Xenon Isotope Data Research Articles

Possible discontinuous evolution of atmospheric xenon suggested by Archean barites

The Earth's atmosphere has continually evolved since its formation through interactions with the mantle as well as through loss of volatile species to space. Atmospheric xenon isotopes show a unique and progressive evolution during the Archean that stopped around the Archean-Proterozoic transition. The Xe isotope composition of the early atmosphere has been previously documented through the analysis of fluid inclusions trapped within quartz and barite. Whether this evolution was continuous or not is unclear, requiring additional analyses of ancient samples, which may potentially retain remnants of the ancient atmosphere. Here we present new argon, krypton and xenon isotopic data from a suite of Archean and Proterozoic barites ranging in age from 3.5 to 1.8 Ga, with the goal of providing further insights in to the evolution of atmospheric Xe, whilst also outlining the potential complications that can arise when using barites as a record of past atmospheres. Xenon released by low temperature pyrolysis and crushing of two samples which presumably formed around 2.8 and 2.6 Ga show Xe isotope mass dependent fractionation (MDF) of 11‰.u−1 and 3.4‰.u−1, respectively, relative to modern atmosphere. If trapped Xe is contemporaneous with the respective formation age, the significant difference in the degree of fractionation between the two samples provides supporting evidence for a plateau in the MDF-Xe evolution between 3.3 Ga and 2.8 Ga, followed by a rapid evolution at 2.8–2.6 Ga. This sharp decrease in MDF-Xe degree suggests the potential for a discontinuous temporal evolution of atmospheric Xe isotopes, which could have far reaching implications regarding current physical models of the early evolution of the Earth's atmosphere.

The evolution of the continental crust and the onset of plate tectonics.

The Earth is the only known planet where plate tectonics is active, and different studies have concluded that plate tectonics commenced at times from the early Hadean to 700 Ma. Many arguments rely on proxies established on recent examples, such as paired metamorphic belts and magma geochemistry, and it can be difficult to establish the significance of such proxies in a hotter, older Earth. There is the question of scale, and how the results of different case studies are put in a wider global context. We explore approaches that indicate when plate tectonics became the dominant global regime, in part by evaluating when the effects of plate tectonics were established globally, rather than the first sign of its existence regionally. The geological record reflects when the continental crust became rigid enough to facilitate plate tectonics, through the onset of dyke swarms and large sedimentary basins, from relatively high-pressure metamorphism and evidence for crustal thickening. Paired metamorphic belts are a feature of destructive plate margins over the last 700 Myr, but it is difficult to establish whether metamorphic events are associated spatially as well as temporally in older terrains. From 3.8-2.7 Ga, suites of high Th/Nb (subduction-related on the modern Earth) and low Th/Nb (non-subduction-related) magmas were generated at similar times in different locations, and there is a striking link between the geochemistry and the regional tectonic style. Archaean cratons stabilised at different times in different areas from 3.1-2.5 Ga, and the composition of juvenile continental crust changed from mafic to more intermediate compositions. Xenon isotope data indicate that there was little recycling of volatiles before 3 Ga. Evidence for the juxtaposition of continental fragments back to ~2.8 Ga, each with disparate histories highlights that fragments of crust were moving around laterally on the Earth. The reduction in crustal growth at ~ 3 Ga is attributed to an increase in the rates at which differentiated continental crust was destroyed, and that coupled with the other changes at the end of the Archaean are taken to reflect the onset of plate tectonics as the dominant global regime.

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).

Noble gas and nitrogen isotopic components in Oceanic Island Basalts

We present helium, argon, xenon and nitrogen isotopic data from Oceanic Island Basalts (OIBs), obtained from stepped heating and vacuum crushing experiments. Signatures of 3He/ 4He in the present samples, except for those from the Canary Islands, are significantly higher (up to 20 × the air ratio) than the MORB signature (8.5 × air ratio). The argon ( 40Ar/ 36Ar) and xenon ( 129Xe/ 132Xe and 136Xe/ 132Xe) isotopic data are consistent with a two-component mixture of gases from the mantle (either MORB or OIB source) and air contamination. In the stepwise heating data, δ 15N varies from − 20‰ to + 15‰ in the different heating steps. The vacuum crushing data show a narrower range (− 5‰ to + 8‰) of δ 15N, which, except for one Réunion sample, is somewhat heavier than the totals from the stepped heating experiments. Simultaneous argon and nitrogen isotopic systematics of the present data suggest contributions from mantle (somewhat different from MORB), recycled materials and air contamination. This is also consistent with the 36Ar/ 132Xe elemental ratio. The present stepped heating data are consistent with a nitrogen isotopic component with δ 15N ~ − 25‰ in the OIB mantle. In line with the oxygen isotopic composition of the bulk Earth, this would be consistent with a contribution from enstatite chondrite-like volatiles to the planet's accretion.

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.

Xenon isotopes in size separated nanodiamonds from Efremovka: 129Xe*, Xe-P3, and Xe-P6

Xenon isotopic data were acquired by high resolution step pyrolysis and combined step pyrolysis/combustion of aliquots of size separated nanodiamonds. 129Xe excess ( 129Xe*) from in situ decay of 129I is preferentially associated with the larger grain size separates. This observation rules out trapping by recoil from surrounding material. The releases of Xe-P3 and 129Xe occur in the same low temperature pyrolysis steps and exhibit similar distributions among the size separates. These observations imply a common site for the components and, in consequence, suggest a common incorporation event. Whether one component or two, our observations require that 129Xe* and Xe-P3 were incorporated into a subpopulation of nanodiamonds before nanodiamonds were mixed and incorporated into parent bodies. Their susceptibilities to loss during heating in the laboratory are similar, but the ratio of 129Xe* to Xe-P3 varies among nanodiamond separates from different meteorites (literature data). We conclude that the 129Xe* we observe today was present as 129I during parent body processing. Furthermore, the range of 129Xe*/ 132Xe P3 ratios across all the separates requires that even nanodiamonds from CI chondrites were at least 5–10× more rich in Xe-P3 during 129I decay than they are today. We present a simple model involving one degassing event per parent body between incorporation of nanodiamonds and final decay of 129I. The observed variations among parent bodies require degassing events separated by several 129I half lives (∼50Ma), consistent with low-temperature processing on parent bodies but longer than expected for nebular processing. In this model, nanodiamonds from ALHA77307 degassed at an unusually early stage, suggesting they alone may retain the signature of processing in the nebula in their P3 and 129Xe* abundances. The isotopic signature associated with Xe-P6 is also found only in the larger size separates. Concentration of Xe-HL increases with increasing grain size, but its relative abundance with respect to Xe-P3 and P6 is higher in smaller grain-size fractions. We argue that Xe-P6 is best seen as a variant of Xe-HL, and that they are both mixtures of a “normal” component akin to solar xenon and a slightly variable exotic component. We show that both current models of Xe-H formation can account for the observed variability, and propose a scenario according to which Xe-HL and P6 were implanted into separate diamond populations before incorporation of Xe-P3 and 129I.

Primordial noble gases in a graphite‐metal inclusion from the Canyon Diablo IAB iron meteorite and their implications

Abstract— We have carried out noble gas measurements on graphite from a large graphite‐metal inclusion in Canyon Diablo. The Ne data of the low‐temperature fractions lie on the mixing line between air and the spallogenic component, but those of high temperatures seem to lie on the mixing line between Ne‐HL and the spallogenic component. The Ar isotope data indicate the presence of Q in addition to air, spallogenic component and Ar‐HL. As the elemental concentration of Ne in Q is low, we could not detect the Ne‐Q from the Ne data. On the other hand, we could not observe Xe‐HL in our Xe data. As the Xe concentration and the Xe/Ne ratio in Q is much higher than that in the HL component, it is likely that only the contribution of Q is observed in the Xe data. Xenon isotopic data can be explained as a mixture of Q, air, and “El Taco Xe.” The Canyon Diablo graphite contains both HL and Q, very much like carbonaceous chondrites, retaining the signatures of various primordial noble gas components. This indicates that the graphite was formed in a primitive nebular environment and was not heated to high, igneous temperatures. Furthermore, a large excess of 129Xe was observed, which indicates that the graphite was formed at a very early stage of the solar system when 129I was still present. The HL/Q ratios in the graphite in Canyon Diablo are lower than those in carbonaceous chondrites, indicating that some thermal metamorphism occurred on the former. We estimated the temperature of the thermal metamorphism to about 500–600 °C from the difference of thermal retentivities of HL and Q. It is also noted that “El Taco Xe” is commonly observed in many IAB iron meteorites, but its presence in carbonaceous chondrites has not yet been established.

Mixing, volatile loss and compositional change during impact-driven accretion of the Earth.

The degree to which efficient mixing of new material or losses of earlier accreted material to space characterize the growth of Earth-like planets is poorly constrained and probably changed with time. These processes can be studied by parallel modelling of data from different radiogenic isotope systems. The tungsten isotope composition of the silicate Earth yields a model timescale for accretion that is faster than current estimates based on terrestrial lead and xenon isotope data and strontium, tungsten and lead data for lunar samples. A probable explanation for this is that impacting core material did not always mix efficiently with the silicate portions of the Earth before being added to the Earth's core. Furthermore, tungsten and strontium isotope compositions of lunar samples provide evidence that the Moon-forming impacting protoplanet Theia was probably more like Mars, with a volatile-rich, oxidized mantle. Impact-driven erosion was probably a significant contributor to the variations in moderately volatile element abundance and oxidation found among the terrestrial planets.

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.

Primordial noble gases from Earth's mantle: identification of a primitive volatile component

Carbon dioxide well gases in Colorado, New Mexico, and South Australia show excesses of (124-128)Xe correlated with (129)I-derived (129)Xe and (20)Ne/(22)Ne ratios that are higher than the atmospheric (20)Ne/(22)Ne ratio. The xenon isotopic data indicate the presence of a solarlike component deep within Earth. The presence of this component in crustal and upper mantle reservoirs may be explained by a steady-state transport of noble gases from the lower mantle, which still retains much of its juvenile volatile inventory. These measurements also indicate that the mantle source of these noble gases in the carbon dioxide well gases cannot be the source of Earth's present atmosphere. The variations observed in (129)Xe/(130)Xe between solar wind xenon, Earth's atmosphere, and mantle samples may be generated by variations of iodine/xenon in terrestrial reservoirs, as opposed to rapid early degassing.

A noble gas study of cubic diamonds from Zaire: constraints on their mantle source

Cubic diamonds are known to contain fluid in submicrometer inclusions which are thought to originate from the mantle beneath the continental crust. Noble gas elemental and isotopic compositions of sixteen cubic diamonds from Zaire are noticeably different from those in MORB. The 3He/ 4He ratios observed in the diamonds are (5–12) × 10 −6 and lower than the typical MORB value of 1 × 10 −5. The 20Ne/ 22Ne ratios (≤11) and the 21Ne/ 22Ne ratios (≤0.06) show a rough linear correlation and have a slope that is lower than that defined for MORB. The excess 21Ne responsible for the shallower slope may be produced by nuclear reactions either in the source mantle or in the fluid trapped in the diamonds. A nucleogenic origin for excess 21Ne in the cubic diamonds relative to MORB is consistent with their lower 3He/ 4He ratios. Positively correlated excesses of 129Xe and 131–136Xe of up to 10% relative to the atmospheric Xe ratios are also observed. They are attributed to the decay of extinct 129I and to spontaneous fission of extinct 244Pu and/or extant 238U, respectively. Xenon isotopic data for the cubic diamonds lie on the same correlation line as that defined for MORB in the three isotope diagram of 136Xe/ 130Xe vs. 129Xe/ 130Xe. Very high 40Ar/ 36Ar ratios of up to 35000 are found and are similar to the expected value for the MORB source mantle. From the 3He/ 4He and 40Ar/ 36Ar ratios, some constraints can be made on the origin of cubic diamonds. The observed ratios can be explained if the cubic diamonds crystallized in a fluid which separated from a mantle source previously enriched in incompatible elements. This is consistent with the previously suggested model for the origin of fluid- bearing diamonds. The 38Ar/ 36Ar ratios in the cubic diamonds are slightly but significantly higher than the atmospheric ratio. This high 38Ar/ 36Ar ratio may represent the primordial isotopic ratio preserved in the mantle. Alternatively, the observed excess 38Ar may be attributed to the nuclear reaction 35Cl(α,p) 38Ar in the fluid phase if the production rate of nucleogenic 38Ar is about ten times higher than the previously reported value and the age of the fluid inclusions is quite old (>10 9 yr).

Plutonium-244 and strange xenon components in the solar system

A number of strange xenon components have been reported in the literature during the past three decades; for example, AVCC (average carbonaceous chondrite), CCF (carbonaceous chondrite fission) xenon, xenon-X, xenon-H, xenon-L, xenon-S, xenon-U, SUCOR (surface correlated xenon), BEOC (Bern Oberflachen-Correliert) xenon, and so on. It is often assumed that they reprsent the isotopic compositions of more or less ‘pure’ or ‘primordial’ components of xenon. If one attempts to interpret the existing xenon isotope data for meteorites and lunar samples, assuming that they are ‘pure’ or ‘primordial’, however, one encounters all sorts of problems and no coherent theory concerning the variation of the isotopic composition of xenon in the solar system emerges. We have therefore re-examined over 4,000 sets of existing xenon isotope data for meteorites and lunar samples. The results indicate that these strange xenon components are mixtures of244Pu fission xenon and atmospheric xenon, whose isotopic compositions have been altered by the processes of a) mass-fractionation, b) spallation and c) neutron-capture reactions.

Plutonium-244 dating

Re-examination of all known xenon isotopic data for ordinary chondrites reveals that244Pu fission xenon can be resolved in about one-fourth of the meteorites of this class. The amounts of244Pu fission xenon found in these meteorites range from ca. 1–2 up to 6–8·10−12 ccSTP/g. These meteorites started to retain their xenon some 200–500 million years later than did the carbonaceous chondrites Allende, Groznaya, Mokoia, Murchison, Murray, and Renazzo which began to retain their xenon over 4800 million years ago.

Plutonium-244 dating VII. Initial abundances of uranium-235 and plutonium-244 in lunar samples

Re-examination of a vast amount of lead and xenon isotope data that have been accumulated since the Apollo 11 landing on the moon in July 1969 reveals that some of the lunar fines and breccia started to retain their radiogenic lead and fissiogenic xenon isotopes about 5 billion years ago when the ratios of235U and244Pu to238U in the early solar system were approximately 4 and 2 atoms per 10 atoms of238U, respectively.

Noble gases in submarine glasses from mid-oceanic ridges and Loihi seamount: Constraints on the early history of the Earth

Isotopic and elemental compositions of noble gases in glass samples from mid-oceanic ridges (Mid-Atlantic Ridge, East Pacific Rise, and Galapagos Ridge) and from Loihi seamount (Hawaii) were analyzed with a sector-type mass spectrometer system. Our results for MORB (Mid-Oceanic Ridge Basalt) samples are consistent with the well-known MORB-type noble gas signatures: rather uniform 3He/ 4He ratios (R/R a ~ 8), variable 40Ar/ 36Ar ratios from nearly the atmospheric ratio to 15,200, and the presence of excesses in 129Xe and 132−136Xe. We also observed linearly correlated anomalies in 20Ne/ 22Ne ratios (up to ~ 13) and 21Ne/ 22Ne ratios (up to ~0.06), which are consistent with the MORB correlation found by Sarda et al. (1988). High 20Ne/ 22Ne ratios (up to 11.74) and relatively high 40Ar/ 36Ar ratios (up to 2780) are also found in some Loihi samples. Neon isotopic compositions for these samples are quite consistent with the Loihi-Kilauea correlation line recently found by Honda et al. (1991) but inconsistent with the MORB correlation line. Loihi data plotted in a 3He/ 4He vs. 20Ne/ 22Ne diagram also suggest that the high 20Ne/ 22Ne ratios found in Loihi samples are not the results of contamination of MORB-type neon but are indigenous to the source of Loihi. This suggests that the solar-type high 20Ne/ 22Ne ratios are not only the signature of the source mantle of MORB (upper mantle) but also that of the source of Loihi (possibly lower mantle), and hence, possibly the signature of the whole mantle. The fact that isotopic composition in the mantle ( 20Ne/ 22Ne ~ solar) and in the present atmosphere ( 20Ne/ 22Ne = 9.8) are different seems to contradict a simple degassing model of the atmosphere, which implies isotopically identical compositions for the mantle and the atmosphere. A possible scenario would be that neon in the present atmosphere had been fractionated from the original solar-type ratio ( 20Ne/ 22Ne ~ 13.6) down to the present ratio (9.8) by extensive loss of the (proto-) atmosphere at an early stage of the Earth's history. If the Earth's accretion was “heterogeneous,” mixing of a solar-type Ne (derived from most of the mantle) and a planetary-type Ne (derived from late-veneer, volatile-rich material) would be an alternative explanation for the present atmospheric Ne. In either case, the model should be consistent with other noble gas data, especially xenon isotopic data.

Plutonium-244 dating VI. Initial ratios of plutonium to uranium in achondrites

Re-examination of all known xenon isotopic data for achondrites reveals that244Pu fission xenon can be resolved in about three-fourths of the meteorites of this class. The amounts of244Pu fission xenon found in these meteorites range from ca. 1–2 up to 20–40·10−12 ccSTP/g. These meteorites started to retain their xenon some 200–500 million years later than did the carbonaceous chondrites Allende, Groznaya, Mokoia, Murchison, Murray, and Renazzo, which began to retain their xenon over 4800 million years ago.

Plutonium-244 dating

Re-examination of all known xenon isotope data for the carbonaceous chondrites Murray and Murchison reveals that these meteorites contain (25±1)•10 12 and (23±1)•10 −12 ccSTP 136f Xe/g of 244 Pu fission xenon, respectively, and they started to retain their xenon at about the same time the Allende meteorite started to retain its xenon more than 4800 million years ago. Some of the mineral inclusions isolated from these meteorites contain xenon and barium isotopes which had been exposed to very high fluences of thermal neutrons

Plutonium-244 dating I. Initial ratio of plutonium to uranium in the allende meteorite

Re-examination of all known xenon isotope data for the carbonaceous chondrite Allende reveals that this meteorite contains as much as (22±1)·10−1 2 csSTP per gram of fissogenic136Xe (136fXe) from the extinct nuclide244Pu and it appears to have started to retain its xenon more than 4800 million years ago, when the244Pu to238U ratio in the solar system was 0.113±0.006 (atom/atom).

Plutonium-244 dating

Re-examination of xenon isotope data for lunar fines, breccia and rocks reveals that in situ decay product of the spontaneous fission of 244 Pu is widely distributed in the lunar samples and some of the lunar samples contain in excess of 1000 0 10 −12 ccSTP 136f Xe/g of 244 Pu fission xenon. The 244 Pu ages calculated from the ratios of 136f Xe to 238 U in these samples vary from 3965 to 4909 million years

The pre-Fermi natural reactor: A note on the periodic mode of operation

The isotopic compositions of xenon released from the Oklo reactor at temperatures below 1000°C are such that the abundances of131Xe,132Xe and134Xe relative to136Xe are markedly enhanced when compared to the relative fission yields from the thermal neutron-induced fission of235U. These anomalies can be attributed to the fact that131Xe,132Xe and134Xe have fairly long-lived precursors: 8.04-day131I, 78.2-hour132Te and 42-minute134Te, respectively. It is possible to determine the duration of the time when the reactor was turned off from the ratios of excess132Xe to excess134Xe in these anomalous xenon fractions released from the Oklo reactor. Calculations based on the available xenon isotope data that the time period during which the reactor was turned off was approximately 2 to 3 hours.