Soil CO2 degassing along tectonic structures of Mount Etna (Sicily): the Pernicana fault

Carbon dioxide emissions from the soil have been investigated along lines of equally spaced sampling points perpendicular to the Pernicana fault on Mt Etna. Anomalous values of soil CO2 have been found not only along the fault plane, but also along directions parallel to it, both to the N and to the S of the main fault. The acquired data seem to reveal a shallow step-like geometry of the Pernicana fault system with parallel faults being generally not deeper than the interface between Etnaʹs volcanic cover and its sedimentary basement (a few hundred meters). The distribution of the anomalous CO2 emissions has also revealed that the Pernicana fault continues at least as far as the Ionian sea, in an area where only sedimentary rocks crop out. This finding would suggest that the main structure is deeper than the base of the volcanic cover, thus cutting at least the uppermost portion of Etnaʹs sedimentary basement. Isotopic analyses of C carried out in samples from locations of high CO2, seem to indicate that the emitted CO2 is a mixture of an organic shallow component and a minor deeper magmatic one. Both chemical and isotopic data on soil gases emitted in the easternmost part of the studied area distinguished another tectonic structure which seems to be much deeper than the Pernicana fault and is roughly directed NNE-SSW, this direction being coincident with an important structural trend of eastern Sicily.