CO2 magmatism in Italy: from deep carbon to carbonatite volcanism

The importance of CO2 in the Italian mantle and magmatism is supported by the presence of Middle-Upper Pleistocene carbonatites along the Italian Apennine graben-systems. Carbonatites are co-eruptive and chemically conjugate to kamafugites (kalsilite melilitite or foidite). Immiscibility phenomena largely explain the genetic relationship between the two rock-types. Their peculiar geochemistry reflects the differing solubility of the high field strength elements in rocks which have different peralkalinities. Dolomite and calcite dominated inclusions occur in mantle nodules and plutonic rocks such as soviets and melilitolites, which have been brought up by extrusive carbonatites. Nyerereite was found in melilite and apatite inclusions although the Italian extrusive carbonatites are always calcitic. Sequestration by abundant leucite, kalsilite, haüyne and nepheline, and dispersion of alkalis in subvolcanic aqueous fluids, may explain the low alkaline character of Italian carbonatites. The high Ca, CO2, F, S, Cl content of primitive melt inclusions in high pressure crystals suggests that these elements were not assimilated by the magma from the crust during its ascension towards the surface. In addition, the high radiogenic isotopic composition and compatible element content are regarded as primary magmatic characteristics. Veined mantle nodules show pervasive reaction with carbonatitic melts as illustrated by the presence of amphibole, fassaitic cpx and phlogopite phases. Metasomatising carbonatitic melts are thought to be released from a deep plume. The geodynamic and geochemical setting of Italian carbonatites implies a very deep source for heavy Carbon and it has even been speculated that this Carbon could be originated from the Earth's core.