An overview of monogenetic carbonatitic magmatism from Uganda, Italy, China and Spain: Volcanologic and geochemical features

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 (CO 2 /H 2 O) ratio. The presence of discrete, large peridotitic nodules implies a high-velocity propagation of magma, while the associated large CO 2 emission suggests a high proportion of juvenile CO 2 . Magma fragmentation is inferred to occur as a consequence of explosive CO 2 exsolution at the upper mantle level (diatresis) followed by immiscibility. Based on field evidence, carbonatitic maar formation could be due to violent CO 2 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.