Deep structures and carbon dioxide degassing in Central Italy

Abstract

In Tyrrhenian Central Italy large amounts of CO 2 are produced at depth mainly by metamorphism of marine carbonate rocks. During their ascent, the gases are trapped in deep structures, made up of Mesozoic permeable limestones covered by impermeable terrains, which become sources of a high CO 2 flux toward the surface. The anomalous CO 2 concentrations are detectable in groundwaters. The general map of the groundwater PCO 2 values showes a decrease in the CO 2 production moving from the western geothermal areas of Tuscany and Latium to the eastern sector, which is characterized by a normal heat flow. The PCO 2 distribution suggests that the NW-SE extensional faults, which bound Plio-Pleistocene grabens, provide the easiest routes for the gas ascent. The geological, geophysical and geothermal deep drilling data suggest that the CO 2 anomalies found in the western sectors correspond to deep permeable structures of possible geothermal interest.