Evidence for mantle heterogeneities in the westernmost Mediterranean from a statistical approach to volcanic petrology

The geological evolution of the westernmost Mediterranean region is characterised by widespread volcanic activity, with subduction (orogenic) or intraplate (anorogenic) geochemical imprints. Major, trace elements and isotopic ratios of 283 orogenic and 310 anorogenic volcanic samples from the western and central Mediterranean areas were merged in a single database that was processed using a statistical approach. Factor analysis, performed using the Principal Component Analysis (PCA) method, reduced the original 36 geochemical parameters that were expressed as oxides, elements or isotopic ratios to seven factors that account for ~ 84% of the variance. Combining these factors in binary diagrams clearly separates the anorogenic and orogenic fields. Anorogenic samples usually fall into a narrow compositional range, while orogenic rocks are characterised by greater variability and by alignment along different trends. These different trends are a result of large heterogeneities of the lithospheric mantle beneath the Mediterranean area because of extensive recycling of geochemically different lithologies, at least since Palaeozoic times. The results support the requirement for different mantle reservoirs in the origin of the Mediterranean volcanism. We find that the double subduction polarity model, recently proposed for the westernmost Mediterranean area, is compatible with the volcanic petrology of the last 30 My.