Isotopes Of He Research Articles

Cosmogenic 3He anomaly K1 vs. the early Campanian isotopic event (ECE) as recorded in pelagic limestones of the Umbria-Marche succession (Italy)

In this paper, we report on a biostratigraphic, magnetostratigraphic, and stable isotope (δ13C and 3He) analysis across three pelagic limestone sections of the Campanian Scaglia Rossa Formation exposed in the classic Bottaccione Gorge at Gubbio (Umbria region), near the village of Furlo, and near the town of Apiro (both in the Marche region), all located in the Umbria-Marche basin of the northeastern Apennines of central Italy. These sections record the coincidental occurrence of an extraterrestrial 3He (3HeET) anomaly known as K1 and a negative shift in the δ13C record known as the early Campanian event. Cyclostratigraphic spectral analysis of the Furlo section based on a high-resolution magnetic susceptibility record in these pelagic limestones revealed that the regular orbitally forced Milankovitch cycles are somewhat disturbed or blurred through the interval of the coincident 3HeET K1 anomaly and the early Campanian event isotopic anomaly, suggesting a causal effect resulting from the enhanced influx of extraterrestrial material (i.e., interplanetary dust particles and a myriad of small meteorite impacts). This would have altered the transparency of the atmosphere, causing a short-lived climate change event.

Rotational quenching of C2 with 3He and 4He collisions at ultracold temperatures

Quantum mechanical closed coupling scattering calculations are carried out at temperatures ranging from 10-8 K to 100 K for studying rotational transitions of C2 due to collisions with 3He and 4He employing our new C2-He potential energy surface computed at the CCSD(T)- F12b/aug-cc-pVQZ level of theory. Among the isotopes of He, the heavier 4He isotope has larger value of rotational quenching cross section than 3He isotope. Wigner’s threshold law holds below 10-1 cm−1. Quenching rate coefficients suggest that C2 can be cooled with 4He buffer gas. The dominance of 4He on C2 molecule is further addressed by calculating the predissociation lifetime of C2.

ОСОБЛИВОСТІ МЕТАМОРФІЧНИХ ДІАМАНТІВ

For the first time a new type of diamond-bearing non-kimberlite rocks with microdiamonds was discovered in the Kokchetav massif of Kazakhstan – diamond microcrystals were found in rocks of ancient metamorphic complex and placers of different ages. Subsequently, similar microcrystals were found in the metamorphic rocks of the Dabie Shan massif (Central China), the Fjortoft Islands (Northern Norway), the Erzgebirge Massif (Germany) and the Bohemian Massif (Czech Republic), in metamorphic massifs of the Rhodopes (Greece and Bulgaria), the Western Alps (Italy) and the Eastern Alps (Slovenia), and in many other localities. The mineralogy of diamonds of the Kokchetav and the Erzgebirge massifs is studied in the most detail. We summarized original and literature data on the mineralogy of metamorphic diamonds. Information on the geology of their diamond-bearing rocks and their indicator minerals is briefly covered – distribution, age, geological position of ultrametamorphic rocks, indicators of their diamond-bearing capacity and minerals of diamond paragenesises. Peculiarities of metamorphic diamonds are characterized by often big content in rocks, their micron size and diversity of crystal shape, structural imperfection and normal growth mechanism of many crystals, dominant light isotopic composition of their carbon, high content of nitrogen impurities and their low type of aggregation, spectral types Ib–IaA, enrichment of impurities, the content of specific solid inclusions and the unusualness of mineral associations. There are many hypotheses about the formation of metamorphic diamond crystals, including their metastable growth. The hypothesis of their subduction origin in the mantle at rather high PT-parameters is considered to be the most probable. Kokchetav microdiamonds from metamorphic rocks of Kazakhstan and Samotkan microdiamonds from Neogene sands of the Middle-Dniprо area (Ukrainian Shield) are compared. According to the comparison indicators, Samotkan microdiamonds and Kokchetav microdiamonds differ markedly in crystal size and morphology, content of nitrogen impurities and degree of its aggregation, the ratio of spectral types, the ratio of helium isotopes 3He /4He and a set of mineral inclusions. Samotkan diamonds are larger, no skeletal forms have been identified among them, the range of their carbon isotope composition is wider, among them, there is quite a lot of nonnitrogen and low-nitrogen crystals, different spectral types of crystals represent them, and some of them contain mineral inclusions of peridotite association.

The Evolution of Research on Abundances of Solar Energetic Particles

Sixty years of study of energetic particle abundances have made a major contribution to our understanding of the physics of solar energetic particles (SEPs) or solar cosmic rays. An early surprise was the observation in small SEP events of huge enhancements in the isotope 3He from resonant wave–particle interactions, and the subsequent observation of accompanying enhancements of heavy ions, later found to increase 1000-fold as a steep power of the mass-to-charge ratio A/Q, right across the elements from H to Pb. These “impulsive” SEP events have been related to magnetic reconnection on open field lines in solar jets; similar processes occur on closed loops in flares, but those SEPs are trapped and dissipate their energy in heat and light. After early controversy, it was established that particles in the large “gradual” SEP events are accelerated at shock waves driven by wide, fast coronal mass ejections (CMEs) that expand broadly. On average, gradual SEP events give us a measure of element abundances in the solar corona, which differ from those in the photosphere as a classic function of the first ionization potential (FIP) of the elements, distinguishing ions and neutrals. Departures from the average in gradual SEPs are also power laws in A/Q, and fits of this dependence can determine Q values and thus estimate source plasma temperatures. Complications arise when shock waves reaccelerate residual ions from the impulsive events, but excess protons and the extent of abundance variations help to resolve these processes. Yet, specific questions about SEP abundances remain.

Low‐energy nuclear fusion reactions in solids: Experiments

Replicable experimental results about low-energy nuclear fusion reactions based on initially reacting deuterium nuclei giving cold nuclear fusion synthesis of helium (both isotopes 3He and 4He) and energy release as final products are reported in this article. These final products are results of interaction of deuterium with the solids in experimental system including two specimens: molybdenum metal and palladium nanowires. Experimental proofs about cold nuclear fusion synthesis of both 3He and 4He are provided. It reported a correlation between concentration of the generated helium and the measured temperature of the sample holder. It is found that the concentrations of both 3He and 4He increase with increase of the kinetic energies of the interacting deuterium nuclei and also with increase of the temperature of the sample holder.

Cluster radioactivity in superheavy nuclei 299-306122

Cluster radioactivity is an intermediate between alpha decay and spontaneous fission. It is also an exotic decay obtained in superheavy nuclei. When a cluster decay is detected in superheavy nuclei, the daughter nuclei is having near or equal to doubly magic nuclei. We have investigated cluster decay of isotopes of He, Li, Be, Ne, N, Mg, Si, P, S, Cl, Ar and Ca in the superhaevy nuclei region 299-306122. We have also compared the logarithmic half-lives of cluster decay with that of other models such as Univ [1], NRDX [2], UDL [3] and Horoi [4]. From this study it is concluded that cluster decay of 4He, 22Ne, 26Mg, 28Si 30Si, 34S, 40Ca and 46Ca are having shorter logarithmic half-lives compared to exotic cluster decay modes.

Geochemistry of gas and water discharge from the magmatic-hydrothermal system of Guallatiri volcano, northern Chile

This work presents the first chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O, and δD) data for fluid discharges from Guallatiri volcano, a remote and massive stratovolcano, which is considered as the second most active volcano of the Central Volcanic Zone (CVZ) in northern Chile. Fumarolic gases had outlet temperatures of between 80.2 and 265 °C, and showed a significant magmatic fluid contribution marked by the occurrence of SO2, HCl, and HF that are partially scrubbed by a hydrothermal aquifer. The helium isotope ratios (< 3.2) were relatively low compared to those of other active volcanoes in CVZ, possibly due to contamination of the magmatic source by 4He-rich crust and/or crustal fluid addition to the hydrothermal reservoir. Geothermometry in the H2O-CO2-CO-H2-CH4 system suggests equilibrium temperatures of up to 320 °C attained in a vapor phase at redox conditions intermediate between those typical of hydrothermal and magmatic environments. Thermal springs located 12 km northwest of the volcano’s summit had outlet temperatures of up to 50.1 °C, neutral to slightly basic pH, and a sodium bicarbonate composition, typical of distal fluid discharges in volcanic systems. Cold springs at the base of the volcanic edifice, showing a calcium sulfate composition, were likely produced by interaction of shallow meteoric water with CO2- and H2S-rich gases. A geochemical conceptual model was constructed to graphically represent these results, which can be used as an indication for future geochemical monitoring and volcanic hazard assessment.

Geochemical survey of the Colpitas-Taapaca volcanic-hydrothermal system, northern Chile

This work presents chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O and δD) data of fluid discharges from Colpitas-Taapaca volcanic-hydrothermal system, located close to the Taapaca Volcanic Complex, with the aim to investigate the physical-chemical conditions of the fluid source and to provide a preliminary evaluation of the geothermic potential of the study area. Colpitas thermal springs (to 56 °C) and part of the cold springs (≤18°C) from this area have a Na+-Cl- composition and Total Dissolved Solids (TDS) values (from 6,059 to 19,118 mg/L). Putre springs also show a Na +-Cl -composition, TDS values up to 7,887 mg/L, and outlet temperatures from 21 to 31 °C. Colpitas cold springs, with a Ca2+-SO42- composition and relatively low TDS values (≤1,350 mg/L), are likely produced by interaction of shallow water with uprising H2S- rich hydrothermal gases. This process is likely also controlling the chemistry of Jurase thermal springs, which have the highest outlet temperatures of the study area (up to 68 °C), a Ca2+-SO42- composition and TDS values ≤2,355 mg/L. Eventually, Las Cuevas springs have temperatures up to 36 °C, a Na+-HCO3- composition and low TDS values (≤1,067 mg/L), typical features of springs related to a shallow aquifer. The δ18O-H2O and δD-H2O values indicate that all waters have a dominant meteoric origin. Enrichments in 18O and D shown by Colpitas and Putre thermal waters are likely due to steam loss and water- rock interaction, masking a possible direct steam contribution from magmatic degassing. Gas emissions from Colpitas bubbling pools are dominated by CO2, with significant concentrations of CH4, H2S and H2. The Rc/Ra values (up to 2.04) of Colpitas gases indicate a significant contribution of magmatic to mantle He, whereas the high CO2/ 3He ratios, combined with d 13C-CO2 values ranging from -7.66 to -5.63 ‰ vs. PDB, imply a dominant crustal CO2 source, mostly involving limestone. Estimated temperatures based on the composition of waters and gases from Colpitas are up to 215 °C. Higher temperatures (240 °C) are estimated for Putre thermal waters, although these waters, as well as those from Jurase and Las Cuevas, are too immature for a reliable application of geothermometric techniques. Based on the theoretical reservoir temperature and the measured Cl total output, the thermal energy released from Colpitas thermal area is estimated at up to 13.9 Mw. Such results suggest the occurrence of a promising heat source, possibly related to Taapaca volcanic complex, and encourage the development of future research based on combined geophysical and geochemical approaches, in order to provide a reliable evaluation of the geothermal potential of the whole area.

Paroxysmal eruptions tracked by variations of helium isotopes: inferences from Piton de la Fournaise (La R\xe9union island)

Helium (He) with its isotopes (3He, 4He) is a key tracer enabling the Earth’s mantle and dynamics to be characterized. Enrichment in primordial helium (3He) has been detected in volcanic gases of numerous magmatic systems in different geodynamic settings. Despite past use to monitor volcano-tectonic unrest, temporal 3He/4He variability in volcanic emissions is still poorly constrained. Here, we investigate noble gas chemistry of Piton de la Fournaise hotspot volcano, where temporal fluctuations of 3He/4He in response to the eruptive activity have never been studied. We compare the 3He/4He signature of volcanic gases and fluid inclusions and we highlight analogous evolution of the 3He/4He signature in both during the last decades of eruptive activity (1990–2017), even during the same eruption. We show that the maximum enrichment in 3He is found in magmatic fluids that fed the most voluminous eruptions which culminated in caldera collapse events. We argue that this enrichment in 3He mostly reflects a greater contribution of magmatic fluids from a primitive component of the mantle plume. These results emphasize that He isotopes may provide warnings of increases in deep magmatic contributions that potentially herald paroxysmal eruptions, as documented here at Piton de la Fournaise (2007) and also at Kilauea (2018).

A generalized any‐particle propagator theory: Calculations of nucleon's binding energies

AbstractGeneralized one‐particle propagator calculations were performed for fermions in atoms: neutrons, protons, and electrons. For this purpose, multicomponent Hartree‐Fock equations were implemented using Gaussian basis sets where, for nucleons, we consider a non‐Coulombic interaction, through a two‐term Yukawa scalar potential and the interaction between electrons and the electrons with positive charge (protons) through a Coulombic potential. The strategy for evaluating the required interaction integrals follows Obara‐Saika and Head‐Gordon recurrence relations combined with the generalized Boys function suggested by Ten‐no. Calculations on the isotopes 2H, 3H, 3He, 4He, 6Li, 6Be, 7Li, and 8Be were realized to test the accuracy of Koopmans' approximation and a second‐order generalized one‐particle propagator. Yukawa potentials were parametrized to reproduce nuclear properties as kinetic energies and radial distributions of density. These potentials produced the reference nuclear Hartree‐Fock calculations on which fully ab initio propagator calculations were performed for these non‐Coulombic potentials. This allowed us to explore the electronic structure of isotopes in an extended nucleus context.

Mobility of radiogenic isotopes 4He and 3He and their retention in a mineral (using amphibole as an example)

Studies of 40Ar and 4He mobility in minerals (performed for isotope geochronometry problems) generally assumed that the migration parameters, obtained for the atoms preserved in a mineral, described the mobility of all atoms that were produced in the mineral, including those that were lost in the past. To test this assumption, an analysis of the U-Th-Li-4He-3He isotope system in amphiboles, separated from alkaline granites of the Ponoi massif, Kola Peninsula, was performed. The retention of He isotopes was determined, i.e., the ratio of the amount of radiogenic He remaining in a mineral to its amount, which should have been accumulated since the formation (metamorphism) of the mineral. It turned out that 36% of 3He and only 14% of 4He were preserved in the mineral. The results of experiments on 3He and 4He migration from amphibole grains during their step wise heating in vacuum were successfully approximated by a diffusion model. However, the parameters, obtained during the simulations, did not allow reproducing the above retentions of He isotopes. The mechanisms of 3He and 4He migration in the past, which have led to such different retentions, differ from the diffusion mechanism, which adequately describes migration of the atoms remaining in the mineral.

Origin, Occurrence, and Mobility of He and Ar Isotopes in Meliphanite

The U, Th, and 4He contents of meliphanite correspond to an age of metamorphism (1800 Ma) indicating good preservation of radiogenic 4He in mineral but contradicting the experience of U–Th–4He dating. For the analysis of this result, we studied preservation of 3He, which was found to be very low (~2%). The 3,4He isotopes occur in radiation tracks, the intersection of which with cleavage planes provide for their migration from the mineral. Thus, 4He originated from U and Th decay should be completely lost. Meliphanite entraps He, which probably occurs in specific volumes of its crystal structure. Extraction of He isotopes from meliphanite upon vacuum heating supports this conclusion. Application of only one U–Th–4He system for dating (as often applied in thermochronology) may yield erroneous results. Identification of the origin of He in minerals requires using both isotopes (3He and 4He).

3He along the ultraslow spreading AMOR in the Norwegian-Greenland Seas

The majority of undiscovered hydrothermal vent fields are thought to be located on slow and ultraslow spreading ridges. Locating new vent sites on these ridges is important due to their tendency to host large seafloor massive sulfide deposits. It is also important as it can increase our understanding of the tectonics at ultraslow spreading ridges as well as giving us an understanding of how hydrothermal venting in these regions affect and interact with the surrounding water column. To assess the hydrothermal productivity of the slow to ultraslow spreading Mohns and Knipovich ridge segments of the Arctic Mid-Ocean Ridge we used the primordial isotope 3He. Due to the conservative nature of 3He, this isotope can function as a tracer both for hydrothermal activity and on the ocean current pathways. In addition to assessing the hydrothermal productivity of the ridges we also studied the impact the ridges have on ocean circulation. Between 2006 and 2016, 400 water samples were collected along the Mohns Ridge and the Knipovich Ridge and 117 samples were collected in two transects crossing each ridge. The results show that the surface mixed layer (500–0 m depth) directly above each ridge has higher than equilibrium values of δ3He, which we interpret as an effect of the bottom topography on the vertical mixing. We also observe direct indications of at least two undiscovered vent sites along the Mohns Ridge, making the total count of 7 vent fields along this 550 km ridge segment, which gives a vent field frequency (Fs) of 1.27 sites/100 km. This number is comparable to the vent field frequency on other ultraslow ridges. By comparing the current speed to non-buoyant plume measurements obtained at the previously discovered Loki's Castle and the Jan Mayen vent fields (JMVF) we made an estimate of the 3He flux at these vent fields. This estimate gave a flux of 0.22 mmol/km/mm/yr from Loki's Castle, which is well below the world's average of 0.33 mmol/km/mm/yr. However, the flux rate estimated here is comparable to estimates previously calculated from the ultraslow Gakkel ridge. The northeastern termination of the Mohns Ridge, where Loki's Castle is located, is also the thinnest part of the ridge segment indicating a low magmatic influence. The flux rate of the JMVF was 0.40 mmol/km/mm/yr and thus higher than the global average. This could indicate an influence from the Jan Mayen hot spot as similar flux rates has been found at other hot spot influenced vent sites. This study not only illuminates the hydrothermal productivity of ultraslow spreading ridges, but also adds a considerable dataset of helium isotopes in Nordic Seas.

Evidence for vapor transport of the base and precious metals in the Panormos Bay Ag-Au-Te deposit, Tinos Island, Cyclades

Tellurium-bearing, base and precious metal sulfides from the Au-Ag-Te mineralization at Panormos Bay, Tinos Island, Cyclades, preceded and followed the main telluride-forming event. Ore petrography and chemistry of the sulfides suggest that they have precipitated under supersaturation conditions, i.e., grown with hopper habit, enriched in Zn, Fe, Ag, Cd and Pb, and Te in stage II, III and VI sulfides and incorporate nanoparticles with variable Ag/(Pb + Ag + Cu + Fe + Zn)% values. The noble gas, i.e., He, Ar and Ne isotope compositions obtained from these sulfides form two distinct populations, the “Liquids” and “Vapors”. All these features constitute overwhelming evidence that favors vapor transport for the base and precious metals by the vapor-like Panormos ore fluid.The widespread occurrence of CO2-effervescence and boiling at the Panormos Bay Au-Ag-Te ores provoked degassing of the CO2, HCl(g), H2S(g), H2Te(g), Te2(g), light noble gas isotopes (3He, 36Ar, 20Ne, and 21Ne), base- and precious-bearing laden vapors from the mineralizing fluid and transported a fraction of the base and precious metals to vapor. Geochemical simulation suggests that supersaturation in the vapor phase, rapid up-vapor transport, and subsequent condensation in the Panormos Bay ore solution of H2Te(g), Te2(g), and base and precious-bearing vapors led to the precipitation of sulfide (stages II, III and VI) and telluride (stage V) mineral assemblages.

Carbonic springs as distal manifestations of geothermal systems, highlighting the importance of fault pathways and hydrochemical mixing: Example from the Jemez Mountains, New Mexico

We examine a series of carbonic warm and hot springs in northern New Mexico, USA: 1) Tierra Amarilla springs 2) Penasco Springs and 3) Soda Dam, Jemez and Indian hot springs. Spring geochemistry is compared to waters from the Valles Caldera geothermal system and to groundwater in nearby sedimentary aquifers. Multiple hydrochemical tracers are applied to quantitatively evaluate flow paths and mixing at varying distances from the caldera. We test three hypotheses for source and transport of waters to Tierra Amarilla and Penasco Springs: San Juan basin origin, meteoric flow from the Nacimiento Mountains, and/or influence from the Valles Caldera geothermal system. Geochemically, carbonic spring groups are distinct from meteoric and sedimentary aquifer waters. Based on isotopes of He and Sr, and concentrations of Cl, SO4, Li and B, we interpret these carbonic springs to be distal manifestations of fluid circulation along faults with a mixture of Valles Caldera geothermal waters, local meteoric and Paleozoic aquifer waters, with the potential for small contributions from the San Juan Basin aquifers. Semi-confined fault conduits, the Jemez fault and Nacimiento fault systems, provide connectivity and help explain geochemical similarities and mixing trends within carbonic spring systems, and between these systems and the distal Valles Caldera. In addition, Penasco Springs are interpreted to reflect a component of outflow from the geothermal system that crosses the Nacimiento Mountain basement block along NE-trending faults. Input of deeply sourced waters can degrade water quality by contributing significant salinity and trace metals to groundwater at distances of >50 km from geothermal systems, with faults acting as conduits for subsurface fluid flow.

Influence of quantum intermolecular interaction on internal flows of rarefied gases

In order to model gaseous flows over the whole temperature range beginning from 1 K, the intermolecular interaction should be considered on the basis of quantum approach. Such a consideration becomes important in case of light gases like helium and hydrogen. Recently, the direct simulation Monte Carlo (DSMC) method widely used to calculate flows of gases has been generalized to implement the quantum approach to intermolecular collisions. To evaluate the influence of the quantum scattering on typical flows of light gases, a benchmark problem has been solved for two helium isotopes 3He and 4He using an ab initio potential. More specifically, the flow-rate and flow-field of helium flowing through an orifice have been calculated over the temperature range from 1 K to 300 K for various values of the pressure ratio with the numerical error of 0.5%. As expected, no influence of the quantum effects on the flow-rate has been detected for the temperature 300 K. Though, the quantum approach requires less computational effort than the classical one at this temperature. For temperatures lower than 300 K, the influence of the quantum effects exceed the numerical error and reaches 41% at the temperature of 3 K. In this case, the quantum interaction is the only approach to model gas flows.

Modeling of transport phenomena in gases based on quantum scattering

A quantum interatomic scattering is implemented in the direct simulation Monte Carlo (DSMC) method applied to transport phenomena in rarefied gases. In contrast to the traditional DSMC method based on the classical scattering, the proposed implementation allows us to model flows of gases over the whole temperature range beginning from 1 K up any high temperature when no ionization happens. To illustrate the new numerical approach, two helium isotopes 3He and 4He were considered in two canonical problems, namely, heat transfer between two planar surfaces and planar Couette flow. To solve these problems, the ab initio potential for helium is used, but the proposed technique can be used with any intermolecular potential. The problems were solved over the temperature range from 1 K to 3000 K and for two values of the rarefaction parameter δ=1 and 10. The former corresponds to the transitional regime and the latter describes the temperature jump and velocity slip regime. No influence of the quantum effects was detected within the numerical error of 0.1% for the temperature 300 K and higher. However, the quantum approach requires less computational effort than the classical one in this temperature range. For temperatures lower than 300 K, the influence of the quantum effects exceed the numerical error and reaches 67% at the temperature of 1 K. Numerical data provided in Supplemental Material can be used to model any kind of helium flow at any temperature.

Reconstructing mantle carbon and noble gas contents from degassed mid-ocean ridge basalts

The fluxes of volatile elements from the mantle have long been used to understand mantle structure and evolution, and are critical controls on Earth's climate stability. Because of the ubiquity of magmatic degassing, inferring pre-degassing volatile concentrations from measured basalts requires the application of a degassing model. Such models, including the commonly-applied equilibrium Rayleigh distillation, typically assume equilibrium or solubility-based partitioning between melt and vapor. Here, we demonstrate that ratios of radiogenic isotopes of He, Ne, Ar and, especially, Xe measured in global mid-ocean ridge basalts (MORBs) are inconsistent with equilibrium degassing models, even when not considering He. We conclude that kinetic disequilibrium is a crucial process affecting volatile abundances during degassing. We present a simple disequilibrium Rayleigh distillation model to reconstruct pre-degassing MORB noble gas and carbon concentrations, which predicts that He and Ne achieve nearly equilibrium partitioning between melt and vesicles, but the slower-diffusing heavier noble gases are strongly affected by disequilibrium, resulting in non-equilibrium fractionation of noble gas elemental ratios, and other volatile element ratios like CO2/He.We apply our model to a large set of MORB data, and find average pre-degassing 3He, 22Ne, and 36Ar concentrations of 4.4 ± 0.9 × 10−10, 6.6 ± 1.4 × 10−11, and 6.8 ± 4.5 × 10−10 ccSTP/g (2σ), with variations of approximately 2 orders of magnitude, similar to other highly incompatible elements. Pre-degassing noble gas concentrations imply a mid-ocean ridge 3He flux of 800 ± 170 mol/yr and upper mantle 3He/22Ne and 3He/36Ar ratios of 6.6 ± 2.0 and 0.64 ± 0.44, but substantial variability in these ratios between samples. Applying our model to CO2, we calculate an average mantle CO2/3He molar ratio of 1.67 ± 0.21 × 109, which, when combined with our estimate of 3He flux, implies an upper mantle CO2 flux of 5.9 ± 1.0 × 1013 g/yr and a CO2 concentration of approximately 110 ppm.Our estimate of the mantle 3He flux is the first determined independently of oceanographic 3He measurements, and consequently represents a time-integrated flux substantially longer than ∼1000 years. And although at the high end of the range of previous estimates, our estimate does not resolve the long-standing heat-helium paradox. Additionally, our requirement for heterogeneous pre-degassing 3He/22Ne and 3He/36Ar ratios between samples is contrary to conclusions of previous applications of disequilibrium degassing models, which advocated uniform ratios. Furthermore, we find that CO2/Ba ratios are highly variable in MORB samples, but still consistent with an average mantle mass ratio of ∼100. However, estimating pre-degassing CO2 concentrations and the mantle CO2 flux depend strongly on the poorly-constrained carbon diffusivity. Consequently, our demonstration of the prevalence of disequilibrium during mid-ocean ridge degassing, and the potential for disequilibrium in other volcanic settings, highlights the need for better characterization of the physical parameters associated with volcanic degassing.

A noble gas data collection of lunar meteorites

AbstractWe collected the published noble gas data of altogether 35 lunar meteorites. This compilation includes the stable isotopes of He, Ne, Ar, Kr, and Xe. We also give a summary of cosmogenic, trapped, and radiogenic noble gas components of lunar meteorites for which data are available in the literature.

Cosmic‐ray exposure ages of six chondritic Almahata Sitta fragments

AbstractThe Almahata Sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. We analyzed stable isotopes of He, Ne, Ar, Kr, and Xe, and the cosmogenic radionuclides10Be,26Al, and36Cl in six chondritic Almahata Sitta fragments (EL6 breccia,EL6,EL3‐5,CB,LL4/5, R‐like). The cosmic‐ray exposure (CRE) ages of five of the six samples have an average of 19.2 ± 3.3 Ma, close to the average of 19.5 ± 2.5 Ma for four ureilites. The cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with Almahata Sitta. This corroborates that Almahata Sitta chondrite samples were part of the same asteroid as the ureilites. However,MS‐179 has a lowerCREage of 11.0 ± 1.4 Ma. Further analysis of short‐lived radionuclides in fragmentMS‐179 showed that it fell around the same time, and from an object of similar size as Almahata Sitta, making it almost certain thatMS‐179 is an Almahata Sitta fragment. Instead, its lowCREage could be due to gas loss, chemical heterogeneity that may have led to an erroneous21Ne production‐rate, or, perhaps most likely,MS‐179 could represent the true 4π exposure age of Almahata Sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. Finally,MS‐179 had an extraordinarily high activity of neutron‐capture36Cl, ~600 dpm kg−1, the highest activity observed in any meteorite to date, related to a high abundance of the Cl‐bearing mineral lawrencite.