupted in this region: a deeper asthenospheric man- tle source, from which the Tyrrhenian magmas also derived and a lithospheric mantle source enriched by slab- derived fluids. The contribution of the enriched-lithospheric mantle became more pronounced moving from the Tyrrhenian abyssal plain through the Italian Peninsula where it dominates, likely in response to the thickening of the lithosphere observed under the Peninsula
Highlights
The Campanian Plain is located between the western margin of the Apennine chain and the eastern border of the Tyrrhenian abyssal plain
Calculation based on the quantitative EC-AFC (Energy Conservation-Assimilation Fractional Crystallisation) approach that accounts for mass and energy conservation (Bohrson and Spera, 2001; Spera and Bohrson, 2001) indicates that the isotopic variations relative to the magmas feeding eruptions at Campi Flegrei and Somma-Vesuvius are explained by contamination with less than 40% of crustal rocks (Pappalardo et al, 2002, 2004)
When the role of low-P evolution processes has been evaluated, the most primitive rocks erupted from Procida and Ischia islands have: i) lower LILE/HFSE ratios with respect to those erupted at Campi Flegrei and Somma-Vesuvius
Summary
The Campanian Plain is located between the western margin of the Apennine chain and the eastern border of the Tyrrhenian abyssal plain (fig. 1a,b). To shed light on this problem, our paper compares the available compositional data (major-, trace-elemental, and isotopes) from rocks erupted from Campanian volcanoes both situated inland (Somma-Vesuvius and Campi Flegrei) and offshore (Procida and Ischia), with that from magmas erupted on the Thyrrenian abyssal plain. In this way, the regional chemical and isotopic variations of magmas going from east to west can be investigated in relation to the deepening of the crust - mantle boundary (Ferrucci et al, 1989) and the increase in lithospheric thickness (Cella et al, 1998) observed moving from Tyrrhenian Basin towards the Apennine Chain. We assume that if significant modification of the deep mantle magmas occurs en route to the surface and/or by the crust, such a process should be revealed by comparing the geochemical and isotopic signatures of offshore and inland volcanic complexes
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