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This study explores the estimation of solubility-induced elemental fractionation of noble gases in hydrocarbon-based oils through existing empirical and theoretical models, complemented by a novel molecular simulation-based approach. Quantifying such fractionation is essential for a deeper understanding of fluid processes and migration in subsurface geological resources, an area currently lacking in experimental data. To address this, the research introduces a predictive model that employs the Peng-Robinson equation of state and a fugacity-coefficient-based method to assess noble gas elemental fractionation in hydrocarbons, including normal alkanes, cycloalkanes, and aromatics. However, this model struggles with precise quantitative predictions, prompting the introduction of adjusted cross-interaction parameters to enhance its performance. Furthermore, molecular simulations, in conjunction with the refined equation of state, are shown to offer a novel method for calculating noble gas fractionation coefficients across different hydrocarbon solvents. A key finding is the identification of a universal master curve, demonstrating that noble gas solubility fractionation at low pressure in simple hydrocarbon solvents can be quantitatively determined by temperature and density alone, without the need for detailed compositional information. Consequently, a new correlation is proposed for deriving elemental fractionation coefficients based solely on oil temperature and density, offering significant improvements over existing empirical methods for a wide range of temperatures. Although limitations are noted when applying this approach to oils rich in complex heavy components like resins and asphaltenes, it allows to address inconsistencies observed in traditionally used experimental correlations at high temperatures. [ABSTRACT FROM AUTHOR]

The chemical and isotopic composition of gases emitted by subduction zone volcanoes can provide insights into the origin of magmatic volatiles. In volcanic arcs, magmatic volatiles can be supplied from the mantle, the subducting slab, or the rocks of the arc crust. Determining the relative contributions of these distinct sources is important for understanding the transfer of volatiles between Earth's interior and exterior reservoirs, which has implications for the physical and chemical evolution of both the mantle and the atmosphere. Each subduction zone has a different recycling efficiency, controlled by the composition of the slab and the pressure-temperature path it experiences upon subduction, and accordingly all volcanic arc emissions can be characterised by their chemical and isotopic compositions. In this study, we analyse the composition of volcanic gases from Rabaul caldera in the New Britain subduction zone, Papua New Guinea, and show that the emissions are substantially influenced by slab recycling of carbon and nitrogen. We find helium emissions are dominated by a mantle contribution, with little influence from the arc crust. Carbon isotopes point towards a mixture of mantle, carbonate and organic sediment-derived contributions, with the dominant input coming from carbonates. This may be of sedimentary origin, seafloor calcareous muds, or altered basalts of the subducting oceanic crust. Nitrogen isotopes also indicate a significant influence of sedimentary nitrogen and, potentially, a contribution from altered ocean crust. Our study is the first comprehensive investigation of volatile sources in the New Britain subduction zone and our results and interpretation are consistent with previous studies of element recycling based on New Britain arc lavas. [ABSTRACT FROM AUTHOR]

[Display omitted] • B 3 C 2 H 5 structure was designed and inductive charge transfer from Ng atoms was investigated for the first time. • E HOMO , E LUMO , E g , E ad , and analyses were utilized for studying the electronic changes upon interactions with Ng atoms. • LOL, ELF, and RDG analyses were used for studying the interaction nature. Quantum chemical calculations were performed to study the binding affinity of the B 3 C 2 H 5 cluster with noble gases. The results indicate that noble gas atoms especially the heavier ones such as Xe and Kr can form stable complexes with this cluster. Detailed analysis of the interaction mechanism reveals that the noble gas atoms serve as donor fragments in the formation of Ng@B 3 C 2 H 5 , 2Ng@B 3 C 2 H 5 , and 3Ng@B 3 C 2 H 5 donor–acceptor complexes. [ABSTRACT FROM AUTHOR]

Villarrica volcano, in the southern Andes, is a composite mafic volcano whose persistent open-vent activity is punctuated by frequent Strombolian/Hawaiian eruptions and, more rarely, by more energetic (sub-Plinian) events. Here, we investigate the volatile composition of the parental melts that sustain this activity, and the conditions of pre-eruptive magma storage, by characterizing the composition of olivine-hosted melt and fluid inclusions. We concentrate on inclusions entrapped in minerals from pyroclastic materials erupted from both Villarrica summit and from its flank Minor Eruptive Centers (MECs) post the 14.5–13.5 kyr caldera collapse event that formed the Licán ignimbrite. Our micro-FTIR and SIMS measurements indicate that the Pucón eruption records the highest volatile contents, with 6.0 wt% H 2 O, >1500 ppm CO 2 , 1330 ppm S, 1556 ppm Cl, and 2055 ppm F. These volatile contents imply a volatile-saturated magma originating from a depth of 14.4 to 17 km below Villarrica. Results for other flank eruptions highlight a similarly deep (17–21 km depth) source for basaltic CO 2 -rich mafic magmas erupted at regional MECs (Los Nevados, Caburgua). Melt inclusion results also reveal that deep rising mafic magma batches, when temporarily stored at 1–5 km depth, produce the more differentiated and degassed magma batches that sustain the decadal-old persistent effusive-explosive eruptive activity at Villarrica. Helium isotope ratios (3He/4He; Rc/Ra when corrected for atmosphere) measured in bulk noble gases from olivines (Fo 75 – 88) indicate that the parental magmatic fluid signature (Rc/Ra = 6.7–7.6; CO 2 /3He = 4.7–7.5E+08) is only recorded during central paroxysmal sub-Plinian eruption, and that this primitive gas signal is diluted in lateral MECs (Rc/Ra < 6.5; CO 2 /3He = 1.4 × 10+9–3.1E+10). • Pucón Ignimbrite represent Villarrica post-glacial primitive mafic magma. • Polygenetic eruptive vents source >17 km depth CO 2 -rich volatile melts. • Villarrica and lateral vent degas mafic magma at <5 km storage depths. • Shallow atmospheric and mixed crustal 4He in volcanic arc fluids. • Subplinian paroxysms preserve MORB-like 3He/4He fluid ratios. [ABSTRACT FROM AUTHOR]

Whether auriferous hydrothermal fluid is generated during crustal metamorphism or by subcrustal processes to form orogenic gold deposits is hotly debated. Noble gas isotope and halogen abundance ratios can provide important constraints to help resolve this controversy. The Danba gold deposit is a rare example of a Jurassic age hypozonal orogenic gold deposit on the western margin of the Yangtze Craton, China. It is characterized by thick barren quartz veins with fractures infilled by thin auriferous quartz veinlets. The syn -gold quartz veinlets are associated with plagioclase and pyrrhotite and are distinguished from the barren quartz vein hosts on the basis of cathodoluminescence, trace-element content and Raman spectroscopy and microthermometry of fluid inclusions. The dominant fluid inclusions in the gold-bearing quartz and plagioclase are H 2 O–CH 4 with vapor fill of ∼ 15–45 vol% and high pressure-corrected trapping temperatures of ∼ 500 °C, low salinities (<4 wt% NaCl equiv.) and high Mg/Fe ratios. Crushing syn -gold quartz and plagioclase released fluid inclusions with 40Ar/36Ar ratios of between 490 and 710, molar Br/Cl ratios of (0.3–0.7) × 10−3 and molar I/Cl ratios of (18–60) × 10−6. Crushing syn -gold pyrrhotite released fluid inclusions with 3He/4He ratios of 0.21–0.38 Ra (Ra = air value, 1.39 × 10−6) that are higher than typical crustal values of < 0.1 Ra, and 40Ar/36Ar of 330–640 that are similar to the gold-related quartz-hosted inclusions. The combined noble gas and halogen data do not favor an auriferous fluid derived from K- and U-rich Proterozoic granitic basement, which is expected to have radiogenic 40Ar/36Ar and 3He/4He ratios. Instead, the data are more consistent with a fluid source from underlying mantle lithosphere containing a high proportion of altered ocean crust (AOC). The auriferous fluid that formed the Danba gold deposit is thus considered to have been derived from a source comprising both metasomatized mantle lithosphere that had been fertilized in a Neoproterozoic subduction event and a portion of relict AOC beneath the western margin of the Yangtze Craton. In contrast with syn -gold fluid inclusions, those in pre-gold barren quartz are H 2 O–CO 2 dominated. Crushing pre-gold quartz released fluid inclusions with 40Ar/36Ar ratios of 2410–5450, Br/Cl ratios of (1.2–1.5) × 10−3 and I/Cl ratios of (60–80) × 10−6 that are distinctly different to the gold-ore stage. The higher 40Ar/36Ar ratios of the pre-gold fluids are consistent with a source for the barren host quartz veins from prograde greenschist- to amphibolite-facies metamorphism of the Proterozoic granitic basement. [ABSTRACT FROM AUTHOR]

• High precision of e-CPA in predicting noble gas solubility in solutions. • Salting-out effect investigation of electrolytes on noble gas solubility in water. • Enhancing the model accuracy based on noble gas dissolution behavior. • Effective modeling tool for achieving sustainable water resource management. Dissolved noble gases in water hold significant potential as tracers and precursors in various hydrogeological and geological applications, particularly in understanding surface water-groundwater interactions. These applications necessitate precise solubility predictions. Employing the fugacity-fugacity approach, our study models the solubilities of Neon, Argon, Krypton, Xenon, and Radon in both pure water and electrolyte solutions. Leveraging the Cubic-Plus-Association Equation of State, we achieve remarkable accuracy, with average deviations below 2.5 % for vapor pressure, liquid, and vapor-phase densities. Additionally, in water–gas binary systems, deviations in gas solubilities within pure water remain under 5.0 %. Extending our analysis to water–gas-salt ternary systems, our model demonstrates deviations smaller than 5.6 %. Alongside discussing the gas dissolution mechanism, this work emphasizes the adaptability of the model, informed by robust experimental and modeling data. The interpretations derived from modeling hydrogeological conditions are poised to enhance our understanding of hydrological processes, thereby assisting planners and water managers in achieving sustainable development and management of water resources. [ABSTRACT FROM AUTHOR]

• Experimental data on the sputtering coefficient of TiC and MAX phase Ti2AlC by noble gas ions Ne, Ar and Xe are summarized. • The sputtering coefficients of TiC and MAX phase Ti2AlC were calculated using a semi-empirical model. • A comparison of the experimental and calculated data showed satisfactory agreement. Information on sputtering coefficients of materials is necessary for coating deposition technologies and studying the interaction of ion beams and plasma with the surface. This paper summarizes experimental data on sputtering coefficients of TiC and MAX phase Ti 2 AlC by noble gas ions Ne, Ar, and Xe. The sputtering coefficients of TiC and MAX phase Ti 2 AlC were calculated using a semi-empirical model. A comparison of the experimental and calculated data showed satisfactory agreement. [ABSTRACT FROM AUTHOR]

Novel analytical approaches to determining the trapped 38Ar/36Ar ratio of gases contained within Martian meteorites are presented and applied to the Martian regolith breccia Northwest Africa (NWA) 7034 and paired stone NWA 11220. The resulting data indicate that extensive mass-dependent fractionation of atmospheric Ar may have occurred within 150 million years of planetary formation, ostensibly as a result of diffusion-limited hydrodynamic escape. The inferred fractional loss of Ar and lighter atmospheric constituents exceeds 50%. These data suggest that volatiles derived from planetary outgassing and/or impactors may dominate the present abundance of atmospheric Ar. [ABSTRACT FROM AUTHOR]

Noble gases are ideal natural tracers to characterize the storage, migration and origin of fluids in geological environments. They are chemically and biologically inert and therefore are only partially separated by physical processes including the one related to the molecular diffusion phenomenon, so called kinetic fractionation. However, its precise quantification is difficult to achieve and its modeling is still open for debates. Thus, in this work, we have investigated the capability of simple and predictive models to estimate elemental and isotopic fractionation of noble gases in various geological fluids. To do so, molecular dynamics simulations on noble gases in water, gas and oil under sub-surface conditions were performed. These numerical results were found to be consistent with previous ones including experiments and molecular simulations when available, i.e. in water. Interestingly, it appeared that the widely used square-root law is able to provide a good prediction for elemental fractionation between noble gases in all solvents, except for helium. Such unexpected result from the theoretical point of view is explained by a peculiar relationship between the molecular mass and the molecular size of noble gas elements. Regarding the noble gas isotopic fractionation, the square-root law is shown to be unable to provide reasonable results, confirming recent experimental and numerical works. As expected, it has been noticed that the kinetic theory relation provides a reasonable estimate of the isotopic fractionation in gas whereas it deteriorates in water and in oil. Finally, using the previous findings, we propose a simple and predictive scheme for the isotopic fractionation of noble gases in all studied geo-fluids which is noticeably better than both the square-root and the kinetic theory relations. [ABSTRACT FROM AUTHOR]

[Display omitted] • We report the first subduction-related helium composition of Patagonian peridotites. • Cryptic metasomatism is observed in anhydrous peridotites from Coyhaique, Patagonia. • P-T estimates show that the lherzolites equilibrated in the spinel stability field. Spinel lherzolite xenoliths from Coyhaique, Chilean Patagonia, are located ~320 km from the Chile Trench and, therefore, their geochemical and isotopic compositions may record slab-derived metasomatism from current and/or earlier subduction zones. We present new mineral and whole-rock major and trace elements that are discussed together with noble gas data (He, Ne, Ar) and Sr-Nd isotopic ratios. Partial melting is recorded by negative correlations between basaltic elements vs. MgO in whole-rock and minerals. In general, silicate minerals show depleted light-rare earth element (LREE) over heavy-REE (HREE) patterns. Whole-rock compositions and clinopyroxene record variable degrees of partial melting (1–15%), which is corroborated by the Sr-Nd depleted character of the lherzolites. Cryptic metasomatism is evidenced by: 1) enriched LREE patterns in whole-rock and type-2 clinopyroxenes; 2) negative anomalies of Nb-Ta-Ti in whole-rock samples coupled with enrichment of large ion lithophile elements and chalcophile elements over high field strength elements and HREE; 3) positive correlations of Pb and U vs. La and negative correlations of Nb/Nb* and Ti/Ti* vs. La in clinopyroxene, and 4) positive anomalies of Li in all silicate minerals. Geochemical differences between whole-rocks and their mineral constituents indicate selective enrichment of the whole-rock samples due to grain-boundary components. 3He/4He ratios reported here are the first strongly radiogenic values found in the Patagonian subcontinental lithospheric mantle (SCLM; 0.20–2.52 R A). Most Ne isotopic ratios are indistinguishable from air composition with few samples showing a nucleogenic component, whereas Ar isotopic ratios are extensively affected by an atmospheric component. The correlation between 3He/4He and 4He/40Ar* corroborates the metasomatism recorded by lithophile and chalcophile elements. Therefore, we identify a heterogeneous SCLM affected by low but variable degrees of partial melting and subsequent enrichment by melts or fluids from recycled subduction-related materials in the spinel stability field (1.06–1.90 GPa and 886–1150 °C). [ABSTRACT FROM AUTHOR]

• Chang'e-5 lunar soil reveals a non-binary mixture. • Cometary and meteoritic component identified, adding to compositional diversity. • 134,136Xe depletion link to cometary isotopes rather than early atmospheric escape. • Previous models insufficient in explaining Kr and Xe fractionation in lunar soils. • Chang'e-5 contributes to billions of years of solar system history. The extent of volatile elements on the surface and interior of the Moon remains a highly debated topic. Previous studies conducted on bulk lunar soil samples and solar wind samples collected by the Genesis mission indicate a discernible isotope mass- or non-mass-dependent fractionation of krypton and xenon. However, a detailed investigation of these processes is missing, particularly in determining the possible incorporation of cometary volatiles in the lunar regolith. New lunar soil samples returned by the Chang'e-5 mission provide a chance to answer these key questions. In this study, noble gas isotopes of nine subsamples from a Chang'e-5 scooped sample were analysed through stepwise-heating and total fusion laser extraction. The results reveal that a simple binary mixture of solar wind and cosmogenic components did not explain alone the isotopic composition of these samples. The Xe data shows insignificant amounts of atmospheric Xe and presents clear evidence of cometary contributions to the lunar regolith, with a significant depletion of 134,136Xe compared to that in the solar wind. Additionally, a meteoritic component is identified. Compared to the Apollo results, our findings further validate the theory of Earth's atmospheric escape, substantiate the plausibility of these exogenous admixtures to elucidate the isotopic fractionation mechanisms of Kr and Xe within the lunar regolith, and provide novel insights into long-term constancy in the solar wind composition. [ABSTRACT FROM AUTHOR]

Determining solubilities of pure noble gases and He–CO 2 /CH 4 /N 2 gas mixtures in aqueous solutions is essential for various applications of noble gases in geological processes and for understanding the migration and accumulation of helium. This study developed two thermodynamic models for calculations of solubilities of five pure noble gases (i.e. He, Ne, Ar, Kr, and Xe) and He–CO 2 /CH 4 /N 2 gas mixtures in water and in aqueous NaCl solution. The first model is constructed by extending the improved SAFT-LJ equation of state (EOS) to five binary H 2 O-noble gas systems and four ternary systems (i.e. H 2 O–He–NaCl, H 2 O–He–CO 2 , H 2 O–He–CH 4 , and H 2 O–He–N 2). Both the non-ideality of aqueous phase and that of vapor phase of these systems were described using the improved SAFT-LJ EOS (φ - φ model). The second model is developed by modifying the gas solubility model proposed by Duan and his coworkers (one type of γ-φ model). The Pitzer theory was used to describe the non-ideality of aqueous phase and the improved SAFT-LJ EOS was used to describe the non-ideality of vapor phase. Both binary adjustable parameters of the improved SAFT-LJ EOS and parameters of the modified solubility model for pure gas were evaluated from experimental solubility data for pure gas. Both models are predictive for solubilities of gas mixtures since there is no need to evaluate their parameters from solubility data of gas mixtures. Comparisons of calculations of two models with experimental data show that both models can well represent solubilities and Henry's coefficients of five noble gases in pure water, as well as the solubility of He in aqueous NaCl solutions over a wide P - T range (273–600 K, 1–2000 bar for the solubility of He in water). The absolute average deviation of the improved SAFT-LJ EOS from experimental solubility data for five noble gases in pure water is 3.14% and that of the modified solubility model is 2.21%. Predictions of the improved SAFT-LJ EOS for Henry's coefficients for He in the He–CO 2 –H 2 O system are consistent with available experimental data. According to predictions of the improved SAFT-LJ EOS, Henry's coefficient for He in the He–CO 2 –H 2 O system is always lower than that in the He–H 2 O system at the same depth. Within 0–5 km depth, He solubility of He–CO 2 gas mixture is much greater than that of pure He at the same depth and He partial pressure, He solubility of He–N 2 mixture is a little greater than that of pure He, and He solubility of He–CH 4 mixture is between that of He–CO 2 mixture and that of He–N 2 mixture. A computer program for calculations of solubilities of pure noble gases and He–CO 2 /CH 4 /N 2 gas mixtures in pure water and in aqueous NaCl solutions can be obtained from the corresponding author via email. • Two thermodynamic models are developed to calculate solubilities of pure noble gases and He–CO 2 /CH 4 /N 2 gas mixtures. • Calculations of both models for solubilities of He–CO 2 /CH 4 /N 2 gas mixtures are predictive. • Both models can well represent solubilities of He in water and in aqueous NaCl solutions over a wide pressure-temperature range. [ABSTRACT FROM AUTHOR]

Helium is a critical, strategic and nonrenewable resource with limited reserves and unstable supplies. However, the helium sources and migration processes in petroliferous basins remain unclear. The Qaidam Basin features multiple reservoir layers, multiple genetic types of natural gas, and varying helium concentrations, providing an ideal natural laboratory for understanding the helium enrichment processes. Here, we present the original noble gas isotopic compositions and major gas components of 11 microbial gas samples from three gas layers in the Sebei No.1 gas field, eastern Qaidam Basin, China. The helium isotopic ratios range from 0.007 to 0.057 Ra, reflecting a predominantly crustal source. The Quaternary Sebei microbial gas features much lower helium concentration (0.0003–0.001%), 21Ne/22Ne ratio (0.031–0.034), and 40Ar/36Ar ratio (292–380) than thermogenic natural gases in the Qaidam Basin. The middle gas layer (II) of the Sebei gas field features higher 21Ne/22Ne and 40Ar/36Ar ratios than the top and bottom gas layers, displaying positive correlations with higher 4He groundwater concentrations before degassing, as calculated from 4He/20Ne ratios and 20Ne concentrations in air-saturated water. However, the correlations between the 4He contents in natural gas and the 21Ne/22Ne and 40Ar/36Ar ratios are unclear, suggesting that 4He dissolves into the groundwater system before degassing into a gas reservoir and that the variations in the 4He concentration in the gas phase are caused by the different levels of hydrocarbon dilution. Quantitative calculations of helium production revealed an external helium flux from the crustal basement except for the in-situ production from sedimentary strata even in this broadly-defined self-generating and self-preserving natural gas system. The helium resources in the Qaidam Basin are mainly distributed in tectonically active zones with uplifted pre-Jurassic basement rocks (providing sufficient helium sources), ancient groundwater systems (accumulating more helium) and suitable hydrocarbon production (acting as a carrier gas but diluting helium as slightly as possible). • Crust-derived features and poor resource prospects are revealed for helium in Qaidam microbial gases. • Noble gas isotopes correlations identify the exsolution process of dissolved helium from groundwater. • External helium flux from the crustal basement is an important contributor to helium enrichment. • Helium resources in the Qaidam Basin are mainly distributed in the tectonic zones with uplifted pre-Jurassic basement, ancient groundwater system and suitable hydrocarbon production. [ABSTRACT FROM AUTHOR]

[Display omitted] • The xenotime U–Pb age of 426 ± 6.0 Ma (2σ) records a regional metamorphic event. • Two hydrothermal xenotime yielded U–Pb ages of 256.0 ± 4.1 Ma (2σ) and 254.4 ± 2.1 Ma. • Hydrothermal titanite shows an age of 255.4 ± 0.8 Ma. • Ore-forming fluids dominantly originated from the crustal sources. The Haoyaoerhudong gold deposit, located in the northwestern part of the North China craton (NCC), has produced over 120 metric tonnes (t) of gold since 2007. It has a total reserve of > 240 t at average gold grade of 0.62 g/t, making it one of the largest open pit gold mines in China. The steeply dipping, large-tonnage, low-grade, vein- or veinlet-type gold orebodies are hosted in strongly-deformed Mesoproterozoic carbonaceous schist of the Bayan Obo Group. The laminated/boudinaged veins/veinlets in the sinistral ductile–brittle shear zones are dominated by quartz, biotite, gold-bearing löllingite, pyrrhotite, (arseno)pyrite, with minor native gold, titanite and xenotime. In this paper, we present new in situ U–Pb geochronological data on magmatic zircon from the pre-ore dikes, on metamorphic and hydrothermal xenotime, and on hydrothermal titanite from the hydrothermally altered carbonaceous schist and auriferous quartz–sulfides veins/veinlets, as well as He-Ar isotopic analysis on gold-bearing (arseno)pyrite in the syn -ore stage. The metamorphic xenotime U–Pb age of 426 ± 6.0 Ma (2σ) records a regional metamorphic event, possibly related to the accretion of the Bainaimiao arc onto the NCC. Two pre-ore andesitic dikes yielded similar emplacement ages at ∼ 278 Ma constrained by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U–Pb zircon data. Hydrothermal xenotime grains from the altered carbonaceous schist and auriferous quartz–sulfides veins yielded U–Pb ages of 256.0 ± 4.1 Ma (2σ) and 254.4 ± 2.1 Ma (2σ), respectively, overlapping with that of the hydrothermal titanite at 255.4 ± 0.8 Ma (2σ) from the laminated quartz–sulfides veinlets. This indicates that the gold mineralization occurred at ca. 255 Ma. The ∼ 255 Ma gold mineralization age is much younger than the previously reported Early–Middle Permian regional magmatic activity (ca. 291 Ma to 268 Ma), and may be associated with the regional sinistral strike-slip event in the late orogenic cycle related to the collision between the Siberian craton and the NCC. The 3He/4He (R/Ra) and 40Ar/36Ar values of the gold-bearing (arseno)pyrite are 0.04 to 0.09 (average = 0.07) and 375.8 to 2023 (average = 1045), which reveal the ore-forming fluids dominantly originated from the crustal rocks, with limited involvement from the mantle. Collectively, our new geochronological data, noble gas isotopic analyses, and geological evidence support a typical orogenic gold deposit model at Haoyaoerhudong. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recent progress on Xe/Kr adsorption and separation using MOF adsorbents was reviewed. • Innovative strategies to boost Xe/Kr separation in MOF materials have been disclosed. • The importance of advanced computational studies in Xe/Kr separation were described. • The promises, challenges and next steps in MOFs for Xe/Kr separation were presented. Xenon (Xe) and krypton (Kr) separation is of great interest and plays an essential role in the industry. However, the identical properties and ultra-low concentrations of Xe and Kr are the main challenges related with the separation. Compared with the conventionally used cryogenic process, porous materials-based physical adsorption is promising for efficient and cost-effective separation processes. Herein, this review targets on recent development in the design, synthesis, and Xe/Kr capture and separation performances of metal–organic frameworks (MOFs). We thoroughly evaluate and discuss innovative strategies to enhance Xe/Kr capture and separation in MOFs. Along with the discussions of strategies and developments in MOF, a brief discussion about the advances of computational studies was also provided. Finally, future challenges and prospects of MOFs for Xe/Kr capture and separation are highlighted. We believe that this review will effectively guide readers in the design and selection of suitable MOFs for Xe/Kr adsorption and separation in future endeavors. [ABSTRACT FROM AUTHOR]

Surface water (SW) - groundwater (GW) interactions exhibit complex spatial and temporal patterns often studied using tracers. However, most natural and artificial tracers have limitations in studying SW–GW interactions, particularly if no significant contrasts in concentrations between SW and GW exist or can be maintained for long durations. In such context, (noble) gases have emerged as promising alternatives to add to the available tracer methods, especially with the recent development of portable mass spectrometers, which enable continuous monitoring of dissolved gas concentrations directly in the field. However, long-duration gas injection into river water presents logistical challenges. To overcome this limitation, we present an efficient and robust diffusion-injection apparatus for labeling large amounts of river water. Our setup allows fine, real-time control of the gas injection rate, and is suitable for extended injection durations and different gas species. To illustrate the effectiveness of our approach, we present a case study where helium (He) is used as an artificial tracer to study river water infiltration into an alluvial aquifer. Our injection of He as a tracer increased the dissolved He concentration of the river water by one order of magnitude compared to air-saturated water concentration for 35 days. This experiment yields valuable information on travel times from the river to a pumping well and on the mixing ratios between freshly infiltrated river water and regional groundwater. • Gas can be injected into rivers by diffusion through a semi-permeable membrane. • Diffusive gas injection is much more efficient than bubbling injection. • Portable mass spectrometers allow on-site continuous monitoring of the injected gases. • Infiltrating river water tagged with gas tracers was identified in groundwater. • Gas tracers provide valuable insight into aquifer heterogeneity. [ABSTRACT FROM AUTHOR]

The low thermodynamic cycle efficiency of the plasma synthetic jet actuator (PSJA) limits its application in flow control of supersonic aircraft. To improve the thermodynamic cycle efficiency of the PSJA, the energy conversion process of the PSJA under single discharge has been investigated by thermodynamic theory analysis and numerical simulation. The relations between thermodynamic cycle efficiency, specific heat ratio of gas medium, non-dimensional energy deposition and heating efficiency are established by theoretical deduction. Employing the three-dimensional nonconstant electrode center energy deposition model, energy conversion processes in the PSJA with six different gas mediums have been investigated. The simulation results show that the thermodynamic cycle efficiency of the PSJA with noble gas medium can exceed 3.2 %, which is 1.92 times of the PSJA with air medium due to their low volume specific heat. The maximum jet x-velocity of helium can reach 493.11 m/s, which is 3.3 times higher than that of air. Consequently, noble gases prove to be effective in improving the thermodynamic cycle efficiency of the PSJA and enhancing the strength of the synthetic jet. The advancement in the performance of the PSJA contributes to their enhanced capabilities in the field of active flow control. [ABSTRACT FROM AUTHOR]

Closed Brayton cycle (CBC) having single-shaft, centrifugal type compressor is considered as an efficient energy-conversion option associated for gas-cooled reactor (GCR) heat source. In terrestrial power plants and space power systems noble gases are considered as an efficient working fluid for most of the GCR's and CBC engines. The effectiveness of various noble gases as working fluid in closed cycle power plants for the power conversion units is of imperative concern. Although pure helium is relatively difficult to compress nonetheless it is measured as the best coolants for closed Brayton cycle power plants due to its better transport properties. Due to compression properties, its use resulted in the requirement of more mass, bigger size, higher cost and relatively more dynamic problems of rotatory machines in energy conversion system. The mixture of xenon with helium up to a molecular weight of <40 g/mol resulted in an increase of the coefficient of heat transfer as well as the significant increase in the loading of the compressor. Therefore, performance analysis is conducted for a novel design of helium xenon centrifugal compressor. The performance analysis is conducted with different molecular weight mixtures of helium xenon using similarity criteria. It is concluded that the use of helium xenon 40 g/mol is the optimum choice for space applications and 15 g/mol for closed Brayton cycle terrestrial power plants. • Centrifugal compressor performance analysis conducted using similarity criteria. • First time numerical simulation conducted considering similarity parameters. • Concluded that use of HeXe 40 g/mol is the optimum choice for space applications. • For CBC terrestrial power plants HeXe 15 g/mol is the optimum choice. [ABSTRACT FROM AUTHOR]

The recent expansion of studies at hydrothermal submarine vents from investigation of abiotic methane formation to include abiotic production of organics such acetate and formate, and rising interest in processes of abiotic organic synthesis on the ocean-world moons of Saturn and Jupiter, have raised interest in potential Earth analogs for investigation of prebiotic/abiotic processes to an unprecedented level. The deep continental subsurface provides an attractive target to identify analog environments where the influence of abiotic carbon cycling may be investigated, particularly in hydrogeological isolated fracture fluids where the products of chemical water-rock reactions have been less overprinted by the biogeochemical signatures of the planet's surficial water and carbon cycles. Here we report, for the first time, a comprehensive set of concentration measurements and isotopic signatures for acetate and formate, as well as the dissolved inorganic and organic carbon pools, for saline fracture waters naturally flowing 2.4 km below surface in 2.7 billion year-old rocks on the Canadian Shield. These geologically ancient fluids at the Kidd Creek Observatory were the focus of previous investigations of fracture fluid geochemistry, microbiology and noble gas-derived residence times. Here we show the fracture waters of Kidd Creek contain high concentrations of both acetate and formate with concentrations from 1200 to 1900 µmol/L, and 480 to 1000 µmol/L, respectively. Acetate and formate alone account for more than 50–90% of the total DOC – providing a very simple "organic soup". The unusually elevated concentrations and profoundly 13C-enriched nature of the acetate and formate suggest an important role for abiotic organic synthesis in the deep carbon cycle at this hydrogeologically isolated site. A variety of potential abiotic production reactions are discussed, including a radiolytically driven H, S and C deep cycle that could provide a mechanism for sustaining deep subsurface habitability. Scientific discoveries are beginning to reveal that organic-producing reactions that would have prevailed on Earth before the rise of life, and that may persist today on planets and moons such as Enceladus, Europa and Titan, can be accessed in some specialized geologic settings on Earth that provide valuable natural analog environments for the investigation of abiotic organic chemistry outside the laboratory. [ABSTRACT FROM AUTHOR]

The luminescence spectra for noble gases and their binary mixtures excited by Ar ions with energies up to 70 MeV were examined in the range of 200–980 nm. The emissions at the transitions of heteronuclear ionic molecules ArXe+, ArKr+, KrXe+ were studied for a gas-mixture, with a wide variation in the percentage composition. The noble gases atomic spectra are dominated by lines of (n + 1)p-(n + 1)s-transitions (2p-1s in Pashen's notation); lines of d-(n + 1)p-transitions were also observed. The distribution of radiation over 2p-levels of noble gas atoms was also measured. The sharp predominance of the fraction of radiation from the levels 2p 2 of Ar, 2p 6 of Kr and 2p 5 of Xe is partially explained by the relatively small values of the rate constants for the deactivation of these levels, by own atoms. The mechanisms of levels population under the excitation of noble gases by ionizing radiation are discussed. [ABSTRACT FROM AUTHOR]

To investigate paleoclimate conditions and mean annual ground temperatures at the time of infiltration, concentrations of dissolved atmospheric noble gases, 18O, 2H and 14C were studied in Sfax deep groundwater in southeastern of Tunisia. Carbon-14 corrected ages are up to 40 Ka BP suggesting that most of this water infiltrated during Late Pleistocene. Noble gas temperatures (NGTs) clearly show the presence of water that infiltrated under much cooler conditions than at present. According to the NGT's, the mean annual temperature in this mid latitude coastal site during the last glacial maximum (LGM) was 5.5 ± 1.0 °C colder than during the Holocene. This transition of Holocene –Pleistocene is well marked by a depletion of oxygen-18 isotope composition by 1.5‰ when compared to the modern rain water signature. Furthermore, the amount of excess air, which is closely linked to the magnitude of groundwater table fluctuations, provides further information on drought and wet period alternations during Late Pleistocene in Northern Africa. [ABSTRACT FROM AUTHOR]

Ureilites are equilibrated carbon-rich olivine-pyroxene rocks from the partially melted mantle of a large (>500 km diameter) heterogeneous parent body. Recently the ureilite parent body was interpreted as an incomplete mixture of material from two carbon-rich chondritic reservoirs, one (Mg-rich) with reduced iron, low Δ17O and low δ13C, and the other with oxidised iron, high Δ17O and high δ13C. Here we analyse noble gases (Ar, Kr and Xe) in six equilibrated (unbrecciated) ureilites from Northwest Africa (NWA 2236, NWA 7686, NWA 8049, NWA 8172, NWA 11032 and NWA 11368). We observe weak positive and negative correlations of Δ17O and Mg# with the elemental ratios of Ar/Xe and Kr/Xe, respectively, as well as a weak positive correlation of Mg# with the heavy isotopes of Xe. These correlations broadly support the idea of the two-component mixing hypothesis. Our analyses further suggest that the Mg-rich endmember was rich in Xe from presolar grains (HL-Xe) while the Mg-poorer component may have contained solar-derived noble gases. The observed correlations are less straightforward to reconcile with a recent model for the origin of the ureilite parent body, involving oxidation of metal by H 2 O from accreted ice with 'heavy' oxygen isotopes. [ABSTRACT FROM AUTHOR]

The migration of hydrocarbons from source-rock to reservoir is a critical stage in petroleum system evolution. However, as migration occurs along confined pathways over geologically rapid timescales it is challenging to place quantitative constraints on migration behaviour in terms of interaction with other basinal fluids, flux, and lengthscales associated with this process. Due to their inert nature, noble gases are ideal tracers of fluid provenance and physical processes in a variety of subsurface systems, and thus can serve as a potential geochemical indicator of migration distance. The recent proliferation of unconventional hydrocarbon production (i.e., production directly from source-rocks) allows for the analysis of fluids from these strata. Here we present noble gas data from natural gas samples produced from 27 related conventional and unconventional wells within the East Texas basin. These data enable characterisation of fluids during migration from source-rock to conventional reservoir. Unconventional gases and fluids are produced from the Haynesville shale (n = 8), and conventional gases and fluids are sourced from the overlying Cotton Valley (n = 5), Travis Peak (n = 9), and James Lime (n = 5) formations. Samples consist primarily of methane (>70%), with small contributions from longer-chain hydrocarbons, and other gases including CO 2 and N 2. Atmosphere-derived 36Ar, which is introduced into natural gas accumulations via interaction with groundwater during hydrocarbon generation and migration, is consistently higher in samples that have undergone a greater migration distance from the source interval. Thus, calculated volume ratios of gas-water interaction (V g /V w) show a far greater incidence of groundwater interaction in migrated samples. Radiogenically-produced 40Ar is also consistently elevated in migrated samples, despite these reservoirs being located in geologically younger strata. We derive the representative volume of rock required to produce the observed radiogenic 40Ar in each sample and show that samples that have migrated further have acquired radiogenic isotopes from larger volumes of rock. Furthermore, our volumetric parameters derived from atmospheric and radiogenic isotopes are consistent with a simple conceptual model of migration. We quantitatively apply this model to demonstrate that migration occurs along relatively localised pathways. Helium (3He/4He) and argon (40Ar/36Ar) isotopes are correlated and show elevated amounts of mantle-derived 3He and radiogenic 40Ar in migrated samples. We interpret this to represent mixing between a pristine source-rock signature and an endmember characterised by elevated 3He/4He and 40Ar/36Ar, likely representative of mantle-enriched groundwater circulating in the wider hydrogeological basin. Finally, we use an advection-diffusion model to show that enriched mantle 3He in the shallower strata and towards the southern edge of the basin can be explained by influx of mantle helium along the fault-bounded southern edge of the basin over timescales of millions of years. Together these approaches represent the first complete noble gas based characterization of a hydrocarbon system, sampling migration from source-rock to trap. We show conclusively that both atmospheric and radiogenic noble gases are entrained in the hydrocarbon phase during migration and that concentrations scale proportionally with migration distance, as greater volumes of groundwater and host rock are encountered. [ABSTRACT FROM AUTHOR]

Extraterrestrial materials have He and Ne isotopic compositions that are distinct from those of the Earth's surface. In order to track the extraterrestrial material accreted onto Earth during the Ediacaran period, we have analyzed the He and Ne isotopic composition of thirteen sedimentary rocks in the age range ~550–600 Ma, coming from the Huqf supergroup in Oman for which carbon and sulfur isotopic data have been characterized previously. 3He/4He ratios range between 0.006 ± 0.003 and 0.27 ± 0.01 R A , with R A being the atmospheric ratio. 3He/4He ratios show a positive relationship with 3He contents ranging between 0.6 and 31 × 10−13 cm3 STP·g−1. The 3He contents are within the literature data for 3 to 480 Myr old samples with evidence of IDP 3He (IDP for interplanetary dust particles), suggesting that extraterrestrial 3He is still retained in such old samples. 20Ne/22Ne ratios are close to or below the modern atmospheric ratio of 9.8 with the minimum value equal to 9.05 ± 0.03. 21Ne/22Ne ratios show a high range of variation, going from 0.0345 ± 0.0009 to 0.0935 ± 0.0023. The Ne isotopic compositions follow a nucleogenic trend similar to that of crustal fluids from the literature and predicted continental crust. However, one sample (3404) shows an unusual Ne isotopic composition with a lower 20Ne/22Ne at similar 21Ne/22Ne compared to the other samples. Two hypotheses can explain this singular Ne isotopic composition. First, it could be the result of a particular nucleogenic trend due to the presence of F-bearing minerals in this sample. SEM-EDS elemental mapping showed that although F- and Ca-rich phases, which could correspond to fluorites, are present in sample 3404. However, their abundance of ~0.15% seems too low to explain the unusual Ne isotopic composition. However, due to the high uncertainty of the calculations, we cannot totally rule out this hypothesis. Alternatively, the singular Ne isotopic composition could be due to the presence of a Ne-A component, a component characterizing pre-solar diamonds contained in chondrites. This would indicate that a major object impacted the Earth at the time the sediment was forming, between ~600 and ~550 Ma, which is coherent with the estimated age range of the Acraman impact in Australia. • Helium and neon isotopes have been measured in Huqf supergroup in Oman • Neon shows a peculiar isotopic signature suggesting either a major extraterrestrial impact or a peculiar enrichment in fluorine • Extraterrestrial 3He has been observed [ABSTRACT FROM AUTHOR]

CO 2 sequestration in the form of carbonate minerals via alteration of oceanic crust and upper mantle is an important part of the global carbon cycle, but the annual rate of CO 2 mineralization is not well quantified. This study aimed to constrain groundwater ages within the Samail ophiolite, Sultanate of Oman. Such ages could provide upper bounds on the time required for ongoing low temperature CO 2 mineralization. While we were able to estimate apparent groundwater ages for modern waters, results from hyperalkaline boreholes and springs were disappointing. Waters from boreholes and hyperalkaline springs within the ophiolite were characterized using multiple environmental tracers including tritium (3H), noble gases (3He, 4He, Ne, Ar, Kr, Xe), stable isotopes (δ 18 O, δ 2 H), and chemical parameters (pH, Ca, Mg, DIC, etc.). Shallow peridotite groundwater and samples from boreholes near the mantle transition zone have a pH < 9.3, are 4-40 yrs old, have little to no non-atmospheric He accumulation, NGTs (noble gas temperatures) equivalent to the modern mean annual ground temperature, and stable isotopes within the range of current local precipitation. In contrast, hyperalkaline springs and deeper samples from peridotite boreholes have pH > 10, are pre-H-bomb (older than 1952), have significant non-atmospheric helium accumulation (30-70% of dissolved helium), often are isotopically heavier (enriched in δ 18 O), and can have NGTs 6-7 °C lower than the modern ground temperature. These differences suggest that groundwater in deep (>50 m) peridotite aquifers is considerably older than shallow groundwater in peridotite and water in deeper aquifers near the mantle transition zone. Unfortunately, how much older remains an open question. The low NGT of groundwater from one deep (300 m) peridotite borehole indicates it is probably glacial in origin. If so, it must date back to at least the late Pleistocene, the most recent glacial period; He accumulation suggests it could be from 20-220 ka. The inefficacy of this suite of environmental tracers to quantitatively estimate apparent groundwater age for hyperalkaline fluids necessitates the use of different techniques. Future work to constrain groundwater ages should utilize a packer system to isolate discrete depth intervals within boreholes and less common environmental tracers such as 39Ar and 81Kr. • Environmental tracers were used to evaluate water in peridotite aquifers in Oman. • Shallow peridotite and deeper mantle transition zone boreholes contain modern water. • pH > 11 boreholes and springs contain old water (apparent age still unknown). • pH > 11 water has pre-bomb 3H levels and accumulation of non-atmospheric He. • pH > 11 water can be glacial, with lower recharge temperatures and δ 18 O enrichment. [ABSTRACT FROM AUTHOR]

Abstract Dissolved noble gases are ideal conservative tracers of physical processes in the Earth system due to their chemical and biological inertness. Although bulk concentrations of dissolved Ar, Kr, and Xe are commonly measured to constrain physical models of atmosphere, ocean, and terrestrial hydrosphere processes, stable isotope ratios of these gases (e.g. 136Xe/129Xe) are seldom used because of low signal-to-noise ratios. Here we present the first results from a new method of dissolved gas sampling, extraction and analysis that permits measurement of stable Ar, Kr, and Xe isotope ratios at or below ∼5 per meg amu−1 precision (1 σ), two orders-of-magnitude below conventional Kr and Xe isotopic measurements. This gain in precision was achieved by quantitative extraction and subsequent purification of dissolved noble gases from 2-L water samples via helium sparging and viscous dual-inlet isotope ratio mass spectrometry. We have determined the solubility fractionation factors (α sol) for stable Ar, Kr, and Xe isotope ratios between ∼2 and 20 °C via laboratory equilibration experiments. We have also conducted temperature-controlled air-water gas exchange experiments to estimate the kinetic fractionation factors (α kin) of these isotope ratios. We find that both α sol and α kin , normalized by isotopic mass difference (Δm), decrease in magnitude with atomic number but are proportional to Δm for isotope ratios of the same element. With the new ability for high precision isotopic measurements, we suggest that dissolved Kr and Xe isotope ratios in groundwater represent a promising, novel geochemical tool with important applications for groundwater modeling, water resource management, and paleoclimate. Highlights • We present a method for high-precision dissolved Ar, Kr, and Xe isotope analyses. • Solubility and kinetic fractionation factors are experimentally determined. • Ar isotopes exhibit the greatest sensitivity to these fractionation processes. • Kr and Xe fractionation factors are proportional to isotopic mass difference. • Weak Kr and Xe fractionation in water is promising for paleoclimate applications. [ABSTRACT FROM AUTHOR]

Here, we report that the Finero phlogopite peridotite massif, southern Italy, a sliver of the former subcontinental lithospheric mantle (SCLM), experienced two stages of fluid/melt percolation, which had different origins and scales in the mantle wedge based on noble gas analysis and the deformation structure. In the field investigation, we found a mylonite zone several tens of meters wide in the massif, inferred to have been caused by deformation in the mantle. Systematic differences in noble gas compositions between samples from inside and outside the mylonite zone reflect two stages of fluid/melt infiltration. In the first event, the fluid/melt with a noble gas mixture of seawater, radiogenic, and mantle components penetrated the Finero SCLM. It likely occurred simultaneously with the famous metasomatism that crystallized phlogopite and amphibole throughout the massif. This first event produced a 4He/40Ar ratio much higher than those of the convecting mantle and crustal components, probably during metasomatism by hydrous melt derived from the slab in the mantle wedge. The second event was probably synchronous with the development of mylonitization and locally supplied seawater-rich components. The 40Ar/36Ar ratios tend to be atmospheric as mylonitization progresses. Our results provide two insights: (i) the first demonstration of the formation of extremely high He/Ar ratios during mantle metasomatism of natural samples and (ii) differences in the deformation structure affecting the noble gas composition and distribution in the SCLM. Regarding (i), the elemental fractionation can be attributed to two factors: one is the difference in the solubility between noble gas elements in particular minerals in the slab, and the other is the difference in the diffusion coefficients of He and Ar. Our results imply that the recycling of volatiles within subduction zones is significantly influenced by the thermal structures of slabs. This is because these thermal structures control the stability of hydrous minerals on the slabs, temperature conditions, and potentially the efficiency of diffusion in mantle wedges. • Two types of samples, coarse-grained and mylonitized harzburgites from the phlogopite peridotite unit, were used. • The He and Ar compositions reflect the two stages of fluid/melt infiltration of the Finero phlogopite peridotite. • The coarse-grained harzburgites show extremely high He/Ar, probably formed during mantle metasomatism. • The high He/Ar may result from the He and Ar difference in solubilities in the slab or that in diffusivities in the mantle. [ABSTRACT FROM AUTHOR]

• Stream metabolism essential to carbon cycling and food-web studies. • Hydropower plants can physically supersaturate water with dissolved gases. • New method using O 2 :Ar ratio allows estimation of metabolism in tail water ecosystems. • Results were in good agreements with concomitant changes in dissolved CO 2 • New method more applicable with portable mass inlet mass spectrometers (MIMS). The estimation of whole stream metabolism, as determined by photosynthesis and respiration, is critical to our understanding of carbon cycling and carbon subsidies to aquatic food-webs. The mass development of aquatic plants is a worldwide problem for human activities and often occurs in regulated rivers, altering biodiversity and ecosystem functions. Hydropower plants supersaturate water with gases and prevent the use of common whole stream metabolism models to estimate ecosystem respiration. Here we used the inert noble gas argon to parse out biological from physical processes in stream metabolism calculations. We coupled the O 2 :Ar ratio determined by gas chromatography in grab samples with in-situ oxygen concentrations measured by an optode to estimate aquatic plant photosynthesis and ecosystem respiration during supersaturation events through a parsimonious approach. The results compared well with a more complicated two-station model based on O 2 mass balances in non-supersatured water, and with associated changes in dissolved CO 2 (or dissolved inorganic carbon). This new method provides an independent approach to evaluate alternative corrections of dissolved oxygen data (e.g. through the use of total dissolved gases) in long term studies. The use of photosynthesis-irradiance models allows the determination of light parameters such as the onset of light saturation or low light use efficiency, which could be used for inverse modelling. The use of the O 2 :Ar approach to correct for oversaturation may become more applicable with the emergence of portable mass inlet mass spectrometers (MIMS). Photosynthesis was modest (2.9-5.8 g O 2 m2 day−1) compared to other rivers with submerged vegetation, likely indicating nutrient co-limitations (CO 2 , inorganic N and P). Respiration was very low (-2.1 to -3.9 g O 2 m2 day−1) likely due to a lack of allochthonous carbon supply and sandy sediment. [Display omitted] [ABSTRACT FROM AUTHOR]

Here, we characterize the temporal evolution of volatiles during the Tajogaite eruption by analyzing the elemental (He-Ar-CO 2 -N 2) and isotopic (He-Ar-Ne) composition of fluid inclusions (FI) in phenocrysts (olivine+pyroxene) identified in erupted lavas. Our 2021 lava samples identify substantial temporal variations in volatile composition. We show that, during the 2021 Tajogaite eruption, the He-CO 2 -N 2 concentrations in FI increased since October 15th; this increase was accompanied by increasing 40Ar/36Ar ratios (from ∼300 to >500), and paralleled a major shift in bulk lava chemistry, with increasing Mg contents (Mg#, from 47 to 52 to 55–59), CaO/Al 2 O 3 (from 0.65 to 0.74 to 0.75–0.90), Ni and Cr, and decreasing TiO 2 , P 2 O 5 and incompatible elements. The olivine core composition also became more forsteritic (from Mg# = 80–81 to Mg# = 84–86). Mineral thermobarometry and FI barometry results indicate that the eruption was sustained by magmas previously stored in at least two magma accumulation zones, at respectively ∼6–12 km and 15–30 km, corroborating previous seismic and FI evidence. We therefore propose that the compositional changes seen throughout the eruption can be explained by an increased contribution - since early/mid-October - of more primitive, less-degassed magma from the deeper (mantle) reservoir. Conversely, Rc/Ra values (3He/4He ratios corrected for atmospheric contamination) remained constant throughout the whole eruption at MORB-like values (7.38 ± 0.22 Ra, 1σ), suggesting an isotopically homogeneous magma feeding source. The Tajogaite He isotope signature is within the range of values observed for the 1677 San Antonio lavas (7.37 ± 0.17Ra, 1σ), but is more radiogenic than the 3He/4He values (>9 Rc/Ra) observed in the Caldera de Taburiente to the north. The 3He/4He ratios (6.75 ± 0.20 Ra, 1σ) measured in mantle xenoliths from the San Antonio volcano indicate a relatively radiogenic nature of the mantle beneath the Cumbre Vieja ridge. Based on these results and mixing modeling calculations, we propose that the homogeneous He isotopic signatures observed in volatiles from the Tajogaite/San Antonio lavas reflect three component mixing between a MORB-like source, a radiogenic component and small additions (6–15%) of a high 3He/4He reservoir-derived (>9Ra) fluid components. The simultaneous occurrence of high 3He/4He (>9Ra)- and MORB-like He signatures in northern and southern La Palma is interpreted to reflect small-scale heterogeneities in the local mantle, arising from spatially variable proportions of MORB, radiogenic, and high 3He/4He components. • He-CO 2 -N 2 contents inside FI increase during the 2021 Tajogaite eruption. • An increase in 40Ar/36Ar and bulk Mg# suggest the arrival of a more primitive magma. • A dual magma storage zone feeding the Tajogaite eruption explains uniform 3He/4He. • He-Sr-Nd-W systematics records an isotopically homogeneous magmatic source. • A mixing of high 3He/4He, MORB and radiogenic components in the local mantle. [ABSTRACT FROM AUTHOR]

Highlights • Gas-surface potentials for Al-inert gas systems developed using DFT simulations. • Gas temperature exerts a weak effect on energy accommodation coefficient (α). • Effective energy exchange and greater α for deeper potential wells. • α vs µ curve characterized by a maximum at a specific mass ratio (µ = M g / M s). • Mass ratio exerts stronger effect than well depth on α (α Ar > α Xe > α He). ABSTRACT Molecular dynamics (MD) simulations are conducted to determine non-equilibrium energy accommodation coefficients for aluminum-inert gas systems for a surface temperature of 300 K and gas temperatures in the range of 1000–3000 K. Three different gases are considered: helium, argon, and xenon. Density functional theory (DFT) simulations are conducted to obtain gas-surface interaction potentials and these are then fed as inputs to MD simulations. Effects of temperature and atomic weight of the gas on the accommodation coefficient are explored. Calculated accommodation coefficients are of the order of 0.1 and it is weakly dependent on gas temperature, in contrast to the predictions of Altman's model. Results suggest that energy accommodation coefficients are greatest for argon and lowest for helium for all temperatures considered in this study. This is explained by independently probing the effects of well depth and mass ratio and determining the relative importance of these two effects for the systems under consideration. Lorentz–Berthelot mixing rules substantially over predict the potential well depth, resulting in higher accommodation coefficients. The underlying physics and mechanisms are unraveled using a simple 1-D collision model. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

The ratio of 3 He and 22 Ne varies throughout the mantle. This observation is surprising because 3 He and 22 Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3 He/ 22 Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3 He/ 22 Ne of OIB mantle approaches planetary precursor 3 He/ 22 Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3 He/ 22 Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3 He/ 22 Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3 He/ 22 Ne. Subduction of high 3 He/ 22 Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3 He/ 22 Ne. Mixing models suggest that to preserve a high 3 He/ 22 Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3 He/ 22 Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing. [ABSTRACT FROM AUTHOR]

Site-specific and regional analysis of time-series hydrologic and geochemical data collected from 15 monitoring wells in the Piceance Basin indicated that a leaking gas well contaminated shallow groundwater with thermogenic methane. The gas well was drilled in 1956 and plugged and abandoned in 1990. Chemical and isotopic data showed the thermogenic methane was not from mixing of gas-rich formation water with shallow groundwater or natural migration of a free-gas phase. Water-level and methane-isotopic data, and video logs from a deep monitoring well, indicated that a shale confining layer ~125 m below the zone of contamination was an effective barrier to upward migration of water and gas. The gas well, located 27 m from the contaminated monitoring well, had ~1000 m of uncemented annular space behind production casing that was the likely pathway through which deep gas migrated into the shallow aquifer. Measurements of soil gas near the gas well showed no evidence of methane emissions from the soil to the atmosphere even though methane concentrations in shallow groundwater (16 to 20 mg/L) were above air-saturation levels. Methane degassing from the water table was likely oxidized in the relatively thick unsaturated zone (~18 m), thus rendering the leak undetectable at land surface. Drilling and plugging records for oil and gas wells in Colorado and proxies for depth to groundwater indicated thousands of oil and gas wells were drilled and plugged in the same timeframe as the implicated gas well, and the majority of those wells were in areas with relatively large depths to groundwater. This study represents one of the few detailed subsurface investigations of methane leakage from a plugged and abandoned gas well. As such, it could provide a useful template for prioritizing and assessing potentially leaking wells, particularly in cases where the leakage does not manifest itself at land surface. [ABSTRACT FROM AUTHOR]

Ophiolitic serpentinites and secondary peridotites formed by serpentinite dehydration were investigated to improve constraints on the fates of noble gases and halogens during subduction zone metamorphism. The work extends previous studies to encompass F and four stages of serpentinization and serpentinite dehydration including: (i) oceanic serpentinites preserving the features of seafloor serpentinization; (ii) subducted high grade (olivine bearing) antigorite-serpentinites; (iii) spinifex and granofels textured chlorite harzburgites; and (iv) a garnet peridotite. Serpentinites and secondary peridotites from different ophiolites are shown to have characteristic ranges of 40 Ar/ 36 Ar: chrysotile and antigorite serpentinites from Erro Tobbio (Western Alps) have 40 Ar/ 36 Ar of ∼ 296–390; antigorite serpentinites and chlorite harzburgites from Cerro del Almirez (Betic Cordillera) have 40 Ar/ 36 Ar of ∼ 340–600, and chlorite harzburgites and garnet peridotites from Cima di Gagnone (Swiss Alps) have 40 Ar/ 36 Ar of ∼ 600–1100. The variation of 40 Ar/ 36 Ar is unrelated to metamorphic grade at each locality but is broadly correlated with variation in other radiogenic isotopes ( 206 Pb/ 204 Pb and 87 Sr/ 86 Sr) between localities. This suggests excess 40 Ar was derived from terrigenous sediments with characteristic ranges of 40 Ar/ 36 Ar and 87 Sr/ 86 Sr in different subduction zones. The secondary chlorite harzburgites have 20 Ne/ 36 Ar ratios of greater than seawater, contain parentless (or excess) 4 He, and have higher F concentrations than any of the serpentinites investigated. The 20 Ne/ 36 Ar is broadly correlated with 40 Ar/ 36 Ar in samples from Cerro del Almirez suggesting derivation of excess 40 Ar and atmospheric 20 Ne from a common source. The chlorite is shown to have higher concentrations of F, Ne and other noble gases than coexisting olivine and enstatite, which contain fluid-related inclusions. The high F content and high 20 Ne/ 36 Ar ratios of the chlorite harzburgites are ascribed to fluxing of dehydrating serpentinites with F-, 40 Ar-, 4 He- and 20 Ne-rich fluids derived from metasediments in the subducting slab, and an inferred high compatibility of F and Ne in chlorite. The garnet peridotite from Cima di Gagnone records the final and complete dehydration of serpentinite. Based on the analysis of mineral separates minimally affected by retrogression (marked by garnet breakdown and the appearance of Cl-rich hornblende), nominally anhydrous garnet peridotite retains Cl, Br, I and non-radiogenic noble gas concentrations up to an order of magnitude higher than average depleted mantle. The data are consistent with serpentinised lithosphere and related secondary peridotites as major sources of deeply subducted seawater-derived volatiles in the Earth’s mantle. The data also demonstrate that the relative abundances of volatiles subducted into the mantle are controlled by multiple factors including: original seafloor alteration, the relative compatibilities of different noble gases and halogens in minerals forming during different stages of subduction and chemical exchange between different lithologies during subduction. The combination of these processes has produced elevated 20 Ne/ 36 Ar in chlorite harzburgites from two unrelated localities. This suggests that subduction of atmospheric Ne could be significantly more efficient than previously realised, which has implications for interpretation of the mantles primordial 20 Ne/ 22 Ne ratio and how the Earth accreted. [ABSTRACT FROM AUTHOR]

A non-destructive spectroscopic method based on core level photoelectron energy loss spectra (PEELS) measured at variable emission angle is proposed for depth profiling of implanted atoms in a solid matrix. Extrinsic plasmon excitation during the photoelectron path to the solid surface being the dominant loss mechanism and neglecting elastic scattering, analytic relations are obtained for several depth profiles (Gaussian, triangular, square) between calculated relative intensities of first-order and second-order plasmon excitation peaks and the distribution characteristics (average depth and width ). This method is illustrated by PEELS analysis of a model system, namely shallow implantation of argon ions ( E ION  = 2.0 keV, 35° incidence, 3 ML) into Al(001) matrix. The average depth ( d PEELS  = 2.0 ± 0.1 nm) of subsurface Ar bubbles obtained from energy loss spectra of Ar 2p photoelectrons (inelastic mean free path IMFP = 2.15 nm at E KIN  = 1011 eV) is significantly smaller than the average depth of the distribution calculated from SRIM code ( d SRIM  = 3.8 nm). This discrepancy, found for all model depth profiles, is attributed to significant sputtered thickness (≈1.7 nm) of Al, as well as some possible diffusion of argon-vacancy complexes towards the surface during Ar ion implantation. [ABSTRACT FROM AUTHOR]

Groundwater dating by radio-krypton ( 81 Kr; half-life of about 229,000 years) was applied to the sedimentary basin aquifer of the North China Plain (NCP). Krypton gas extracted from deep groundwater in the Coastal Plain was analyzed for 81 Kr/Kr ratios by Atom Trap Trace Analysis, which yielded normalized ratios of 0.05 to 0.20, corresponding to groundwater residence times of 0.5–1 million years. Helium isotope compositions were determined on groundwater samples collected from the Central Plain and the Coastal Plain along a flow path of about 200 km. Helium dissolved in the groundwater samples are a mixture of atmospheric, crustal radiogenic and mantle derived sources. Mantle derived 3 He contributes up to 30% of the total, and the area of occurrence coincides with zones of previous magmatic/tectonic activities. By contrast, >90% of 4 He is derived from crustal reservoirs and correlates with 81 Kr ages. The absolute groundwater ages ( 81 Kr) and radiogenic 4 He concentrations permit us to calibrate the 4 He flux into the aquifer as well as the vertical diffusion rate of 4 He to utilize the radiogenic 4 He in groundwater as a quantitative age tracer. Previously, groundwater showed 14 C activities near the limit of detection (30–40 k yr), in contrast Kr and radiogenic 4 He data reveal progressively older ages from the recharge area to the Coastal Plain, from <20,000 yr to 0.5 to 1 Ma along the flow path of the NCP aquifers. [ABSTRACT FROM AUTHOR]

Noble gas concentrations in water are ideal probes to study surface and groundwater dynamics by providing indications of flow paths, connectivity between aquifers, and water residence times. Recent studies have pointed out anomalies in noble gas concentrations derived from groundwater in fractured systems, likely due to the presence of rapid infiltration and preferential flow paths. It has been suggested that such anomalies originate from conditions at high altitude when rainwater has had insufficient time to equilibrate with surface conditions. Potential sources also include snow, never previously investigated for its noble gas composition. In order to document the noble gas signature in snow, noble gas concentrations and isotopic ratios were measured in samples collected between 2013 and 2016. Here, we outline a methodology for measuring noble gases in collected snow samples that involves a two-step procedure where He and Ne are measured independently from Ar, Kr and Xe. Our results show that snow has elevated He concentrations with depleted concentrations of other noble gases with respect to air-saturated water (ASW). However, samples collected in 2013 show significant He and Ne depletion compared to those collected in 2014, 2015 and 2016. We suspect that, despite the well-controlled conditions of storage, the 2013 batch sample might have significantly re-crystalized, leading to a reduction in the characteristic diffusion length scale of the snow crystal structure. In addition, He and Ne concentrations display relatively low variability among all measured samples (<14%), while Ar, Kr and Xe show large variability in their concentrations (>40%). Our results confirm that He and Ne, which have small atomic radii, are likely dissolved within the ice/snow crystal lattice itself while the heavy noble gases (Ar, Kr and Xe) are likely accommodated by fluid inclusions, including air and quenched liquid water inclusions. Consequently, the smaller variability recorded in light noble gases may be due to the fact that He and Ne are hosted within plentiful host sites within the snow crystal lattice structure, whereas heavy noble gases rely on the presence of comparatively rare fluid inclusions. [ABSTRACT FROM AUTHOR]

The effect of the type of C3–C6 alcohol, solution temperature, and dissolved gas on the rate of Au(III) reduction was investigated in NaAuCl 4 aqueous alcohol solution with a 200-kHz ultrasound irradiation system. It was confirmed in the presence of C3–C6 alcohol that more highly hydrophobic alcohols more effectively accumulated at the argon bubble interface region, and the reducing radicals formed here. To avoid changes in the bubble temperature during collapsing bubble, the effects of the solution temperature on the rate of Au(III) reduction and on the rate of formation of the gaseous compounds (CO, CO 2 , CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 ) were investigated in the presence of low concentration (1.0-mM) of 1-hexanol. Both of the rates showed a good relationship with the gas solubility: the amount of dissolved gas at different solution temperatures affected the number of high-temperature bubbles formed. The changes in the concentrations of the gaseous compounds formed from 1-hexanol degradation suggested that CO and the pyrolysis radicals acted as reductants. Finally, the effect of the type of dissolved gas was investigated in the presence of 1.0-mM Au(III) and 1.0-mM 1-hexanol. The rates of 1-hexanol degradation, Au(III) reduction, and gaseous compound formation increased in the order He < Ne < Ar < Kr < Xe, and this order was related to the amount of noble gas dissolved in the aqueous solution. [ABSTRACT FROM AUTHOR]

We show that fluid volumes residing within the Precambrian crystalline basement account for ca 30% of the total groundwater inventory of the Earth (> 30 million km 3 ). The residence times and scientific importance of this groundwater are only now receiving attention with ancient fracture fluids identified in Canada and South Africa showing: (1) microbial life which has existed in isolation for millions of years; (2) significant hydrogen and hydrocarbon production via water–rock reactions; and (3) preserving noble gas components from the early atmosphere. Noble gas (He, Ne, Ar, Kr, Xe) abundance and isotopic compositions provide the primary evidence for fluid mean residence time (MRT). Here we extend the noble gas data from the Kidd Creek Mine in Timmins Ontario Canada, a volcanogenic massive sulfide (VMS) deposit formed at 2.7 Ga, in which fracture fluids with MRTs of 1.1–1.7 Ga were identified at 2.4 km depth (Holland et al., 2013); to fracture fluids at 2.9 km depth. We compare here the Kidd Creek Mine study with noble gas compositions determined in fracture fluids taken from two mines (Mine 1 & Mine 2) at 1.7 and 1.4 km depth below surface in the Sudbury Basin formed by a meteorite impact at 1.849 Ga. The 2.9 km samples at Kidd Creek Mine show the highest radiogenic isotopic ratios observed to date in free fluids (e.g. 21 Ne/ 22 Ne = 0.6 and 40 Ar/ 36 Ar = 102,000) and have MRTs of 1.0–2.2 Ga. In contrast, resampled 2.4 km fluids indicated a less ancient MRT (0.2–0.6 Ga) compared with the previous study (1.1–1.7 Ga). This is consistent with a change in the age distribution of fluids feeding the fractures as they drain, with a decreasing proportion of the most ancient end-member fluids. 129 Xe/ 136 Xe ratios for these fluids confirm that boreholes at 2.4 km versus 2.9 km are sourced from hydrogeologically distinct systems. In contrast, results for the Sudbury mines have MRTs of 0.2–0.6 and 0.2–0.9 Ga for Mines 1 and 2 respectively. While still old compared to almost all groundwaters reported in the literature to date, these younger residence times compared to Kidd Creek Mine are consistent with significant fracturing created by the impact event, facilitating more hydrogeologic connection and mixing of fluids in the basin. In all samples from both Kidd Creek Mine and Sudbury, a 124-128 Xe excess is identified over modern air values. This is attributed to an early atmospheric xenon component, previously identified at Kidd Creek Mine but which has to date not been observed in fluids with a residence time as recent as 0.2–0.6 Ga. The temporal and spatial sampling at Kidd Creek Mine is also used to verify our proposed conceptual model which provides key constraints regarding distribution, volumes and residence times of fracture fluids on the smaller, regional, scale. [ABSTRACT FROM AUTHOR]

In the Southern Volcanic Zone (Chile-Argentina), the active Caviahue-Copahue Volcanic Complex (CCVC) is approximately 30 km east of the main N-S trending volcanic front, where the Nazca Plate subducts under the South American Plate. CCVC activity includes three major stages: the 5–4 Ma old Ante-Caviahue series, the 2.6 Ma old Caviahue series, and Copahue volcano that has been active since 1.2 Ma ago. CCVC volcanism results from extension and slab steepening since 2.6 Ma ago that produces the asthenospheric influx under Copahue. Here we investigate the link between the geochemical and multi-element (He, Li, N, Sr, Nd, Hf, and Pb) isotopic composition of CCVC magmas and evolution of the subduction regime since 5 Ma ago. The CCVC magmatic source is characterized by a mid-ocean ridge basalt-like mantle signature (high 3 He/ 4 He = 8 Ra) and a high δ 15 N (+ 5.8‰) related to subducted sediments. These data suggest a significant degree of N recycling, but low 4 He recycling over time. Trace element and isotope modeling indicates that the influence of sediments is strongest in Copahue magmatism, whereas the mantle wedge contribution was strongest in Caviahue and Ante-Caviahue magmatism. The light rare earth element-enriched nature of Copahue rocks (compared to Caviahue and Ante-Caviahue rocks) is more likely due to incorporation of sediments from the slab rather than a very low degree of partial melting. The low δ 7 Li (0.44 ± 0.31‰ to 1.42 ± 0.17‰) of Copahue and Caviahue magmas indicates the contribution of a mature slab depleted in 7 Li during previous dehydration events. Conversely, Ante-Caviahue rocks have a moderate δ 7 Li value (2.63‰), suggesting input from a less-dehydrated slab. This is consistent with trace element data, showing that the Copahue (and Caviahue) source is less enriched in fluid-mobile elements (low Ba/Th and U/Th ratios). We propose that the geochemical and isotopic evolution of CCVC magmas records the evolution of the subduction regime under the CCVC. Ante-Caviahue magmas were produced in an arc front extensional regime in which the shallow, extensively dehydrating slab delivered large amounts of fluids to the melting zone. Later slab steepening caused the volcanic front to migrate west of the CCVC, probably due to the beginning of subduction in the Mocha fault zone (south of CCVC) 2.5–5 Ma ago. Crustal attenuation and asthenospheric influx under the CCVC produced Caviahue magmatism. Further progressive slab steepening and successive dehydration events produced a mature slab and dry mantle wedge that explain the particular signature of Copahue magmas. [ABSTRACT FROM AUTHOR]

The evolution of Mars' atmosphere to its currently thin state incapable of supporting liquid water remains poorly understood and has important implications for Martian climate history. Martian meteorites contain trapped atmospheric gases that can be used to constrain both the timing and effectiveness of atmospheric escape processes. In this paper, measurements of xenon isotopes in two ancient Martian meteorites, ALH 84001 and NWA 7034, are reported. The data indicate an early episode of atmospheric escape that mass fractionated xenon isotopes culminated within a few hundred million years of planetary formation, and little change to the atmospheric xenon isotopic composition has occurred since this time. In contrast, on Earth atmospheric xenon fractionation continued for at least two billion years ( Pujol et al., 2011 ). Such differences in atmospheric Xe fractionation between the two planets suggest that climate conditions on Mars may have differed significantly from those on Archean Earth. For example, the hydrogen escape flux may not have exceeded the threshold required for xenon escape on Mars after 4.2–4.3 Ga, which indicates that Mars may have been significantly drier than Earth after this time. [ABSTRACT FROM AUTHOR]

When tuned for maximum sensitivity, the electron bombardment ion source on the ANU (the Australian National University) Helix MC Plus noble gas mass spectrometer produces an Ar ion beam that is mass discriminated as a function of Ar partial pressure. This effect can be reduced substantially or eliminated by adjusting the repeller and trap voltages, although with a sensitivity loss of up to 50%. A recommended procedure for tuning an ion source to reduce pressure dependent mass discrimination is described. Similar procedures can be applied to other noble gases and other ion sources to ensure that pressure dependent mass discrimination is avoided. [ABSTRACT FROM AUTHOR]

Petrographic shock indicators and noble gas signatures are studied in two ordinary chondrites, Grove Mountain (GRV) 13083 (H4) and GRV 13095 (L5), from Antarctica to investigate the degree of shock metamorphism and impact related chronologies on H and L chondrite parent bodies. In the study, we have combined both noble gas signatures and petrographic observations to understand impact effects. Based on the impact features in silicates and metal-troilite assemblages, the shock stages of the samples are classified as S6 and S5 for GRV 13095 (L5) and GRV 13083 (H4) respectively. The nominal K-Ar gas retention age of GRV 13095 (L5, S6) using bulk sample is estimated as 459 ± 13 Ma, supporting the recent major catastrophic break up event at 470 Ma on the L-chondrite parent body. The cosmic ray exposure age based on He, Ne and Ar noble gas measurements is estimated as 14.1 ± 2.5 Ma. The radiogenic gas contents in GRV 13095 (avg. 4 He = 61.5 × 10 −8 ccSTP/g and avg. 40 Ar = 173.5 × 10 −8 ccSTP/g) are observed as depleted. The depletion in radiogenic gases is consistent with the severe shock metamorphism in GRV 13095 as indicated by olivine-ringwoodite transformation in it. The estimated nominal K-Ar age of 3.67 ± 0.26 Ga for GRV 13083 shows that it falls in the major impact age distribution between 3.5 and 4.0 Ga among H-chondrites. The cosmic ray exposure age of GRV 13083 is 3.9 ± 0.7 Ma, which is younger than the major peak in the exposure age distribution for H-chondrites. The He gas retention ages in both samples are found to be younger/lower than their respective nominal K-Ar ages, which could be due to partial loss of radiogenic He. Trapped gas loss along with radiogenic gas losses in both samples, are the adverse effects of shock metamorphism. [ABSTRACT FROM AUTHOR]

We report noble gas (He, Ne, Ar) signatures of chromite and olivine separates from the Luobusa chromitites in Tibet to better understand the volatile compositions trapped in the minerals, and further to trace the origin of melts responsible for formation of the chromite deposits. The studied samples can be divided into two groups based on petrography and distinct noble gas signatures. Group I samples are free of carbonates and have 3 He/ 4 He ratios from 0.81 to 2.36 Ra (where Ra is the 3 He/ 4 He ratio of air = 1.4 × 10 − 6 ) and air-like Ne and Ar isotopic compositions irrespective of chromitite structure types. Most 3 He/ 4 He ratios of Group I samples are higher than air, suggesting apparent presence of mantle volatiles. Given the 4 He/ 20 Ne and 3 He/ 36 Ar several orders of magnitude higher than air, negligible contributions are from the atmospheric helium. The observed He isotope compositions thus can be regarded as a two-component mixture of mantle-derived and radiogenic He. A broadly positive correlation between 3 He and 36 Ar in nodular chromitite samples indicates a source mixing between mantle and recycled noble gases but not due to shallow air contamination. In addition, the wide distribution range of 20 Ne/ 36 Ar also supports a subduction-related origin of neon and argon. Combined with major element data, the most appropriate tectonic setting to generate such noble gas signatures in Group I samples is subduction zone (probably forearc) where favorable conditions are present for the formation of the chromitites. In contrast, Group II samples containing carbonates have much more radiogenic 3 He/ 4 He ratios of 0.03 to 0.3 Ra but much less radiogenic 40 Ar/ 36 Ar ratios of 344 to 420. In combination with the occurrence of carbonate veins it is suggested that Group II samples are predominated by supracrustal components that may be imparted during or after the emplacement stage. A comparison of these two group samples indicates that the primary noble gas signatures reflecting the characteristics of ore-forming melts can be preserved in chromite and olivine grains (Group I samples) and thus used to trace the origin of podiform chromitites. [ABSTRACT FROM AUTHOR]

The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected 3 He/ 4 He ratios (with atmospheric He removed) range widely from 0.05 to 35.8 times the air 3 He/ 4 He ratio (R A ), with a median of 1.43 R A . Forty-one percent of measured 3 He/ 4 He ratios are ≥4 R A , corresponding to ≥50% mantle He assuming a mantle ratio of 8 R A . These results suggest that mafic magmas were part of the magmatic-hydrothermal system underlying Goldfield and Tonopah, and that associated mantle-sourced volatiles may have played a role in ore formation. The three highest corrected 3 He/ 4 He ratios of 17.0, 23.7, and 35.8 R A indicate a primitive mantle He source and are the highest yet reported for any epithermal-porphyry system and for the Cascades arc region. Compiled 3 He/ 4 He measurements from epithermal-porphyry systems in subduction-related magmatic arcs around the world (n = 209) display a statistically significant correlation between 3 He/ 4 He and Au-Ag grade. The correlation suggests that conditions which promote higher fluid inclusion 3 He/ 4 He ratios (abundance of mantle volatiles and focused upward volatile transport) have some relation to conditions that promote higher Au-Ag grades (focused flow of metal-bearing fluids and efficient chemical traps). Results of this and previous investigations of He isotopes in epithermal-porphyry systems are consistent with the hypothesis posed in recent studies that mafic magmas serve an important function in the formation of these deposits. [ABSTRACT FROM AUTHOR]

We investigate the energetics and clustering trend of noble gas atoms (He, Ne, and Ar) in bcc Fe, and their interactions with vacancy or H/He impurities using first-principles calculations. We determine the formation energy of single and double noble gas atoms inside Fe host lattice as well as the resulted volume changes. The Ne/Ar formation energy is two and three times that of He. The attraction between Ne/Ar and vacancy is stronger than He-vacancy, indicating higher dissolution energy of Ne/Ar. The interstitial Ne-Ne/Ar-Ar pairs have stronger attractions (−1.91 eV/−1.40 eV) than He-He (−0.37 eV), forming stable <110> configurations. Such strong attraction means that He/Ne/Ar tend to aggregate, which can be well explained by the lower electron density induced by interstitial noble gas atoms and its strong repulsion with Fe atoms. Moreover, H/He energetically prefers to occupy the tetrahedral sites nearby Ne/Ar atom. The attraction energies of He-Ne/He-Ar pairs (−1.01 eV/-0.85 eV) are much stronger than those of H-Ne/H-Ar (−0.22 eV/−0.10 eV) and their charge density differences are discussed. The distinct attraction strengths by various noble gas atoms provide a preliminary explanation for the difference in irradiation effects on Fe solid by He, Ne, Ar, and He+H/Ne+He. These findings improve our understanding about the behavior of noble gas atoms and gas bubble formation in iron under irradiation. [ABSTRACT FROM AUTHOR]

The stability of noble gases (He, Ne, Ar, Kr and Xe) in thorium dioxide is studied by means of density functional theory. The computations are performed considering insertion sites of ThO 2 , including the interstitial sites, the thorium vacancies, the oxygen-thorium di-vacancy and three types of Schottky defects. Our results show that there is an approximately linear relation between the energies and the atomic radii. As the size of the noble gas atom increases, the noble gas atoms energetically prefer to incorporate into large vacancy defects rather than into interstitial positions. Moreover, the binding energy of Kr or Xe interstitial in a Schottky defect is larger than the formation energy of a Schottky defect, suggesting the Schottky defects are thermodynamically favorable in the presence of these noble gas atoms. The charged defects are also considered for noble gas atoms trapped in Th and O vacancies. [ABSTRACT FROM AUTHOR]

Argon has the potential to be a novel inhaled therapeutic agent, owing to the neuroprotective and organoprotective properties demonstrated in preclinical studies. Before human trials are performed, an understanding of varying gas properties on airway resistance during inhalation is essential. This study predicts the effect of an 80% argon/20% oxygen gas mixture on the pressure drop through conducting airways, and by extension the airway resistance, and then verifies these predictions experimentally using 3-D printed adult tracheobronchial airway replicas. The predicted pressure drop was calculated using established analytical models of airway resistance, incorporating the change in viscosity and density of the 80% argon/20% oxygen mixture versus that of air. Predicted pressure drop for the argon mixture increased by approximately 29% compared to that for air. The experimental results were consistent with this prediction for inspiratory flows ranging from 15 to 90 slpm. These results indicate that established analytical models may be used to predict increases in conducting airway resistance for argon/oxygen mixtures, compared with air. Such predictions are valuable in predicting average patient response to breathing argon/oxygen mixtures, and in selecting or designing delivery systems for use in administration of argon/oxygen mixtures to critically ill or injured patients. [ABSTRACT FROM AUTHOR]

Trace element partition coefficients between anorthitic plagioclase and basaltic melts ( D ) have been determined experimentally at 0.6 GPa and 1350–1400 °C in a lunar high-Ti picritic glass and a mid-ocean ridge basalt (MORB). Plagioclases with 98 mol% and 86 mol% anorthite were produced in the lunar picritic melt and MORB melt, respectively. Based on the new experimental partitioning data and those selected from the literature, we developed parameterized lattice strain models for the partitioning of monovalent (Na, K, Li), divalent (Ca, Mg, Ba, Sr, Ra) and trivalent (REE and Y) cations between plagioclase and silicate melt. Through the new models we showed that the partitioning of these trace elements in plagioclase depends on temperature, pressure, and the abundances of Ca and Na in plagioclase. Particularly, Na content in plagioclase primarily controls divalent element partitioning, while temperature and Ca content in plagioclase are the dominant factors for REE partitioning in plagioclase. From these models, we also derived a new expression for D Ra / D Ba that can be used for Ra-Th dating on volcanic plagioclase phenocrysts, and a new model for plagioclase-melt noble gas partitioning. Applications of these partitioning models to fractional crystallization of MORB and lunar magma ocean (LMO) indicate that (1) the competing effect of temperature and plagioclase composition leads to small variations of plagioclase-melt D REE during MORB differentiation, but (2) the temperature effect is especially significant and can vary anorthite-melt D REE by over one order of magnitude during LMO solidification. Temperature and plagioclase composition have to be considered when modeling the chemical differentiation of mafic to felsic magmas involving plagioclase. [ABSTRACT FROM AUTHOR]

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies ( E a ) ranging from 83.3 to 110.7 kJ/mol and apparent pre-exponential factors ( D 0 ) spanning three orders of magnitude from 2.4 × 10 −3 to 8.9 × 10 −1 cm 2 s −1 . As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest. [ABSTRACT FROM AUTHOR]