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Recognizing and identifying the transfer of mantle-derived fluids (e.g., CO 2 , N 2 , noble gases) in continental regions is critical for investigating the processes that shape the deep and shallow Earth's evolution, such as subduction, volcanism, natural degassing, active tectonics, and earthquakes (e.g.,

Carbon dioxide (CO2) is released from the Earth’s interior into the atmosphere through both volcanic and non-volcanic sources in a variety of tectonic settings. A quantitative understanding of CO2 outgassing fluxes in different geological settings is thus critical for decoding the link between the global carbon budget and different natural processes (e.g., volcanic eruption and earthquake nucleation) and the effects on the climate evolution over geological time. It has recently been proposed that CO2 degassing from non-volcanic areas is a major component of the natural CO2 emission budget, but available data are still sparse and incomplete. Here, we report the results of a geochemical survey aimed at quantifying CO2 emissions through cold and thermal springs of the tectonically active Pollino Massif and Calabrian arc (Southern Italy). The chemical ad isotopic (He and C) composition of fifty-five dissolved gas samples allows to identify two different domains: 1) a shallow system dominated by gas components of atmospheric signature (helium, hereafter He) and biogenic origin (C), and 2) a deeper system in which crustal/deep fluids (CO2 and He) are dominant. The measured He isotope ratios range from 0.03 to 1.1 Ra (where Ra is the He isotopic ratio in the atmosphere) revealing a variable atmospheric contamination. Furthermore, the He isotopic data indicate the presence of traces of mantle He contributions (2%–3%) in the thermal groundwater. The prevailing low R/Ra values reflect the addition of crustal radiogenic 4He during groundwater circulation. Using helium and carbon isotope data, we explore the possible sources of fluids and the secondary processes (dissolution/precipitation) that act to modify the chemistry of pristine volatiles. For the thermal springs, we estimate a deep C output of 2.3 x 107 to 6.1 x 108 mol year−1. These values correspond to deep CO2 fluxes per square km comparable with those estimated in several active and inactive volcanic areas and in continental regions affected by metamorphic CO2 degassing (e.g., the southern margin of the Tibetan Plateau).

<p>The Eastern Carpathians are characterized by CO<sub>2</sub>-dominated, intense, cold gas emissions starting from the Neogene to Quaternary volcanic structures, the youngest dormant volcano, Ciomadul, but occurring also quite far away from these, in the Cretaceous flysch units.</p> <p>The gases are often transported to the surface through groundwater and appear in the form of bubbling mineral water springs. The major components of these cold gas emissions are: CO<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub> and sometimes H<sub>2</sub>S. This is the most intensive degassing area from Romania. The gas emissions often appear in inhabited areas, representing a natural risk for locals.</p> <p>In the recent years we performed detailed geochemical surveys, in which the chemical composition of the free gases, the origin of the different gas species and also the quantification of fluxes from diffuse emissions from the soil and dissolved gas was investigated. We have used different approaches and methods, starting with a specially designed Multi-GAS instrument for low-temperature gases, towards different monitoring experiments.</p> <p>Our results show that the chemical and isotopic compositions of the investigated fluids throughout the Carpathians are strongly influenced by processes that characterize the geotectonic setting of the study area, such as the former volcanic activity and the subduction. In the present the occurrence of the gas emissions and the high flux areas are dependent on the tectonic structures, namely the nappe systems of the Carpathians and related faults, which represent a pathway for the deep fluids towards the surface.</p> <p>All our investigations gave us a general view on the quantity, flux, geochemistry and origin of the fluids in the study area and helped us to select the most suitable and appropriate sites for future gas monitoring projects.</p> <p>This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2019-1908, within PNCDI III, contract number TE 63/2020.</p>

<p>The Latronico thermal area is located in the southern sector of the Apennines chains, in proximity to the south boundary of the Mt. Alpi. This area is a seismically active region and it is located between Val d’Agri basin and Pollino area, two of the highest seismic risk zones in Italy. It is well documented that tectonic discontinuities act as preferential channels for the uprise of deep fluids trough the continental crust towards the surface (e.g., Caracausi et al. 2013). Hence in seismically areas, these fluids can move across the volume of rocks characterized by an active field of stress and their fluids can take a memory of the occurring rock-water-gas interactions. Taking this into account, we sampled waters and dissolved gases released in the Latronico hydrothermal basin in order to define: i) water-rock interaction processes; ii) thermalism origin; iii) the geochemical model of fluid circulation in a seismic area.  In details, we analysed the chemical and isotopic (C and noble gases) composition both groundwater and dissolved gases. The acquired knowledge will allow us to plan long-term geochemical monitoring useful for identification of the possible relationship between fluid circulation and regional-scale seismicity. We sampled 24 springs, of which 9 belonging to thermal set (Latronico Spa springs) and 15 to cold one. Thermal waters have an average temperature of 21°C, these are slightly alkaline (7.12 <pH< 7.54), show negative Eh values up to −93 mV and are calcium bicarbonate-sulphate water type. The cold springs have temperature values from 7.7 to 14.8 °C, pH from 7.05 to 8.15, with positive Eh values up to 200 mV. These waters are calcium-bicarbonate water type. The oxygen and hydrogen isotopes clearly indicate their meteoric origin. Regarding the gas geochemistry, He and C isotopes have been used as the key tracer for recognizing the contribution of crustal and mantle components and possibly the source of heat. Thermal waters have CO<sub>2 </sub>and He contents of 1 and 2 order of magnitude higher than cold water, respectively. The dissolved gases show an atmospheric component, being Air Saturated Water (ASW). <sup>3</sup>He/<sup>4</sup>He ratios in the gases dissolved are 0.12 Ra ±0.2 (Ra is the He isotopic signature in the atmosphere, 1.39x10<sup>-6</sup>). Assuming that He isotopic signature in typical crustal fluids is < 0.05 Ra, the measured He data show traces of mantle-derived helium, to the mixing between atmospheric and radiogenic end-members (0.02 Ra). Coupling Total Dissolved Inorganic Carbon (TDIC) and δ<sup>13</sup>C<sub>TDIC</sub> data, 2 water sub-sets have been identified: (i) infiltrating waters, with low δ<sup>13</sup>C<sub>TDIC</sub>, and (ii) thermal waters with positive δ<sup>13</sup>C<sub>TDIC</sub> and high TDIC values, indicative of outgassing of deeply sourced CO<sub>2</sub>. This study for the first time proposes a model of fluids origin in the Latronico hydrothermal basin and the main processes that control their chemistry during their circulation through the crust. Hence, geochemical monitoring of the fluids in the region can provide if these fluids are sensitive to chemical variation due to a modification of the field of stress in the preparatory phases of an earthquake</p>