CO₂ Degassing over Seismic Areas: The Role of Mechanochemical Production at the Study Case of Central Apennines

摘要

Field observations coupled with experimental results show that CO₂ can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that degassed from the mantle or produced by thermometamorphism. The evidence that a large amount of carbon dioxide associated with radiogenic-type helium (R/Ra as low as 0.01–0.08) is released through continental areas, denotes the absence of a contribution from the mantle or from mantle-derived fluids. Data collected during the seismic crisis which struck the Central Apennines in 1997–98 have shown an enhanced CO₂ flux not associated with the presence of mantle or thermometamorphic-derived fluids. On the other hand, new experimental results highlight the possibility of producing CO₂ by mechanical energy that acts on the calcite crystalline lattice. While the CO₂ released over the geothermal areas (e.g., Larderello Geothermal Field) is obviously derived by mantle-derived activities, this is not the case of the huge amount of CO₂ released over the seismically active areas where the presence mantle-derived products is ruled out. We propose that mechanical energy, e.g., released during seismic events, microseismicity or creeping processes is a possible additional energy source able to produce CO₂ and thus could explain the presence of CO₂ degassing over tectonic areas where the influence of the mantle is low.