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Abstract Aiming at understanding the source of the fluids that mineralizing within seismically active fault zones, we investigate the noble gas isotopes (i.e., helium (He), neon (Ne), and argon (Ar)) in the fluid inclusions (FIs) trapped in the calcite veins sampled along high‐angle fault zones of the Contursi hydrothermal basin, southern Italy. The latter basin lies in close vicinity of the MW = 6.9, 1980 Irpinia earthquake and exposes numerous fault scarps dissecting Mesozoic shallow‐water carbonates. The analyses of noble gases (He, Ne, Ar) are conducted to identify the origin of the volatiles circulating along the faults at the time of calcite precipitation. Then, outcomes of this discussions are compared with currently outgassing of deep‐sourced CO2 coupled to mantle‐derived He in that area, whose output is larger than those from some volcanic areas worldwide. The results indicate that He in FIs is dominated by a crustal radiogenic component (4He), and by an up to 20% of a mantle‐derived component (3He), with a highest isotopic signature of 1.38 Ra. This value is consistent with the highest percentage of mantle‐derived He associated to high‐flux CO2 gas emission in the investigated area (1.41 Ra). We propose that the variability of the He isotopic signature measured in primary FIs can result from early trapping of fluid inclusions or post trapping processes and seismic activity that modify the pristine He isotopic signature (i.e., derived from the crust and/or mantle) in groundwater along the faults during periods of background seismicity. Such investigations are fundamental to understand fluid migration in fault systems and the role of fluids in processes of earthquake nucleation.

Abstract The investigation of tectonic controls on CH4 and CO2 emissions was conducted by measuring the fluxes of the gases in the different tectonic units along the northwestern margin of the Ordos Block in China, a region renowned for its intricate tectonic configuration. The mean fluxes of CH4 ranged from −1.5 to 1.1 mg m−2 d−1, while CO2 fluxes spanned from 2.0 to 29.2 g m−2 d−1. Notably, the Minqin, Ordos, and Haiyuan blocks primarily exhibited absorption characteristics for CH4. In contrast, within the Hetao and Yinchuan grabens, both degassing and absorption processes coexist. A striking observation was that blocks with high internal deformation exhibited significantly higher CH4 and CO2 fluxes compared to those in the stable blocks. Additionally, regions experiencing extensional deformation demonstrated greater gas emission than those undergoing compressional deformation. The spatial distribution of CH4 and CO2 fluxes at the study points exhibited a similar trend to faults in the Yinchuan Graben. Our findings revealed that CH4 and CO2 are mainly of biogenic origin, accompanied by abiotic emissions from underground. And the gas source, migration pathway, and tectonic stress were the primary factors influencing gas emission, with tectonic stress playing a pivotal role. This stress controlled the formation of tectonic structures, changed the degassing pathway, and served as the driving force for gas migration. The results of this study offer valuable insights into the mechanisms governing CH4 and CO2 emission in faulted regions. Furthermore, our results may contribute to future assessments aimed at quantifying the contribution of geological sources to greenhouse gas emissions.

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).

The article is referred to important consequence of the biosphere oil and gas formation concept, according to which the process of hydrocarbons generation in the subsoil and degassing of the Earth are a single natural phenomenon. The main role in this phenomenon is played by geochemical circulation of carbon and water through the Earth’s surface accompanied by polycondensation synthesis of hydrocarbons by CO2+H2O reaction. This reaction is accompanied by a colossal decomposition of groundwater into hydrogen and oxygen within the sedimentary cover of the earth’s crust. Unreacted CO2, as well as H2 and most of the methane produced during the reaction are degassed into the atmosphere, while resulting C5+ hydrocarbons remain under the surface filling geological traps in the form of oil and gas. The article presents the results of model experiments, which make it possible to estimate the rate of groundwater decomposition and on this basis explain the current rate of Earth’s degassing, as well as the observed CO2, CH4 and H2 ratio in degassing products.

In the review, directions of future studies of the seismic process are considered. The priority shall be given to studies of the barrier effect of degassing and research of processes that take place in marginal structures. A scenario of preparation of the seismic process and associated events is described with regard to uncertainties in development of critical seismotectonic situations.