Earth’s CO₂ degassing in Italy

Maria Luce Frezzotti, Angelo Peccerillo, and Giuliano Panza

Earth’s CO2 emission in Italy includes both volcanic and non-volcanic degassing, with measured CO2 fluxes of about 35 - 60 Mt/y. Zones of non-volcanic CO2 emission include Tuscany, Latium, Campania, the Apennines, Sicily, and Sardinia. Volcanic emissions are particularly abundant at Mt. Etna in Sicily, but also at Vesuvio, Campi Flegrei, Ischia, Vulcano, and Stromboli, in Central-Southern Italy. The anomalous CO2 emission in Italy is related to the complex geodynamic evolution of this area, in which upper crustal rocks, including carbonate sediments, have been introduced into the upper mantle by Oligocene to present subduction processes. Integrated petrological, geochemical and geophysical data allow us to work out a model for the generation of anomalously high lithospheric CO2 fluxes. Melting of sediments and/or continental crust of the subducted Adriatic-Ionian (African) lithosphere at pressure greater than 4 GPa (130 km) is proposed to represent an efficient mean for deep carbon cycling into the upper mantle and into the exosphere in the Western Mediterranean area. Melting of carbonated lithologies, induced by the progressive rise of mantle temperatures behind the eastward retreating Adriatic-Ionian subducting plate formed a carbonated partially molten CO2-rich mantle in the depth range from 130 km to 70 km. Further upwelling of carbonate-rich melts induces massive outgassing of CO2. Buoyancy forces, probably favored by fluid overpressures, are able to allow migration of CO2 from the mantle to the surface, through deep lithospheric faults, and its accumulation beneath the Moho, and within the lower crust.