Geochemistry of fluids discharged over the seismic area of the Southern Apennines (Calabria region, Southern Italy): Implications for Fluid-Fault relationships
The first comprehensive geochemical data-set of the fluids circulating over a 14,000 km2-wide seismicprone
area of the Southern Apennines, Calabria Region (Italy), is presented here. The geochemical investigations
were carried out with the twofold aim of constraining the origin and interactions of the circulating
fluids and to investigate possible relationships with local faults. Sixty samples of both thermal and cold
waters were collected, from which the dissolved gases were extracted. The geochemical features of the
water samples display different types and degrees of water–rock interactions, irrespective of the outlet
temperature. The calculated equilibrium temperatures of the thermal waters (60–160 C) and the low heat
flow of thewhole study area, are consistent with a heating process due to deep water circulation and rapid
upflow through lithospheric structures. The composition of the dissolved gases reveals that crustal-originating
gases (N2 and CO2-dominated) feed all the groundwaters. The 3He/4He ratios of the dissolved He, in
the range of 0.03–0.22Rac for the thermal waters and 0.05–0.63Rac for the cold waters (Rac = He isotope
ratio corrected for atmospheric contamination), are mainly the result of a two-component (radiogenic
and atmospheric) mixing, although indications of mantle-derived He are found in some cold waters. As
the study area had been hit by 18 of the most destructive earthquakes (magnitude ranging from 5.9 to
7.2) occurring over a 280-a time span (1626–1908) in the Southern Apennines, the reported results on
the circulating fluids may represent the reference for a better inside knowledge of the fault-fluid relationships
and for the development of long-term geochemical monitoring strategies for the area