Noble Gas Components Research Articles

Noble gases in presolar diamonds I: Three distinct components and their implications for diamond origins

Abstract— High‐purity separates of presolar diamond were prepared from 14 primitive chondrites from 7 compositional groups. Their noble gases were measured using stepped pyrolysis. Three distinct noble gas components are present in diamonds, HL, P3, and P6, each of which is found to consist of five noble gases. P3, released between 200 °C and 900 °C, has a “planetary” elemental abundance pattern and roughly “normal” isotopic ratios. HL, consisting of isotopically anomalous Xe‐HL and Kr‐H, Ar with high 38Ar/36Ar, and most of the gas making up Ne‐A2 and He‐A, is released between 1100 °C and 1600 °C. HL has “planetary” elemental ratios, except that it has much more He and Ne than other known “planetary” components. HL gases are carried in the bulk diamonds, not in some trace phase. P6 has a slightly higher median release temperature than HL and is not cleanly separated from HL by stepped pyrolysis. Our data suggest that P6 has roughly “normal” isotopic compositions and “planetary” elemental ratios. Both P3 and P6 seem to be isotopically distinct from P1, the dominant “planetary” noble‐gas component in primitive chondrites. Release characteristics suggest that HL and P6 are sited in different carriers within the diamond fractions, while P3 may be sited near the surfaces of the diamonds.We find no evidence of separability of Xe‐H and Xe‐L or other isotopic variations in the HL component. However, because ∼1010 diamonds are required to measure a Xe composition, a lack of isotopic variability does not constrain diamonds to come from a single source. In fact, the high abundance of diamonds in primitive chondrites and the presence of at least three distinct noble‐gas components strongly suggest that diamonds originated in many sources. Relative abundances of noble‐gas components in diamonds correlate with degree of thermal processing (see companion paper), indicating that all meteorites sampled essentially the same mixture of diamonds. That mixture was probably inherited from the Sun's parent molecular cloud.

Noble gases in mafic phenocrysts and xenoliths from New Zealand

We have determined the elemental and isotopic compositions of noble gases in young subduction-related phenocrystic olivine and clinopyroxene samples from the Taupo Volcanic Zone, central North Island, New Zealand, and in behind-arc intraplate phenocrystic and xenolithic olivine samples from the Northland and Auckland Volcanic Provinces, northern North Island, New Zealand. Helium isotopic ratios range from MORB-like 3He 4He values of about 11 × 10 −6 to lower values of about 6 × 10 −6, consistent with previous measurements of helium isotopic ratios in subduction-related samples. 40Ar 36Ar and 21Ne 22Ne ratios range from atmosphere-like compositions to maximum values of about 700 and 0.033, respectively. In contrast, most of the 21Ne 22Ne ratios are generally indistinguishable from atmospheric values. The variations in helium, neon, and argon isotopic ratios are interpreted as resulting from mixing of: 1. (a) a primordial 3He-rich component derived from the upper mantle and characterised by MORB-like 3He 4He ratios of about 12 × 10 −6; 2. (b) a radiogenic 4He-rich component derived from crustal materials and characterised by a 3He 4He ratio of less than 2 × 10 −7, and 3. (c) a helium-poor atmosphere-derived component which dominates the heavier noble gases. By combining the helium and argon isotopic results, it is possible to estimate the relative contribution of each of these three components to the total 40Ar observed in each sample. Based on the present understanding of the origin and evolution of arc magmas, a simple qualitative model of the mechanisms which introduce noble gases to the parent magmas of the samples is developed. However, it remains uncertain whether the atmospheric and crustal-derived noble gas components are introduced to the mantle source regions of the magmas by subduction, or alternatively, are introduced by interactions between the ascending parent magmas and the overlying crust.

Long‐term compositional variation in solar corpuscular radiation: Evidence from nitrogen isotopes in the lunar regolith

Implantation of solar corpuscular radiation into the lunar surface generates a population of solar atoms in the rims of lunar regolith grains. Laboratory analysis of those atoms can yield a measure of solar composition. Nitrogen trapped in the lunar regolith consists of at least two components, putatively originating in the Sun, differing in release temperature and therefore probably in implantation energy. The higher‐energy component is depleted in 15N relative to the lower‐energy component by amounts that range up to at least 20%. These components superficially resemble those identified previously in the solar‐derived light noble gases, though with several marked differences. Thus the higher‐energy noble gas components are depleted in the lighter isotope. Unlike the noble gas case, the 15N/14N ratios of both N components vary with antiquity in a complex fashion; the lower‐energy component echoes the variations in the higher‐energy component which dominate the isotopic evolution of the bulk samples. The magnitude of the bulk sample variation exceeds 30%; the higher‐energy component varies by at least 25%. The bulk long‐term trend in 15N/14N does not result from variations in mixing ratio of the two components. Both the compositional difference between the components and the long‐term variations within them apparently originate in the Sun, though this conclusion is inconsistent with current understanding of solar structure and evolution. The nitrogen isotopic record therefore appears to represent a major challenge to solar physics.

Solar noble gases in the Earth: The systematics of helium-neon isotopes in mantle derived samples

Primordial 3He, together with neon showing enrichment in 20Ne and 21Ne relative to 22Ne compared with atmospheric values, have been identified in many samples derived from the Earth's mantle. To explain the enrichment of 21Ne and 20Ne in the mantle source regions for these samples, it is necessary to mix at least two distinct non-atmospheric neon components. The two most likely candidates are nucleogenic and solar neon. Nucleogenic 21Ne, produced by local decay of U and Th, elevates 21Ne 22Ne ratios. Solar neon is the only known component which has a 20Ne 22Ne ratio greater than both the atmospheric value and the 20Ne 22Ne ratios observed in terrestrial samples. We suggest, therefore, as a working hypothesis to account for the observed non-atmospheric neon, that there has been mixing of two neon components, solar and nucleogenic, in the mantle. If the Earth's primordial composition was solar, then we expect to see a correlation between the helium and neon isotope systematics. This is because primordial helium and neon would all be solar, and variations in the observed 3He 4He and 21Ne 22Ne ratios in the mantle would be due to the time integrated ingrowth of radiogenic 4He ( 4He ∗) and nucleogenic 21Ne ( 21Ne ∗), having a constant 4He ∗ 21Ne ∗ production ratio. This relationship can be explicitly stated as: 21Ne ∗ 22Ne s =}( 4He 3He ) Mantle − ( 4He 3He ) s} 21Ne ∗ 4He ∗ ( 3He 22Ne ) s , where subscript S denotes the solar composition. Using the above equation we can calculate hypothetical 3He 4He ratios related to the neon isotopic compositions in the mantle sources. We are able to correlate the observed 3He 4He ratios of all available samples having non-atmospheric neon isotopic ratios with the slopes of neon mixing lines between mantle and present-day atmospheric neon in 20Ne 22Ne − 21Ne 22Ne space. Thus, the helium and neon isotopic signatures in the mantle can be explained by mixing of a primordial solar component, different fractions of radiogenic and nucleogenic components produced by radioactive processes inside the Earth, and a present-day atmospheric component. The correlation between observed helium and neon isotopic ratios in samples derived from the mantle provides strong support for the notion that a significant primordial noble gas component in the Earth was of solar composition. This provides a critical boundary condition for models regarding how and when the Earth acquired its volatiles, and how its atmosphere evolved.

Experimental technique to investigate the interstellar gas - Preliminary analysis

The Interstellar Gas Experiment (IGE) exposed thin metallic foils to collect neutral interstellar gas particles. These particles penetrate the solar system due to their motion relative to the sun. Thus, it was possible to entrap them in the collecting foils along with precipitating magnetospheric and perhaps some ambient atmospheric particles. For the entire duration of the Long Duration Exposure Facility mission, seven of these foils collected particles arriving from seven different directions as seen from the spacecraft. In the mass spectrometric analysis of the noble gas component of these particles, we have detected the isotopes of He-3, He-4, Ne-20, and Ne-22. In the foil analyses carried out so far, we find a distribution of particle arrival directions which shows that a significant part of the trapped particles are indeed interstellar atoms. The analysis needed to subtract the competing fluxes of magnetospheric and atmospheric particles is still in progress.

Noble Gases in Japanese Chondrites: Their Gas Retention and Cosmic-Ray Exposure Histories.

Noble gas concentrations and isotopic ratios were measured for 12 Japanese chondrites. Cosmic-ray exposure ages and gas retention ages obtained for these chondrites are discussed with those for other Japanese chondrites already reported. Cosmic-ray exposure ages of L chondrites range from 5 to 60 Ma without clear cluster, while H chondrites belong to two clusters around 7 and 30~40 Ma. More than half of L chondrites have U, Th-He, and K-Ar ages lower than 3.0 Ga, indicating gas loss by shock event. The concentrations of trapped Ar, Kr, and Xe agree with those inferred from correlation reported between the trapped gas content and the petrographic type. Shiraiwa (H4), find, is the only exception, whose Xe concentration is in the range of type 6. Noble gas data confirm that Kariyasu is a fragment of the Mino (Gifu) metrorite shower, and Hashima and Kasamatsu are different falls. The enstatite chondrite Kishima has a low concentration of subsolar noble gas component. Because the measured concentrations of the subsolar type noble gases are lower than reported ones in Fukutomi (L4-5), the carrier which provide such noble gases should be heterogeneously distributed in Fukutomi.

Characterisation of Q-gases and other noble gas components in the Murchison meteorite

Noble gases in several HF/HCl resistant residues of the CM2 chondrite Murchison were measured by closed-system stepped etching, in order to study the planetary gases in their major carrier “Q”—an ill-defined minor phase, perhaps merely a set of adsorption sites. Neon, Ar, Kr, Xe, and probably also He in “Q” of Murchison have the same isotopic and nearly the same elemental abundances as their counterparts in Allende (CV3). The isotopic composition of Ne-Q is consistent with mass-dependent fractionation of either solar wind Ne or Ne from solar energetic particles. Unlike Allende, Murchison during HNO 3 attack releases, besides Q-gases, large amounts of two other Ne-components, Ne-E and Ne-A3, a third subcomponent of Ne-A. This work confirms that Q-gases of well-defined composition were an important noble gas component in the early solar system and are now found in various classes of meteorites, such as carbonaceous chondrites, ureilites, and ordinary chondrites. Ne-Q may have played a role in the formation of noble gas reservoirs in terrestrial planets.

Noble gases in lunar anorthositic rocks 60018 and 65315: Acquisition of terrestrial krypton and xenon indicating an irreversible adsorption process

Lunar anorthositic breccias 60018 and 65315 contain a trapped Xe component with isotope ratios similar to those in terrestrial atmospheric Xe. We analyzed all five noble gases in eight grain size fractions of 60018 and in several bulk samples of 65315 in order to characterize the nature of the trapped components. Trapped gas abundances in 60018 are 100 to 1000 times lower than in a typical regolith breccia; they are grain size anticorrelated for grain sizes < 30 μm. In 65315, trapped He, Ne, and Ar concentrations are among the lowest ever observed for lunar material. Except for Xe, the isotopic abundances of the trapped components in both rocks are consistent with solar wind composition. Because of the uncertain results as to the origin of the terrestrial-like Xe component, we crushed samples of 60018 and 65315 in atmospheres spiked with 86Kr and 129Xe. These experiments showed unequivocally that anorthositic samples can be contaminated by Kr and Xe, and maybe also by Ar, from the ambient atmosphere. At least 75% of the acquired terrestrial and spike gases are released only at temperatures above 600°C. Krypton and xenon concentrations are grain-size anticorrelated, indicating surface adherence of the gas atoms. Furthermore, the amount of gas in a sample is approximately proportional to the partial pressure of the gas to which the sample was exposed, as described by Henry's law. Xenon uptake is about one order of magnitude more effective than Kr uptake, and activation energies, measured at room temperature, are in the range of 10–20 kJ/mol. Both characteristics are typical for ordinary physical adsorption. However, the high extraction temperatures show that somehow the gas atoms get fixed, either by strong chemisorptive bonding with activation energies around 200 kJ/mol, or by getting trapped beneath the surface. Therefore, we use the term “irreversible adsorption” for the phenomenon. Fixation is likely to take place during crushing, when mechanical, thermal, and maybe electromagnetic energy is supplied, although the air contamination of an uncrushed 65315 sample cannot be explained in this way. Irreversible adsorption of terrestrial Kr and Xe has been observed for several lunar anorthosites with low solar wind content, but also for some meteoritic samples, in particular diogenites, which are composed mainly of pyroxene. A similar process may have been responsible for the incorporation of nonterrestrial noble gas components into extraterrestrial material, e.g., the planetary trapped gases in meteorites or the surface-correlated components of 129Xe and fission-type Xe in some lunar breccias. Furthermore, other volatile elements might be affected by irreversible adsorption.

Solar noble gases in the unique chondritic breccia Allan Hills 85085

The chemical composition of the chondritic breccia Allan Hills 85085 does not match that of any known group of chondrites. In addition, this meteorite contains extremely fine-grained fragments and small chondrule-like inclusions. We investigated the noble gas isotopic abundances in bulk samples, in a fine-grained silicate fraction, and in a coarse-grained fraction containing the metal phase. Solar gases are present in the fine-grained silicates and indicate processing of the ALH85085 material in an asteroidal regolith. He and Ne are enriched in a < 40 μm grain size fraction indicating surface implantation of solar particles. The solar noble gas component is characterized by an elemental abundance pattern and isotopic ratios typical for lunar and asteroidal regolith material: 4He/ 36Ar= 469 , 20Ne/ 36Ar = 4.2 , 4He/ 3He= 2300 ± 600 , 20Ne/ 22Ne= 12.5 ± 0.4 . The major noble gas component in the bulk and coarse-grained fractions are planetary type trapped gases. Abundances and isotopic composition are similar to those in type-2 and -3 chondrites. In some respects ALH85085 resembles another unique chondrite, Kakangari, but it differs in its FeNi content that is almost twice as high as in Kakangari, and in other characteristics. Both, the cosmic-ray exposure age and the K— 40Ar gas retention age, are relatively low: The travel time of ALH85085 as a small object in space was 1.7 ± 0.8Ma and a fraction of 40Ar was lost as indicated by the 40K— 40Ar retention age of 2900 ± 300Ma.

Interstellar graphite in meteorites

IN a continuation of our search for interstellar 'needles' in the meteoritic 'haystack'1,2, we have now identified graphite grains, 1–4 µm in diameter, in the Murchison C2 chondrite. The interstellar origin of these grains is demonstrated by their 12C/13C ratio, which ranges from 0.09 to 16 times the Solar System value, and by the presence of the noble-gas component 'Ne–E(L)', nearly monoisotopic 22Ne from the decay of 22Na (with a half-life of 2.6 yr). The grains apparently formed in the outflows of novae and red giants, and demonstrate that graphite can form as a circumstellar condensate. Curiously, interstellar graphite is much rarer than interstellar microdiamonds (<2 p.p.m. compared to 400 p.p.m.) or even SiC (6–9 p.p.m.), although diamond is thermodynamically unstable relative to graphite. The main reason may be preferential destruction. Graphite is the third type of circumstellar grain that has become available for laboratory study.

Noble Gas Record of Japanese Chondrites

Abstract Concentrations and isotopic ratios of noble gases are reported for nineteen Japanese chondrites. Among those, Nio (H3-4) is a solar-gas-rich meteorite. U/Th - He ages are younger than K - Ar ages for all meteorites studied. Six of the nine L-chondrites give significantly young K-Ar ages, suggesting gas loss by impact shock heating. The remaining three L-chondrites and seven of the ten H-chondrites have K-Ar ages older than 4 Ga. The L-chondrite Nogata and the H-chondrites Numakai, Ogi and Higashi-Koen have concordant ages. Cosmic-ray exposure ages for six of the H-chondrites show clustering around the 6-Myr peak in the distribution of exposure ages, while those for the L-chondrites, ranging from 8.2 to 64 Myr, do not show clustering. Fukutomi (L4) contains trapped 36Ar in excess, 3.5 times enriched compared to the highest value so far reported for type-4 ordinary chondrites except solar-gas-rich chondrites. The 36Ar/132Xe and 84Kr/132Xe ratios fit along a mixing line between a planetary and a sub-solar (or argon-rich) component found in separates of E-chondrites [43], The Xe isotopic composition is identical with that in Abee and Kenna. The isotopic signatures suggest that this meteorite may contain mineral fragments bearing the noble gas component found in E-chondrites or ureilites. Fukutomi also contains 80Kr, 82Kr and 128Xe produced by epithermal neutron captures on 79Kr, 81Kr and 127I, respectively. From the neutron-produced Kr, the preatmospheric minimum radius is estimated to be 20 cm with an assumption of a spherical meteoroid.

Helium, neon, and argon in meteorites—A data compilation

Noble gases have been measured in meteorites for more than 100 years. The last 50 years have been especially fruitful, with concentration and isotopic compositional analysis of He, Ne, Ar, Kr, and Xe making important contributions to meteorite research. Differently trapped noble gas components are the basis for understanding planetary atmospheres and even different stages of stellar evolution. Noble gases are a valuable tool to detect pairing of meteorite specimens or even to prove whether a rock is a meteorite or not. Noble gas data, however, are distributed over a large number of publications. Sometimes, only concentrations are given for selected isotopes or just a simple derivative quantity is published. We have tried to collect all available measurements of He, Ne, and Ar in meteorites. Here, we present the data in a form that will help easily calculate isotopic or elemental ratios for selected measurements. The present compilation contains all data available as of March 2004.

Isotopic anomalies of Ne, Xe, and C in meteorites. III. Local and exotic noble gas components and their interrelations

Data on gas-rich separates from the Murray and Murchison C2 chondrites are reviewed, in order to characterize their noble-gas components. Revised compositions are obtained for Ne-A1 and Ne-A2, two subcomponents of “planetary” Ne: Ne 20 Ne 22 = 8.86 ± 0.09, 8.46 ± 0.12 ; Ne 21 Ne 22 = 0.0303 ± 0.0007, 0.0348 ± 0.0012 . Ne-AI is associated with a special type of planetary Xe (Xe-P3). Both Ne-A1 and Xe-P3 closely follow Xe-HL, but are located in a separate carrier (Cζ) of high chemical but low thermal resistance (amorphous diamond?); they are present in C1, 2 and unmetamorphosed C3V chondrites, but not in metamorphosed Allende. A new composition is derived for Xe-S: 128/129/130/131/132 = 0.432 ± 0.006/0.119 ± 0.022/1/0.312 ± 0.016/2.030 ± 0.011. However, Xe 130 Xe 132 ratios even in the most enriched samples do not exceed 0.31, suggesting that Xe-S occurs as part of a pseudocomponent, mixed with Xe-P and Xe-HL. A new planetary Xe component, Xe-P5, has been found in the ≥ 1300° fractions of several Murray separates; its carrier is colloidal and resistant to HF and HClO 4 but not H 3PO 4, and hence probably is an oxide mineral. A coarse (>2 μm) spinel fraction from Murray contains fissiogenic Xe matching that from Pu 244 in isotopic composition, but the implied Pu 244 abundance of 1.2 ppb (14 × C1) is surprisingly high. Less than 12% of the fissiogenic Xe can be from Cm 248, which corresponds to an original (Cm 248 Pu 244) o≤ 1.7 × 10 −3 . Murray CJ, a sample strongly enriched in Ne-E(H) and its SiC carrier, contains (2.2) × 10 −8 ml/g of presumably spallogenic Ne 21; a factor 4–6 more than expected from the recent cosmic-ray irradiation. Although a presolar irradiation of the SiC grains is a distinct possibility, more prosaic explanations, such as recoil of Ne 21 from adjacent spinel, must be ruled out first.

Isotopic anomalies of Ne, Xe, and C in meteorites. I. Separation of carriers by density and chemical resistance

In an attempt to characterize the carriers of presolar noble gases, 19—mainly non-colloidal—separates from the Murray and Murchison C2 chondrites were isotopically analyzed for Ne, Xe, and in several cases for C and N. Although most samples were strongly depleted in Xe-HL and enriched in Ne-E(H), Ne-E(L), and Xe-S, the separation methods failed to isolate the noble-gas carriers in pure form. Nonetheless, several new properties of the carriers were established. The carriers of Ne-E(H) and Xe-S are resistant to HCl, HF, boiling HClO 4, and CrO 3-H 2SO 4, and thus must be either diamond or some resistant carbide or oxide (SiC, hibonite, etc.), but not spinel, graphite, or amorphous carbon. These two noble-gas components seem to be associated with two heavy carbon components ( δC 13 ⋍ +1000% . and +1400%.), combusting at ~ 900 and ~ 1200°C, but cannot yet be assigned to either. The carrier of Ne-E(L), Cα, is slowly oxidized by Cr 2O − 7 and HNO 3, and rapidly by boiling HC1O 4. It may be some form of amorphous carbon, of δC 13 ⋍+340% . A new carbon component, Cθ, was found as 0.2–2 μm inclusions in Murchison spinel. It is amorphous, has δC 13 = −50%, and contains little or no noble gas, though the surrounding spinel contains a component of Ne 20 Ne 22 ⋍ 10.7 ± 0.2, possibly Ne-C from solar flares. The Cθ grains require a gas phase of C/O ≥ 1 for their formation, well above the solar ratio of 0.6, and presumably the occluding spinel, too, formed from such a gas. Both Cθ and spinel are enriched by ~4% in C 12 and O 16, respectively. This is of interest in connection with the suggestion by Schramm and Olive (1982) that much of the C 12, O 16, and Ne 20 in the solar system was contributed by a massive, nearby supernova. A new heavy nitrogen component ( δN 15 ≥ +252%.) has been found. It has an abundance of ~ 1 ppm in the bulk meteorite, combusts at 450–500°C, and may be associated with isotopically normal carbon or with Cα.

Isotopic anomalies of Ne, Xe, and C in meteorites. II. Interstellar diamond and SiC: Carriers of exotic noble gases

Continuing our efforts to find the carriers of presolar noble gases, we isolated 15 separates from the Murray C2 chondrite on the basis of grain size and chemical resistance, and analyzed them by mass spectrometry for Ne and Xe. The abundant (570 ppm) Cδ diamond, carrier of Xe-HL and Ne-A1, 2, was efficiently removed by a new type of colloid separation. The rare component Xe-S was enriched ~ 17-fold over the best previous sample; its carrier Cβ appears to be SiC, of much larger size than Cδ (mean diameter ~0.12 μm vs. 0.0026 μm) and lower abundance (~2 ppm), but likewise showing a sharply peaked log-normal size distribution. If these distributions reflect grain growth from circumstellar gas shells, then their near-perfect shape suggests minimal alteration of the grains by secondary processes such as fragmentation or erosion, and hence a short residence time in interstellar space. A third component, Ne-E(H), was enriched ~ 9-fold over the best previous sample in an acid-insoluble residue of SiC, Cδ, and chromite, which was left when a coarse spinel fraction was dissolved. This SiC (~7 ppm), differing from the Cβ-SiC mentioned above, appears to be Cϵ, the carrier of Ne-E(H). The data obtained thus far show that both diamond (Cδ) and amorphous carbon (Cα, Cθ) occur as interstellar grains, along with SiC (Cβ, Cϵ). Crystalline graphite, though long predicted as a stable stellar condensate at high C/O ratios, has not been found. Each noble-gas component is associated with only one carbon allotrope or compound, which suggests that carbon condensation in a given star is strongly selective.

Large isotopic anomalies of Si, C, N and noble gases in interstellar silicon carbide from the Murray meteorite

Primitive meteorites contain several noble gas components with anomalous isotopic compositions which imply that they—and their solid 'carrier' phases—are of exotic, pre-solar origin. Having enriched two of these gas components by a factor of ∼2× 104 in minor fractions of the Murray meteorite1, we found that these fractions contain two minerals not previously seen in meteorites: silicon carbide and an amorphous Si–O phase2, possibly an alteration product of another silicon-bearing mineral. Here we report ion microprobe analyses of these phases which reveal very large isotopic anomalies in silicon, nitrogen and carbon, exceeding the highest anomalies previously measured by factors of up to ˜50. We conclude that these phases are circumstellar grains from carbon-rich stars, whose chemical inertness allowed them to survive in exceptionally well-preserved form.

Local and exotic components of primitive meteorites, and their origin

Most of the material of chondrites was heavily reprocessed in the early Solar System, and hence retains only a dim memory of its interstellar origin even in the least altered meteorites. Opaque matrix, the most primitive material, seems to have taken up Fe2+ and changed its mineralogy and texture. Chondrules and Ca, Al-rich inclusions have been further altered by melting, oxidation or reduction, loss of volatiles, etc. None the less, small amounts of exotic components have survived, as indicated by isotopic anomalies. A dust component enriched in ieO is the most abundant and widespread. It survives in Ca, Al-rich inclusions as anomalous spinel grains, but is recognizable even in highly evolved meteorites and planets from variations in bulk oxygen isotopic composition. A few inclusions show small nucleosynthetic anomalies for many elements (Si, Ca, Ti, Cr, Sr, Ba, Nd, Sm), always coupled with mass fractionation of several of these elements, as well as 0 and Mg. Seven extinct radionuclides ( 26 AI, 41 Ca, 53 Mn, 107 Pd, 129 I, 146 Sm, and 244 Pu) have been recognized from their decay products, and provide clues to the chronology and nucleosynthetic sources of the early Solar System. Highly volatile elements, such as C, N and the noble gases, show especially large and numerous isotopic anomalies. The noble-gas components include Ne-E (monoisotopic 22 Ne from the (B+ decay of 2.6a 22 Na), Xe-HL (enriched 2-fold in the light and heavy isotopes), and Xe-S (enriched in the even-numbered, middle isotopes 128, 130 and 132). They are located in carriers that themselves are anomalous, e.g. carbon enriched up to 2.4-fold in 13 C or depleted by more than 30 % in 15 N, or spinel enriched in 16 O and 13 C. Other anomalies include nitrogen enriched 2-fold in 15 N and hydrogen enriched 5-fold in D ; probably relict interstellar molecules. A variety of astronomical sources seem to be required: novae, red giants, supernovae and molecular clouds.

On the presolar origin of the “normal planetary” noble gas component in meteorites

Several components of planetary noble gases, including CCFXe (Xe‐X), s‐process Kr and Xe, and Ne‐E, are now thought to have had a presolar origin. We propose that the “normal planetary” noble gas component, which contains most of the planetary Ar, Kr, and Xe, is also presolar. This component was trapped in carbonaceous mantles as the mantles formed on grain surfaces in the molecular cloud. The presolar dust grains and their carbonaceous mantles were then incorporated into primitive meteorites. This model naturally explains: (1) the affinity of “normal planetary” noble gases for carbonaceous material in primitive chondrites; (2) the near absence of He and Ne in the “normal planetary” component; (3) the elemental fractionation patterns of the “exotic” and “normal planetary” components; (4) the similarity of the isotopic compositions of “normal planetary” and trapped solar Ar, Kr, and Xe; (5) the high noble gas content of the “normal planetary” gas carrier; (6) several aspects of the chemistry of the “normal planetary” gas carrier; (7) the correlation of planetary noble gases with the fine‐grained material in primitive chondrites; and (8) the widespread occurrence of the planetary fractionation pattern throughout the solar system.

Noble gas composition of deep brines from the Palo Duro Basin, Texas

Deep groundwaters in sedimentary basins can be sufficiently old (> 10 m.y.) to have accumulated both radiogenic 4He and 40Ar∗. Differences in the ratio of(U + Th)K for aquifer lithologies lead to variations for 4He40Ar∗ in the groundwater. These variations can be used to resolve chronologically significant noble gas components. Application of a binary model to brine samples from the Palo Duro Basin, Texas yields (U, Th)-4He residence times of 100 to 300 m.y. Concentrations of two non-radiogenic noble gases (20Ne and 36Ar) provide information on the salinities of the water that recharged these aquifers.

Nucleogenic noble gas components in the Cape York iron meteorite

We report data on neutron capture products of the secondary cosmic ray component, the inferred proton and neutron fluences, and the identification of double beta decay of 82Se in heavily shielded samples of the Cape York iron meteorite. One purpose of this study is to develop a new chronometer for cosmic ray exposure, based on the nuclides 129I (16 My half-life) and 129Xe from low energy cosmic ray reactions on Te. The abundance ratio of these two nuclides permits the determination of an (effective) exposure age of 93 ± 16 My, which represents the first exposure age datum of Cape York. The very small concentrations of spallogenic 38 Ar = 6.5 × 10 −10 cm 3 STP/g in the metal and troilite (per g Fe) document the heavily shielded locations of our sample. An excess of 129Xe in the troilite is shown to be entirely due to the decay of cosmic-ray-produced 129I. On the other hand, an inclusion in the troilite reveals the presence of 129Xe from extinct 129I and documents its ~4.5 Gy formation age. Mono-isotopic excess of 82Kr is identified as due to ββ-decay of 82Se with an inferred half-life of 1.0 × 10 10 y. This represents the first ββ-decay product observed in a meteorite.