Carbonate metasomatism and CO2 lithosphere-asthenosphere degassing beneath the Western Mediterranean: An integrated model arising from petrological and geophysical data

The petrological-geochemical-geophysical model offers an explanation for the present-day anomalously high non-volcanic deep CO2 emission in the Tyrrhenian. Melting of sediments and/or continental crust of the subducted Adriatic–Ionian lithosphere at pressure greater than 4 GPa represents an efficient mean for carbon cycling into the upper mantle and exosphere. Carbonated lithologies generate low fractions of carbonate-rich melts, with low density and viscosity, which can migrate upward through the mantle, forming a carbonated partially molten CO2-rich mantle recorded by tomographic images. 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. The model explains CO2 enrichment of the Etna active volcano. Deep CO2 cycling is tentatively quantified in terms of conservative carbon mantle flux in the investigated area.