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Abstract: We address general features of carbonatite monogenetic volcanic fields located in continental settings which are peculiar being associated with kamafugites or melilite-bearing leucitites. Instructive examples are the Toro Ankole in Uganda, West Qinling in China, and Campo de Calatrava in Spain and the Intra-mountain Ultra-alkaline Province (IUP) of Italy. Maars are the typical volcanic forms, occurring in isolation or in clusters along fault systems. Concentric-shelled juvenile lapilli and bombs, having a upper-mantle peridotite kernel, are unique to this type of volcanism. These pyroclasts are interpreted as the result of deep-seated fragmentation of magma having a high carbon dioxide-water (CO2/H2O) ratio. The presence of discrete, large peridotitic nodules implies a high-velocity propagation of magma, while the associated large CO2 emission suggests a high proportion of juvenile CO2. Magma fragmentation is inferred to occur as a consequence of explosive CO2 exsolution at the upper mantle level (diatresis) followed by immiscibility. Based on field evidence, carbonatitic maar formation could be due to violent CO2 expansion and does not require phreatomagmatic phenomena. Extrusive carbonatites and associated rocks represent very primitive melts having a distinct High Field Strength Elements (HFSE) distribution, the source of which is related to enriched mantle. Carbonated peridotite is a stable paragenesis at depths of 400–600 km; thus, primary carbonatitic silicate magma can be produced at these depths as a consequence of rising deeper melt/fluids that are trapped at the transition zone. In our opinion, carbonatitic carbon is linked to the primary process of deep-mantle differentiation and Earth''s core degassing. [Copyright &y& Elsevier]

Abstract: Alkaline lamprophyres from southern Tuscany are early Cretaceous, ultrabasic, primary mantle melts that have not undergone significant magmatic differentiation. New mineralogical, geochemical and Sr, Pb and Nd isotopic evidence shows contrasting geochemistries with “crustal-like” and mantle geochemical features. High Mg#'s, however, coupled with high compatible elements, rule out any notable mantle melt dilution by bulk crustal contamination. Variations of Zr/Hf and Ta/Nb indicate a source containing residual titanates while their REE geochemistry suggests low degrees of partial melting and possible metasomatism of their source by carbonatitic melts. Arrays in isotope ratio diagrams are consistent with mixing between two distinct mantle end members. One is FOZO-like in character, and supports the involvement of asthenosphere, while the second has 87Sr/86Sr initial values that are much higher than FOZO (>0.70641). High 87Sr/86Sr signatures are present in the other Italian alkaline lamprophyres as well as other potassic–ultrapotassic and carbonatitic rocks of Italy. Our preferred model involves melting of a two component, metasomatised mantle, which can be tied into plume-related magmatism. [Copyright &y& Elsevier]