Isotopic Composition Of Xenon Research Articles

Noble gas evolution of the martian atmosphere in the last 4 Gyr recorded by regolith breccia NWA 8114

The martian meteorite Northwest Africa (NWA) 8114 is a regolith breccia grouped with the NWA 7034 (‘Black Beauty’) stone and others. The meteorite, with its complex rock and mineral load, records over 4.4 billion years of martian geological and atmospheric history. In this work we present new analyses of noble gases in NWA 8114, and consider the constraints they impose on the evolution of the martian atmosphere over the past 4 billion years. We also report a petrographic overview, halogen abundances, and an argon isotope age, which provide context for interpreting the noble gas data.The krypton and xenon elemental signature of NWA 8114 is elementally fractionated with respect to the present-day martian atmosphere as measured in shergottite glasses; there is no requirement for a contribution from the ancient martian atmosphere in our data. The xenon isotopic composition incorporates (i) a component enriched in 129Xe (maximum 129Xe/132Xe = 2.450 ± 0.045 compared with a solar ratio of ∼ 1), which is similar to the present day martian atmosphere, (ii) a cosmic-ray spallation component dominated by production from barium, and (iii) a fission component. We estimate a cosmic ray exposure (CRE) age of 5.7 ± 1.3 Myr from cosmogenic 21Ne and 38Ar.Understanding how the martian atmosphere has changed through the planet’s history is a key part of understanding the planet’s geological history and evolution. We develop a model for the evolution of the martian atmosphere constrained by the amount of spallation-derived xenon in the atmosphere today and the evolution of the 129Xe/132Xe ratio over time. A baseline model in which the early atmosphere collapsed 3.7 Gyr ago (and assuming no further loss) requires a constant degassing of the crustal budget of spallation xenon of 0.034 % Myr−1 to accumulate sufficient spallation-derived xenon in the atmosphere. Combining constraints imposed by the 129Xe/132Xe ratio with the spallation budget requires loss of xenon from the martian atmosphere over the last 3.7 Gyr, with the present day budget being as little as 20 % of that at the start of this period.

Pre-subduction mantle noble gas elemental pattern reveals larger missing xenon in the deep interior compared to the atmosphere

Understanding volatile evolution on Earth provides critical information on the processes that shape the Earth, and hence the solar system. The noble gas elemental and isotopic composition of the Earth's mantle traces the sources of Earth's volatiles as well as evolution processes, such as mantle degassing and regassing via subduction. However, ubiquitous shallow-level atmospheric contamination of mantle-derived samples has hampered determining the deep mantle heavy noble gas (Kr, Xe) isotopic and elemental composition. Moreover, the present-day elemental composition of the mantle reflects mixing of initial volatiles with atmospheric noble gases recycled through subduction that makes understanding the elemental signatures acquired during accretion difficult. Using a recently-developed protocol, we previously measured the krypton and xenon isotopic and elemental compositions of the Galápagos and Iceland plume sources, which have among the most primitive helium and neon isotopic signatures, sampling one of the least degassed, most primordial mantle reservoirs. Based on these measurements, here we introduce a new approach to correct for recycling and hence determine the initial noble gas elemental ratios of the deep mantle. Our study leaves room for a substantial proportion of 36Ar in the mantle to be primordial in origin. Most importantly, we show that the deep mantle, prior to the injection of any atmospheric volatiles, was depleted in Xe relative to Kr by about two orders of magnitude when compared to chondritic compositions, and the Xe depletion was larger in the mantle than in the modern-day atmosphere. Unlike the atmosphere that has protracted history of Xe depletion through the Archean, the deep mantle xenon depletion was acquired very early in Earth's history, most likely during accretion. Hence, missing xenon in the Earth's interior and in the atmosphere appears to be two distinct problems. Three possible scenarios, potentially acting in sync, may have led to the mantle xenon depletion: Xe partitioning into the core, magma ocean outgassing and a xenon deficit in the Earth's parent bodies, such as comets.

Neutron capture 128Xe and 129Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons

AbstractThe petrographic study of the San Juan A2 polished section demonstrated textural and compositional similarities with the Campo del Cielo IAB iron meteorite, with trace element abundances in metal following the pattern of bulk Campo del Cielo. Xenon, neon, and helium isotopic compositions have been measured in radial graphite rims, massive graphite inclusions, fine‐grained graphite aggregates, cliftonite, and platy graphite. Two silicate inclusions and two areas of metal were also analyzed. 3He/4He versus 4He/21Ne data for San Juan metal plot next to the values reported for the El Taco fragment of Campo del Cielo, supporting San Juan being a part of the Campo del Cielo meteorite shower. Based on the Ne isotopic composition of its components, and the observed correlation between 128Xe and 129Xe, the San Juan A fragment of Campo del Cielo was well shielded from the primary galactic cosmic ray high‐energy irradiation. Its size allowed the secondary neutrons to be fairly well thermalized, receiving an equivalent (normalized to the research reactor with highly thermalized neutron spectrum) fluence of thermal and epithermal neutrons of 6.6 × 1017 n cm−2. Considering 1.8 × 108 years single‐stage and constant exposure geometry irradiation history for Campo del Cielo, and assuming the identical neutron flux spectra for the research reactor and Campo del Cielo, the average thermal equivalent neutron flux for San Juan is about 1.2 × 102 n cm−2 s−1. Xe isotopic composition in the radial graphite rims and platy graphite shows evidence of live 129I in San Juan and is consistent with a mixture of iodine‐derived and tellurium‐derived Xe.

Xenon isotopic constraints on the history of volatile recycling into the mantle.

The long-term exchange of volatile species (such as water, carbon, nitrogen and the noble gases) between deepEarth and surface reservoirs controls the habitability of the Earth's surface. The present-day volatile budget of the mantle reflects the integrated history of outgassing and retention of primordial volatiles delivered to the planet during accretion, volatile species generated by radiogenic ingrowth and volatiles transported into the mantle from surface reservoirs over time. Variations in the distribution of volatiles between deep Earth and surface reservoirs affect the viscosity, cooling rate and convective stress state of the solid Earth. Accordingly, constraints on the flux of surface volatiles transported into the deep Earth improve our understanding of mantle convection and plate tectonics. However, the history of surface volatile regassing into the mantle is not known. Here we use mantle xenon isotope systematics to constrain the age of initiation of volatile regassing into the deep Earth. Given evidence of prolonged evolution of the xenon isotopic composition of the atmosphere1,2, we find that substantial recycling of atmospheric xenon into the deep Earth could not have occurred before 2.5 billion years ago. Xenon concentrations in downwellings remained low relative to ambient convecting mantle concentrations throughout the Archaean era, and the mantle shifted from a net degassing to a net regassing regime after 2.5 billion years ago. Because xenon is carried into the Earth's interior in hydrous mineral phases3-5, our results indicate that downwellings were drier in the Archaean era relative to the present. Progressive drying of the Archean mantle would allow slower convection and decreased heat transport out of the mantle, suggesting non-monotonic thermal evolution of the Earth's interior.

Meteorite constraints on Martian atmospheric loss and paleoclimate

The evolution of Mars' atmosphere to its currently thin state incapable of supporting liquid water remains poorly understood and has important implications for Martian climate history. Martian meteorites contain trapped atmospheric gases that can be used to constrain both the timing and effectiveness of atmospheric escape processes. In this paper, measurements of xenon isotopes in two ancient Martian meteorites, ALH 84001 and NWA 7034, are reported. The data indicate an early episode of atmospheric escape that mass fractionated xenon isotopes culminated within a few hundred million years of planetary formation, and little change to the atmospheric xenon isotopic composition has occurred since this time. In contrast, on Earth atmospheric xenon fractionation continued for at least two billion years (Pujol et al., 2011). Such differences in atmospheric Xe fractionation between the two planets suggest that climate conditions on Mars may have differed significantly from those on Archean Earth. For example, the hydrogen escape flux may not have exceeded the threshold required for xenon escape on Mars after 4.2–4.3 Ga, which indicates that Mars may have been significantly drier than Earth after this time.

The Genesis solar xenon composition and its relationship to planetary xenon signatures

The fluence and isotopic composition of solar wind xenon have been determined from silicon collector targets flown on the NASA Genesis mission. A protocol was developed to extract gas quantitatively from samples of ∼9–25mm2, and xenon measured using the RELAX mass spectrometer. The fluence of implanted solar wind xenon is 1.202(87)×106 atoms 132Xecm−2, which equates to a flux of 5.14(21)×106 atoms 132Xecm−2year−1 at the L1 point. This value is in good agreement with those reported in other studies. The isotopic composition of the solar wind is consistent with that extracted from the young lunar regolith and other Genesis collector targets.The more precise xenon isotopic data derived from the Genesis mission confirm models of relationships among planetary xenon signatures. The underlying composition of Xe-Q is mass fractionated solar wind; small, varying contributions of Xe-HL and 129Xe from 129I decay are present in reported meteorite analyses. In contrast, an s-process deficit is apparent in Xe-P3, which appears to have been mass fractionated to the same extent as Xe-Q from a precursor composition, suggesting similar trapping mechanisms. Solar wind xenon later evolved by the addition of ∼1% (at 132Xe) of s-process xenon to this precursor. As an alternative model to a single source reservoir for Xe-P3, we propose that trapping of xenon onto carbonaceous carriers has been an ongoing process across galactic history, and that preparation of the residues in which Xe-P3 has been identified preferentially preserves longer lived host phases; a higher proportion of these sample xenon isotopic compositions from earlier in galactic chemical evolution, allowing the s-process deficit to become apparent. The relationships among SW-Xe, Xe-Q and Xe-P3 predict that the 124Xe/132Xe ratio for the solar wind is 0.00481(6).

Adsorption of xenon ions onto defects in organic surfaces: Implications for the origin and the nature of organics in primitive meteorites

Noble gases trapped in primitive meteorites are quantitatively hosted by a poorly defined organic phase, labeled phase Q. Xenon is enriched in heavy isotopes by +1.30 ± 0.06% per atomic mass unit (amu, 1 σ) in phase Q relative to solar. To understand the origin of this fractionation, we have performed adsorption experiments of xenon atoms and ions, ionized in a radiofrequency plasma. Within the reaction vessel, anthracite was heated and the resulting smoke deposited onto the walls of the vessel, resulting in carbon-rich films. Xenon was trapped in the carbon films either as ions in the ionization zone of the vessel, or as neutral atoms outside this zone. Xenon trapped as ionic Xe is tightly bound and is enriched by +1.36 ± 0.05%/amu (1 σ) in heavy isotopes, reproducing the isotopic fractionation of xenon trapped in phase Q relative to solar. Neutral xenon is more loosely trapped, is in much lower concentration, and is not isotopically fractionated. Ionized conditions allow the constant xenon isotopic composition observed in meteorite during stepwise heating release to be reproduced. Furthermore, the trapping efficiency of Xe + estimated from these experiments is consistent with the high xenon concentration measured in phase Q of primitives meteorites. Xenon was not trapped in the film by implantation because the energies of the incident Xe atoms and ions were far too low (<1 eV). From the difference of behavior between ionic and neutral forms, we propose that xenon ions were trapped via chemical bonding at the surface of the newly created C-rich film. The observed mass-dependent fractionation of xenon is unlikely to have occurred in the gas phase. It is more probably related to variations in chemical bonding strengths of Xe isotopes as chemical bonds involving heavy Xe isotopes are more stable than those involving light ones. For young stars, including the young Sun, photons emitted in the far UV energy range able to ionize noble gases (<100 nm) were orders of magnitude more abundant than for the Present-day Sun, allowing efficient ionization of gaseous species. A way to achieve Q-noble gas fractionation and trapping was UV irradiation by nearby young stars from O/B association of the surface of growing organic grains in the outer part of the solar system or by the young Sun at the edge of the disk.

Xenon in Archean barite: Weak decay of 130Ba, mass-dependent isotopic fractionation and implication for barite formation

In order to investigate radioactive decay of 130Ba and 132Ba which have half-lives on the order 10 20–10 21 a, the isotopic composition of xenon has been measured in 3.5 Ga barite of the Dresser Formation, Pilbara, Western Australia. The analyzed samples were collected at about 86 m depth from a diamond drill core (Pilbara Drilling Project). The fact that the sample has been shielded from modern cosmic ray exposure reduces the number of potentially interfering production pathways, simplifying interpretation of the Xe isotope spectrum. This spectrum is clearly distinct from that of either modern or ancient atmospheric Xe. A strong excess of 130Xe is identified, as well as other isotopic excursions which are attributed to mass-dependent isotopic fractionation and contributions from products of uranium fission. The mass-dependent fractionation, estimated at 2.1 ± 0.3% amu −1, can be accounted for by mutual diffusion and Rayleigh distillation during barite formation that is consistent with geological constraints. After correction for mass-dependent fractionation, the concentrations of fissiogenic Xe isotopes demonstrate that the U–Xe isotope system has remained closed over 3.5 Ga. From the excess of 130Xe, the two successive electron capture half life of this isotope is estimated at 6.0 ± 1.1 × 10 20 a, which is 3.4 times faster than previously estimated ( Meshik et al., 2001). We could not find evidence of 132Ba decay within our Xe isotope spectra.

Noble gases in spinel peridotite xenoliths from Mt Quincan, North Queensland, Australia: Undisturbed MORB-type noble gases in the subcontinental lithospheric mantle

Noble gas elemental and isotopic compositions have been determined for a suit of fresh spinel peridotite xenoliths from Mt Quincan, North Queensland (Northeast Australia). The observed helium, argon and xenon isotopic compositions are very similar to those reported for mid-ocean ridge basalts (MORB) in that they have following features: (1) 3He/ 4He ratios covering a narrow range from 8 Ra to 10 Ra, (2) 40Ar/ 36Ar (300–4000) and the 3He/ 36Ar (0.0012–0.07; corrected for some recent elemental fractionation) values that plot on the well-established MORB line, and (3) correlated excesses in 129Xe and 136Xe with regard to atmospheric xenon. MORB-like noble gas compositions suggest fluids ultimately derived from the asthenopshere are present in the subcontinental lithospheric mantle beneath northeastern Australia. The absence of any subduction-related noble gas signature precludes the preservation of fluids in the xenoliths added during Paleozoic subduction at the eastern margin of Australia. We also note that there is no mantle plume noble gas signature found in the Mt Quincan xenoliths, despite its location close to the suspected hotspot track across eastern Australia. These features are consistent with Sr and Nd isotopic characteristics of Mt Quincan xenoliths [Handler, M.R., Bennett, V.C., Carlson, R.W. 2005. Nd, Sr and Os isotope systematics in young, fertile peridotite xenoliths from northern Queensland, Australia: A unique view of depleted MORB mantle? Geochim. Cosmochim. Acta 69, 5747–5763.]. Thus, the fluid-entrapment is likely associated with subsequent rifting tectonic settings when asthenospheric fluid (and magma) could rise into the subcontinental lithospheric mantle and was able to overwrite any pre-existing signatures or even replace it with “MORB”-like mantle by physical removal of previously metasomatised lithospheric mantle. Additionally, differing from noble gas compositions previously considered typical for the subcontinental lithospheric mantle, the north Queensland data highlight the existence of noble gas isotopic heterogeneity in the subcontinental lithospheric mantle on a global scale.

What CO 2 well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Study of commercially produced volcanic CO2 gas associated with the Colorado Plateau, USA, has revealed substantial new information about the noble gas isotopic composition and elemental abundance pattern of the mantle. Combined with published data from mid-ocean ridge basalts, it is now clear that the convecting mantle has a maximum (20)Ne/(22)Ne isotopic composition, indistinguishable from that attributed to solar wind-implanted (SWI) neon in meteorites. This is distinct from the higher (20)Ne/(22)Ne isotopic value expected for solar nebula gases. The non-radiogenic xenon isotopic composition of the well gases shows that 20 per cent of the mantle Xe is 'solar-like' in origin, but cannot resolve the small isotopic difference between the trapped meteorite 'Q'-component and solar Xe. The mantle primordial (20)Ne/(132)Xe is approximately 1400 and is comparable with the upper end of that observed in meteorites. Previous work using the terrestrial (129)I - (129)Xe mass balance demands that almost 99 per cent of the Xe (and therefore other noble gases) has been lost from the accreting solids and that Pu-I closure age models have shown this to have occurred in the first ca 100Ma of the Earth's history. The highest concentrations of Q-Xe and solar wind-implanted (SWI)-Ne measured in meteorites allow for this loss and these high-abundance samples have a Ne/Xe ratio range compatible with the 'recycled-air-corrected' terrestrial mantle. These observations do not support models in which the terrestrial mantle acquired its volatiles from the primary capture of solar nebula gases and, in turn, strongly suggest that the primary terrestrial atmosphere, before isotopic fractionation, is most probably derived from degassed trapped volatiles in accreting material.By contrast, the non-radiogenic argon, krypton and 80 per cent of the xenon in the convecting mantle have the same isotopic composition and elemental abundance pattern as that found in seawater with a small sedimentary Kr and Xe admix. These mantle heavy noble gases are dominated by recycling of air dissolved in seawater back into the mantle. Numerical simulations suggest that plumes sampling the core-mantle boundary would be enriched in seawater-derived noble gases compared with the convecting mantle, and therefore have substantially lower (40)Ar/(36)Ar. This is compatible with observation. The subduction process is not a complete barrier to volatile return to the mantle.

Constraints on Nucleosynthesis from Xenon Isotopes in Presolar Material

By applying theoretical constraints to three-dimensional fits of xenon isotope data from presolar grains, we show that they strongly suggest a nucleosynthesis process that produces isotopes without producing s-process isotopes (128Xe, 130Xe) and without producing the conventional r-process isotope 136Xe. It is one of three distinct nucleosynthetic sources that are necessary and sufficient to explain the gross variation in xenon isotopic data across all presolar material. The other source contributing r-process isotopes is responsible for the heavy isotope signature identified in nanodiamonds, which is also present in presolar SiC, and is associated with light isotope enrichment. The relative enrichments of heavy and light isotopes in this component in nanodiamonds and SiC grains are different, implying that the parent nucleosynthetic processes are not inextricably linked. Because minor variations in the isotopic compositions of xenon trapped in nanodiamonds show that two distinct sites contributed nanodiamonds to the early solar system within the average grain lifetime, it is suggested that Type IIa supernovae (SNe IIa) are not the source of the nanodiamonds. The s-process signature derived is consistent with that derived from mixing lines between grain subpopulations for isotopes on the s-process path. This implies that a pure end-member is present in the grains (although not approached in analyses). Our approach is more general and provides a less restrictive set of numerical constraints to be satisfied by proposed theoretical treatments of nucleosynthesis.

Cause for a llama

Subduction zones, where oceanic plates plunge into the deep Earth, were thought to be effective barriers to the recycling of noble gases back into the interior. But now a study of the xenon isotopic composition of mantle gases from a natural gas field in New Mexico suggests that heavy noble gases are reintroduced into the mantle at subduction zones, and that the main source of heavy noble gases in the Earth is recycled seawater. This finding provides an important constraint for future models of convection in the Earth.

Geochemical constraints on mantle dynamics in the Hadean

Mantle convection is intimately linked with terrestrial degassing through decompression melting, magma generation. Hence tracers of mantle degassing through time shed light on mantle dynamics from the Hadean to Present. Xenon isotopes provide an exceptional set of such tracers: 129Xe was produced by the now extinct β-decay of 129I with T 1 / 2 = 15.7 Myr, 131−136Xe were produced by the now extinct spontaneous fission of 244Pu with T 1 / 2 = 82 Myr, and 131−136Xe are produced by the extant spontaneous fission of 238U which decays with T 1 / 2 = 4.45 Gyr. We report new data on the isotopic composition of xenon in the deep mantle, as sampled by the Kola (Russia) mantle plume. According to the relative abundances of radiogenic/nucleogenic/fissiogenic noble gas isotopes, the 244Pu contribution is estimated to be 33–60% of total fission 136Xe. This value is significantly lower than what is expected for a chondritic reservoir (96%), and is equal to, or higher than, the previously proposed best estimate for the MORB mantle. We show that both MORB and plume sources have lost ≥ 99% fission Xe produced by the decay of 244Pu. In comparison, the mantle has lost only ∼50% of radiogenic argon produced by 40K ( T 1 / 2 = 1.25 Gyr). Therefore, the major loss of fissiogenic Xe isotopes from 244Pu took place before quantitative accumulation of noble gas isotopes produced by long–lived radioactivities. As constrained by the half-life of 244Pu, such loss post-dated the major episodes of terrestrial accretion and differentiation that took place within the first 100 Myr, and occurred mostly during the Hadean. The xenon record of early mantle dynamics is consistent with extensive loss of volatile elements in the first 100 Myr ASSC, during terrestrial accretion and magma ocean episodes, but also indicates global mantle differentiation that affected both the source of mantle plumes and that of mid-ocean ridge basalts for several hundreds of Myr (e.g., 400–700 Myr ASSC). During this period, the loss rate of volatile elements was at least one order of magnitude higher than at Present, implying a much more thermally active Earth during the Hadean. In contrast, Mars became an essentially static planet during this time period. Our view may also imply that the atmosphere was open for time intervals longer than those generally thought.

Anomalous xenon in Archean cherts from Pilbara Craton, Western Australia

We report the discovery of anomalies in the xenon isotopic composition of Archean cherts belonging to the metasedimentary sequences of Pilbara Craton, Western Australia. The cherts show contemporary excesses of 129Xe and 131–136Xe, compared to atmospheric Xe. The 129Xe excesses are comparable to those observed in mantle-derived samples, such as MORBs, xenoliths, diamonds and CO 2-rich well gases and correlate with excesses of 238U fissiogenic-produced 136Xe, close to the mantle ratio. However, isotope 131Xe is in excess of 238U fissiogenic-Xe production. The 129Xe/ 131Xe ratio ranges from 0.7 to 3.2 and it is consistent with production of these two isotopes by neutron-capture reactions with tellurium. These anomalies are analogous to those measured in metamorphic rocks (gneisses and amphibolites) in the KTB borehole in Germany and probably were produced by reactions with Te.

Variation of the isotopic composition of xenon in the solar system

Re-examination of a vast amount of existing xenon isotope data, which have been accumulated in the literature since the 1960's, reveals that the variation of the isotopic composition of xenon in the solar system can be attributed to a combined effect of (a) mass-fractionation, (b) spallation and (c) stellar-temperature neutron-capture reactions plus the addition of (d) the beta-decay product of 129I and of (e) the spontaneous fission products of 244Pu. The effect of each of the above-mentioned processes can be extremely large, due, primarily to the fact that these processes occurred in the interior of a supernova, which exploded about 5.1 billion years ago.

Helium, Argon, and Xenon Isotopic Compositions of Ore‐forming Fluids in Jinding‐Baiyangping Polymetallic Deposits, Yunnan, Southwest China

Abstract The Jinding superlarge lead and zinc deposit has attracted the attention of geologists of the world and its metallogenesis has long been in dispute. This paper takes the Jinding deposit and the Baiyangping Cu‐Ag‐Co deposit which was recently found at about 30 km north of Jinding as one ore belt, and, based on researches on the helium, argon, and xenon isotopic compositions of primary inclusions in ore‐forming solutions of the main stage, the authors have found that the 3He/4He ratio of the ore‐forming fluid is 2.7×10−6 (varying from 0.19 to 1.97 Ra), the 4He/40Ar ratio (0.24–3.12) is close to the mantle characteristic ratio, and the xenon isotopic composition and evolution show characters of the mantle xenon. The above results reveal the characteristics of mantle source and crust‐mantle fluid mixing (mantle helium reaching 32%) and the metallogenic contributions of the deep processes in the Jinding‐Baiyangping ore belt.

Isotopic composition of xenon in petroleum from the shell bullwinkle field

We have measured the abundance and isotopic composition of xenon in petroleum samples from the Shell Bullwinkle Field off the coast of Louisiana. We used an oxidation and purification procedure designed to insure complete extraction and clean up of xenon from the petroleum.The xenon isotopic composition was found to be similar to the atmospheric value for one petroleum sample. While the results of the second sample suggest possible enrichment of the heavier isotopes, the errors associated with these excesses preclude a definitive statement to that effect. No monoisotopic enrichment in129Xe was detected in either sample, the presence of which might have allowed us to deduce the petroleum age. Our results represent only the second xenon measurement from petroleum, and the concentrations are within the range of values published in the earlier report.

Application of Nuclear Chemistry in the Study of the Universe

Isotopic compositions of the strange Xenon components-HL and the s-type xenon can be explained in a straightforward manner as due to the alteration of the isotopic composition of xenon caused by a combined effect of (a) mass-fractionation, (b) spallation and (c) stellar-temperature neutron-capture reactions. As much as 42.49% of total 136Xe (Σ 136Xe) found in the Allende diamond inclusions is 244Pu fission xenon (136fXe) and the trapped xenon is severely mass-fractionated in such a manner that the lighter xenon isotopes are systematically depleted relative to the heavier isotopes. The relative abundances of 130Xe and 132Xe in the trapped xenon component are both markedly enhanced indicating that it was irradiated with a total flux of 1.2·1023 n·cm-2 of stellar-temperature (10 keV) neutrons. The xenon found in the s-type xenon, on the other hand, resemble that of the atmospheric xenon irradiated with a total flux of about 6.0·1023 n·cm-2 of 10 keV neutrons. These results indicate that we are seeing here the effects of nuclear processes occurring inside of a star, such as the exploding supernova.

Plutonium-244 fission xenon and primordial xenon in the Allende meteorite

The carbonaceous chondrite Allende contains (22±1)·10−12 cm3STP/g of244Pu fission xenon and two kinds of primordial xenon: Type I and Type II. The former represents the isotopic composition of a primordial xenon, which resided in the vicinity of a supernova shortly before it exploded, while the latter represents that of the xenon, which resided in the supernova. The isotopic composition of xenon found in the pink inclusion of the Allende meteorite, corrected for the presence of very large excesses of244Pu fission xenon,129Xe from the decay of129I, and of128Xe from the neutron-capture reactions on127I, resembles that of Type-I primordial xenon. The isotopic composition of xenon found in the diamond inclusions of the Allende meteorite, on the other hand, represents that of Type-II primordial xenon and it resembles that of a mixture of Type-I primordial xenon whose isotopic composition is severely altered by a combined effect of (a) mass-fractionation, (b) spallation, (c) stellar-temperature neutron-capture reactions, and (d) the presence of a large excess of244Pu fission xenon.

Noble gas systematics of deep rift zone glasses from Loihi Seamount, Hawaii

We report new noble gas fusion and crushing data for six pillow rim glasses, recovered between 3 and 5 km water depth on the south rift zone of Loihi Seamount, Hawaii. Helium abundances of the glasses vary from 0.3 to 2.3 μcc/g, with 4He/3He ratios between 30000 and 27000 (24–27 RA), similar to previously reported values. The neon data form a correlation line which is similar to the Loihi-Kilauea line reported by Honda et al. [1], but extends to much higher ratios, up to 12.9 and 0.0382 for the 20Ne/22Ne and 21Ne/22Ne ratios, respectively. This provides conclusive evidence for the suggestion that the Hawaiian plume, thought to originate in the lower mantle, has a solar-like 20Ne/22Ne composition [1], but a slightly higher 21Ne/22Ne ratio. 40Ar/36Ar ratios of the deep rift-zone glasses are as high as 2600, and show a positive correlation with neon isotopic ratios. In contrast to neon and argon, all xenon isotopic compositions are isotopically indistinguishable from air, which either suggests preferential atmospheric contamination of xenon, or could indicate an atmospheric xenon isotopic composition for the lower mantle.