Insights on the active Southern Matese Fault system through geological, geochemical, and geophysical investigations of the CO2 gas vent in the Solopaca area (southern Apennines, Italy).

The south-eastern sector of the Matese Massif (southern Apennines, Italy) includes several nonvolcanic gas (mainly CO2) vents. The gas emissions in the northern part (Ciorlano-Ailano sector) have been associated with the Southern Matese Fault system, whereas a similar relationship is not evident in the southern part (Telese-Solopaca sector). Hence, we investigated the latter area (hills north of Solopaca town) through a multidisciplinary study of the principal CO2-degassing vent (Santantuono spring). The main goal is to reconstruct the structural architecture of the area and study the role of the fault array in conveying the gas migration to the surface. In particular, an integrated approach that combines structural and stratigraphic investigations with CO2 flux and geoelectrical surveys is proposed to shed light on the relationships between near-surface faults and gas rising. The main results from the geological-structural investigation suggest that thrust faults are the oldest structures, mainly verging to NNW, crosscut by high-angle N-S and younger NW-SE normal faults. This understanding is supported by the results of the CO2 flux survey, which records the highest flux values in correspondence with the mapped young normal faults, especially at their intersections. Moreover, the hypothesized tectonic and stratigraphic structure at depth is entirely consistent with the 3D geoelectrical model of the survey area provided by a 3D electrical resistivity tomography investigation, which also identifies the main NW-SE striking fault as the preferential pathway for gas migration. Finally, we suggest that the reconstructed NW-SE faults are the prolongation of the active Southern Matese Fault system bounding the SW Matese Massif margin defined by different segments with dominant normal kinematics and several gas vents.