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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. Key Points: Paleofluids in the studied seismogenic fault derive from the mixing between crustal and mantle (∼20%) derived fluidsThe variability of the He isotopic signature registered in fluid inclusions results from either early trapping processes (due to past possible earthquakes events) or post trapping processes by addition of radiogenic 4He produced within fractured calcite veins over time (vein aging)The pristine mantle source has been active in the Irpinia area (southern Italy) for at least 1 Ma based on the post trapping process [ABSTRACT FROM AUTHOR]

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. Key Points: Tectonic controls on CH4 and CO2 emissions were investigated along the western margin of the Ordos Block in ChinaExtensional deformation regions demonstrated greater gas degassing than compressional deformation regionsSpatial distribution of gas fluxes mirrored fault patterns in the Yinchuan Graben [ABSTRACT FROM AUTHOR]

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.

In the north of the shallow East Siberian Arctic Shelf (the Laptev and East Siberian seas), based on CDP (common depth point) seismic data for 71 lines with total length of 15 630 km, velocities of refracted waves propagation in the upper part of the section were studied. Fundamentally new information was obtained on the state of the shelf permafrost and significant decrease of the zone of possible occurrence of frozen ground and methane hydrates was substantiated. Based on the comprehensive analysis of areas of subsea frozen ground degradation in the Laptev, East Siberian, Chukchi and Beaufort seas, the low probability of a significant contribution of methane, released due to gas hydrates dissociation, to global climate change was substantiated. [ABSTRACT FROM AUTHOR]

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 places of hydrogen emanation, prolonged exposure to significant concentrations of hydrogen under natural conditions led to the inhibition or death of agricultural plants. Under the conditions of model experiments, it was shown that plants in a short-term current of hydrogen experience stress, which negatively affects their physiological functions. Different types of plants reacted differently both to the effect of molecular hydrogen and to the removal of its load. In experiments with watercress, plants did not recover after the removal of the hydrogen load but died after a triple exposure. Wheat was less sensitive; the plants were only stably (30%) depressed during the whole observation period. [ABSTRACT FROM AUTHOR]

During recent geological history, the endorheic saline Caspian and Aral seas have displayed inexplicably strong fluctuations of their individual sea level. For example, since 1980 the level of the major Caspian has been swelling (by some 4 metres) - thereby adding the same volume of water that had been lost during the preceding 5 decades (1930-1980). Thus, the combined sea-level pattern is apparently impossible to handle by application of traditional surface hydrological mechanisms (the balance between river inflow and outflow through evaporation). To make things even worse for traditional thinking, the nearby shallow Aral Sea (a much smaller body of water) is rapidly shrinking. The present paper views the longstanding and puzzling sea-level histories within the context of a persistently degassing Earth. It seems difficult to avoid the conclusion that expelled hydrous fluids from the interior are adding (episodically) juvenile water to the Caspian and Aral basins. But due to Earth's slightly variable rotation, in addition to the actions from tidal and inertial effects, the internal hydrostatic pressure would produce a kind of hydraulic device - giving rise to surging effects on the internal hydrous fluids filling up the open fracture network of the deep. In consequence, the surface products of the internal surging system would be in terms of transgressiveregressive cyclicity of variable intensity. This explanation is supported by observations from modern deep continental drilling in association with classical geophysical mechanisms. It is inferred that the periodicity in surface water histories (at the deeper levels water would be in its supercritical state) are closely related to basically all other prominent regional phenomena - including 1) the expulsion of oil and natural gas from the deep interior Earth to the highly prolific Caspian hydrocarbon province, in association with 2) the world's highest concentration of mud volcanoes. In fact, the presence of highly reactive supercritical fluids in the lower crust and mantle is likely to be one of the most critical agents for crustal attenuation. For example, since the late Cretaceous-Lower Tertiary global tectonic unrest, episodic sub-crustal denudation processes have turned the once shallow South Caspian Sea into its present deep-water state - resulting in one of the thickest sedimentary basins in the world. Thus, beginning in the late Neogene - some 5 million years ago - the South Caspian crust began its youngest stage of foundering and sedimentation, in association with uplift of the surrounding mountains. This tectonic event is also thought to be the time of origin of the Aral Sea depression. [ABSTRACT FROM AUTHOR]

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.

This work presents findings of deep geological and geophysical studies, which have revealed new and often unexpected features of the structure of the Earth's crust and the upper mantle of the continents and oceans, not easily explainable by current geodynamic concepts. For example, deepwater drilling has shown the old age of the oceanic crust and its inhomogeneous composition. Seismic studies of long-range profiles with nuclear explosions and laboratory studies of mantle xenoliths at high pressures and temperatures have revealed that the advection of energy-intensive and geochemically active deep fluids is central to the formation of the upper mantle structure. A comprehensive analysis of these data provides a geodynamic model for the natural transformation of the upper mantle substance influenced by deep fluids and the formation of continents and oceans as a result of unevenly distributed degassing of the Earth. The global variability of the deep fluid advection intensity led to formation of two hemispheres: the Indo Atlantic Hemisphere where almost all continents are located and the Pacific Hemisphere that consists of oceans. This formation of the hemispheres can be explained by the specific features of the Earth's rotation in the Earth-Moon-Sun system. This work provides a review and analysis of these data and then offers a possible explanation based on an integrated geodynamic model. • Deep drilling in oceans and seismic studies revealed unexpected lithosphere features. • The crust of oceans is old and subcontinental lithosphere was found in all oceans. • Lithosphere roots of continents are composed of depleted decreased density material. • Earth degassing with energy-intensive fluids transformed the upper mantle material. • Earth's rotation in the Earth-Moon-Sun system formed the oceanic Pacific Hemisphere. [ABSTRACT FROM AUTHOR]

A large volume of underground gas in the permafrost region of the Qinghai-Tibetan Plateau has been identified. Although many studies were performed to investigate the soil organic carbon dynamics and Earth degassing in volcanic areas, this is the first report of a large amount of non-volcanic CO contained in permafrost. The gas was mostly CO (81.76 vol. %) and nitrogen (14.59 vol. %). The gas composition and the evidence from carbon stable isotope values (−23.9 ‰, PDB) suggested that the gases possibly had a deep origin. The gas emissions may be triggered by permafrost degradation, which means mitigation of the barrier effect of permafrost for the gas. In addition, plate tectonic processes may also lead to gas emissions, as the tectonic activity is strong in the area. Therefore, particular attention should be paid to the underground gases in the study of global change and permafrost degradation. [ABSTRACT FROM AUTHOR]

Abstract: We describe the results of a detailed hydrogeochemical campaign on the groundwater circulating in two regional aquifers located in the area of the Abruzzo 2009 earthquakes. The influx of deeply derived CO2 rich gases into the two aquifers is highlighted by the 13C isotopic composition of dissolved carbon species. The source of the gas is roughly localised beneath the epicentral area of the earthquakes where the presence of sources of fluids under high pressure is suggested by seismological investigations. The carbon isotopic-mass balance of the aquifers indicates that the amount of the deep CO2 dissolved and transported by the groundwaters is ~530t/day. The chemical and isotopic composition of the gas entering the aquifers, named Abruzzo gas, has been derived by comparing the data measured in the springs with the results of a gas–water–rock reaction model, that simulates the evolution of the chemical and isotopic composition of groundwater affected by the input of a deeply-derived CO2 rich gas phase. The composition of Abruzzo gas is compared to that of 40 large gas emissions located in central Italy. The gas becomes progressively richer in radiogenic elements (4He and 40Ar) and in N2, from the volcanic complexes in the west to the Apennines in the east. The Abruzzo gas, in agreement with its location, well matches the composition of the gases emitted in the pre-Apennine region. These geochemical features, consistent with the structural setting of the region, indicate increasing residence times of the gas in the crust moving from west to east. In particular we suggest that the strong increase in radiogenic crustal gases reflects the occurrence of deep traps where the gas is stored at high pressures for a long time and that such high pressure gas pockets play a major role in the generation of Apennine earthquakes. [Copyright &y& Elsevier]

This article describes the results of a comprehensive analysis of the causes of intensive gas emission over a large zone (ca. 80 × 220 km) of the Central Laptev shelf area. The upper parts of 28 sections of common depth point (CDP) seismic lines acquired by the JSC MAGE, covering a total length of 5930 km over an area of 55,000 km2, were interpreted and 519 anomalous objects potentially connected with gas saturation were revealed. For the first time, the boundary between frozen and thawed sediments was defined in the Laptev Sea. The absence of subsea permafrost and gas hydrates in the intensive gas seepage zone was determined. The connection between gas seeps and deep-seated faults identified in seismic sections was substantiated. This study demonstrated that seismotectonic factors caused a large spatial window of long-term Earth degassing with direct intensive migration of deep thermogenic gas to the hydrosphere through a system of faults. A zone of potential gas hydrate distribution was observed on the continental slope. • Permafrost and gas hydrates are not predicted in the zone of gas seeps in the Central Laptev area. • Gas seeps in the Central Laptev area are connected with deep-seated faults. • Seismotectonic factors must contribute to gas seepage in the Central Laptev area. • Gas hydrates are predicted on the continental slope of the Laptev Sea. [ABSTRACT FROM AUTHOR]

Abstract: The CO2 degassing process from a large area on the Tyrrhenian side of central Italy, probably related to the input into the upper crust of mantle fluids, was investigated in detail through the geochemical study of gas emissions and groundwater. Mass-balance calculations and carbon isotopes show that over 50% of the inorganic carbon in regional groundwater is derived from a deep source highlighting gas−liquid separation processes at depth. The deep carbonate−evaporite regional aquifer acts as the main CO2 reservoir and when total pressure of the reservoir fluid exceeds hydrostatic pressure, a free gas phase separates from the parent liquid and escapes toward the surface generating gas emissions which characterise the study area. The distribution of the CO2 flux anomalies and the location of high PCO2 springs and gas emissions suggest that the storage and the expulsion of the CO2 toward the atmosphere are controlled by the geological and structural setting of the shallow crust. The average CO2 flux and the total amount of CO2 discharged by the study area were computed using surface heat flow, enthalpy and CO2 molality of the liquid phase circulating in the deep carbonate−evaporite aquifer. The results show that the CO2 flux varies from 1×104 mol y−1 km−2 to 5×107 mol y−1 km−2, with an average value of 4.8×106 mol y−1 km−2, about five times higher than the value of 1×106 mol y−1 derived by Kerrick et al. [Kerrick, D.M., McKibben, M.A., Seward, T.M., Caldeira, K., 1995. Convective hydrothermal CO2 emission from high heat flow regions. Chem. Geol. 121, 285–293] as baseline for terrestrial CO2 emissions. The total CO2 discharged from the study area is 0.9×1011 mol y−1, confirming that Earth degassing from Tyrrhenian central Italy is a globally relevant carbon source. [Copyright &y& Elsevier]

Geochemical and isotopic studies have been undertaken to assess the origin of CO2-rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na–HCO3 mineral waters. The δ2H and δ18O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an 18O-shift indicates there has been no high temperature water–rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low 14C activity (up to 9.9 pmC) measured in some of the cold CO2-rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of 3H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The δ13C values of CO2 gas and dissolved inorganic carbon range between −6‰ and −1‰ versus Vienna-Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO2 (14C-free) introduced from deep-seated (upper mantle) sources, masking the 14C-dating values. The differences in the 87Sr/86Sr ratios of the studied thermal and mineral waters seem to be caused by water–rock interaction with different granitic rocks. Chlorine isotope signatures (−0.4‰ < δ37Cl < +0.4‰ versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks. [ABSTRACT FROM AUTHOR]

Both the shallow (organic-derived) and deep (mantellic–magmatic–metamorphic) fluxes of CO2 [ΦCO2, mass time-1] and specific fluxes of CO2 [ϕCO2 mass time-1 surface-1] dissolving in the shallow groundwaters of the volcanic areas of Amiata, Vulsini-Vico-Sabatini, Albani, Roccamonfina, Vesuvio, Vulture, and Etna were evaluated by partitioning the composed population of total dissolved inorganic carbon in two individual populations and subsequent subtraction of local background population.The flux of deep CO2 released from the geothermal fields of Piancastagnaio (Amiata), Torre Alfina, Latera, Marta, Bracciano south, Cesano, and Mofete and from the Overall Northern Latium Hydrothermal Reservoir were also evaluated by means of the total surface heat flux and the enthalpy and CO2 molality of the single liquid phase circulating in each geothermal reservoir.These data suggest that the ϕCO2 released to the atmosphere varies from 9.5×106 to 3.0×106 mol year-1 km-2, over the geothermal fields of Bracciano south and Cesano, respectively, and that a total ΦCO2 of 3.8×108 mol year-1 is cumulatively released from the geothermal fields of Torre Alfina, Latera and Cesano extending over an area of only 66 km2.In addition, a flux of ∼2.2×1011 to 3.8×1011 mol year-1 of gaseous CO2 entering the atmosphere is obtained for the entire anomalous area of central Italy, extending from the Tyrrhenian coastline to the Apennine chain (45,000 km2). Thus terrestrial CO2 emission in central-southern Italy appears to be a significant carbon source. [Copyright &y& Elsevier]