Аннотация
Sr-Nd-Pb-B isotope and incompatible trace element investigations were
carried out on volcanics of the Phlegrean Volcanic District, which
includes Campi Flegrei and the islands of Ischia and Procida (Campanian
region, southern Italy). The results of these investigations allowed
us to define several components in the genesis of magmas, including
transitional mid-ocean-ridge basalt (MORB)-type asthenospheric mantle,
aqueous fluids, oceanic sediment melts derived from the subducted
Ionian slab, and continental crust. A source contamination process
that introduces variable proportions of slab-derived components into
the mantle can explain the observed isotopic variations among the
products of Ischia and Procida, and of Campi Flegrei older than 39
ka. Furthermore, comparison between Phlegrean Volcanic District and
Aeolian arc volcanic rocks shows a different role of aqueous fluids
and sediment melts from southeast to northwest. Energy-constrained
assimilation and fractional crystallization modeling suggests that
younger than 39 ka Campi Flegrei potassic trachybasalt magmas could
have assimilated up to 2\% of crustal melt, while evolving to trachyte
during stagnation at -8 km depth. Crustal assimilation and mixing/mingling
processes among isotopically distinct magma batches at shallower
depth account for geochemical and isotopic variations of younger
than 39 ka Campi Flegrei volcanic rocks.
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