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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 China Extensional deformation regions demonstrated greater gas degassing than compressional deformation regions Spatial distribution of gas fluxes mirrored fault patterns in the Yinchuan Graben

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 fluids The 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

AbstractIn 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.

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 2 contained in permafrost. The gas was mostly CO 2 (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.

Valuation of the analysis performed on groundwater of Central Lazio by ACEA ATO2 SpA from 2001 to 2016, according to the model proposed by Chiodini et al. in 2004 that identifies in the Tyrrhenian coast of central and southern Italy, two notable releasing areas of the CO2 produced by the sub-crustal magma activity, or two areas of natural degassing of the planet: the TRDS area (Tuscan Roman degassing structure) and the CDS area (Campanian degassing structure). Reconstruction of the CO2 produced by degassing through the analysis of the components of inorganic carbon measured in groundwater of Central Lazio (Rome and Rieti districts) between 2001 and 2016. Causal relationship of the activity of mantle degassing in the TRDS area with the disastrous earthquake occurred at L’Aquila in April 6, 2009. Current use of the dissolved inorganic carbon measurement in the Peschiera and Capore spring waters to monitor the activity of mantle degassing in the TRDS area, in order to have an early warning signal of possible seismic activity in the Central Apennines. Revision and data updating after the earthquake in August 24, 2016 at Amatrice.

A wide range of geological and geophysical methods was carried out on the Yamal Peninsula in the Arctic in the period 2014–2022. The results were analyzed together with data from remote sensing of the Earth. Fundamentally new data on the gas-dynamic mechanisms of dangerous processes in permafrost have been obtained. These data included catastrophic gas blowouts and explosions with the formation of giant craters. More than three thousand zones of powerful gas blowouts with the formation of craters at the bottom of thermokarst lakes, rivers, and the coast of the Kara Sea have been discovered. According to data on remote sensing of the Earth, large mud volcanic structures, located at the bottom of the Labvarto and Yambuto thermokarst lakes, were discovered on the Yamal Peninsula in 2022–2023 for the first time. Monitoring of their state with the use of retrospective satellite images showed the presence of periodic release of underground fluids, including gas. A conclusion was made about the discovery of active mud volcanoes on the Yamal Peninsula.

AbstractThe purpose of this work was to analyze the causes of intensive gas emission in the central part of the Laptev Sea. On the basis of a seismic survey of the JSC Marine Arctic Geological Expedition, the wave fields have been studied on 28 profiles with a total length of 5930 km. Zones with refracted waves from the high-velocity horizons, associated with frozen sediments and possible occurrence of gas hydrates, have been revealed. For the first time for the region, a cartographic scheme of change in the refracted wave propagation velocity and physical state of bottom sediments (frozen or thaw) has been created. The absence of permafrost and gas hydrates in the area of active gas emission was proved, and the deep origin of gas and its migration along tectonic faults were grounded.

The behavior of C, H, and S in the solid Earth depends on their oxidation states, which are related to oxygen fugacity (fO₂). Volcanic degassing is a source of these elements to Earth’s surface; therefore, variations in mantle fO₂ may influence the fO₂ at Earth’s surface. However, degassing can impact magmatic fO₂ before or during eruption, potentially obscuring relationships between the fO₂ of the solid Earth and of emitted gases and their impact on surface fO₂. We show that low-pressure degassing resulted in reduction of the fO₂ of Mauna Kea magmas by more than an order of magnitude. The least degassed magmas from Mauna Kea are more oxidized than midocean ridge basalt (MORB) magmas, suggesting that the uppermantle sources of Hawaiian magmas have higher fO₂ than MORB sources. One explanation for this difference is recycling of material from the oxidized surface to the deep mantle, which is then returned to the surface as a component of buoyant plumes. It has been proposed that a decreasing pressure of volcanic eruptions led to the oxygenation of the atmosphere. Extension of our findings via modeling of degassing trends suggests that a decrease in eruption pressure would not produce this effect. If degassing of basalts were responsible for the rise in oxygen, it requires that Archean magmas had at least two orders of magnitude lower fO₂ than modern magmas. Estimates of fO₂ of Archean magmas are not this low, arguing for alternative explanations for the oxygenation of the atmosphere.

The Karakoram fault (KKF) is an important strike‐slip boundary for accommodating deformation following the India‐Asia collision. However, whether the deformation is confined to the crust or whether it extends into the mantle remains highly debated. Here, we show that the KKF is overwhelmingly dominated by crustal degassing related to a 4He‐ and CO2‐rich fluid reservoir (for example, He contents up to ∼1.0–1.6 vol.%; 3He/4He = 0.027 ± 0.013 RA (1σ, n = 47); CO2/N2 up to 3.7–57.8). Crustal‐scale active deformation driven by strike‐slip faulting could mobilize 4He and CO2 from the fault zone rocks, which subsequently accumulate in the hydrothermal system. The KKF may have limited fluid connections to the mantle, and if any, the accumulated crustal fluids would efficiently dilute the uprising mantle fluids. In both cases, crustal deformation is evidently the first‐order response to strike‐slip faulting. Plain Language Summary Bubbling hot springs are common in fault zones along which Earth's lithosphere cracks. Chemical and isotopic compositions of spring gases can offer key information on the subsurface connectivity of the deep‐rooting faults that is not easily visible. To assess whether the Karakoram fault (KKF) in western Tibetan Plateau is developing in the crust or extends into deeper mantle, we studied the origin and transport of spring gases and found that the KKF is overwhelmingly dominated by degassing of a crustal fluid reservoir that contains high amounts of helium (He) and CO2. This could be attributed to He‐CO2 mobilization of deforming and fracturing fault zone rocks at crustal depths, suggesting that the KKF is primarily developing in the crust and may have limited fluid connections to the mantle. Key Points New He isotope data show that southern Karakoram fault (KKF) is overwhelmingly dominated by degassing of crustal fluids A crustal 4He‐ and CO2‐rich fluid reservoir is identified and linked to crustal‐scale active deformation driven by strike‐slip faulting KKF may have limited fluid connections to the mantle and requires further evaluation based on He isotope and seismic data

The composition of Earth’s atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth’s core started to form. Through high-pressure experiments, we found that Fe2+ in a deep magma ocean would disproportionate to Fe3+ plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO₂ from the atmosphere to precipitate as diamond at depth. This explains Earth’s carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.