On the preservation of Xe of the isotopically normal component of noble gases in meteoritic nanodiamonds and 4He in lunar soil according to the data of gas desorption during stepped pyrolysis

The release kinetics of Xe of the isotopically normal component of noble gases (P3 component) from the coarse-grained fraction of nanodiamonds from the Orgueil (CI) meteorite and the kinetics of ⁴He release from lunar soil were studied by means of a numerical simulation. It is demonstrated that the release of these gases as a peak with a single pronounced maximum may not correspond to the diffusion model with a single activation energy and can in fact be controlled by a spectrum of activation energies with a number of peaks a number of peaks remaining unresolved at stepped pyrolysis. In particular, the amount of Xe-P3 preserved in nanodiamonds during thermal metamorphism of the Orgueil meteorite calculated using parameters of the diffusion process (activation energy and frequency factor) that were determined in the model with a single activation energy indicates that practically all Xe should be lost during a very short time. These losses are inconsistent with both the duration of thermal metamorphism of the meteorite parent bodies and the Xe-P3 concentrations measured in these meteorites. A much higher preservation of Xe-P3 during thermal metamorphism lasting for hundreds of years follows from calculations based on diffusion with a spectrum of activation energiesa for Xe release. The results of isothermal pyrolysis of a nanodiamonds fraction from Orgueil confirms a presence of several activation energies for Xe-P3 release from the nanodiamonds. The application of the diffusion model with a spectrum of activation energies to He release from lunar soil samples also shows that He can be retained in these samples at 20°C during a much longer time than it follows from the model with a single activation energy (Anufriev, 2010).     

On the siting of noble gases in E-chondrites

We have investigated the siting of noble gases in 6 E-chondrites, by analyzing fractions separated by density, grain size, and chemical resistance from Qingzhen (E3), Indarch (E4), Abee and Saint Sauveur (E4-5) and Yilmia and North West Forrest (E6).The new “subsolar” (i.e. Ar-rich) component in E6's is concentrated in the main, ensatite-rich fraction of the meteorites, with density 3.06–3.3 g/cm³. It is unaffected by HCl and HNO₃ treatments of such fractions and remains in unchanged concentration when the samples are partially dissolved by HF. These properties suggest that the subsolar component is located in enstatite, or less likely, in a phase closely associated with it. E4-5's have at least half of their subsolar gases in HCl- and HNO₃-resistant sites (enstatite?), but fail to show the increasing gas concentration with decreasing grain size that is characteristic of most other primordial gas carriers. This may mean that the subsolar gases originally were in some other phase, but were then transferred to enstatite by metamorphism.Most of the ¹²⁹Xe_r of E6's is concentrated in the same fractions as the subsolar gases, again suggesting enstatite or an associated phase as the host. Only a few percent of the ¹²⁹Xe_r is contained in fractions enriched in other major and minor minerals. In E4's, on the other hand, ¹²⁹Xe_r is enhanced in finegrained, low density fractions and is also partly associated with chondrules. Perhaps ¹²⁹I was originally contained in fine-grained matrix, but was transferred to enstatite during metamorphism.A carbon-rich fraction of Indarch (E4) is enhanced in Ne-A, CCF-Xe, and L-Xe. Interestingly, both the isotopic composition of Xe and the Ne/CCF-Xe ratios resemble those of C-chondrites, yet these two meteorite classes probably formed rather far apart. Thus, if these components were mixed at a late stage, it must have been in fairly constant ratio over a large scale. Alternatively, they may have been mixed at an earlier stage, into a common carrier that was spread through a significant portion of the solar nebula.The primordial gases of Qingzhen (E3) resemble those of Indarch: they are present in moderate amounts (${}^{20}\text{Ne}{}_{\mathrm{p}}\text{= 1.2 × 10}{}^{\mathrm{?8}}\text{cc/g,}{}^{132}\text{Xe = 10 × 10}{}^{\mathrm{?10}}\text{cc/g)}$, with little or no contribution from the subsolar component. Thus Qingzhen reinforces our earlier finding that E-chondrites show no regular increase in noble gas content with decreasing petrologic type. One notable feature of Qingzhen is its very low ${}^3\text{He}{}^{21}\text{Ne}$ ratio of 1.07, which indicates that ³He has been lost by solar heating. Solar heating may also account for its low, discordant gas retention ages (U,Th-He age = 1.1 AE, KAr age = 3.2AE).     

Laboratory simulation of meteoritic noble gases. I. Sorption of xenon on carbon: Trapping experiments

We have studied trapping of radioactive ¹²⁷Xe in three types of carbon: carbon black (lamp black  LB), pyrolyzed polyvinylidene chloride (PVDC), and pyrolyzed acridine (C₁₃H₉N). A total of 86 samples were exposed to Xe at T between 100 and 1000°C, for times between 5 min and 240 hours, at p_xe ~ 5 × 10^?7 atm. Excess gas phase and loosely sorbed Xe were pumped away and the remaining, tightly bound Xe was measured by γ-spectrometry.At 100°C,× >90% of the Xe desorbs within a few minutes' pumping but a small amount remains even after 4000 min. Distribution coefficients for this tightly bound Xe are ~1 × 10^?2, 1 and 10 ccSTP/g atm for LB, acridine and PVDC carbons. The tightly bound Xe consists of two components. One occurs over the entire range 100–1000°C, becoming less abundant at high T; it appears to be physisorbed. The other occurs only at T > 500°C and is probably due to volume diffusion. The adsorbed component in LB has an apparent ΔH between ?2.3 and ?5.7 kcal/mole. The diffused component, which occurs in LB and possibly in acridine carbon, has an activation energy Q = 27 ± 8 kcal/mole and a diffusion coefficient D = 1.3 × 10^?17 cm²/sec at 1000°C. These values are comparable to those found for other types of amorphous carbon (Morrisonet al., 1963; Nakai et al., 1960).The low-T component displays two paradoxical features: low ΔH_ads, in the range for Xe physisorbed on carbon, but exceedingly long adsorption or desorption times (~10³ min at 100–400 or 1000°C). Although these long times seem to suggest a high energy process such as chemisorption, our results are best explained by a model that invokes physisorption within a labyrinth of micropores—of atomic dimensions—known to exist in amorphous carbons. The long adsorption/desorption times reflect either the long distances (~5 cm) Xe atoms must migrate by random walk to enter or leave the labyrinth, or the long times needed for Xe atoms to traverse tight spots or constricted pores that connect interior and exterior surfaces of the carbon (activated entry). Both variants of this model predict long equilibration times for the observed ΔH_ads of ?2 to ?6 kcal/mole. Apparently, xenon can be tightly trapped in carbon without resorting to high-energy bonding or to exotic mechanisms.These results suggest that “planetary” type noble gases in meteorites, located at or near grain surfaces of amorphous carbon, may be trapped by adsorption in micropores, whereas components such as CCFXe, which are uniformly distributed in their carrier phases, may be trapped by mechanisms such as volume diffusion or ion implantation.     

Laboratory simulation of meteoritic noble gases. II. Sorption of xenon on carbon: Etching and heating experiments

Sixteen amorphous carbon (lampblack) samples that had been exposed to Xe¹²⁷ and pumped for >9 hrs to remove the most labile gas were examined by etching with HNO₃, for comparison with the release pattern of meteoritic xenon. Samples originally exposed at 100–200°C lost 90% of their Xe very readily, when the surface had been etched to a mean depth of only ~0.2 Å. This suggests that the Xe is adsorbed mainly at rare sites that are unusually reactive to HNO₃. The adsorbed Xe survived several months' storage in vacuum, but on exposure to air, part of it was lost within a few hours, while the remainder persisted without measurable exchange. Samples exposed at 800–1000°C had a similar adsorbed component, as well as a second, tightly bound component extending to a mean depth of up to 30 Å; this component had apparently diffused into the carbon during exposure. The (microscopic) diffusion coefficient for graphitic crystallites is 5 × 10^?20 cm²/sec at 1000°C.PVDC carbon lost its adsorbed Xe at about the same rate as lampblack on exposure to air or HNO₃, though it differs from lampblack in being non-graphitizable and more porous. It had only a small diffused component, however.The most tightly bound part of the Xe adsorbed on lampblack resembles planetary Xe in most characteristics: surface siting, etchability, persistence in vacuum, and lack of exchange with atmospheric Xe. The Xe concentrations—if interpreted as equilibrium distribution coefficients—are some 10⁶× too small to account for meteoritic Xe, but it appears that equilibrium had not been reached by any of the samples, even after 1 day's exposure to Xe. If the uptake of Xe is controlled by rate rather than equilibrium, then the high noble gas concentrations in meteorites may simply reflect the much longer uptake times in the solar nebula. It seems likely that the trapping mechanisms discussed here can also explain two other features: elemental fractionations of noble gases, and the close correlation between planetary Xe and CCFXe.     

The nature of dark-etching rims in meteoritic taenite

Taenite fields when etched develop a cloudy brown rim with approximate compositional limits of 25 and 40 per cent Ni. In iron meteorites this cloudy zone is only a few microns wide, with a sharp, high-Ni edge about 1 μm from the kamaciteinterface and a diffuse edge several microns from the central plessite. It is always present in irons unless the meteorite has been cosmically or terrestrially reheated.X-Ray and electron diffraction of grains scratched from exceptionally large areas of cloudy taenite in the mesosiderite Estherville show that this etching zone contains a fine exsolution of kamacite. Electron microscopy reveals a cellular structure with kamacite walls surrounding taenite volumes about 1000 Å in diameter; about one-third of the total volume is kamacite. Electron diffraction from a thin foil of Tazewell indicates that for several microns the cloudy border consists of a single crystal of kamacite interpenetrating a single crystal of taenite.Detailed electron-probe investigations of taenite in Estherville show that there is a step in the M-shaped Ni profile at the sharp, high-Ni edge of the cloudy region, the Ni dropping suddenly from approximately 45 to 42 per cent. It is proposed that exsolution in the cloudy region effectively froze in the Ni profile at that temperature. On subsequent cooling only the clear outer taenite continued to equilibrate with the kamacite matrix producing the kink in the M profile.Cloudy taenite is therefore a variety of plessite differing from the usual varieties in that it forms at lower temperatures in areas much richer in Ni, and the morphology is not crystallographically oriented. Its absence can provide a sensitive indication of reheating.     

Solubilities of noble gases in magnetite: implications for planetary gases in meteorites

Solubilities of noble gases in magnetite were determined by growing magnetite in a noble-gas atmosphere between 450 and 700°K. Henry's law is obeyed at pressures up to 10^?2 atm for He, Ne, Ar and up to 10^?5 atm for Kr, Xe, with the following distribution coefficients at 500° (cc STP g^?1 atm^?5): He 0.042, Ne 0.016, Ar 3.6, Kr 1.3, Xe 0.88, some 10²–10⁵ times higher than previous determinations on silicate and fluoride melts. Apparent heats of solution in kcal/mole are: He ?2.42 ±0.12, Ne ?2.20 ±0.10, Ar ?15.25 ±0.25, Kr ?13.0 ±0.3, Xe ?12-5 ± 0.5. These values, too, stand in sharp contrast with earlier determinations on melts which were small and positive, but are comparable to the values for clathrates. Presumably the gases are held in anion vacancies.Extrapolation of the magnetite data to the formation temperature of C1 chondrites, 360°K, shows that the Ar_p³⁶ content of Orgueil magnetite could be acquired by equilibrium solubility at a total nebular pressure of 4 × 10^?6 atm. In the absence of data for silicates (the principal host phase of planetary gas), an attempt is made to estimate the solubilities required to account for planetary gases in meteorites. These values do not appear grossly unreasonable in the light of the magnetite data, when structural differences between the two minerals are taken into account. It seems that equilibrium solubility may be able to account for four features of planetary gas: elemental ratios, amounts, correlations with other volatiles and retentive siting. It cannot account for the isotopic fractionation of planetary gas, however.     

煤热解气体主产物及热解动力学分析

为了研究不同煤化程度煤的热解气相产物、热解动力参数,采用热重-红外光谱-质谱（TG-IR-MS）联用技术对4种不同热演化程度的煤进行了热解实验。实时记录了4种煤样在30~1 100℃、10/min℃升温速率、氦气气氛下热解过程中释放的各种气体成分及其释放量的变化趋势。研究结果表明,随煤热演化程度升高,煤的失重率和最大失重速率逐渐降低,与煤的干燥无灰基挥发分呈正相关关系;随着热解温度的升高,煤中逐渐释放出水、甲烷、二氧化碳、氢气和二氧化硫等小分子气体,且随着煤化程度的升高,各种气体的释放峰逐渐向高温处偏移,说明煤的热稳定性逐渐升高。不同变质程度煤的热解动力学分析结果表明,随着煤变质程度增高,其活化能逐渐降低,说明其热效应强度和发生热解反应的能力在逐渐降低。     

Xe in glacial ice and the atmospheric inventory of noble gases

We report noble gas abundance data for four Antarctic glacial ice samples which were selected to test the hypothesis that the apparent Xe deficiency in the earth's atmosphere relative to meteoritic abundance is due to incorporation of Xe in glacial ice. Our measurements indicate that the concentrations of Xe in glacial ice fall far short (~10⁴) of what the hypothesis requires. The present results complete the survey of all significant atmospheric reservoirs and show that the “missing Xe” is not contained in any of them. It must either be in the solid earth in yet unsampled reservoirs, or else it simply does not exist and the noble gas abundance pattern of the earth is dissimilar to that in meteorites.     

Atmospheric and juvenile noble gases in the Skaergaard layered igneous intrusion

Gabbro and diorite from the Skaergaard layered igneous intrusion contain noble gases which are mixtures of atmospheric and juvenile components. Atmospheric noble gases predominate in samples that have undergone extensive oxygen isotope exchange with meteoric-hydrothermal water. The source of the atmospheric noble gas component is inferred to be the hydrothermal circulation system. A juvenile component with ${}^{40}\text{Ar}{}^{36}\text{Ar}\text{≥ 6100}$ and containing fission xenon is also present This component predominates in samples showing unaltered magmatic oxygen isotope compositions. Neon of atmospheric isotopic composition is associated with the juvenile radiogenic ⁴⁰Ar and fission xenon. The source of this second noble gas component may be either the crustal country rock or the upper mantle. If the neon is juvenile primordial neon from a mantle source region, terrestrial primordial ${}^{20}\text{Ne}{}^{22}\text{Ne}$ is the same as atmospheric to within 4%. However, subduction of atmospheric noble gases into the upper mantle may provide an alternate source of neon and other noble gases in the mantle.     

Dissolved noble gases in the porewater of lacustrine sediments as palaeolimnological proxies

This paper presents results from the numerical modelling of the transport of atmospheric noble gases (He, Ne, Ar, Kr, Xe), tritiated water and ³He produced by radioactive decay of ³H, in unconsolidated lacustrine sediment. Two case studies are discussed: (1) the evolution of ³H and ³He concentrations in the sediment porewater of Lake Zug (Switzerland) from 1953 up to the present; and (2) the response of dissolved atmospheric noble gas concentrations in the sediment porewater of a subtropical lake to an abrupt climatic change that occurred some 10 kyr before the present. (1) Modelled ³H and ³He porewater concentrations are compared with recent data from Lake Zug. An estimate of the effective diffusion coefficients in the sediment porewater is derived using an original approach which is also applicable also to lakes for which the historical ³H and ³He concentrations in the water column are unknown. (2) The air/water partitioning of atmospheric noble gases is sensitive to water temperature and salinity, and thus provides a mechanism by which these environmental variables are recorded in the concentrations of atmospheric noble gases in lakes. We investigate the feasibility of using noble gas concentrations in the porewater of lacustrine sediments as a proxy for palaeoenvironmental conditions in lakes. Numerical modelling shows that heavy noble gases in sediment porewater, because of their comparatively small diffusion coefficients and the strong temperature sensitivity of their equilibrium concentrations, can preserve concentrations corresponding to past lake temperatures over times on the order of 10 kyr. Noble gas analysis of sediment porewaters therefore promises to yield valuable quantitative information on the past environmental states of lakes.     

Solubilities of nitrogen and noble gases in silicate melts under various oxygen fugacities: implications for the origin and degassing history of nitrogen and noble gases in the earth

Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO₂) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wüstite buffer) and the other at high pressures (P_total ∼ 2 × 10⁸ Pa), 1500°C and fO₂ ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (¹⁵N¹⁵N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN₂ of up to ∼250 atm (2.5 × 10⁷ Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO₂ ∼ IW + 10). All these results support physical dissolution of nitrogen as N₂ molecules in silicate melts for fO₂ from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3-5 × 10⁻⁹ mol/g/atm) is comparable to that of Ar (2-4 × 10⁻⁹ mol/g/atm), and much lower than that of Ne (11-14 × 10⁻⁹ mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N₂/³⁶Ar ratios in the Earth's atmosphere (∼10⁴) and that in the mantle (∼10⁶) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation.     

The solubility of noble gases in water and in NaCl brine

A direct-sampling, mass-spectrometric technique has been used to measure simultaneously the solubilities of He, Ne, Ar, Kr, and Xe in fresh water and NaCl brine (0 to 5.2 molar) from 0° to 65 °C, and at 1 atm total pressure of moist air. The argon solubility in the most concentrated brines is 4 to 7 times less than in fresh water at 65 °C and 0°C, respectively. The salt effect is parameterized using the Setschenow equation.

$\text{ln}\text{[}\text{β}{}^{\mathrm{i}}{}_{\mathrm{o}}\text{(T)}\text{β}{}^{\mathrm{i}}\text{(T)}\text{= MK}{}^{\mathrm{i}}{}_{\mathrm{M}}\text{(T)}$

where M is NaCl moiarity, βⁱ_o(T) and βⁱ(T) the Bunsen solubility coefficients for gas i in fresh water and brine, and Kⁱ_M(T) the empirical salting coefficient. Values of Kⁱ_M(T) are calculated using volumetric concentration units for noble gas and NaCl content and are independent of NaCl molarity. Below about 40°C, temperature coefficients of all Kⁱ_M are negative. The value of K^He_M is a minimum at 40°C. K^Ar_M decreases from about 0.40 at 0°C to 0.28 at 65 °C. The absolute magnitudes of the differences in salting coefficients (relative to K^Ar_M) decrease from 0° to 65°C. Over the range of conditions studied, all noble gases are salted out, and K^He_M ? K^Ne_M < K^Ar_M < K^Kr_M < K^Xe_M.From the solubility data, we calculated $\text{Δ}\text{G}{}^0{}_{\mathrm{tr}}$, $\text{Δ}\text{S}{}^0{}_{\mathrm{tr}}$, $\text{Δ}\text{H}{}^0{}_{\mathrm{tr}}$ and $\text{Δ}\text{C}{}^{\mathrm{O}}{}_{\mathrm{p,tr}}$ for the transfer of noble gases from fresh water to 1 molar NaCl solutions. At low temperatures $\text{Δ}\text{S}{}^0{}_{\mathrm{tr}}$, is positive, but decreases and becomes negative at temperatures ranging from about 25°C for He to 45°C for Xe. At low temperatures, the dissolved electrolyte apparently interferes with the formation of a cage of solvent molecules about the noble gas atom. At higher temperatures, the local environment of the gas atom in the brine appears to be slightly more ordered than in pure water, possibly reflecting the longer effective range of the ionic fields at higher temperature.The measured solubilities can be used to model noble gas partitioning in two-phase geothermal systems at low temperatures. The data can also be used to estimate the temperature and concentration dependence of the salt effect for other alkali halides. Extrapolation of the measured data is not possible due to the incompletely-characterized minima in the temperature dependence of the salting coefficients. The regularities in the data observed at low temperatures suggest relatively few high-temperature data will be required to model the behavior of noble gases in high-temperature geothermal brines.     

Reconstruction of climatic change quantitatively with dissolved noble gases in groundwaters

One kind of climatic proxies only can describes the comparative change of temperature or rainfall, but dissolved noble gases in groundwater can be used to date groundwater, calculate temperature and rainfall, and this method can give the exact change value of three parameters in one time. Dissolved noble gases in groundwater has four sources, radioactivity-formed noble gases which are from radioactive decay of some radioactive elements in the aquifers, balance-dissolved noble gases from dissolved air in balance condition in the course of supplying, excess noble gases from excess air for groundwater-air mixing and water table changing during infiltrating, and outer-interfused noble gases from outer interfusing air in open conditions during runoff. Because the contents of radioagenic noble gases in groundwater are correlated to flowing time, such as He, the age of groundwater can be dated with 4He based on the solubility of He and the radioactive intensity of aquifers. The solubility of noble gases is the function of temperature. We can compare the contents of balance-dissolved noble gases in groundwater with the temperature-solubility experimental curves of noble gases, and calculate the forming temperature of groundwater. The contents of excess noble gases are related to the water column of infiltration which can reveal the volume of rainfall in a given period of time in general, and it may increase along with the pressure of aquifers when groundwater table rises greatly. So we can calculate the value of rainfall by comparing the contents of excess noble gases in groundwater samples with those in modem groundwater. Reconstruction of climatic change on a quantitative basis with the method of dissolved noble gases in Hebei plain （China） shows that the temperature changed from 3.8 to 19.7℃ in the past forty thousand years, it decreased to 3.8℃ in 16000 a B.P. but higher than 19.7℃ in 5060 a B.P. The rainfall was about 600mm during 40000 to 15000 a B.P., then decreased gradually to 410mm in 11000 a B.P., but subsequently increased to 950mm in 4400 a B.P. The change of noble gas temperature is consistent with 180 shift, and 6D varied with the change of other climatic proxy, such as rainfall.     

Isotopic composition of noble gases in geothermal fluids of the Krušné Hory Mts., Czechoslovakia,and the nature of the local geothermal anomaly

The contents and isotopic composition of all noble gases in the fluids from two localities (Karlovy Vary and Franti?kovy Lázně) in Western Czechoslovakia are given. The data show: (1) atmospheric Ne, Ar, Kr and Xe, which indicates meteoric recharge; (2) excess He, attributed to radiogenic contributions; (3) a small excess of Ne, but the data shed no light on its origin. Even though there is no evidence of any juvenile component in these mineral waters, part of the dissolved He is believed to be of deep (mantle) origin.Correlation between the ratio ${}^3\text{He}{}^4$He and heat flow has been reported in the literature: our data enabled a direct test of this relationship and proved its fairly good validity. The combined interpretation of the heat flow and isotopic composition shows that the local heat flow anomaly in the Kru?né Hory graben is of deep origin and was produced by the mass outflow which occurred during the Alpine activation of the Bohemian Massif.     

Low-pressure adsorption of Ar, Kr, and Xe on carbonaceous materials (kerogen and carbon blacks), ferrihydrite, and montmorillonite: Implications for the trapping of noble gases onto meteoritic matter

Noble gases trapped in meteorites are tightly bound in a carbonaceous carrier labeled “phase Q.” Mechanisms having led to their retention in this phase or in its precursors are poorly understood. To test physical adsorption as a way of retaining noble gases into precursors of meteoritic materials, we have performed adsorption experiments for Ar, Kr, and Xe at low pressures (10⁻⁴ mbar to 500 mbar) encompassing pressures proposed for the evolving solar nebula. Low-pressure adsorption isotherms were obtained for ferrihydrite and montmorillonite, both phases being present in Orgueil (CI), for terrestrial type III kerogen, the best chemical analog of phase Q studied so far, and for carbon blacks, which are present in phase Q and can be considered as possible precursors.Based on adsorption data obtained at low pressures relevant to the protosolar nebula, we propose that the amount of noble gases that can be adsorbed onto primitive materials is much higher than previously inferred from experiments carried out at higher pressures. The adsorption capacity increases from kerogen, carbon blacks, montmorillonite to ferrihydrite. Because of its low specific surface area, kerogen can hardly account for the noble gas inventory of Q. Carbon blacks in the temperature range 75 K-100 K can adsorb up to two orders of magnitude more noble gases than those found in Q. Irreversible trapping of a few percent of noble gases adsorbed on such materials could represent a viable process for incorporating noble gases in phase Q precursors. This temperature range cannot be ruled out for the zone of accretion of the meteorite precursors according to recent astrophysical models and observations, although it is near the lower end of the temperatures proposed for the evolving solar nebula.     

New constraints on the release of noble gases during in vacuo crushing and application to scapolite Br–Cl–I and Ar/Ar age determinations

The release of irradiation-produced noble gas isotopes (³⁸Ar_Cl, ⁸⁰Kr_Br, ¹²⁸Xe_I and ³⁹Ar_K) during in vacuo crushing scapolite has been investigated and is compared to quartz. Three thousand crushing strokes released 98% of fluid inclusion-hosted noble gas from quartz. In comparison, 3000 crushing strokes released only 4% of the lattice-hosted ³⁸Ar_Cl from a scapolite gem. In vacuo crushing released lattice Ar preferentially relative to lattice Kr or Xe and prolonged crushing released 88% of the lattice-hosted noble gas in 96,000 crushing strokes. We suggest fast diffusion pathways generated by crushing are an important noble gas release mechanism and we demonstrate two applications of prolonged in vacuo crushing on irradiated scapolite.Firstly, scapolite molar Br/Cl and I/Cl values are shown to vary over a similar range as crustal fluids. The Cl-rich scapolite gem from Hunza, Pakistan has Br/Cl of 0.5–0.6 × 10⁻³ and I/Cl values of 0.3–2 × 10⁻⁶, that are similar to fluids that have dissolved evaporites. In contrast, three out of four skarn-related scapolites from the Canadian Grenville Province have molar Br/Cl values of 1.5–2.4 × 10⁻³, and I/Cl values of 11–24 × 10⁻⁶, that are broadly consistent with skarn formation by magmatic fluids. The fourth Grenvillian scapolite, with only 0.02 wt% Cl, has an exceptionally elevated molar Br/Cl value of up to 54 × 10⁻³ and I/Cl of 284 × 10⁻⁶. It is unclear if these values reflect the composition of fluids formed during metamorphism or preferential incorporation of Br and I in Cl-poor meionitic scapolite.Secondly, the Grenvillian scapolites give plateau ages of between 830 Ma and 400 Ma. The oldest ages post-date regional skarn formation by 200 Myr, but are similar to feldspar cooling ages in the Province. The age variation in these samples is attributed to a combination of factors including variable thermal history and the presence of mineral sub-grains in some of the samples. These sub-grains control the release of ³⁹Ar_K, ³⁸Ar_Cl and ⁴⁰Ar* during in vacuo crushing as well as the samples ⁴⁰Ar* retentivity in nature. Scapolite is suggested as a possible analogue for K-feldspar in thermochronologic studies.     

A carbonaceous inclusion from the Krymka LL-chondrite: noble gases and trace elements

A black inclusion from the Krymka LL3 chondrite was analyzed for 20 trace elements and five noble gases, by radiochemical neutron activation and mass spectrometry. The trace element pattern somewhat resembles that of C1 or C2 chondrites, but with several unique features. Elements of nebular condensation T ? 1000 K (U, Re, Os, Ir, Ni, Pd, Au, Sb and Ge) are essentially undepleted, as in C1 chondrites, but $\text{Re}\text{Ir}$ is 1.49 × higher than the characteristic Cl value. Among elements condensing below 1000 K, Cs, Se, Te, and In are depleted to approximately C2 levels (~0.6 × C1), whereas Ag, Bi, Tl are enriched to ~ 1.6 × C1. Such enrichments are thought to be characteristic of late nebular condensates.The noble-gas pattern also is unique. Gas contents are higher than in C1s, by factors of 2.6 to 19 for Ne through Xe. The $\text{Ar}{}^{36}\text{Xe}{}^{132}$ ratio of 500 is higher than mean values for C1s or C2s (109 or 89) and exceeds even the highest value seen in C3Os, 420, whereas the $\text{He}{}^4\text{Ne}{}^{20}$ ratio of 62 is much lower than the values for C1s and C2s (200–370). The $\text{Xe}{}^{129}\text{Xe}{}^{132}$ and $\text{Xe}{}^{136}\text{Xe}{}^{\mathrm{l32}}$ ratios of 1.040 and 0.320 resemble those of C1 chondrites, and seem to imply typical proportions of radiogenic Xe¹²⁹ and ‘fissiogenic’ xenon.It appears that the inclusion represents a new primitive meteorite type, similar to C-chondrites, but probably a late condensate from a region of higher nebular pressure.     

矿物流体包裹体中稀有气体的保存能力初探

查明流体包裹体中稀有气体的保存能力,对于判断其初始组分特征是否因后生作用而发生改变具有重要意义.文章以Ar为例,从扩散动力学角度对稀有气体地球化学研究中常用的矿物中流体包裹体稀有气体的保存能力进行了定量分析和系统比较,计算了Ar在这些矿物中的封闭温度以及不同温度条件下的保存时间,得出相同条件下各矿物对Ar、He等保存能...     

On the origin of the anomalous component Xe-HL in nanodiamonds of chondrites

Doklady Earth Sciences -