Intensive sampling of noble gases in fluids at Yellowstone: I. Early overview of the data; regional patterns

The Roving Automated Rare Gas Analysis (RARGA) lab of Berkeley's Physics Department was deployed in Yellowstone National Park for a 19 week period commencing in June, 1983. During this time 66 gas and water samples representing 19 different regions of hydrothermal activity within and around the Yellowstone caldera were analyzed on site. Routinely, the abundances of five stable noble gases and the isotopic compositions of He, Ne, and Ar were determined for each sample. In a few cases the isotopes of Kr and Xe were also determined and found to be of normal atmospheric constitution.Correlated variations in the isotopic compositions of He and Ar can be explained within the precision of the measurements by mixing of only three distinct components. The first component is of magmatic origin and is enriched in the primordial isotope ³He with ${}^3\text{He}{}^4\text{He}\text{≥ 16}$ times the air value. This component also contains radiogenic ⁴⁰Ar and possible ³⁶Ar with ${}^{40}\text{Ar}{}^{36}\text{Ar}\text{≥ 500}$, resulting in a ${}^3\text{He}{}^{36}\text{Ar}$ ratio ≥ 41,000 times the air value. The second component is assumed to be purely radiogenic ⁴He and ⁴⁰Ar (${}^{41}\text{He}{}^{401}\text{Ar}\text{= 4.08 ± .33}$). This component is the probable carrier of observed excesses of ²¹¹Ne, attributed to the α,n reaction on ¹⁸O. Its radiogenic character implies a crustal origin in U. Th, and Krich aquifer rocks. The third component, except for possible mass fractionation, is isotopically indistinguishable from the noble gases in the atmosphere. This component originates largely from infiltrating run-off water saturated with atmospheric gases.In addition to exhibiting nucleogenic ²¹¹Ne, Ne data show anomalies in the ratio ${}^{20}\text{Ne}{}^{20}\text{Ne}$, which correlate roughly with the ${}^{21}\text{Ne}{}^{22}\text{Ne}$ anomalies for the most part, but not as would occur from simple mass fractionation. Some exaggerated instances of the ${}^{20}\text{Ne}{}^{22}\text{Ne}$ anomaly occur which could be explained by combined mass fractionation of Ne and Ar isotopes to a severe degree coupled with remixing with normally isotopic gases. Otherwise exotic processes have to be invoked to explain the ²⁰Ne data.Relative abundances of the non-radiogenic and non-nucleogenic noble gases (²²Ne, ³⁶Ar, ⁸⁴Kr, and ¹³²Xe) are highly variable but strongly correlated. High Xe/Ar ratios are always accompanied by low Ne/ Ar ratios and vice versa. Except for water from the few cold (T < 20°C) springs analyzed, none of the samples have relative abundances consistent with air saturated water and the observed variations are not readily explained by the distillation of air saturated water.In characterizing each area of hydrothermal activity by the highest ${}^3\text{He}{}^4\text{He}$ ratio found for that area, we find that within the caldera this parameter is somewhat uniform at ~7 ± 1 times the air value. There are exceptions, most notably at Mud Volcano, an area located along a crest of recent and rapid uplift. Here the maximum ${}^3\text{He}{}^4\text{He}$ ratio is ~ 16 times the air value. Also noteworthy is Gibbon Basin which is in the vicinity of the most recent rhyolitic volcanism and exhibits a ${}^3\text{He}{}^4\text{He}$ ratio ~ 13 times the air value. Immediately outside the caldera the maximum $\text{sol}{}^3\text{He}{}^4\text{He}$ ratio decreases rapidly to values < ~3 times the air value.     

Inert gases in a terra sample: measurements in six grain-size fractions and two single particles from Luna 20

The inert gases have been measured in six size fractions covering the range below 500 μm, in a single feldspathic fragment weighing 523 μg, and in an agglutinate particle weighing 465 μg. The two size fractions between 125 and 250 μm as well as 250 and 500 μm were separated into magnetic and non-magnetic portions, which were measured separately. Like the Apollo and Luna 16 fines, the terra fines represented by Luna 20 are very rich in trapped solar-wind gases, but they contain relatively less He⁴ and Ne²⁰, which is revealed by their average $\text{He}{}^4\text{Ne}{}^{20}$ ratio of 35 and $\text{Ne}{}^{20}\text{Ar}{}^{36}$ ratio of 2.9. Obviously the terra materials are less retentive for solar-wind He and Ne than typical mare fines such as 10084. Whether this is due to the relatively small TiO₂ or the relatively large plagioclase content of the former is not resolved. ($\text{Ar}{}^{36}\text{Kr}{}^{84}\text{)}{}_{\mathrm{trapped}}$ and ($\text{Ar}{}^{36}\text{Xe}{}^{132}\text{)}{}_{\mathrm{trapped}}$ ratios are relatively large; the average values are 2800 and 14400, respectively. The apparent Ne²¹ radiation ages of all the size fractions are in the range 209–286 × 10⁶ yr; the average is 260 × 10⁶ yr. This is in the range of values known for the Apollo and Luna 16 fines. The feldspathic fragment has a much greater apparent Ne_c²¹ age of 780 × 10⁶ yr. The Ar⁴⁰-Ar³⁶ systematic reveals the presence of two Ar⁴⁰ components, because Ar⁴⁰ = (1.41 ± 0.076)Ar³⁶ + (0.490 ± 0.130) × 10^?4 (cm³ STP/g). The $\text{Ar}{}^{40}\text{Ar}{}^{36}$ slope of 1.41 is not inconsistent with an origin of the sample from a relatively old terra region.     

Noble-gas-rich separates from ordinary chondrites

Acid-resistant residues were prepared by HCl-HF demineralization of three H-type ordinary chondrites: Brownfield 1937 (H3), Dimmitt (H3,4), and Estacado (H6). These residues were found to contain a large proportion of the planetary-type trapped Ar, Kr, and Xe in the meteorites. The similarity of these acid residues to those from carbonaceous chondrites and LL-type ordinary chondrites suggests that the same phase carries the trapped noble gases in all these diverse meteorite types. Because the H group represents a large fraction of all meteorites, this result indicates that the gas-rich carrier phase is as universal as the trapped noble-gas component itself. When treated with an oxidizing etchant, the acid residues lost almost all their complement of noble gases. In addition, the Xe in at least one oxidized residue, from Dimmitt, displayed isotopic anomalies of the type known as CCFX or DME-Xe, which is characterized by simultaneous excesses of both the lightest and heaviest isotopes. The anomaly in the Dimmitt sample differs from that observed in carbonaceous-chondrite samples, however, in the relative proportions of the light- and heavy-isotope excesses.The results of this study do not show an inverse correlation between trapped ${}^{20}\text{Ne}{}^{36}\text{Ar}$ and trapped ³⁶Ar abundance, as has been reported for acid-resistant residues from LL-chondrites. The results of this work therefore fail to support the hypothesis that meteoritic trapped noble gas abundances were established at the time of condensation.     

Noble gas evidence for two fluids in the Baca (Valles Caldera) geothermal reservoir

Noble gas elemental and isotopic abundances were measured in steam from four wells in the Baca geothermal reservoir located in the Valles Caldera, New Mexico. The ${}^{40}\text{Ar}{}^{36}\text{Ar}$ ratio and noble gas elemental abundances relative to ³⁶Ar are all strongly correlated with 1/³⁶Ar, the inverse of the argon content. Ratios of (α,n)-produced ²¹Ne1 and radiogenic ⁴⁰Ar1 to total ⁴He (dominantly radiogenic) are nearly constant at 2.1 × 10?8 and 0.20, respectively. The ${}^3\text{He}{}^4\text{He}$ ratio covers a restricted range of 3.9 to 4.8 times atmospheric. The high ³He content of the gas indicates the presence of a helium component ultimately derived from the mantle. Kr and Xe isotopic compositions are close to atmospheric; excess ¹²⁹Xe1 is <0.25% of the total ¹²⁹Xe.The high degree of linear correlation among the various noble gas results strongly suggests that the Baca reservoir contains two distinct fluids that are produced in varying proportions from individual wells. The noble gases in fluid A (~2900 mg/1 C1) are air-like, but with lighter gases and isotopes preferentially enriched. The fluid A ³⁶Ar content is low, only 13% that of 10°C air-saturated water (ASW). The second fluid, B (~ 1700 mg/1 C1), is the dominant carrier of the radiogenic and mantle-derived gases. The heavier non-radiogenic gases are preferentially enriched in fluid B, and its ³⁶Ar content is very low, only 5–7% ASW. The source of the noble gases in fluid A is tentatively ascribed to leaching of the relatively young (<1.4 m.y.) volcanic Bandelier Tuff. The radiogenic gases and mantle-derived helium in fluid B suggest a deeper source, possibly including gases escaping from a magma.     

Noble gas contents of shergottites and implications for the Martian origin of SNC meteorites

Isotopic concentrations of the noble gases have been measured in several different phases of Elephant Moraine A79001 and in whole rock samples of Zagami and Allan Hills A77005, three meteorites which belong to the rare group of SNC achondrites that may have originated from the planet Mars. Shocked phases of EETA79001 contain a trapped Ar, Kr, and Xe component characterized by ${}^{84}\text{Kr}{}^{132}\text{Xe}$ ～15, ${}^{40}\text{Ar}{}^{36}\text{Ar}\text{> 2000}$, ${}^{129}\text{Xe}{}^{132}\text{Xe ≥ 2}$, and ${}^4\text{He}{}^{40}\text{Ar}\text{≤ 0.1}$. These elemental and isotopic ratios are unlike those for any other noble gas component except analyses of the Martian atmosphere made by Viking spacecraft. The isotopic composition of the trapped Kr shows an approximate 1% per mass unit enrichment of lighter isotopes compared to terrestrial Kr, and the traped Xe may show either a fission component or a fractionated enrichment of heavier isotopes compared to terrestrial Xe. It is hypothesized that these gases represent a portion of the Martian atmosphere which was shock-implanted into EETA79001, and that they constitute direct evidence of a Martian origin for the shergottite meteorites. Cosmic ray-produced gases in the eight known SNC meteorites form three distinct groups with exposure ages of ～11 MY (Chassigny and the nakhlites), ～2.6 MY (Shergotty, Zagami, and ALHA77005), and ～0.5 MY (EETA79001). These ages suggest three distinct events and cannot have been produced by irradiation for a common time under greatly different shielding. Comparison of cosmogenic ${}^3\text{He}{}^{21}\text{Ne}$ measured in EETA79001 with two independent models for the production of this ratio as a function of shielding indicates that this meteorite was irradiated in space as a relatively small object. If the SNC meteorites were ejected from Mars ～ 180 My ago, the shock age of the shergottites, they must have been relatively large objects (>6 meters diameter) which experienced at least three space collisions to initiate cosmic ray exposure. Ejection from Mars by three events at the times of initiation of cosmic ray exposure would permit the ejected objects to have been much smaller (<1 meter diameter), but would require three such events on 1.3 Gy Martian terraine in the past ～10 MY and would not explain the common 180 MY shock age seen in all four shergottites.     

Noble gas concentrations and cosmic ray exposure ages of eight recently fallen chondrites

Abundances and isotopic compositions of He, Ne, Ar, and Xe have been measured in eight recently fallen chondrites. Ratios of concentrations of cosmic ray-produced ³He, ²¹Ne, ²²Ne and ³⁸Ar indicate that all eight samples experienced less than average cosmic ray shielding. ³He and ²¹Ne exposure ages were calculated using shielding corrected chondritic production rates and the measured ${}^{22}\text{Ne}{}^{21}\text{Ne}$. Exposure ages calculated from ${}^{22}\text{Na}{}^{22}\text{Ne}$ and ${}^{26}\text{Al}{}^{21}\text{Ne}$ ratios and constant relative production rates show a bias between the two ages due to variations in ${}^{22}\text{Na}{}^{26}\text{Al}$. Arguments are presented that this bias is due to irradiation hardness differences, and therefore the use of constant values for both the ${}^{22}\text{Na}{}^{22}\text{Ne}$ and ${}^{26}\text{Al}{}^{21}\text{Ne}$ production ratios is not permitted. Dwaleni, Swaziland, was found to be an unusual gas-rich chondrite with high concentrations of solar-derived He and Ne and planetary-type Xe.     

Isotopic anomalies of noble gases in meteorites and their origins—IV. C3 (Ornans) carbonaceous chondrites

The C3O chondrites Kainsaz, Lancé and Ornans were studied by an acid dissolution technique, to characterize the noble-gas components in 3 mineral fractions: HF, HCl-solubles (99% of the meteorite), chromite and carbon (0.3–0.9%), and ‘phase Q’, a poorly characterized trace mineral (0.05–0.4%) containing most of the Ar, Kr, Xe. For all fractions, gas contents decline in the order Kainsaz > Lancé > Ornans; this trend parallels volatile contents but not heterogeneity of olivine composition or degree of metamorphism and seems to reflect progressively higher condensation temperatures from the solar nebula.Solubles contain nearly unfractionated Xe, and show ${}^{136}\text{Ar}{}^{132}\text{Xe}$ ratios up to 850. Hence the high $\text{Ar}\text{Xe}$ ratios (200–400) of bulk C3O chondrites must be due to an HF-soluble mineral (possibly magnetite). Phase Q contains ordinary planetary gases and a Ne component of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 10.3 ± 0.4.}$Chromite and carbon contain Ne of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 8.6 ± 0.1}$ and ‘CCF’ xenon (a peculiar component of possibly fissiogenic origin, enriched in the heavy isotopes but accompanied by a component enriched in the light isotopes).In all primitive chondrites, both the amount and the chemical separability of CCFXe parallel the abundance of promordial noble gases and other volatiles, such as C, N, Tl, Bi and In. The close correlation of CCFXe with various properties of undoubtedly local origin (volatile content, petrologic type, presence of ferrichromite and carbon, etc.) is more consistent with a local than with an extrasolar origin of this component. A volatile superheavy element seems to be the most plausible source, but the evidence is not conclusive.     

Variability of the He3 and Ne21 production rates in ordinary chondrites

Al²⁶ and noble gas contents of 6 ordinary chondrites with $\text{He}{}^3\text{Ne}{}^{21}$ ratios above 6.0 or below 4.0 are used to infer the variability of the production rates of He³ and Ne²¹ (P_He³ and P_Ne²¹). The ratio of the observed Al²⁶ content to a calculated, normal value is taken as a measure of the change of P_Ne²¹ from its normal value. The corresponding change in P_He³ is then computed from the observed $\text{He}{}^3\text{Ne}{}^{21}$ ratio and an average value of P_He³.According to these calculations which exclude orbital effects, P_He³ will be near the average value in meteorites with high $\text{He}{}^3\text{Ne}{}^{21}$ ratios, while P_Ne²¹ will be about 30 per cent below normal. In meteorites with low $\text{He}{}^3\text{Ne}{}^{21}$ ratios, P_He³ may be depressed by as much as 25 per cent from normal while P_Ne²¹ may be 15–20 per cent above the average.     

On the calculation of cosmic-ray exposure ages of stone meteorites

Abundances of cosmic ray-produced noble gases and ²⁶Al, including some new measurements, have been compiled for some 23 stone meteorites with exposure ages of < 3 × 10⁶ yr. Concentrations of cosmogenic He, Ne, and Ar in these meteorites have been corrected for differences in target element abundances by normalization to L-chondrite chemistry. Combined noble gas measurements in depth samples of the Keyes and St. Séverin chondrites are utilized to derive equations for normalizing the production rates of cosmogenic ³He, ²¹Ne, and ³⁸Ar in chondrites to an adopted ‘average’ shielding: ${}^{22}\text{Ne}{}^{21}\text{Ne}\text{= 1.114.}$ The measured unsaturated ²⁶Al concentrations and the calculated equilibrium ²⁶Al for these meteorites are combined to estimate exposure ages. These exposure ages are statistically compared with chemistry- and shielding-corrected concentrations of cosmogenic He, Ne, and Ar to derive absolute production rates for these nuclides. For L-chondrites, at ‘average’ shielding, these production rates (in 10^?8 cm³/g 10⁶ yr) are: ³He = 2.45,²¹Ne = 0.47, and ³⁸Ar = 0.069, which are ~ 25% higher than production rates used in the past. From these production rates and relative chemical correction factors, production rates for other classes of stone meteorites are derived.     

Isotopic anomalies of noble gases in meteorites and their origins—III. LL-chondrites

Nine LL-chondrites were studied by a selective etching technique, to characterize the noblegas components in three mineral fractions: HF-HCl-solubles (silicates, metal, troilite, etc.; comprising ～ 99% of the meteorite), chromite and carbon (～ 0.3–0.7%) and Q (a poorly characterized mineral defined by its solubility in HNO₃, comprising ～ 0.05% of the meteorite but containing most of the Ar, Kr, Xe and a neon component of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 10.9 ± 0.8}$). The ${}^{20}\text{Ne}{}^{36}\text{Ar}$ ratio in Q falls wi petrologic type and rising ³⁶Ar content, as expected for condensation from a cooling solar nebula, but contrary to the trend expected for metamorphic losses. Chondrites of different petrologic types therefore cannot all be derived from the same volatile-rich ancestor, but must have formed over a range of temperatures, with correspondingly different intrinsic volatile contents.The CCFXe (carbonaceous chondrite fission) component varies systematically with petrologic type. The most primitive LL3s (Krymka, Bishunpur, Chainpur) contain substantial amounts of CCFXe in chromite-carbon, enriched relative to primordial Xe as shown by high ${}^{136}\text{Xe}{}^{132}\text{Xe}$ (0.359–0.459, vs 0.310 for primordial Xe). These are accompanied by He and by Ne with ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{≈ 8.0}$ and by variable amounts of a xenon component enriched in the light isotopes. The chromite in these meteorites is compositionally peculiar, containing substantial amounts of Fe(III). These meteorites, as well as Parnallee (LL3) and Hamlet (LL4) also contain CCFXe in phase Q, heavily diluted by primordial $\text{Xe}\text{(}{}^{136}\text{Xe}{}^{132}\text{Xe}\text{= 0.317–0.329)}$. On the other hand, LL5s and 6s (Olivenza, St. Séverin, Manbhoom and Dhurmsala) contain no CCFXe in either mineral. This deficiency must be intrinsic rather than caused by metamorphic loss, because Q in these meteorites still contains substantial amounts of primordial Ne.If CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components in certain combinations. These minerals must be appropriately distributed over the petrologic types, together with locally produced Q containing primordial gases, and they must be isotopically normal, in contrast to the gases they contain. On the other hand, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to progressively less complete condensation from the solar nebula. Ad hoc assumptions must of the host phase Q, its association with ferrichromite and the origin of the associated xenon component enriched in the light isotopes.Soluble minerals in LL3s and LL4s contain a previously unobserved, solar xenon component, which, however, is not derived from the solar wind. Three types of ‘primordial’ xenon thus occur side-by-side in different minerals of the same meteorite: strongly fractionated Xe in ferrichromite and carbon, lightly fractionated Xe in phase Q, and ‘solar’ Xe in solubles. Because the first two can apparently be derived from the third by mass fractionation, it seems likely that all were trapped from the same solar nebula reservoir, but with different degrees of mass fractionation.     

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.     

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.     

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).     

Isotopic anomalies of noble gases in meteorites and their origins—VII. C3V carbonaceous chondrites

Noble gases were measured in bulk samples of the C3V chondrites Grosnaja, Vigarano, and Leoville, and in HF,HCl-insoluble residues before and after etching with HNO₃. The residues were characterized by INAA and SEM. Gas components were determined, directly or by subtraction, for the following fractions: HF,HCl-solubles (?98% of the meteorite), ‘sphase Q’, a poorly characterized trace mineral that is insoluble in HCl-HF but soluble in HNO₃, and an insoluble residue, consisting of ferrichromite, carbonaceous matter, and spinel.Bulk meteorites show some correlation of the noble-gas pattern with McSween's subclasses: two ‘oxidized’ C3V's—Allende (LEWIS et al, 1975) and Grosnaja— have lower Ar/Xe but higher Ne/Xe ratios than the ‘reduced’ C3V's—Vigarano and Leoville—which are transitional to LL3's and C3O chondrites in both respects. An HCl-soluble mineral of high Ar/Xr ratio seems to be responsible. In other respects, the 3 C3V's of this study resemble Allende, with only moderate differences. Phase Q contains most of the Ar, Kr, Xe, but only small amounts of Ne; the etched residues contain planetary Ne ($\text{Ne}{}^{20}\text{Ne}{}^{22}\text{? 8.5}$) and the controversial CCFXe component, enriched in the heavy Xe isotopes ($\text{Xe136}\text{Xe132 ? 0.4–0.5}$). The CCFXe is accompanied by an ‘L-Xe’ component that is enriched in the light Xe isotopes. The proportion of the two is virtually constant in C3V's. as in all other C-chondrites. in contrast to the ~ 2-fold variation in ordinary chondrites.C3V's have systematically higher $\text{Xe}{}^{136}\text{Xe}{}^{132}$ ratios, and hence higher ratios of CCFXe to planetary Xe, than do other chondrite classes. This may reflect some peculiarity in their formation conditions, favoring uptake of CCFXe.     

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.     

The 21Ne production rate in stony meteorites estimated from 10Be and other radionuclides

The ¹⁰Be contents of 28 stony meteorites with known ²¹Ne contents range from 0.97 to 23 dpm/kg and give an average ²¹Ne production rate (P₂₁) of (0.28 ± 0.02) × 10⁸ cm³ STP/g-Myr for shielding conditions corresponding to ${}^{22}\text{Ne}{}^{21}\text{Ne}\text{= 1.114}$ in an H-chondrite. Our $\text{P}{}_{21}\text{(}{}^{10}\text{Be)}$ agrees with others' P₂₁ based on ²²Na, ⁸¹Kr and ⁵³Mn but not on ²⁶A1. Temporal variations in the cosmic ray flux do not explain the disagreement satisfactorily; major errors in the radionuclide half-lives are not indicated. The discrepancy seems rooted in the data selection and the difficulties of making accurate corrections for shielding, chemical composition and other sources of variability.     

Noble gases in E-chondrites

Noble gas data are reported for 12 E-chondrites. Combined with literature data, they show that K-Ar ages are >4 Æ for 14 out of 18 meteorites, yet U, Th-He ages are often shorter, perhaps due to late, mild reheating. Cosmic-ray exposure ages differ systematically between types 4 and 6, with E4's mostly below 16 Myr and E6's above 30 Myr. This may mean that the E-chondrite parent body contains predominantly a single petrologic type on the (~ 1 km) scale of individual impacts, in contrast to the more thoroughly mixed parent bodies of the ordinary chondrites.The heavy noble gases consist of at least two primordial components: the usual planetary component (${}^{36}\text{Ar}{}^{132}\text{Xe}\text{~ 80}$) and a less fractionated, ‘subsolar’ component ($\text{2700 ≤}{}^{36}\text{Ar}{}^{132}\text{Xe}\text{≤ 3800}$). The latter is found in highest concentration in the E4 chondrite South Oman (³⁶Ar = 760 × 10^?8cc/g, ${}^{36}\text{Ar}{}^{132}\text{Xe}\text{= 2700}$). The isotopic compositions of both components are similar to typical planetary values, indicating that some factor other than mass controlled the noble gas elemental ratios. The heavy Xe isotopes occasionally show some of the lowest ${}^{134}\text{Xe}{}^{132}\text{Xe}$ and ${}^{136}\text{Xe}{}^{132}\text{Xe}$ ratios measured in bulk chondrites, suggestive of nearly fission-free Xe (e.g. ${}^{136}\text{Xe}{}^{132}\text{Xe}\text{= 0.3095 ± 0.0020}$). Amounts of planetary gas in E4 E6 chondrites fall in the range for ordinary chondrites of types 4–6, but, in contrast to the ordinary chondrites. fail to correlate with petrologic type or volatile trace element contents. Another unusual feature of E-chondrites is that primordial Ne is present even in most 4's and 5's (²⁰Ne_p ~ 1 to 7 × 10^?8cc/g). with an isotopic composition consistent with planetary Ne.Analyses of mineral separates show that the planetary gases are concentrated in an HF- and HCl-insoluble mineral similar to phase Q, the poorly characterized, HNO₃-soluble carrier of primordial gases in carbonaceous and ordinary chondrites. The subsolar gases, on the other hand, are located in an HCl- and HNO₃-resistant phase, possibly enstatite or a minor phase included in enstatite. Much of the ¹²⁹Xe_r (50% for E4's, > 70% for E6's) is in HCl-resistant but HF-soluble sites, suggestive of a silicate.A similar subsolar component may be responsible for the high ${}^{36}\text{Ar}{}^{132}\text{Xe}$ ratios of some C3's, unequilibrated ordinary chondrites, and the unique aubrite Shallowater. The planet Venus also has a high $\text{Ar}\text{Kr}$ ratio, well above the planetary range, and hence may have acquired its noble gases from an E-chondrite-like material, similar to South Oman.