In order to investigate the variability of helium degassing in continental regions, its release from rocks and emission into the atmosphere, here we studied the degassing of volatiles in a seismically active region of northern Italy (Mw_MAX = 6) at the Nirano-Regnano mud volcanic system. The emitted gases in the study area are CH₄–dominated and it is the carrier for helium (He) transfer through the crust. Carbon and He isotopes unequivocally indicate that crustal-derived fluids dominate these systems. An high-resolution 3-dimensional reconstruction of the gas reservoirs feeding the observed gas emissions at the surface permits to estimate the amount of He stored in the natural reservoirs. Our study demonstrated that the in-situ production of ⁴He in the crust and a long-lasting diffusion through the crust are not the main processes that rule the He degassing in the region. Furthermore, we demonstrated that micro-fracturation due to the field of stress that generates the local seismicity increases the release of He from the rocks and can sustain the excess of He in the natural reservoirs respect to the steady-state diffusive degassing. These results prove that (1) the transport of volatiles through the crust can be episodic as function of rock deformation and seismicity and (2) He can be used to highlight changes in the stress field and related earthquakes.

In this study we discuss the occurrence of mantle‐derived heat and volatiles (i.e., helium and CO₂) feeding hydrothermal systems in a seismically active margin between two convergent plates (African and European) without any signals of volcanism. The helium (He) isotopes clearly indicate a mantle‐derived component in the outgassing volatiles. The estimated mantle‐derived He fluxes are up to two to three orders of magnitude greater than those in a stable continental area. Such high He fluxes cannot be provided by a long‐lasting diffusion, thereby implying a more efficient transport (i.e., advective transport through faults). He data coupled to heat‐He relationship suggest the occurrence of active degassing of magmatic intrusions in this area of continental collisional. Geophysical data indicate the presence of a hot mantle wedge below the outgassing of mantle volatiles and a system of faults cutting the continental crust down to the hot mantle wedge. Here we discuss the hot mantle wedge and possible associated magmatic intrusions as the source of the mantle‐derived volatiles outgassing in the region. We also assessed the output of mantle‐derived CO₂ from the investigated hydrothermal basins. The possible occurrence of magma at depth as well as the geometry of the thick‐skinned deformed wedge unambiguously indicates delamination processes that are related to continental subduction. Hence, we show that delamination processes can really produce magma at depth without evidences of volcanism at the surface. Finally, we have also provided the fault systems that work as a network of pathways and actively sustain the advective transfer of the mantle fluids toward the surface.

Gas from mud volcanoes, dry mofettes, springs, and wells were sampled in a region of active tectonics and high seismicity in the southern Apennines (Italy), where there is a long history of disastrous earthquakes, with the latest (M_s = 6.9) occurring in 1980. The fluids consist of a mixture of mantle‐derived and crust‐derived volatiles, with a low atmosphere‐derived contribution, as identified by the He isotope signature and He/Ne ratio measurements. One year of monthly monitoring of the He concentrations and He isotopes revealed no seasonal modifications or variations induced by low seismicity. There are extraordinary high outputs of ⁴He produced in the crust in the area (up to 2.5 × 10²⁸ atoms yr⁻¹). These outputs cannot be solely due to the whole‐rock production rate and a long‐lasting diffusion degassing through the crust of the produced ⁴He. This study explored the relation between the volume of fractured rock and the related release of He. The results support that crustal degassing can be controlled by tectonic events resulting in earthquakes. The high seismicity in this sector of the Apennines provides the conditions necessary for a massive release of He that has accumulated in the rock over a long time period. We identified that the assessed high crustal ⁴He output can be attributed to an intense fracturing of a calculable volume of rock, which gives new constraints on the volume of rock involved in high‐magnitude earthquakes in the region.

We report on the results of an extensive geochemical survey of fluids released in the Vardar zone (central‐western Serbia), a mega‐suture zone at the boundary between Eurasia and Africa plates. Thirty‐one bubbling gas samples are investigated for their chemical and isotopic compositions (He, C, Ar) and cluster into three distinct groups (CO₂‐dominated, N₂‐dominated, and CH₄‐dominated) based on the dominant gas species. The measured He isotope ratios range from 0.08 to 1.19 Ra (where Ra is the atmospheric ratio), and reveal for the first time the presence of a minor (<20%) but detectable regional mantle‐derived component in Serbia. δ¹³C values range from −20.2‰ to −0.1‰ (versus PDB), with the more negative compositions observed in N₂‐dominated samples. The carbon‐helium relationship indicates that these negative δ¹³C compositions could be due to isotopic fractionation processes during CO₂ dissolution into groundwater. In contrast, CO₂‐rich samples reflect mixing between crustal and mantle‐derived CO₂. Our estimated mantle‐derived He flux (9.0 × 10⁹ atoms m⁻² s⁻¹) is up to 2 orders of magnitude higher than the typical fluxes in stable continental areas, suggesting a structural/tectonic setting favoring the migration of deep‐mantle fluids through the crust.

Magmatic fluids entering Mt. Etna volcano system from depth exceed those outgassed into atmosphere during inter-eruptive phases.

This study is focused on fluids characterization and circulations through the crust of the Irpinia region, an active seismic zone in Southern Italy, that has experienced several high-magnitude earthquakes, including a catastrophic one in 1980 (M = 6.9 Ms). Using isotopic geochemistry and the carbon‑helium system in free and dissolved volatiles in water, this study aims to explore the processes at depth that can alter pristine chemistry of these natural fluids. Gas-rock-water interactions and their impact on CO₂ emissions and isotopic composition are evaluated using a multidisciplinary model that integrates geochemistry and regional geological data. By analyzing the He isotopic signature in the natural fluids, the release of mantle-derived He on a regional scale in Southern Italy is verified, along with significant emissions of deep-sourced CO₂. The proposed model, supported by geological and geophysical constraints, is based on the interactions between gas, rock, and water within the crust and the degassing of deep-sourced CO₂. Furthermore, this study reveals that the Total Dissolved Inorganic Carbon (TDIC) in cold waters results from mixing between a shallow and a deeper carbon endmember that is equilibrated with carbonate lithology. In addition, the geochemical signature of TDIC in thermal carbon-rich water is explained by supplementary secondary processes, including equilibrium fractionation between solid, gas, and aqueous phases, as well as sinks such as mineral precipitation and CO₂ degassing. These findings have important implications for developing effective monitoring strategies for crustal fluids in different geological contexts and highlight the critical need to understand gas-water-rock interaction processes that control fluid chemistry at depths that can affect the assessment of the CO₂ flux in atmosphere. Finally, this study highlights that the emissions of natural CO₂ from the seismically active Irpinia area are up to 4.08·10⁺⁹ mol·y^-1, which amounts is in the range of worldwide volcanic systems.