HR: 10:20h
AN: T42B-01 INVITED     [Abstracts]
TI: Carbon Dioxide Earth Degassing and Structural Setting in Italy
AU: * Chiodini, G
EM: chiod@ov.ingv.it
AF: Osservatorio Vesuviano - INGV, via Diocleziano, 328, Naples, 80124 Italy
AB: A modelling of the water-rock-gas interaction in the groundwaters circulating in the aquifers of central southern Italy has shown that most of the dissolved inorganic carbon (DIC) derives from deep carbon sources with an isotopic composition in the range of the CO₂ emitted in Italy from active volcanoes, geothermal fields, and the many cold gas emissions located in the region. This suggests that a common, deep and inorganic source of CO₂ is active in Italy as highlighted by the regional map of CO₂ degassing that has been elaborated on the base of the deeply derived carbon dissolved in the groundwater. The map shows that two large degassing structures affect the Tyrrhenian side of the Italian peninsula. The northern degassing structure (TRDS, Tuscan Roman degassing structure) includes Tuscany, Latium and part of Umbria regions (~30000 km²) and releases ~ 1.4 × 10¹¹ mol/year of deeply derived CO₂. The southern degassing structure (CDS, Campanian degassing structure) occupies the Campania region (~ 10000 km²) and releases ~ 0.7 × 10¹¹ mol/year of deeply derived CO₂. The total CO₂ released by TRDS and CDS (~ 2.1 × 10¹¹) is globally significant, being ~ 10 % of the estimated present-day total CO₂ discharge from sub aerial volcanoes of the Earth. The central parts of both TRDS and CDS coincide with the quaternary volcanism of Italy and with regions of high heat flow where were drilled many geothermal systems containing fluids saturated in CO₂, i.e. with dissolved CO₂ concentrations correspondent to the saturation values at the pressures (depths) of the geothermal reservoirs. These geothermal reservoirs represent the shallowest storage zone of the CO₂ of deep provenance before the expulsion of the gas either directly in the atmosphere trough the numerous natural gas emissions of the area, or as dissolved gas species in the main aquifers. It is our opinion that the two degassing structures are the surface expression of two large plumes of mantle fluids which intrude, saturate and heat the Italian Tyrrhenian crust. The comparison between the maps of CO₂ degassing and of the location of the Italian earthquakes highlights that the anomalous CO₂ flux suddenly disappears in the Apennine in correspondence of a narrow band where most of the Italian seismicity concentrates. Here, at the eastern borders of TRDS and CDS plumes, the CO₂ from the mantle intrudes the deeper, now inactive thrusts affecting the Moho and accumulate in crustal traps generating overpressurised reservoirs two of which have been reached by 4-5 km deep wells. These CO₂ overpressurised level can play a major role in triggering the Apennine earthquakes by reducing fault strength and potentially controlling the nucleation, arrest, and recurrence of earthquake rupture.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 8010 Fractures and faults
SC: Tectonophysics [T]
MN: Fall Meeting 2005