Noble gas elemental and isotopic abundances in deep-sea trenches in the western Pacific

Noble gas elemental and isotopic abundances were measured in seven deep-sea water samples from five different sampling sites in the Nankai Trough, the Japan Trench and the Kuril Trench. The samples were obtained by the manned submersible “Nautile”. Most of the sampling sites are associated with clam colonies and/or fluid venting. Excesses both in³He/⁴He ratio and He concentration are observed in a seawater sample collected a few kilometers off the clam colonies which were found at a depth of 3830 m at the mouth of the Tenryu Canyon. Concentrations of noble gases (Ne, Ar, Kr and Xe) in this sample show progressive depletion from Ne to Xe relative to those in 1°C air-saturated seawater, which can be attributed to mixing of hot water ( 15°C) with cold ambient water ( 1°C). Isotopic compositions of Ne, Ar, Kr and Xe in this sample are atmospheric. These observations may reflect venting of hot pore water around the Tenryu Canyon. All the other samples show a significant excess in concentration of all noble gases relative to 1°C air-saturated seawater and the isotopic compositions are atmospheric. This excess of noble gas concentrations may appear to be air contamination in the samples. However, results of hydrocarbon analyses of the Kaiko samples imply that such large amount of air contamination is improbable. Decomposition of gas hydrate in deep-sea sediments is a more likely explanation for the observed excess of noble gas concentration.     

Atmospheric noble gases in volcanic glasses from the southern Lau Basin: origin from the subducting slab?

Noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the Valu Fa Ridge (VFR) in the southern Lau Basin. The samples are the least differentiated ones from this area, and they display enrichments in fluid-mobile elements similar to the nearby island arc. ³He/⁴He ratios are slightly below average MORB (6.8–7.8 times atmospheric), whereas Ne, Ar, Kr, and Xe have isotopic compositions very similar to air. Together with previously published data from the Valu Fa Ridge and other spreading segments in the Lau Basin, our data show a systematic latitudinal variation of increasing Ne, Ar, Kr, and Xe abundances from north to south as well as Ne and Ar isotopic compositions changing from MORB-like to atmosphere-like in the same direction. Moreover, isotopic compositions and noble gas abundances of the lavas correlate strongly with Ba/Nb ratios and H₂O concentrations. Based on these observations and mass balance arguments, we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust. Our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar He and Ne. In addition to the fact that ratios of He to heavy noble gases are small in aged ocean crust, He has possibly fractionated from the other noble gases due to its higher diffusivity, and thus He transport from the subducting slab into the mantle wedge is probably insignificant. We propose that the ³He/⁴He ratios lower than MORB observed in the VFR lavas result from radiogenic ingrowth of He in a highly depleted, and hence degassed, mantle wedge after the enrichment of U and Th released from the downgoing slab.     

Anomalous noble gases in josephinite and associated rocks?

In this paper we report Ne, Ar, Kr and Xe analyses of josephinite, Josephine Peridotite, and serpentinized Josephine Peridotite. In all three samples the elemental abundance patterns resemble patterns associated with surface waters, the Ne data do not exhibit the large²¹Ne enrichments observed earlier, and the Kr and Xe compositions are indistinguishable from atmospheric composition at all isotopes, including¹²⁹Xe. Our data thus offer no significant evidence for isotopic anomalies in the noble gases. We also argue that the previous claims for primordial atmospheric-like Ar, anomalous Kr and Xe, excess¹²⁹Xe, and 4.6 × 10⁹-year age are all questionable interpretations which cannot be defended against more prosaic alternatives. This leaves excess²¹Ne as the only noble gas argument for exotic origin; we suggest that this might be an experimental artifact. Until the²¹Ne question can be settled by more definitive experimentation, we feel that noble gas data cannot be used to support arguments that the origin of josephinite is more exotic than crustal serpentinization.     

Noble gases in the earth's mantle

The abundances and isotopic compositions of noble gases in two samples from ultramafic xenoliths in alkali basalt, a young kaersutitic amphibole separated from a peridotite xenolith from Dish Hill, California and an ancient whole-rock lherzolite xenolith from Baja California, are reported and compared with the results of analyses on other mantle samples. In addition to previously recognized excesses of ³He and ¹²⁹Xe, our results indicate that ambient gases in the mantle show a general enrichment of the lighter-mass nonradiogenic isotopes of Ar, Kr and Xe, and Ar with ⁴⁰Ar/³⁶Ar = 3 · 10².     

Atmospheric noble gas signatures in deep Michigan Basin brines as indicators of a past thermal event

Atmospheric noble gases (e.g., ²²Ne, ³⁶Ar, ⁸⁴Kr, ¹³⁰Xe) in crustal fluids are only sensitive to subsurface physical processes. In particular, depletion of atmospheric noble gases in groundwater due to boiling and steam separation is indicative of the occurrence of a thermal event and can thus be used to trace the thermal history of stable tectonic regions. We present noble gas concentrations of 38 deep brines (~ 0.5–3.6 km) from the Michigan Basin. The atmospheric noble gas component shows a strong depletion pattern with respect to air saturated water. Depletion of lighter gases (²²Ne and ³⁶Ar) is stronger compared to the heavier ones (⁸⁴Kr and ¹³⁰Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. We show that this atmospheric noble gas depletion pattern is best explained by a model involving subsurface boiling and steam separation, and thus, consistent with the occurrence of a past thermal event of mantle origin as previously indicated by both high ⁴He/heat flux ratios and the presence of primordial mantle He and Ne signatures in the basin. Such a conceptual model is also consistent with the presence of past elevated temperatures in the Michigan Basin (e.g., ~ 80–260 °C) at shallow depths as suggested by previous thermal studies in the basin. We suggest that recent reactivation of the ancient mid-continent rift system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. Relative enrichment of atmospheric Kr and Xe with respect to Ar is also observed, and is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, following the hydrothermal event. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions.     

Contributions of slab fluid and sediment melt components to magmatism in the Mariana Arc–Trough system: Evidence from geochemical compositions and Sr,Nd, and noble gas isotope systematics

This study presents new major and trace element, mineral, and Sr, Nd, and noble gas isotope geochemical analyses of basalts, gabbro, and clinopyroxenite from the Mariana Arc (Central Islands and Southern Seamount provinces) including the forearc, and the Mariana Trough (Central Graben and Spreading Ridge). Mantle source compositions beneath the Mariana Arc and the Mariana Trough indicate a mantle source that is depleted in high field strength elements relative to MORB (mid‐oceanic ridge basalt). Samples from the Mariana Arc, characterized by high ratios of Ba/Th, U/Th, ⁸⁴Kr/⁴He and ¹³²Xe/⁴He, are explained by addition of fluid from the subducted slab to the mantle wedge. Correlations of noble gas data, as well as large ion lithophile elements, indicate that heavy noble gases (Ar, Kr, and Xe) provide evidence for fluid fluxing into the mantle wedge. On the other hand, major elements and Sr, Nd, He, and Ne isotopic data of basalts from the Mariana Trough are geochemically indistinguishable from MORB. Correlations of ³He/⁴He and ⁴⁰Ar/³⁶Ar in the Mariana Trough samples are explained by mixing between MORB and atmosphere. One sample from the Central Graben indicates extreme enrichment in ²⁰Ne/²²Ne and ²¹Ne/²²Ne, suggesting incorporation of solar‐type Ne in the magma source. Excess ¹²⁹Xe is also observed in this sample suggesting primordial noble gases in the mantle source. The Mariana Trough basalts indicate that both fluid and sediment components contributed to the basalts, with slab‐derived fluids dominating beneath the Spreading Ridge, and that sediment melts, characterized by high La/Sm and relatively low U/Th and Zr/Nb, dominate in the source region of basalts from the Central Graben.     

Ar,Kr, and Xe in terrestrial materials

³⁶Ar, ⁸⁴Kr, and ¹³²Xe abundances along with Kr and Xe isotopic compositions are reported for two African shales and samples of chert from the Gunflint Formation in Canada. It is observed that these data and similar abundance data from other terrestrial materials show correlations between ³⁶Ar-⁸⁴Kr and between ⁸⁴Kr-¹³²Xe. The elemental ratios defined by all the above data differ significantly from and show greater variations than those measured in carbonaceous chondrites, a well-investigated class of extraterrestrial material. Physical absorption and equilibrium solubility acting on the atmosphere are investigated as explanations for the observations. The Kr and Xe isotopic spectra are also consistent with a mass-dependent incorporation process acting on a reservoir of atmospheric composition.     

The Antarctic meteorite Yamato 74123 — a new ureilite

The rare gases He, Ne, Ar, Kr and Xe were measured in bulk samples of Yamato 74123. The ³He and ²¹Ne exposure ages are found to be 5.50 Ma and 2.83 Ma, respectively. In addition to the cosmogenic component the samples contain primordial rare gases of the fractionated type in amounts typical of ureilites. In a three-isotope plot neon turns out to be a mixture of planetary neon and cosmogenic neon.The elements Na, Mg, Al, Si, P, S, K, Ca, Cr, Mn, Fe, Co, and Ni have been determined by spark source mass spectrometry in Yamato 74123 and for comparison in the ureilites Haveröand Kenna. The chemical composition as well as the noble gas abundance pattern identify Yamato 74123 as an ureilite.     

Noble gas state of the ancient mantle as deduced from noble gases in coated diamonds

Cores and coats of five coated diamonds, one from Botswana and four from Zaire, were separately analyzed for their noble gases. Noble gases in the diamonds are essentially of a trapped origin, including radio- and nucleogenic components such as⁴He, ⁴⁰Ar, ²¹Ne_excess and excesses in Xe isotopes (129, 131–136). The fairly precise elemental and isotopic abundances allow us to infer the noble gas state in the ancient mantle. ²⁰Ne/²²Ne ratios are fairly constant (11.8 ± 0.4), and very close to that of SEP (solar energetic particle)-Ne, but distinctly different from the atmospheric ratio. ²¹Ne/²²Ne ratios range from 0.028 to 0.06, which is attributed to nucleogenic ²¹Ne from ¹⁸O(α, n)²¹Ne and ²⁴Mg(n, α)²¹Ne reactions. The difference in ²⁰Ne/²²Ne between atmosphere and mantle can be attributed to the hydrodynamic escape of hydrogen from the primitive atmosphere during the very early stage in the Earth's history. ³⁸Ar/³⁶Ar and Kr isotopic ratios are identical to the atmospheric values within 1%. After correction for ²³⁸U- or ²⁴⁴Pu-fission Xe, the ^131–136Xe abundance ratios are indistinguishable from atmospheric ratios. Lighter Xe isotopes (^124–128Xe) are also likely to be atmospheric, but a final conclusion must wait until better data are obtained.In a ¹³⁶Xe/¹³⁰Xe−¹²⁹Xe/¹³⁰Xe diagram, diamond data lie on the same line as defined for MORB. The observed identical correlation for both diamonds and MORB's appears to suggest that the progenitor of the excess^131–136Xe is ²⁴⁴Pu, but not²³⁸U, though the direct Xe isotopic measurements was not precies enough to decide unanimously the progenitor.     

Noble gases in submarine pillow volcanic glasses

Fifteen submarine glasses from the East Pacific Rise (CYAMEX), the Kyushu-Palau Ridge (DSDP Leg 59) and the Nauru Basin (DSDP Leg 61) were analysed for noble gas contents and isotopic ratios. Both the East Pacific Rise and Kyushu-Palau Ridge samples showed Ne excess relative to Ar and a monotonic decrease from Xe to Ar when compared with air noble gas abundance. This characteristic noble gas abundance pattern (type 2, classified by Ozima and Alexander) is interpreted to be due to a two-stage degassing from a noble gas reservoir with originally atmospheric abundance. In the Kyushu-Palau Ridge sample, noble gases are nearly ten times more abundant than in the East Pacific Rise samples. This may be attributed to an oceanic crust contamination in the former mantle source.There is no correlation between the He content and that of the other noble gas in the CYAMEX samples. This suggests that He was derived from a larger region, independent from the other noble gases.Except where radiogenic isotopes are involved, all other noble gas isotopic ratios were indistinguishable from air noble gas isotopic ratios. The³He/⁴He in the East Pacific Rise shows a remarkably uniform ratio of (1.21±0.07)×10^?5, while the⁴⁰Ar/³⁶Ar ranges from 700 to 5600.     

Rare gas isotopic compositions in natural gases of Japan

Isotopic and elemental compositions of rare gases in various types of gas samples collected in the Japanese Islands were investigated. Excess³He was found in most samples. Many samples showed a regionally uniform high³He/⁴He ratio of about 7 times the atmospheric ratio. The He concentrations varied from 0.6 to 1800 ppm, and they were low in CO₂-rich gases and high in N₂-rich gases. Ne isotopic deviations from the atmospheric Ne were detected in most volcanic gases. The deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components, one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements. Ar was a mixture of mass fractionated Ar, atmospheric Ar and radiogenic Ar, and the contribution of radiogenic⁴⁰Ar was small in all samples. Except for He, elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere. Several samples were highly enriched in Kr and Xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water. The component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust.     

He,Ne and Ar isotopic composition of Fe-Mn crusts from the western and central Pacific Ocean and implications for their genesis

The noble gas nuclide abundances and isotopic ratios of the upmost layer of Fe-Mn crusts from the western and central Pacific Ocean have been determined. The results indicate that the He and Ar nu- clide abundances and isotopic ratios can be classified into two types: low 3He/4He type and high 3He/4He type. The low 3He/4He type is characterized by high 4He abundances of 191×10-9 cm3·STP·g-1 on average, with variable 4He, 20Ne and 40Ar abundances in the range (42.8―421)×10-9 cm3·STP·g-1, (5.40―141)×10-9 cm3·STP·g-1, and (773―10976)×10-9 cm3·STP·g-1, respectively. The high 3He/4He samples are characterized by low 4He abundances of 11.7×10-9 cm3·STP·g-1 on average, with 4He, 20Ne and 40Ar abundances in the range of (7.57―17.4)×10-9 cm3·STP·g-1, (10.4―25.5)×10-9 cm3·STP·g-1 and (5354―9050)×10-9 cm3·STP·g-1, respectively. The low 3He/4He samples have 3He/4He ratios (with R/RA ratios of 2.04―2.92) which are lower than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (447―543) which are higher than those of air (295.5). The high 3He/4He samples have 3He/4He ratios (with R/RA ratios of 10.4―12.0) slightly higher than those of MORB (R/RA=8±1) and 40Ar/36Ar ratios (293―299) very similar to those of air (295.5). The Ne isotopic ratios (20Ne/22Ne and 21Ne/22Ne ratios of 10.3―10.9 and 0.02774―0.03039, respectively) and the 38Ar/36Ar ratios (0.1886―0.1963) have narrow ranges which are very similar to those of air (the 20Ne/22Ne, 21Ne/22Ne, 38Ar/36Ar ratios of 9.80, 0.029 and 0.187, respectively), and cannot be differentiated into different groups. The noble gas nuclide abundances and isotopic ratios, together with their regional variability, suggest that the noble gases in the Fe-Mn crusts originate primarily from the lower mantle. The low 3He/4He type and high 3He/4He type samples have noble gas characteristics similar to those of HIMU (High U/Pb Mantle)- and EM (Enriched Mantle)-type mantle material, respectively. The low 3He/4He type samples with HIMU-type noble gas isotopic ratios occur in the Magellan Seamounts, Marcus-Wake Seamounts, Marshall Island Chain and the Mid-Pacific Sea- mounts whereas the high 3He/4He type samples with EM-type noble gas isotopic ratios occur in the Line Island Chain. This difference in noble gas characteristics of these crust types implies that the MagellanSeamounts, Marcus-Wake Seamounts, Marshall Is- land Chain, and the Mid-Pacific Seamounts originated from HIMU-type lower mantle material whereas the Line Island Chain originated from EM-type lower mantle material. This finding is consistent with varia- tions in the Pb-isotope and trace element signatures in the seamount lavas. Differences in the mantlesource may therefore be responsible for variations in the noble gas abundances and isotopic ratios in the Fe-Mn crusts. Mantle degassing appears to be the principal factor controlling noble gas isotopic abundances in Fe-Mn crusts. Decay of radioactive isotopes has a negligible influence on the nuclide abundances and isotopic ratios of noble gases in these crusts on the timescale of their formation.     

Noble gases in pillow basalt glasses from the northern Mariana Trough back-arc basin

Noble gas concentrations and isotopic compositions have been measured in eight samples of pillow basalt glasses collected from seven different localities along 250 km of the Mariana Trough spreading and rifting axis. The samples have uniform and mid-ocean ridge basalt (MORB)-like ³He/⁴He values of 9–12 × 10^–6 (6.4–8.6 times atmospheric) despite large variations in ⁴He. Concentrations of the noble gases Ne, Ar, Kr, and Xe show much smaller variations between samples, but larger variations in isotopic compositions of Ne, Ar, and Xe. Excess radiogenic ²¹Ne is observed in some samples. ⁴⁰Ar/³⁶Ar varies widely (atmospheric to 1880). Kr is atmospheric in composition for all samples. Some samples show a clear excess ¹²⁹Xe, which is a well-known MORB signature. Isotopic compositions of the heavier noble gases (Ar, Kr, and Xe) in some samples, however, show more atmospheric components. These data reflect the interaction of a MORB-like magma with an atmospheric component such as seawater or of a depleted mantle source with a water-rich component that was probably derived from the subducting slab.     

Trapped solar and cosmogenic noble gas abundances in Apollo 15 and 16 deep drill samples

Abundances and isotopic compositions of all the stable noble gases have been measured in 19 different depths of the Apollo 15 deep drill core, 7 different depths of the Apollo 16 deep drill core, and in several surface fines and breccias. All samples analyzed from both drill cores contain large concentrations of solar wind implanted gases, which demonstrates that even the deepest layers of both cores have experienced a lunar surface history. For the Apollo 15 core samples, trapped⁴He concentrations are constant to within a factor of two; elemental ratios show even greater similarities with mean values of⁴He/²²Ne= 683±44,²²Ne/³⁶Ar= 0.439±0.057,³⁶Ar/⁸⁴Kr= 1.60±0.11·10³, and⁸⁴Kr/¹³²Xe= 5.92±0.74. Apollo 16 core samples show distinctly lower⁴He contents,⁴He/²²Ne(567±74), and²²Ne/³⁶Ar(0.229±0.024), but their heavy-element ratios are essentially identical to Apollo 15 core samples. Apollo 16 surface fines also show lower values of⁴He/²²Ne and²²Ne/³⁶Ar. This phenomenon is attributed to greater fractionation during gas loss because of the higher plagioclase contents of Apollo 16 fines. Of these four elemental ratios as measured in both cores, only the²²Ne/³⁶Ar for the Apollo 15 core shows an apparent depth dependance. No unambiguous evidence was seen in these core materials of appreciable variations in the composition of the solar wind. Calculated concentrations of cosmic ray-produced²¹Ne,⁸⁰Kr, and¹²⁶Xe for the Apollo 15 core showed nearly flat (within a factor of two) depth profiles, but with smaller random concentration variations over depths of a few cm. These data are not consistent with a short-term core accretion model from non-irradiated regolith. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. The lack of large variations in solar wind gas contents across core layers is also consistent with appreciable pre-accretion irradiation. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmogenic gases below ～65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper ～70 cm of the core. Cosmogenic gas concentrations of several Apollo 16 fines and breccias are consistent with ages of North Ray Crater and South Ray Crater of ～50·10⁶ and ～2·10⁶ yr, respectively.     

Noble gases in CO2 well gas,Harding County,New Mexico

The abundance and isotopic composition of noble gases were determined in samples of CO₂ well gas from Harding County, New Mexico. Our results confirm the presence of radiogenic¹²⁹Xe and fissiogenic^131–136Xe. Relative to noble gases in air, the CO₂ gas is selectively depleted in the lighter weight, nonradiogenic noble gases, except at neon. It is suggested that loss of atmospheric neon into space could account for an apparent excess of neon in juvenile gases.     

A Portable Membrane Contactor Sampler for Analysis of Noble Gases in Groundwater

To enable a wider use of dissolved noble gas concentrations and isotope ratios in groundwater studies, we have developed an efficient and portable sampling device using a commercially available membrane contactor. The device separates dissolved gases from a stream of water and collects them in a small copper tube (6 mm in diameter and 100 mm in length with two pinch‐off clamps) for noble gas analysis by mass spectrometry. We have examined the performance of the sampler using a tank of homogeneous water prepared in the laboratory and by field testing. We find that our sampling device can extract heavier noble gases (Ar, Kr, and Xe) more efficiently than the lighter ones (He and Ne). An extraction time of about 60 min at a flow rate of 3 L/min is sufficient for all noble gases extracted in the sampler to attain equilibrium with the dissolved phase. The extracted gas sample did not indicate fractionation of helium (³He/⁴He) isotopes or other noble gas isotopes. Field performance of the sampling device was tested using a groundwater well in Vienna and results were in excellent agreement with those obtained from the conventional copper tube sampling method.     

Inert gas abundances in basalts of the Lesser Antilles island arcs: possible implications for their volcanic evolution

Measurements of noble gas element abundances in igneous rock samples from the Lesser Antilles island arc (LAIA) show an enrichment of Ne, Kr and Xe relative to Ar, when compared to the atmospheric inert gas composition. The element concentrations vary as a function of time and a cyclic variation appears to occur in the pre-Pliocene stage of arc development. The pattern of elemental abundances closely resembles that of ocean floor basalts, suggesting that, (1) the origin of the inert gases in these samples is related to the subduction of oceanic lithosphere responsible for the formation of the LAIA, and (2) the subduction process does not modify the noble gas patterns of the materials being subducted.There is no evidence of a change in concentration or composition of noble gases occurring at ca. 9 Ma, the time when it has been suggested the LAIA shifted to form the western, younger, volcanic Caribbees. However, a major hiatus in the noble gas evolution is recognised at ca. 16 Ma.     

Noble gas components in clasts and separates of the Abee meteorite

The noble gas components and their distributions were studied in a variety of clasts and in separated phases of clast 2,2 using a detailed stepwise release program. The results show the presence of two distinct trapped components: one appears to be similar to Kenna-type gas [28], the other is characterized by element ratios³⁶Ar/⁸⁴Kr < 370 and³⁶Ar/¹³²Xe ≥ 900 and is termed Ar-rich component. Silicate phases are identified as carriers of both components; but since they are differentially released, the results imply that multiple carrier phases are required. Unlike results from other meteorites, HF attack removes all but 15% of the xenon. Substantial amounts of trapped and, in many cases, unfractionated air were observed, apparently in reaction products of reduced and easily oxidized minerals. The¹²⁹Xe_r release systematics imply the presence of two distinct carriers of extinct¹²⁹I and suggest lithophilic behavior of I in Abee. The U/Th-⁴He and K-⁴⁰Ar data are consistent with a 4.5 Gy age. Amounts of spallogenic He, Ne and Ar yield a cosmic ray exposure age of 8 My. We compare the Ar-rich component to noble gas abundances in planetary atmospheres and we discuss a suggested model of origin.     

Rare gas constraints on hydrocarbon accumulation, crustal degassing and groundwater flow in the Pannonian Basin

The isotopic composition and abundances of He, Ne and Ar have been measured in a sequence of vertically stacked gas reservoirs at Hajduszoboszlo and Ebes, in the Pannonian Basin of Hungary. The gas reservoirs occur at depths ranging from 727 to 1331 m, are CH₄ dominated and occupy a total rock volume of approximately 1.5 km³. There are systematic variations in both major species abundances and rare gas isotopic composition with depth: CO₂ and N₂ both increase from 0.47 and 1.76% to 14.1 and 30.5%, respectively, and ⁴⁰Ar/³⁶Ar and ²¹Ne/²²Ne increase systematically from 340 and 0.02990 at 727 m to 1680 and 0.04290 at 1331 m. A mantle-derived He component between 2 and 5% is present in all samples, the remainder is crustal-radiogenic He. The Ar and Ne isotope variations arise from mixing between atmosphere-derived components in groundwater, and crustally produced radiogenic Ar and Ne. The atmosphere-derived ⁴⁰Ar and ²¹Ne decreases from 85 and 97% of the total ⁴⁰Ar and ²¹Ne at 727 m to 18 and 68% at 1331 m. The deepest samples are shown to have both atmosphere-derived and radiogenic components close to the air-saturated water and radiogenic production ratios. The shallowest samples show significant fractionation of He/Ar and Ne/Ar ratios in atmosphere-derived and radiogenic rare gas components, but little or no fractionation of He/Ne ratios. This suggests that diffusive fractionation of rare gases is relatively unimportant and that rare gas solubility partitioning between CH₄ and H₂O phases controls the observed rare gas elemental abundances.The total abundance of atmosphere-derived and radiogenic rare gas components in the Hajduszoboszlo gas field place limits on the minimum volume of groundwater that has interacted with the natural gas, and the amount of crust that has degassed and supplied radiogenic rare gases. The radiogenic mass balance cannot be accounted for by steady state production either within the basin sediments or the basement complex since basin formation. The results require that radiogenic rare gases are stored at their production ratios on a regional scale and transported to the near surface with minimal fractionation. The minimum volume of groundwater required to supply the atmosphere-derived rare gases would occupy a rock volume of some 1000 km³ (assuming an average basin porosity of 5%), a factor of 670 greater than the reservoir volume. Interactions between groundwater and the Hajduszoboszlo hydrocarbons has been on a greater scale than often envisaged in models of hydrocarbon formation and migration.     

The case for a martian origin of the shergottites: nitrogen and noble gases in EETA 79001

Nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite EETA 79001. A nitrogen component trapped in the glass, but not present in the matrix, has a δ¹⁵N value at least as high as +190‰. Ratios of⁴⁰Ar/¹⁴N and¹⁵N/¹⁴N in the glass are consistent with dilution of a martian atmospheric component (δ¹⁵N = 620 ± 160‰,⁴⁰Ar/¹⁴N= 0.33 ± 0.03) by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock. Trapped noble gases in the glass reproduce, within error, the elemental and isotopic compositions measured in Mars' atmosphere by Viking, and are in general agreement with previous measurements except for much lower abundances of neutron-generated krypton and xenon isotopes. The most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the EETA 79001 glass, and that this meteorite, and thus the shergottites and probably the nakhlites and chassignites as well, originated on Mars.Nitrogen in the non-glassy matrix of EETA 79001 amounts to less than 0.5 ppm and has a spallation-corrected δ¹⁵N value in the range 0 to ?20‰; it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen. Spallogenic noble gases yield single-stage exposure ages between 400,000 and 900,000 years, depending on irradiation geometry. Trapped argon may have an unusually low³⁶Ar/³⁸Ar ratio. Trapped krypton, except for a small excess at⁸⁰Kr, is smoothly mass-fractionated with respect to either terrestrial or chondritic Kr. The trapped xenon composition is consistent with addition of neutron-capture, radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric Xe. The elemental⁸⁴Kr/¹³²Xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio.