Primordial neon,helium, and hydrogen in oceanic basalts

A primordial neon component in neon from Kilauea Volcano and deep-sea tholeiite glass has been identified by the presence of excess²⁰Ne; relative to atmospheric neon the²⁰Ne enrichments are 5.4% in Kilauea neon and about 2.5% in the basalts. The²⁰Ne anomalies are associated with high³He/⁴He ratios; the ratio in Kilauea helium is 15 times the atmospheric ratio, while mid-ocean ridge basalts from the Atlantic, Pacific, and Red Sea have uniform ratios about 10 times atmospheric. Mantle neon and helium are quite different in isotopic composition from crustal gases, which are highly enriched in radiogenic²¹Ne and⁴He. The²¹Ne/⁴He ratios in crustal gases are consistent with calculated values based on G. Wetherill's¹⁸O (α,n) reaction; the lack of²⁰Ne enrichment in these gases shows that the mantle²⁰Ne anomalies are not radiogenic.²¹Ne enrichments in Kilauea neon and “high-³He” Pacific tholeiites are much less than in crustal neon, about 2 ± 2% vs. present atmospheric neon, as expected from the much lower⁴He/Ne ratios.Neon concentrations in two Atlantic tholeiites were found to be only 1–2% of the values obtained by Dymond and Hogan; helium concentrations are slightly greater and our He/Ne ratios are greater by a factor of 150. The large Ne excess relative to solar wind and meteoritic gases is thus not confirmed. Pacific and Atlantic basalts appear to be quite different in He/Ne ratios however, and He and Ne may be inversely correlated. He concentration variations due to diffusive loss can be distinguished from variations due to two-phase partitioning or mantle heterogeneity by the effects on³He/⁴He ratios. The He isotopic and concentration measurements on “low-³He” basalts are consistent with diffusive loss and dilution of the 3/4 ratio by in-situ radiogenic⁴He, and may provide a method for dating basalt glasses.Deuterium/hydrogen ratios in Atlantic and Pacific tholeiite glasses are 77% lower than the ratio in seawater. The inverse correlation between deuterium and water content observed by Friedman in erupting Kilauea basalts is consistent with a Rayleigh separation process in which magmatic water is separated from an initial melt with the same D/H ratio as observed in deep-sea tholeiites. The consistency of the D/H ratios in tholeiites containing primordial He and Ne components indicates that these ratios are probably characteristic of primordial or juvenile hydrogen in the mantle.     

Primordial gases in graphite-diamond-kamacite inclusions from the Haveröureilite

Stepwise heating experiments on separated graphite-diamond-kamacite aggregates have revealed a pronounced difference in the release patterns of spallogenic³He and trapped gases. About half the³He is released at T ? 920°C, without being accompanied by significant amounts of primordial gases; the latter, together with the remaining³He, is given off only at T ? 1200°C. Acid treatment of an aliquant dissolved about 2/3 of the total Fe in the sample but did not cause a significant change in the gas concentrations. It is concluded that (a) there is no evidence for a loss of spallogenic³He from the graphite-diamond-kamacite aggregates, (b) one major constituent of the aggregates - graphite - is almost void of trapped gases, (c) kamacite is not a main carrier of the gases. This leaves diamond as the most probable site of the primordial gases.The elemental abundance pattern in the noble gases is essentially as reported previously. In particular, the excellent correlation between relative depletion factors, normalized to the cosmic abundance ratios, and the respective ionisation energies is confirmed. Other important features of the trapped gases are a²⁰Ne/²²Ne ratio of 12.3 ± 0.6, intermediate between solar wind and solar flare implanted Ne,³⁶Ar/³⁸Ar = 5.20 ± 0.06 and a measured⁴⁰Ar/³⁶Ar ratio (before blank correction) of 0.0076.Possible modes of trapping of the noble gases are discussed.     

The extent of lunar regolith mixing

The activity of solar cosmic-ray-produced⁵³Mn has been measured as a function of depth in the upper 100 g/cm² (～55 cm) of lunar cores 60009–60010 and 12025–12028. Additional samples which supplement our earlier work were analyzed from the Apollo 15 and 16 drill stems. These data, taken in conjunction with our previously published results and the²²Na and²⁶Al data of the Battelle Northwest group, indicate that in at least three of the four cases studied the regolith has been measureably disturbed within the last 10 m.y. In one case gardening to 19 g/cm² is required. Activities measured in the uppermost 2 g/cm² indicate frequent mixing within this depth range. No undisturbed profiles were observed nor were any major discontinuities observed in the profiles. The Monte Carlo gardening model of Arnold has been used to derive profiles for the gardened moon-wide average of⁵³Mn and²⁶Al as a function of depth. The⁵³Mn and²⁶Al experimental results are compared with these theoretical predictions. Agreement is good in several respects, but the calculated depths of disturbance appear to be too low.     

Cosmogenic 21Ne exposure dating of young basaltic lava flows from the Newer Volcanic Province,western Victoria,Australia

Cosmogenic ²¹Ne was utilised to determine exposure ages of young subaerial basaltic lava flows from the Newer Volcanic Province, western Victoria, Australia. The ages (36–53 ka) determined from co-existing cosmogenic ²¹Ne and ³He in olivines separated from basalts are consistent within analytical uncertainties with ages previously determined by cosmogenic ³⁶Cl exposure dating. This paper illustrates the potential of cosmogenic neon exposure ages in studying the eruption, surface morphology, and erosion history of young volcanic rocks, which are difficult to date using other conventional methods, such as K-Ar or ⁴⁰Ar/³⁹Ar dating. The present study demonstrates that combined cosmogenic ³He and ²¹Ne dating, specifically measured cosmogenic ³He/²¹Ne ratios, on the same samples, is powerful for evaluating the validity of calculated cosmogenic ³He and ²¹Ne surface exposure ages.     

The reaction Mg(n,α)Ne at 14.1 and 14.7 MeV: cross sections and implications for meteorites

Mass spectrometric analyses of neutron-irradiated targets of natural magnesium yield cross sections of59 ± 14,160 ± 8, and11.0 ± 3.3mb for²⁰Ne,²¹Ne, and²²Ne, respectively, at 14.1 MeV and of94 ± 8,152 ± 12, and13.0 ± 2.0mb at 14.7 MeV. With the incorporation of these cross sections, calculations modeling cosmic-ray interactions in stony meteoroids of radii 20 and 26 cm predict that between the surface and center the²²Ne/²¹Ne ratio falls more than 10% while the²¹Ne production rate rises about 30%. The reaction²⁴Mg(n,α)²¹Ne predominantly controls these trends: the²²Ne/²¹Ne ratio due to magnesium decreases over 15% while that due to silicon remains constant with increasing depth. The calculations are compared with published neon measurements for the Keyes and St. Séverin meteorites.     

Cosmic ray exposure ages of chondrites,pre-irradiation and constancy of cosmic ray flux in the past

A systematic calibration of the production rate of one specific cosmic-ray-produced nuclide in chondrites, that of²¹Ne, was achieved by using four independent methods:P₂₁(1.11) = 0.507 ± 0.039, 0.302 ± 0.013, 0.312 ± 0.017and0.292 ± 0.019 (in units of 10^?8 cm³ STP/g My) based on²⁶Al-age,⁵³Mn-age,⁸¹Kr-⁸³Kr and²²Na-²²Ne methods, respectively. These production rates are all normalized to a shielding parameter ratio²²Ne/²¹Ne= 1.11 and to the chemical composition of L chondrites. The results obtained by the latter three methods are in good agreement, but they disagree in a systematic way with the²⁶Al-age calibration. Based on these results, we recommend a valueP₂₁(1.11) = 0.31 and a production rate equation:P₂₁ = 4.845 P₂₁ (1.11) F[21.77(²²Ne/²¹Ne) ? 19.32]^?, whereF = 1.00 for L and LL, andF = 0.93 for H chondrites, for the calculation of cosmic ray exposure ages on the basis of Ne concentrations. In an attempt to assess possible causes for this discrepancy, we discuss the²⁶Al half-life measurements, we evaluate effects resulting from pre-irradiation of meteorites, and we discuss the evidence regarding the constancy of the cosmic ray flux in the past, in the light of some recent astronomical observations.     

Neon isotope variations in Mid-Atlantic Ridge basalts

The isotopic composition of neon was measured for seventeen samples of submarine basalt glass from the Mid-Atlantic Ridge between 54° and 73°N. They include the Reykjanes, Kolbeinsey, and Mohns Ridge segments. Neon isotopic anomalies, relative to the atmospheric ratios, exist in both²⁰Ne/²²Ne and²¹Ne/²²Ne. A maximum excess²⁰Ne of 7% was measured in two samples from the Reykjanes Ridge. Samples with lower²⁰Ne excesses (six samples with δ²⁰Ne between 2 and 4%) from all three ridge segments, appear to result from mixing of a mantle component with a δ²⁰Ne of 7% and atmospheric neon.²¹Ne/²²Ne ratios are up to 8% above the atmospheric value, with no apparent correlation with the²⁰Ne excesses. The anomalies in²⁰Ne/²²Ne are difficult to explain by mass fractionation of an atmospheric reservoir since several of the samples have δ²⁰Ne values greater than could be produced by single-stage fractionation. Most likely, the excess²¹Ne results from nuclear reactions in the mantle source, although there is no definite correlation between the δ²¹Ne or the excess²¹Ne (cm³ STP/g) and the uranium concentration. Large variations in the observed⁴He/²⁰Ne ratio (40–12,000) remain unexplained at this time.     

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

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

Depth profile of53Mn in the lunar surface

Measurements of cosmic-ray produced⁵³Mn are reported for a series of lunar surface samples down to a depth of 416 g/cm². These results clearly illustrate the decrease in activity with depth as the incident galactic cosmic rays are absorbed. Below 60 g/cm² the production rate decreases exponentially with a mean length, λ, of about 220 g/cm². These results indicate that, at the Apollo 15 site, the lunar regolith has been unmixed, on a meter scale, for the last 5 my. The neutron activation technique for⁵³Mn, which allowed samples smaller than 200 mg to be used for these measurements, is described.     

Cosmogenic neon produced from sodium in meteoritic minerals

Cosmogenic neon in sodium-rich oligoclase feldspar from the ordinary chondrites St. Severin and Guaren?a is characterized by an unusually high²²Ne/²¹Ne = 1.50 ± 0.02. This high ratio is due to the cosmogenic²²Ne/²¹Ne production ratio in sodium which is 2.9 ± 0.3, two to three times the production ratio in any other target element. The relative production rate of²¹Ne per gram sodium is one quarter the production rate per gram magnesium. The striking enrichment of²²Ne relative to²¹Ne in sodium arises from enhanced indirect production from²³Na via²²Na.The unusual composition of cosmogenic neon in sodium and sodium-rich minerals explains the high²²Ne/²¹Ne ratios observed in inclusions of the Allende carbonaceous chondrite, and observed during low-temperature extraction of neon from ordinary chondrites. The isotopic composition of cosmogenic neon released during the stepwise heating of a trapped gas-rich meteorite containing sodium-rich phases can be expected to vary, and use of a constant cosmogenic neon composition to derive the composition of the trapped gas may not be justified. Preferential loss of this²²Ne-enriched cosmogenic neon from meteoritic feldspar can result in a 2–3% drop in the measured cosmogenic²²Ne/²¹Ne ratio in a bulk meteorite sample. This apparent change in composition can lead to overestimation of the minimum pre-atmospheric mass of the meteorite by a factor of two.     

He and Ne isotopes in oceanic crust: implications for noble gas recycling in the mantle

In an attempt to determine the helium and neon isotopic composition of the lower oceanic crust, we report new noble gas measurements on 11 million year old gabbros from Ocean Drilling Program site 735B in the Indian Ocean. The nine whole rock samples analyzed came from 20 to 500 m depth below the seafloor. Helium contents vary from 3.3×10⁻¹⁰ to 2.5×10⁻⁷ ccSTP/g by crushing and from 5.4×10⁻⁸ to 2.4×10⁻⁷ ccSTP/g by melting. ³He/⁴He ratios vary between 2.2 and 8.6 Ra by crushing and between 2.9 and 8.2 by melting. The highest R/Ra ratios are similar to the mean mid-ocean ridge basalt (MORB) ratio of 8±1. The lower values are attributed to radiogenic helium from in situ α-particle production during uranium and thorium decay. Neon isotopic ratios are similar to atmospheric ratios, reflecting a significant seawater circulation in the upper 500 m of exposed crust at this site. MORB-like neon, with elevated ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios, was found in some high temperature steps of heating experiments, but with very small anomalies compared to air. These first results from the lower oceanic crust indicate that subducted lower oceanic crust has an atmospheric ²⁰Ne/²²Ne ratio. Most of this neon must be removed during the subduction process, if the ocean crust is to be recirculated in the upper mantle, otherwise this atmospheric neon will overwhelm the upper mantle neon budget. Similarly, the high (U+Th)/³He ratio of these crustal gabbros will generate very radiogenic ⁴He/³He ratios on a 100 Ma time scale, so lower oceanic crust cannot be recycled into either MORB or oceanic island basalt without some form of processing.     

Al andBe production in iron meteorites

We have measured by accelerator mass spectrometry the²⁶Al contents of 20 and the¹⁰Be contents of 14 iron meteorites. The²⁶Al contents are typically 30% or more lower than values obtained by counting techniques; the¹⁰Be contents are 10–15% lower. The production rates (P) of these nuclides decrease by more than a factor of two as the⁴He/²¹Ne ratio increases with increasing shielding from 200 to 400. For the lighter shielding conditions expected in stony meteorites we estimateP₂₆(Fe) as 3–4 dpm/kg andP₁₀(Fe) as 4–5 dpm/kg. The average P/₁₀P₂₆ activity ratio is close to 1.5. Exposure ages calculated from²¹Ne/²⁶Al ratios cannot be calibrated so as to agree with both⁴⁰KK/ ages and ages based on the shorter-lived nuclides³⁹Ar and³⁶Cl. If agreement with the latter is forced, then the disagreement with⁴⁰KK/ ages may signal a 35% increase in the cosmic-ray intensity during the last 10⁷ a.     

Helium-3 and manganese at the 21°N East Pacific Rise hydrothermal site

Water samples collected at the 21°N hydrothermal site on the East Pacific Rise crest, including Deep-Tow and hydrocast samples collected in 1977 and three hot vent water samples collected recently with the submersible “Alvin”, contain significant additions of³He,⁴He, and Mn. Although the vent water collections were at least 50-fold diluted with ambient seawater, they are up to 53 times enriched in³He and 7.4 times enriched in⁴He relative to saturated seawater, with concentrations of total dissolvable manganese (TDM) up to 310 μg/kg.³He and⁴He covary in the vent samples, with³He/⁴He about 8 times the atmospheric ratio, reflecting a mantle helium source. In contrast to the helium isotopes the Mn/³He ratio in the vent samples is variable, ranging from 4.3 × 10⁴ up to 1.0 × 10⁵ g/cm³. Profiles of³He/⁴He and TDM in the water column at 21°N show a sharp maximum ofδ(³He) = 47%and TDM= 0.69 μg/kg, much higher than the average values of 34% and 0.2 μg/kg for the deep water in this region. This spike in³He and Mn occurs at 2400 m depth, 200 m above the level of the 21°N vents, and 100 m higher than any local bathymetry, evidence for upward transport of the hydrothermal discharge via rising plumes of hot vent water. Two of the 21°N Deep-Tow samples associated with small (?0.010°C) temperature anomalies hadδ(³He) = 38%and TDM= 0.28 and 0.58 μg/kg, also slightly elevated relative to background. The Deep-Tow and hydrocast samples have lower Mn/³He ratios than average vent samples due to Mn removal by scavenging. Comparison of vent samples and water column measurements at 21°N indicate that the pure vent water could be detected using³He and Mn even when diluted ～10⁵ times with seawater, confirming that these two tracers are extremely sensitive indicators of submarine hydrothermal activity.     

Cosmogenic21Ne and22Ne depth profiles in chondrites

The production rate profiles of²¹Ne and²²Ne as a function of depth in meteoroids due to spallation by solar flare cosmic rays (SCR) and galactic cosmic rays (GCR) are calculated and their dependence on size and composition of meteoroids has been evaluated. The GCR production rate at a given depth increases with size for radii<25cm and then decreases whereas the²²Ne²¹Ne ratio (NeR) generally decreases with size and depth. The calculated GCR production rates and NeR are consistent with the measurements in several Chondrites. A plot of track production rate vs. NeR shows that some chondrites have NeR values smaller than those expected for their sizes. Thes obeervation suggestsat least a two-stage irradiation for such meteorites; the meteoroid exposure as a small body in the interplanetary space must have been preceded by exposure under deep shielding, possibly in its parent body.     

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

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

Inert gases in twelve particles and one “dust” sample from Luna 16

The inert gases were measured mass-spectrometrically in 12 fragments and 1 “dust” sample from Luna 16. The fragments were classified petrologically by microscopic inspection. The major petrologic types were breccias and basalts. The former were much richer in trapped gases than the latter, and were apparently formed by the welding of local fines. However, there was no clear-cut difference in gas content of either breccias or basalts between zone A (top) and zone G (bottom). The⁴He/²⁰Ne ratio of the breccias (average 49) was systematically smaller than that of the basalts (average 78), probably because of He-Ne fractionation during or after the formation of the breccias. We suggest that the⁴He/²⁰Ne ratios of bulk fines in general may reflect the proportions of basaltic and breccia (plus cindery glasses) fragments in the fines. Substantial variations of⁴He/³He were found, which could not be explained with the presence of variable proportions of cosmogenic³He_c. Either the solar-wind value has changed in time, or the fragments with the small ratios were exposed to solar flares rich in³He and/or⁴He. Exposure ages of four fragments are several hundred million years. The⁴⁰Ar/³⁶Ar slopes of breccias and basalts are identical: 0.65.     

Complex multiple cosmogenic nuclide concentration and histories in the arid Rio Lluta catchment,northern Chile

Terrestrial cosmogenic nuclide (TCN) concentrations measured in river sediments can be used to estimate catchment‐wide denudation rates. By investigating multiple TCN the steadiness of sediment generation, transport and depositional processes can be tested. Measurements of ¹⁰Be, ²¹Ne and ²⁶Al from the hyper‐ to semi‐arid Rio Lluta catchment, northern Chile, yield average single denudation rates ranging from 12 to 75 m Myr^–1 throughout the catchment. Paired nuclide analysis reveals complex exposure histories for most of the samples and thus the single nuclide estimates do not exclusively represent catchment‐wide denudation rates. The lower range of single nuclide denudation rates (12–17 m Myr^–1), established with the noble gas ²¹Ne, is in accordance with palaeodenudation rates derived from ²¹Ne/¹⁰Be and ²⁶Al/¹⁰Be ratio analysis. Since this denudation rate range is measured throughout the system, it is suggested that a headwater signal is transported downstream but modulated by a complex admixture of sediment that has been stored and buried at proximal hillslope or terrace deposits, which are released during high discharge events. That is best evidenced by the stable nuclide ²¹Ne, which preserves the nuclide concentration even during storage intervals. The catchment‐wide single ²¹Ne denudation rates and the palaeodenuation rates contrast with previous TCN‐derived erosion rates from bedrock exposures at hillslope interfluves by being at least one order of magnitude higher, especially in the lower river course. These results support earlier studies that identified a coupling of erosional processes in the Western Cordillera contrasting with decoupled processes in the Western Escarpment and in the Coastal Cordillera. Copyright © 2008 John Wiley & Sons, Ltd.     

Interlaboratory comparison of cosmogenic 21Ne in quartz

We performed an interlaboratory comparison study with the aim to determine the accuracy of cosmogenic ²¹Ne measurements in quartz. CREU-1 is a natural quartz standard prepared from amalgamated vein clasts which were crushed, thoroughly mixed, and sieved into 125–250 μm and 250–500 μm size fractions. 50 aliquots of CREU-1 were analyzed by five laboratories employing six different noble gas mass spectrometers. The released gas contained a mixture of 16–30% atmospheric and 70–84% non-atmospheric (predominantly cosmogenic) ²¹Ne, defining a linear array on the ²²Ne/²⁰Ne-²¹Ne/²⁰Ne three isotope diagram with a slope of 1.108 ± 0.014. The internal reproducibility of the measurements is in good agreement with the formal analytical precision for all participating labs. The external reproducibility of the ²¹Ne concentrations between labs, however, is significantly overdispersed with respect to the reported analytical precision. We report an average reference concentration for CREU-1 of 348 ± 10 × 10⁶ at [²¹Ne]/g[SiO₂], and suggest that the 7.1% (2σ) overdispersion of our measurements may be representative of the current accuracy of cosmogenic ²¹Ne in quartz. CREU-1 was tied to CRONUS-A, which is a second reference material prepared from a sample of Antarctic sandstone. We propose a reference value of 320 ± 11 × 10⁶ at/g for CRONUS-A. The CREU-1 and CRONUS-A intercalibration materials may be used to improve the consistency of cosmogenic ²¹Ne to the level of the analytical precision.     

Planetary-type rare gases in an upper mantle-derived amphibole

All twenty-three stable rare gas isotopes have been measured in a mantle-derived amphibole, kaersutite. The elemental abundance pattern of the rare gases is similar to the “planetary” rare gas pattern as defined by carbonaceous chondrites. The³He/⁴He ratio, (4.9 ± 0.6) × 10^?5, is suggestive of primordial He degassing from the mantle. Excess²¹Ne is present. The measured⁴⁰Ar/³⁶Ar ratio,400 ± 5, may represent a mantle⁴⁰Ar/³⁶Ar ratio <240 when corrected for radiogenic⁴⁰Ar. The heavy isotopes of Kr and t0he Xe isotopes are within error of the atmosphere values.