The Cretaceous to Paleogene within-plate magmatism of Pachino-Capo Passero (southeastern Sicily) and Adria (La Queglia and Pietre Nere, southern Italy): Geochemical and isotopic evidence against a plume-related origin of circum-Mediterranean magmas

摘要

The Pachino-Capo Passero centre, located at the south-easternmost portion of Sicily, represents an Upper Cretaceous volcano within the Pelagian Block, a fragment in lithospheric continuity with the African Plate. The volcanic rocks of the Pachino-Capo Passero centre show fairly homogeneous mafic characteristics with a typical within-plate signature. Two groups with different levels of alkali and incompatible trace element enrichment have been recognised. Trace element modelling indicates that the two groups might be originated at different degrees of partial melting. The geochemical data suggest that Cretaceous rocks of Pachino-Capo Passero originated at greater depth than the neighbouring Neogene volcanic products of the Hyblean Plateau, likely from an asthenospheric mantle source. Sr-Nd-Pb isotope compositions of Pachino-Capo Passero rocks are presented along with those of Paleocene and Eocene lamprophyric dikes and small intrusive bodies from the adjacent Adria block, now representing the Apulian foreland (i.e., Pietre Nere and La Queglia dykes) in the context of investigating the presence and origin of a Common Mantle Reservoir beneath the Central Mediterranean area. The Sr-Nd-Pb isotopes of the Pachino-Capo Passero rocks are extremely similar to the recently redefined FOZO component whilst other suites (i.e., Pietre Nere) might require additional enriched components. Highly radiogenic Pb isotopes, along with high TiO _2 contents and fractionated MREE/HREE argue for the presence of significant amount of recycled mafic oceanic crust in the mantle sources of these magmas as eclogitic lithologies dispersed within a depleted peridotitic mantle. The Sr-Nd-Pb isotope compositions of the studied rocks are also compared with literature data from the Canary Islands, as representative of a putative plume component contaminating the mantle region. The data show a clear distinction, especially in δ7/4 vs. δ8/4, indicating that the age and composition of the mafic crust recycled within the source of Pachino-Capo Passero rocks must be older and bear higher time-integrated U/Th ratios. The geochemical and isotope composition of Pachino-Capo Passero magmas, Pietre Nere and La Queglia is interpreted as a feature of the ambient asthenospheric mantle, due to the extremely widespread process of prolonged subduction and recycling of mafic oceanic crust of variable age and composition. Therefore no need for a unique reservoir related to a mantle plume is envisaged.