Multidisciplinary approach to reconstruct the pathways of the CO2 nonvolcaning degassing in the thermal springs of Contursi and Oliveto Citra sector (southern Appennines, Italy)

The southern Apennines are a fold-and-thrust belt characterized by the superpositions of different thrust sheets. The orogenic construction defined by thin- and thick-skinned tectonics occurred from the Paleocene to the early Pleistocene. In this orogen, evidence of nonvolcanic degassing is widely reported. The orogenic chain hosts the Mefite d'Ansanto (MdA) vent, the most significant nonvolcanic natural emission of low-temperature CO2 on Earth. Other degassing areas are located in the Sele River Valley, where several vents are aligned along major faults, including the thermal springs of Contursi and Oliveto Citra (COC).

Different investigations on these nonvolcanic emissive structures mark a close relation between degassing phenomena and tectonics, evidencing a likely dominant crustal gas origin for the COC vent. In any case, poor information is available about the characteristics of the CO2 reservoir (including the geometry and depth) and the fluid's rising pathways.

Different surveys have been performed, applying a multidisciplinary approach, including innovative methodologies, aiming to reconstruct the geometry of the shallow degassing pathways and investigate how the different geological and tectonic architecture influences the CO2 seeping and surficial degassing processes. The structures that convey and favour the upward gas migration, seeping and degassing have been imaged using geophysical and structural investigations.

Electrical Resistivity (ERT) and Induced Polarization (IP) tomographies, combined with Self-Potential (SP), Magnetic (Mag), and PH mapping have been performed in correspondence with the most degassing part of the COC area. The joint acquisition of such a multiparametric dataset ended in a better-constrained interpretation of the different detected anomalies. Furthermore, the obtained results allowed us to construct different geophysical maps and geological cross-sections of the investigated area and develop a model of the degassing vents area, highlighting the role of reconstructed lithological and structural settings in the shallow leaking processes.