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.     

I-Xe age and trapped Xe components of the Murray (C-2) chondrite

A neutron-irradiated bulk sample of the Murray (C-2) carbonaceous chondrite was etched with H₂O₂ and then divided into colloidal and non-colloidal fractions. The H₂O₂ treatment removed ～80% of the trapped Xe and greatly increased variations in the¹²⁹Xe/¹³²Xe ratio measured in stepwise heating. The colloid showed very little excess¹²⁹Xe, but the anti-colloid gave a fairly good I-Xe correlation corresponding to formation 3.7 ± 2.1 m.y. after Bjurböle.Variations in the trapped Xe component were also observed; most notably the 550°C anti-colloid fraction has large deficiencies relative to AVCC at the heavy isotopes. A tentative decomposition suggests U-Xe, a “primitive” trapped component, as the dominant component with minor contributions from H-Xe, L-Xe, and S-Xe (s-process nucleosynthesis). The identification of U-Xe rests primarily on the agreement of themeasured¹³⁴Xe/¹³⁶Xe ratio with U-Xe. This observation lends support to proposals for such a “primitive” trapped Xe component and demonstrates that at least some carbonaceous chondrite phases sampled a xenon reservoir nearly devoid of H-Xe.     

Primordial noble gases in separated meteoritic minerals,II

Eight silicate samples from the Orgueil carbonaceous chrondrite were analyzed for He, Ne, Ar, and Xe by a stepwise heating technique. Six of the samples, including two etched with NaOH, were density fractions covering the following ranges: < 2.35, 2.35–2.45, 2.45–2.48, and > 2.48 g/cm³. Two others were grain-size fractions, separated according to their ability to form a colloid at pH 11.5.All fractions are grossly deficient in cosmogenic neon, having retained only 8–33% of their normal complement. Retentivity increases with density.All fractions give low²⁰Ne/²²Ne ratios above 950°C, suggestive of D.C. Black's exotic “Neon-E” component of²⁰Ne/²²Ne ≤ 3.4. The lowest ratios were found in the low-density and especially the non-colloidal fractions. This suggests that the host phase of Ne-E is a clay mineral of lower iron content and coarser grain size than the main silicates of Orgueil.The main fraction,ρ = 2.35–2.45g/cm³, is inhospitable to Xe; it contains less Xe and releases it more readily at low temperatures (30–35% in 1 hour at 550°C) than do any of the other fractions.     

Rare gas isotopic compositions in natural gases of Japan

Isotopic and elemental compositions of rare gases in various types of gas samples collected in the Japanese Islands were investigated. Excess³He was found in most samples. Many samples showed a regionally uniform high³He/⁴He ratio of about 7 times the atmospheric ratio. The He concentrations varied from 0.6 to 1800 ppm, and they were low in CO₂-rich gases and high in N₂-rich gases. Ne isotopic deviations from the atmospheric Ne were detected in most volcanic gases. The deviations and the elemental abundance patterns in volcanic gases can be explained by a mixing between two components, one is mass fractionated rare gases and the other is isotopically atmospheric and is enriched in heavy rare gas elements. Ar was a mixture of mass fractionated Ar, atmospheric Ar and radiogenic Ar, and the contribution of radiogenic⁴⁰Ar was small in all samples. Except for He, elemental abundance patterns were progressively enriched in the heavier rare gases relative to the atmosphere. Several samples were highly enriched in Kr and Xe relative to the abundance pattern of dissolution equilibrium of atmospheric rare gases in water. The component which is highly enriched in heavy rare gases may be released from sedimentary materials in the crust.     

Oxygen isotope fractionation in decarbonation metamorphism: the Mottled Zone event

Calculated univariant equilibria and oxygen isotope compositions of silicates and carbonates support the proposal that the “Mottled Zone Event” is a low-pressure (1–25 atm), high-temperature (200° < T < 1300°C) metamorphism of calcareous siliceous sediments in which the thermal energy is provided by combustion of organic matter. δ¹⁸O of silicates decreases systematically with increasing metamorphic grade from averages of 18.1‰ in protolith shales, to 16.6‰ in grossular-diopside-zeolite rocks, 15.6‰ in wollastonite and anorthite-diopside-gehlenite-grossular fels, 14.1‰ in spurrite-brownmillerite marbles and 11.7‰ in the highest-grade larnite-gehlenite-brownmillerite assemblages. Decarbonation is the principal mechanism influencing the oxygen isotope compositions. The progressive decrease of δ¹⁸O in silicates can be modelled as a Rayleigh distillation of CO₂ approximately 16‰ enriched in ¹⁸O relative to whole rock assemblages i.e., of initial isotopic composition 8.5‰ heavier than the parent carbonates. The mineral assemblage of one sample with an unusual granoblastic texture is in apparent isotopic equilibrium at a temperature of 540°C.     

Microanalysis of nitrogen isotope abundances: association of nitrogen with noble gas carriers in Allende

Current research efforts to explore and account for the distribution of nitrogen isotope abundances in the ancient and present-day solar wind and in meteorites often require measurement of nitrogen abundances and isotopic compositions in very small samples of rare extraterrestrial materials. Isotopic analysis of ～ 1 μg of N₂ is possible with modern techniques of dynamic mass spectrometry, but even this high sensitivity is a limiting factor for certain critical samples. We have utilized a statistically operated mass spectrometer coupled to an ultrahigh vacuum gas extraction and processing system to lower this limit by approximately four orders of magnitude. Quantities of N₂ ranging from ～ 100 ng to < 100 pg are measurable with permil to percent precision in isotope ratios. Nitrogen and all noble gases evolved during stepwise combustion of fine-grained matrix material separated from the Allende meteorite have been meausred simultaneously in a pilot experiment using this technique. Isotopically heavy H-Xe (CCF-Xe) and isotopically light N are co-sited in a carbonaceous carrier phase, supporting a nucleosynthetic origin for¹⁵N-depleted nitrogen in Allende. The great isotopic uniformity of trapped Ar in all carrier phases indicates that simple, physical mass fractionation in gravitational escape of volatiles from the primitive nebula cannot have played a significant role in generating the nitrogen compositions observed in solar system matter.     

Kr and Xe isotopes from spontaneous fission of 248Cm and 250Cf: Comparison with noble gases in carbonaceous chondrites

Relative yields of Kr and Xe isotopes from the spontaneous fission of ²⁴⁸Cm and ²⁵⁰Cf have been determined mass spectrometrically. The yields are as follows: ⁸³Kr/⁸⁴Kr/⁸⁵Kr/⁸⁶Kr = 0.223/0.458/0.596/ ≡ 1.00 and 0.306/0.582/0.793/ ≡ 1.00;¹³¹Xe/¹³²Xe/¹³⁴Xe/¹³⁶Xe = 0.486/0.819/1.075/ ≡ 1.00 and 0.343/0.506/0.851/ ≡ 1.00 from ²⁴⁸Cm and ²⁵⁰Cf, respectively. The Xe yields from ²⁴⁸Cm agree with an earlier determination by Leich et al. [24]. Neither of these yield patterns matches that of “fissiogenic” Kr and Xe in carbonaceous chondrites and hence ²⁴⁸Cm and ²⁵⁰Cf are ruled out as progenitors of the meteoritic Kr and Xe. In general, none of the spontaneously fissioning nuclides of actinide elements can be identified as a possible progenitor. Even the mixtures of actinides, including a combination of ²⁴⁸Cm and ²⁵⁰Cm, are unsuitable. The origin of “anomalous” Kr and Xe in carbonaceous chondrites must then be traced either to the spontaneous fission of a superheavy element or to peculiarities in specific nucleosynthetic reactions.     

Origin of inert gases in “rusty rock” 66095

The amount of trapped inert gases present in rock 66095, as well as the elemental and isotopic composition of these gases can be explained by “contamination” of this rock - on the lunar surface - with as little as 0.2% of fines There is no compelling evidence that these gases come from the impact of a comet or a carbonaceous meteorite on the Moon, or that they represent genuine primordial lunar gas.The²¹Ne radiation age of 66095 is (1.1 ± 0.5) × 10⁶yr, which strongly suggests that this rock was excavated by the South Ray Crater event.     

The variation of cosmogenic Kr and Xe in a core from Estherville mesosiderite: direct evidence that the lunar131Xe anomaly is a depth effect

Kr and Xe were measured by a stepwise heating technique in three samples of a drill core in the “Minnesota” fragment of the Estherville mesosiderite. The cosmogenic⁷⁸Kr/⁸³Kr decreased from the “top” sample to the “bottom” sample(“top” = 0.163 ± 0.005, “bottom” = 0.151 ± 0.005) while the cosmogenic¹³¹Xe/¹²⁶Xe ratio increased(“top” = 5.58 ± 0.35, “bottom” = 6.92 ± 0.17). Cosmic-ray track studies have shown that the “top” sample was indeed closer to the preatmospheric surface than the “bottom” sample by ～ 10 cm. This is the first direct evidence, in a sample of known geometry, that the cosmogenic¹³¹Xe/¹²⁶Xe ratio increases as a function of depth, and as such, confirms the hypothesis that the lunar¹³¹Xe anomaly is a bona fide depth effect due to resonance neutron capture in¹³⁰Ba.     

Cosmogenic and radiogenic noble gases in the Dhajala chondrite

Whole rock and chondrules of the Dhajala chondrite were analyzed for Ne, Ar, Kr and Xe by total melting as well as by stepwise heating techniques. The cosmic ray exposure ages for the whole rock and the chondrules are6.2 ± 0.8 and6.3 ± 1.0m.y. as determined by the²¹Ne method and4.8 ± 1.5 and4.2 ± 2.0m.y. by the³⁸Ar method, respectively. The K-Ar age of the whole rock is4.2 ± 0.4b.y. The elemental composition of the trapped gas in this chondrite is of “planetary” type. The radiogenic¹²⁹Xe contents in the whole rock and chondrules are similar and this component is very retentively sited in the chondrules.     

Atmospheric noble gas signatures in deep Michigan Basin brines as indicators of a past thermal event

Atmospheric noble gases (e.g., ²²Ne, ³⁶Ar, ⁸⁴Kr, ¹³⁰Xe) in crustal fluids are only sensitive to subsurface physical processes. In particular, depletion of atmospheric noble gases in groundwater due to boiling and steam separation is indicative of the occurrence of a thermal event and can thus be used to trace the thermal history of stable tectonic regions. We present noble gas concentrations of 38 deep brines (~ 0.5–3.6 km) from the Michigan Basin. The atmospheric noble gas component shows a strong depletion pattern with respect to air saturated water. Depletion of lighter gases (²²Ne and ³⁶Ar) is stronger compared to the heavier ones (⁸⁴Kr and ¹³⁰Xe). To understand the mechanisms responsible for this overall atmospheric noble gas depletion, phase interaction models were tested. We show that this atmospheric noble gas depletion pattern is best explained by a model involving subsurface boiling and steam separation, and thus, consistent with the occurrence of a past thermal event of mantle origin as previously indicated by both high ⁴He/heat flux ratios and the presence of primordial mantle He and Ne signatures in the basin. Such a conceptual model is also consistent with the presence of past elevated temperatures in the Michigan Basin (e.g., ~ 80–260 °C) at shallow depths as suggested by previous thermal studies in the basin. We suggest that recent reactivation of the ancient mid-continent rift system underneath the Michigan Basin is likely responsible for the release of both heat and mantle noble gases into the basin via deep-seated faults and fracture zones. Relative enrichment of atmospheric Kr and Xe with respect to Ar is also observed, and is interpreted as reflecting the addition of sedimentary Kr and Xe from associated hydrocarbons, following the hydrothermal event. This study pioneers the use of atmospheric noble gases in subsurface fluids to trace the thermal history of stable tectonic regions.     

Deuterium in carbonaceous chondrites

Hydrogen isotopic compositions in seven carbonaceous chondrites lie in the range ?70 to +771‰ relative to SMOW. These values decrease, to a range from ?145 to +219‰, after low-temperature oxidation in an oxygen plasma. Deuterium enrichment is therefore concentrated in the organic matter, the hydrous silicates probably lying close to the terrestrial range for such material. Calculated values for δD of the organic fraction are +450 ‰ for Orgueil and Ivuna and up to +1600‰ for Renazzo. These enrichments, at least for Orgueil and Ivuna, suggest equilibration with protosolar hydrogen at very low temperatures. Assuming a value of 2.5 × 10^?5 for the protosolar D/H ratio, nominal equilibration temperatures of 230°K for silicates and 180°K for organic matter may be derived.     

The case for a martian origin of the shergottites: nitrogen and noble gases in EETA 79001

Nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite EETA 79001. A nitrogen component trapped in the glass, but not present in the matrix, has a δ¹⁵N value at least as high as +190‰. Ratios of⁴⁰Ar/¹⁴N and¹⁵N/¹⁴N in the glass are consistent with dilution of a martian atmospheric component (δ¹⁵N = 620 ± 160‰,⁴⁰Ar/¹⁴N= 0.33 ± 0.03) by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock. Trapped noble gases in the glass reproduce, within error, the elemental and isotopic compositions measured in Mars' atmosphere by Viking, and are in general agreement with previous measurements except for much lower abundances of neutron-generated krypton and xenon isotopes. The most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the EETA 79001 glass, and that this meteorite, and thus the shergottites and probably the nakhlites and chassignites as well, originated on Mars.Nitrogen in the non-glassy matrix of EETA 79001 amounts to less than 0.5 ppm and has a spallation-corrected δ¹⁵N value in the range 0 to ?20‰; it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen. Spallogenic noble gases yield single-stage exposure ages between 400,000 and 900,000 years, depending on irradiation geometry. Trapped argon may have an unusually low³⁶Ar/³⁸Ar ratio. Trapped krypton, except for a small excess at⁸⁰Kr, is smoothly mass-fractionated with respect to either terrestrial or chondritic Kr. The trapped xenon composition is consistent with addition of neutron-capture, radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric Xe. The elemental⁸⁴Kr/¹³²Xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio.     

The Antarctic meteorite Yamato 74123 — a new ureilite

The rare gases He, Ne, Ar, Kr and Xe were measured in bulk samples of Yamato 74123. The ³He and ²¹Ne exposure ages are found to be 5.50 Ma and 2.83 Ma, respectively. In addition to the cosmogenic component the samples contain primordial rare gases of the fractionated type in amounts typical of ureilites. In a three-isotope plot neon turns out to be a mixture of planetary neon and cosmogenic neon.The elements Na, Mg, Al, Si, P, S, K, Ca, Cr, Mn, Fe, Co, and Ni have been determined by spark source mass spectrometry in Yamato 74123 and for comparison in the ureilites Haveröand Kenna. The chemical composition as well as the noble gas abundance pattern identify Yamato 74123 as an ureilite.     

Noble gases in CO2 well gas,Harding County,New Mexico

The abundance and isotopic composition of noble gases were determined in samples of CO₂ well gas from Harding County, New Mexico. Our results confirm the presence of radiogenic¹²⁹Xe and fissiogenic^131–136Xe. Relative to noble gases in air, the CO₂ gas is selectively depleted in the lighter weight, nonradiogenic noble gases, except at neon. It is suggested that loss of atmospheric neon into space could account for an apparent excess of neon in juvenile gases.     

The origins and concentrations of water,carbon, nitrogen and noble gases on Earth

The isotopic compositions of terrestrial hydrogen and nitrogen are clearly different from those of the nebular gas from which the solar system formed, and also differ from most of cometary values. Terrestrial N and H isotopic compositions are in the range of values characterizing primitive meteorites, which suggests that water, nitrogen, and other volatile elements on Earth originated from a cosmochemical reservoir that also sourced the parent bodies of primitive meteorites. Remnants of the proto-solar nebula (PSN) are still present in the mantle, presumably signing the sequestration of PSN gas at an early stage of planetary growth. The contribution of cometary volatiles appears limited to a few percents at most of the total volatile inventory of the Earth. The isotope signatures of H, N, Ne and Ar can be explained by mixing between two end-members of solar and chondritic compositions, respectively, and do not require isotopic fractionation during hydrodynamic escape of an early atmosphere.The terrestrial inventory of ⁴⁰Ar (produced by the decay of ⁴⁰K throughout the Earth's history) suggests that a significant fraction of radiogenic argon may be still trapped in the silicate Earth. By normalizing other volatile element abundances to this isotope, it is proposed that the Earth is not as volatile-poor as previously thought. Our planet may indeed contain up to ~ 3000 ppm water (preferred range: 1000–3000 ppm), and up to ~ 500 ppm C, both largely sequestrated in the solid Earth. This volatile content is equivalent to an ~ 2 (± 1) % contribution of carbonaceous chondrite (CI-CM) material to a dry proto-Earth, which is higher than the contribution of chondritic material advocated to account for the platinum group element budget of the mantle. Such a (relatively) high contribution of volatile-rich matter is consistent with the accretion of a few wet planetesimals during Earth accretion, as proposed by recent dynamical models.The abundance pattern of major volatile elements and of noble gases is also chondritic, with two notable exceptions. Nitrogen is depleted by one order of magnitude relative to water, carbon and most noble gases, which is consistent with either N retention in a mantle phase during magma generation, or trapping of N in the core. Xenon is also depleted by one order of magnitude, and enriched in heavy isotopes relative to chondritic or solar Xe (the so-called “xenon paradox”). This depletion and isotope fractionation might have taken place due to preferential ionization of xenon by UV light from the early Sun, either before Earth's formation on parent material, or during irradiation of the ancient atmosphere. The second possibility is consistent with a recent report of chondritic-like Xe in Archean sedimentary rocks that suggests that this process was still ongoing during the Archean eon (Pujol et al., 2011). If the depletion of Xe in the atmosphere was a long-term process that took place after the Earth-building events, then the amounts of atmospheric ¹²⁹Xe and ^131–136Xe, produced by the short-lived radioactivities of ¹²⁹I (T_1/2 = 16 Ma) and ²⁴⁴Pu (T_1/2 = 82 Ma), respectively, need to be corrected for subsequent loss. Doing so, the I–Pu–Xe age of the Earth becomes ≤ 50 Ma after start of solar system formation, instead of ~ 120 Ma as computed with the present-day atmospheric Xe inventory.     

Noble gas systematics of the Réunion mantle plume source and the origin of primordial noble gases in Earth’s mantle

New noble gas data of ultramafic xenoliths from Réunion Island, Indian Ocean, further constrain the characteristics of primordial and radiogenic noble gases in Earth’s mantle plume reservoirs. The mantle source excess of nucleogenic ²¹Ne is significantly higher than for the Hawaiian and Icelandic plume reservoirs, similar to excess of radiogenic ⁴He. ⁴⁰Ar/³⁶Ar of the Réunion mantle source can be constrained to range between 8000 and 12 000, significant ¹²⁹Xe and fission Xe excess are present. Regarding the relative contribution of primordial and radiogenic rare gas nuclides, the Réunion mantle source is intermediate between Loihi- and MORB-type reservoirs. This confirms the compositional diversity of plume sources recognized in other radioisotope systematics. Another major result of this study is the identification of the same basic primordial component previously found for the Hawaiian and Icelandic mantle plumes and the MORB reservoir. It is a hybrid of solar-type He and Ne, and ‘atmosphere-like’ or ‘planetary’ Ar, Kr, Xe (Science 288 (2000) 1036). ²⁰Ne/²²Ne ratios extend to maximum values close to 12.5 (Ne-B), which is the typical signature of solar neon implanted as solar corpuscular radiation. This suggests that Earth’s solar-type noble gas inventory was acquired by small (less than km-sized) precursor planetesimals that were irradiated by an active early sun in the accretion disk after nebular gas dissipation, or, alternatively, that planetesimals incorporated constituents irradiated in transparent regions of the solar nebula. Previously, such an early irradiation scenario was suggested for carbonaceous chondrites which follow common volatile depletion trends in the sequence CI–CM–CV–Earth. In turn, CV chondrites closely match Earth’s mantle composition in ²⁰Ne/²²Ne, ³⁶Ar/²²Ne and ³⁶Ar/³⁸Ar. This indicates that mantle Ar could well be a planetary component inherited from precursor planetesimals. However, a corresponding conclusion for mantle Kr and Xe is less convincing yet, but this may be just due to the lack of appropriate ‘meteoritic’ building blocks matching terrestrial composition. Alternatively, heavy noble gases in Earth’s mantle could be due to admixing of severely fractionated air, but this effect must have affected all mantle sources to a very similar extent, e.g. by global subduction before the last homogenization of the mantle reservoirs.     

The mineralogy and the isotopic composition of sulfur in hydrothermal sulfide/sulfate deposits on the East Pacific Rise, 21°N latitude

The mineralogy of five groups of hydrothermal chimneys from the East Pacific Rise has been examined. Three of the chimneys, where the exit temperature of the hydrothermal fluids was close to 350°C, are rich in copper sulfides. Exit temperatures from the other two chimneys were less than 300°C; in these, the chimney walls are rich in zinc sulfide. The major sulfides in the chimneys as a whole were found to be wurtzite, chalcopyrite, pyrite, and cubanite. Anhydrite is always the dominant sulfate, and is present in all the deposits. Silicates are also present but in relatively minor amounts. There are considerable differences in the mineralogy of sulfides, sulfates, and silicates between the active and inactive vent deposits.The isotopic composition of sulfur in anhydrites from active vents is close to that of seawater; the δ³⁴S values of the sulfides range from +1.3 to +4.1‰. The isotopic composition of sulfur in the anhydrites is consistent with a derivation predominantly from seawater sulfate. The sulfur in the sulfides must have a complex origin including contributions from both sulfur in basalts and sulfide produced by reduction of sulfate in seawater. Mixing of H₂S-dominated hydrothermal fluids with cold seawater near the seafloor resulted in the precipitation of non-equilibrium assemblages of sulfides and sulfates.     

Noble gas elemental and isotopic abundances in deep-sea trenches in the western Pacific

Noble gas elemental and isotopic abundances were measured in seven deep-sea water samples from five different sampling sites in the Nankai Trough, the Japan Trench and the Kuril Trench. The samples were obtained by the manned submersible “Nautile”. Most of the sampling sites are associated with clam colonies and/or fluid venting. Excesses both in³He/⁴He ratio and He concentration are observed in a seawater sample collected a few kilometers off the clam colonies which were found at a depth of 3830 m at the mouth of the Tenryu Canyon. Concentrations of noble gases (Ne, Ar, Kr and Xe) in this sample show progressive depletion from Ne to Xe relative to those in 1°C air-saturated seawater, which can be attributed to mixing of hot water ( 15°C) with cold ambient water ( 1°C). Isotopic compositions of Ne, Ar, Kr and Xe in this sample are atmospheric. These observations may reflect venting of hot pore water around the Tenryu Canyon. All the other samples show a significant excess in concentration of all noble gases relative to 1°C air-saturated seawater and the isotopic compositions are atmospheric. This excess of noble gas concentrations may appear to be air contamination in the samples. However, results of hydrocarbon analyses of the Kaiko samples imply that such large amount of air contamination is improbable. Decomposition of gas hydrate in deep-sea sediments is a more likely explanation for the observed excess of noble gas concentration.     

Ni isotopic compositions in Allende and other meteorites

A new technique for high-precision isotopic analyses of Ni was developed and applied to terrestrial samples, Allende inclusions and materials from other meteorites. Most of the Allende inclusions analysed here were previously reported to contain isotopically anomalous Ti. In contrast, the Ni isotopic abundances are indistinguishable from normal within presently obtainable precision with only one possible exception. The latter inclusion was shown by others to contain a significantly fractionated magnesium isotopic pattern of 9‰/amu. A normal Ni isotopic pattern has also been observed for the chromite/carbon fraction of an Allende acid residue which is known to contain heavy noble gases of highly anomalous isotopic composition. All other meteoritic samples analysed (Khohar matrix and chondrules, Murray matrix, a Tieschitz chondrule and an Orgueil magnetic fraction) also show normal isotopic compositions of Ni; no evidence for effects from now extinct⁶⁰Fe could be detected. In spite of ubiquitous isotopic anomalies in Ti from normal Allende inclusions, there is no signature of isotopic variations in Ni from the same samples. Possible constraints for the nucleosynthesis of iron peak elements and for astrophysical and cosmochemical conditions during formation of the solar system are discussed.