Reasoning and beliefs about Italian geodynamics

We propose that starting in the late Eocene-early Oligocene, the progressive eastward growth of an asymmetric plume head trapped within the transition zone (410 to 670 km depth) has played an active role in the fragmentation of the European and African continents and in the progressive opening of the Mediterranean Sea. Such an extensional geodynamic environment, as opposed to a subduction-related setting, is supported by the petrological, geochemical and isotopic features of the peri-Tyrrhenian magmatism, and in particular by the abundance of leucite-bearing rocks in peninsular Italy and by the occurrence of the rare carbonatite-kamafugite suite within the intra-Apennine graben system. The plume is isotopically associated with three end-members. Two are similar to FOZO and EM1 defined on the basis of data from ocean island basalts while the third one, ITEM (ITalian Enriched Mantle), is highly radiogenic and has Pb, Sr and Nd isotopic signatures similar to continental crust and to within-plate, deep-mantle, diamond-bearing rocks such as lamproites and micaceous kimberlites. The FOZO-like component, along with EM1, establishes a firm link between Italian magmatism and the deep mantle, and the simplest way of upward migration of mantle rock volumes and volatiles/fluids is by plume activity. ITEM is an unusual end-member, and coupled with its presence in ultramafic ultra-alkaline rocks requires an unusual mantle source. Whether ITEM reflects some fundamental character of the deep mantle, or crustal material associated with subduction is a question that remains to be answered.