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1.
The mineralogy, elemental and isotopic composition of the Shaw meteorite indicate that it is a highly metamorphosed L-group chondrite which has lost a portion of its metal and sulfide. The metal which remains has an unusual composition relative to that in other L-group chondrites. It is enriched in Ga, Ge, Ir, Mo, Os, Pt, Re and Ru and depleted in As, Au, Cu and Sb. A comparison of the relative enrichments and depletions in Shaw to those observed in San Cristobal, the extreme end-member of group IAB iron meteorites, shows that the metal phases in these two meteorites have complementary compositions. This implies that the metal in Shaw represents the residual solid of a partial melting process while the missing metal, which drained away, may have gone to form an iron meteorite, like San Cristobal.  相似文献   

2.
Tungsten concentrations have been determined by instrumental neutron activation in 104 iron meteorites, and range from 0.07 to 5 μg/g. In individual groups, concentrations vary by factors of between 1.5 and 8, but there are negative W-Ni correlations in 8 groups: IAB, IC, IIAB, IID, IIE, IIIAB, IIICD, and IIIF. The lowest W concentrations are found in groups IAB and IIICD, which also have the smallest slopes on a W-Ni plot. Eighteen anomalous irons have W concentrations between 5 μg/g (Butler) and 0.11 μg/g (Rafrüti). The distribution of W in irons shows similarities to that of other refractory siderophilic elements (except Mo), but is closest to the distribution of Ru and Pt.Assuming that chemical trends in group IIIAB were produced by fractional crystallization, a value of 1.6 can be deduced for the distribution coefficient of W between solid and liquid metal, cf. 0.89 for Mo. Experimental evidence in support of these values is tenuous.  相似文献   

3.
The pressure-temperature conditions in the primordial nebula which could produce the observed Ni, Ga and Ge abundances in the major iron meteorite groups have been calculated assuming equilibrium condensation. Included in these calculations are the effect on the metal composition of Fe oxidation and sulphide formation during accretion, GeS and GaCl in the nebula gases and pressure variations in the nebula. It was found that the IIAB irons had their abundances of these elements fixed at the low-pressure extreme of the range which gives the IAB irons, but at 50 ± 10K higher temperatures. IIIAB and IVA formed over the same temperature range as IAB (600–670?40+60 K) in regions where the pressure was lower by a factor of 20 and 104 respectively. Group IVB accreted soon after condensation of the metal and at pressures of less than 10?3 atmosphere. The distribution of sulphur and carbon are consistent with this. The abundance of carbon in group IAB suggests that this and group IIAB accreted at about 10?4 atmosphere, so that IIIAB and IVA accreted where the pressure was 5 × 10?6 and 10?8 atmosphere, respectively.  相似文献   

4.
The main group pallasites and the mesosiderites fall within the oxygen isotope group previously determined for the calcium-rich achondrites (eucrites, howardites and diogenites), consistent with derivation from a common source material, and perhaps a common parent body. The group IIE iron meteorites were derived from the same source material as H-group ordinary chondrites. The chondrite-like silicate inclusions in group IAB iron meteorites are not related to the ordinary chondrites, but may be related to the enstatite chondrites. Several meteorites previously considered “anomalous” fall into these groups: Pontlyfni and Winona with the IAB irons, and Netschaëvo possibly with the H chondrites and IIE irons. The unusual pallasites Eagle Station and Itzawisis have remarkable oxygen isotopic compositions, and have more of the 16O-rich component than any other meteorite. Bencubbin and Weatherford are also unusual in their isotopic compositions, and may bear some relationship to the C2 carbonaceous chondrites. Lodran and Enon are isotopically similar to one another and are close to the achondrite-mesosiderite-pallasite group.  相似文献   

5.
Thermomagnetic and microprobe analyses are carried out and a set of magnetic characteristics are measured for 25 meteorites and 3 tektites from the collections of the Vernadsky Geological Museum of the Russian Academy of Sciences and Museum of Natural History of the North-East Interdisciplinary Science Research Institute, Far Eastern Branch of the Russian Academy of Sciences. It is found that, notwithstanding their type, all the meteorites contain the same magnetic minerals and only differ by concentrations of these minerals. Kamacite with less than 10% nickel is the main magnetic mineral in the studied samples. Pure iron, taenite, and schreibersite are less frequent; nickel, various iron spinels, Fe-Al alloys, etc., are very rare. These minerals are normally absent in the crusts of the Earth and other planets. The studied meteorites are more likely parts of the cores and lower mantles of the meteoritic parent bodies (the planets). Uniformity in the magnetic properties of the meteorites and the types of their thermomagnetic (MT) curves is violated by secondary alterations of the meteorites in the terrestrial environment. The sediments demonstrate the same monotony as the meteorites: kamacite is likely the only extraterrestrial magnetic mineral, which is abundant in sediments and associated with cosmic dust. The compositional similarity of kamacite in iron meteorites and in cosmic dust is due to their common source; the degree of fragmentation of the material of the parent body is the only difference.  相似文献   

6.
New, high-precision W isotope data on iron meteorites are presented that provide important constraints on the timing of silicate–metal segregation in planetesimals. Magmatic iron meteorites all have ε182W within error or less radiogenic than initial ε182W estimated by studies of chondritic meteorites. At face value this implies that iron meteorites are as old and older than refractory calcium–aluminium rich inclusions (CAI), which are widely thought to be the oldest solar system objects. Moreover, different meteorites from the same magmatic groups, believed to be derived from the same planetissimal core, display a range of ε182W. We suggest that the paradoxical ε182W values more negative than initial Solar System Initial (SSI) are most readily explained as a result of secondary, spallation reactions with cosmic rays during transit between parent body and the earth. This is supported by the most negative ε182W being found in meteorites with the oldest exposure ages and the magnitude of the effect is shown to be consistent with known nuclear reactions. On the other hand, it is also striking that none of the magmatic iron group meteorites have ε182W analyses, outside error, more radiogenic than the estimated solar system initial ratio. This suggests that core formation in parent bodies of magmatic iron meteorites occurred ≤ 1.5 Myr after the formation age of CAI [Y. Amelin, A.N. Krot, I.D. Hutcheon, and A.A. Ulyanov, Lead isotopic ages of chondrules and calcium-aluminum inclusions, Science 297, 1678–1683, 2002]. This extremely early metal–silicate differentiation is coeval with the first chondrules [M. Bizzarro, J.A. Baker, and H. Haack, Mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions, Nature 431, 275–278, 2004, A.N. Krot, Y. Amelin, P. Cassen, and A. Meibom, Young chondrules in CB chondrites from a giant impact in the early Solar System, Nature 436, 989–992, 2005]. Formation of later chondrules, and hence the parent bodies of some chondritic meteorites, must therefore have occurred in the presence of planetesimals large enough to possess iron cores. We conclude that early planetary accretion and differentiation was sufficiently fast for 26Al-decay to be an important heat source. Non-magmatic iron meteorites, however, display more radiogenic and varied W isotope signatures. This is in keeping with them being generated later, by impact melting during which the metal (partially) re-equilibrated with the then more radiogenic silicate fraction.  相似文献   

7.
Nearly 4,000 Fe, Ni and Co analyses have been carried out on the metal phases of 12 Antarctic chondritic meteorites by means of the electron microprobe. H-group chondrites show relatively simple patterns of variation for these elements but L- and LL-group members show much more scatter in both Ni and Co concentrations. A single member of the CO3 group investigated shows some scatter in the concentrations and also much higher Co concentrations in the high-Ni (awaruite?) phase (1.25–2%) than in the coexisting kamacite (0.2–0.5%). Thus, analysis of the metal phases can provide not only a means of identifying the group to which a meteorite belongs, but also the possibility of distinguishing between individual chondrites from the same group.

The overall concentrations of Co in the metal particles in the different groups are considered to be related inversely to the abundance of metal grains in meteorites of these groups while the scatter is interpreted as reflecting characteristics inherited at the time of accretion. The absence of homogenisation of the concentrations of Fe, Ni and Co in the metal particles, even in so-called equilibrated chondrites, provides further evidence against the widely held notion that these meteorites have been involved in a high-temperature prograde metamorphism.  相似文献   


8.
Allan Hills 85085 is a chemically and mineralogically unique chondrite whose components have suffered little metamorphism or alteration. This chondrite is unique because it has fewer and smaller chondrules (4 wt. %; mean diameter 16 μm) than any other chondrite, more metallic Fe,Ni (36%) and lithic and mineral silicate fragments (56%), and a lower abundance of troilite (2%) and volatiles. Most chondrules are cryptocrystalline or glassy and are depleted in volatiles, some small chondrules are also very depleted in refractory lithophiles. Matrix lumps (4%) partly resemble CI and CM matrices and may be foreign to the parental asteroid. Despite these differences, the components of ALH 85085 have some features common to most type 2 and the least metamorphosed type 3 chondrites: metallic Fe,Ni grains that contain 0.1–1 wt.% Cr, Si and P; Fe/(Fe + Mg) values of olivines, pyroxenes and chondrules are concentrated in the range 1–6 at.% with a few percent in the range 7–30%; porphyritic chondrules are chondritic in composition (except for their low volatile abundances). Thus the components of ALH 85085 probably have similar origins to those of components in other chondrites, and their properties largely reflect nebular, not asteroidal, processes.The bulk composition of ALH 85085 fits none of the nine groups of chondrites: it is richer in Fe (1.4 × CI levels when normalized to Si) and poorer in Na and S (0.1–0.2 × CI) than other chondrites. Low volatile concentrations are due to a low matrix abundance and loss of volatiles during or prior to chondrule formation, not to volatile loss during metamorphism. Chondrule textures imply extensive heating of chondrule melts above the liquidus, consistent with loss of volatiles from small volumes of melt during chondrule formation. The small size of chondrules is partly due to extensive fragmentation by impacts, which may have occurred on the parent asteroid or in the solar nebula. Collisions between chondrule precursor aggregates in the nebula could also be responsible for the small sizes of chondrules.Assuming that ALH 85085 is a representative sample of an asteroid, its properties lend support to models for the origins of the Earth, eucrite parent body and volatile-poor iron meteorites that invoke chondritic planetesimals depleted in volatiles. The existence of ALH 85085 and Kakangari suggests that the nine chondrite groups may provide a remarkably poor sample of the primitive chondritic material from which the asteroids formed. Certain similarities between ALH 85085 and Bencubbin and Weatherford suggest that the latter two primitive meteorites may actually be chondrites with even higher metal abundances (50–60 wt.%) and very large, partly fragmented chondrules.  相似文献   

9.
This study focuses on the trace and rare earth elements(REE) geochemistry of the Nkporo and Ekenkpon Shales of the Calabar Flank.The main aim is to infer their depositional environment and the degree of their metal enrichment.The shale samples were analyzed using inductively coupled plasma mass spectrometry.The results indicated that the mean concentrations of K,Na,and Fe in Nkporo and Ekenkpon Shales are 1.45,0.4,and 4.17 wt%,and 1.11,0.44,and 5.42 wt%;respectively.The Nkporo Shale is enriched with the following trace elements;PMn Sr Ba Zn Ce Rb Zr VCr Ni and depleted in the following trace elements;Ta GeSb Bi Cd Ag Te In Hg.While the Ekenkpon Shale is enriched with the following trace elements;P Mn Ba Sr VCe Zr Rb Cr Zn Ni and depleted in;Sb Ge Bi Ag Ce Te InHg.The concentration of redox-sensitive elements such as V,Ni,Mo,U,Cu,Cr,Re,Cd,Sb,Ti,Mn,and their ratio V/Mo and U/Mo in the black and grey shale samples show different patterns.The REE obtained from the Nkporo and Ekenkpon Shales were PAAS normalized.The Nkporo Shale showed a slightly flat light rare-earth element(LREE),middle rare-earth element(MREE),and heavy rare earth element(HREE) pattern enrichment.Ce/Ce*ranges from 0.95 to 1.09 in Nkporo Shale and 0.67 to 1.40 in Ekenkpon Shale.The Ekenkpon Shale showed a slight LREE,MREE enrichment,and depleted HREE patterns.The Mn contents and U/Mo ratio in Nkporo and Ekenkpon Shales suggests a poor oxygen transitional environment.The V/Mo and V/(V+Ni) ratios indicated that the Nkporo shales were deposited in an anoxic to suboxic conditions and Ekenkpon shales were also deposited under an anoxic to suboxic conditions.The V/Ni ratio indicated that the organic matter in the Nkporo shale is terrigenous while that of the Ekenkpon shales are both terrigenous and marine in origin.  相似文献   

10.
Total nitrogen contents have been measured by RNA of 30 iron and 4 stony-iron meteorites. Wide variations in N concentrations are noted (0.5 ppm to about 200 ppm). As a group, the IA irons have the highest nitrogen. This element is positively correlated with C, Ga, and Ge. Samples of meteorites that have been exposed to shock do not show any abnormal N distribution.  相似文献   

11.
Liquid metal-liquid silicate partitioning of Fe, Ni, Co, P, Ge, W and Mo among a carbon-saturated metal and a variety of silicate melts (magnesian-tholeiitic-siliceous-aluminous-aluminosiliceous basalts) depends modestly to strongly upon silicate melt structure and composition. Low valency siderophile elements, Fe, Ni and Co, show a modest influence of silicate melt composition on partitioning. Germanium shows a moderate but consistent preference for the depolymerized magnesian melt. High valency siderophile elements, P, Mo, and W, show more than an order of magnitude decrease in metal-silicate partition coefficients as the silicate melt becomes more depolymerized. Detailed inspection of our and other published W data shows that polymerization state, temperature and pressure are more important controls on W partitioning than oxidation state. For this to be true for a high and variable valence element implies a secondary role in general for oxidation state, even though some role must be present. Equilibrium core segregation through a magma ocean of ‘ultrabasic’ composition can provide a resolution to the ‘excess’ abundances of Ge, P, W and Mo in the mantle, but the mantle composition alone cannot explain the excess abundances of nickel and cobalt in chondritic proportions.  相似文献   

12.
Magmatic iron meteorites are considered to be remnants of the metallic cores of differentiated asteroids, and may be used as analogues of planetary core formation. The Fe isotope compositions (δ57/54Fe) of metal fractions separated from magmatic and non-magmatic iron meteorites span a total range of 0.39‰, with the δ57/54Fe values of metal fractions separated from the IIAB irons (δ57/54Fe 0.12 to 0.32‰) being significantly heavier than those from the IIIAB (δ57/54Fe 0.01 to 0.15‰), IVA (δ57/54Fe − 0.07 to 0.17‰) and IVB groups (δ57/54Fe 0.06 to 0.14‰). The δ57/54Fe values of troilites (FeS) separated from magmatic and non-magmatic irons range from − 0.60 to − 0.12‰, and are isotopically lighter than coexisting metal phases. No systematic relationships exist between metal-sulphide fractionation factor (Δ57/54FeM-FeS = δ57/54Femetal − δ57/54FeFeS) metal composition or meteorite group, however the greatest Δ57/54FeM-FeS values recorded for each group are strikingly similar: 0.79, 0.63, 0.76 and 0.74‰ for the IIAB, IIIAB, IAB and IIICD irons, respectively. Δ57/54FeM-FeS values display a positive correlation with kamacite bandwidth, i.e. the most slowly-cooled meteorites, which should be closest to diffusive equilibrium, have the greatest Δ57/54FeM-FeS values. These observations provide suggestive evidence that Fe isotopic fractionation between metal and troilite is dominated by equilibrium processes and that the maximum Δ57/54FeM-FeS value recorded (0.79 ± 0.09‰) is the best estimate of the equilibrium metal-sulphide Fe isotope fractionation factor. Mass balance models using this fractionation factor in conjunction with metal δ57/54Fe values and published Fe isotope data for pallasites can explain the relatively heavy δ57/54Fe values of IIAB metals as a function of large amounts of S in the core of the IIAB parent body, in agreement with published experimental work. However, sequestering of isotopically light Fe into the S-bearing parts of planetary cores cannot explain published differences in the average δ57/54Fe values of mafic rocks and meteorites derived from the Earth, Moon and Mars and 4-Vesta. The heavy δ57/54Fe value of the Earth's mantle relative to that of Mars and 4-Vesta may reflect isotopic fractionation due to disproportionation of ferrous iron present in the proto-Earth mantle into isotopically heavy ferric iron hosted in perovskite, which is released into the magma ocean, and isotopically light native iron, which partitions into the core. This process cannot take place at significant levels on smaller planets, such as Mars, as perovskite is only stable at pressures > 23 GPa. Interestingly, the average δ57/54Fe values of mafic terrestrial and lunar samples are very similar if the High-Ti mare basalts are excluded from the latter. If the Moon's mantle is largely derived from the impactor planet then the isotopically heavy signature of the Moon's mantle requires that the impacting planet also had a mantle with a δ57/54Fe value heavier than that of Mars or 4-Vesta, which then implies that the impactor planet must have been greater in size than Mars.  相似文献   

13.
We report small but significant variations in the 58Ni/61Ni-normalised 60Ni/61Ni and 62Ni/61Ni ratios (expressed as ε60Ni and ε62Ni) of bulk iron and chondritic meteorites. Carbonaceous chondrites have variable, positive ε62Ni (0.05 to 0.25), whereas ordinary chondrites have negative ε62Ni (− 0.04 to − 0.09). The Ni isotope compositions of iron meteorites overlap with those of chondrites, and define an array with negative slope in the ε60Ni versus ε62Ni diagram. The Ni isotope compositions of the volatile-depleted Group IVB irons are similar to those of the refractory CO, CV carbonaceous chondrites, whereas the other common magmatic iron groups have Ni isotope compositions similar to ordinary chondrites. Only enstatite chondrites have identical Ni isotope compositions to Earth and so appear to represent the most appropriate terrestrial building material. Differences in ε62Ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed, but some of the ε60Ni variability could reflect a radiogenic component from the decay of 60Fe. Comparison of the ε60Ni of iron and chondritic meteorites with the same ε62Ni allows us to place upper limits on the 60Fe/56Fe of planetesimals during core segregation. We estimate that carbonaceous chondrites had initial 60Fe/56Fe < 1 × 10− 7. Our data place less good constraints on initial 60Fe/56Fe ratios of ordinary chondrites but our results are not incompatible with values as high as 3 × 10− 7 as determined by in-situ measurements. We suggest that the Ni isotope variations and apparently heterogeneous initial 60Fe/56Fe results from physical sorting within the protosolar nebula of different phases (silicate, metal and sulphide) that carry different isotopic signatures.  相似文献   

14.
The abundances of 23 major and trace elements in the Pontlyfni meteorite have been measured by instrumental neutron activation analysis. The compositions of the metal and silicate fractions suggest a genetic relationship between Pontlyfni and the group IAB irons.  相似文献   

15.
The contents of the moderately volatile elements Ga, Ge, Cu and Sb in ordinary chondrites give us some clues with regard to the metal-silicate fractionation process. Their concentration in coexisting magnetic and non-magnetic portions of members of each ordinary chondrite group will be discussed. Germanium and Sb are mostly siderophilic, but Ga is strongly lithophilic in unequilibrated chondrites; its partition coefficient between magnetic and non-magnetic portions is positively correlated with petrologic type in L and LL chondrites, but not in H4–6 chondrites. From 25 to 50% of the total Cu is found in the non-magnetic fraction of chondrites, but there is no correlation between Cu content and petrologic type. The abundances of Ga, Cu and Sb (relative to Si) are constant in ordinary chondrites, independent of the amount of metal present, indicating that these elements were not in solid solution in the metal phase of chondrites when the metal-silicate fractionation process occurred. Germanium, which is the most volatile among the four elements analyzed, is more abundant in H than in L and LL chondrites, indicating that it was fractionated by this process. Nebular oxidation processes can be responsible for the behavior of Ga if this element was in oxidized form when loss of metal occurred, but cannot explain the results for Cu and Sb which are predicted to condense as metals and accrete mostly in metallic form. It is possible that Cu and Sb, upon condensation, did not form solid solutions with metallic Ni-Fe until after the separation of metal from silicates took place.  相似文献   

16.
If surface anomalies in the composition of the metallic-line A stars (Am stars) are due to a precipitation of planet-like bodies (planetoids) on them, then one should expect a correlation to exist between the overabundance of heavier-than-iron elements on these stars and their “standard” abundances in the solar system (since chondrites provide the “standard” level for these elements). However, an anticorrelation was revealed.Nevertheless, this fact supports the original suggestion on the origin of the metallicism of A stars, and can easily be explained within the author's hypothesis on the formation of the Sun from matter escaping from the proto-Jupiter. During the terminal stages of mass transfer, the matter was strongly depleted in refractories (forming the rocky core of Jupiter). Therefore the composition of the meteorites formed should not coincide with the primary composition of the matter. Thus the Sun's outer layers may also have a distorted composition. The author concludes that it is desirable to revise the “standard” abundances of elements heavier than iron.From a comparison of the surface composition of Am stars with the composition of lunar anorthosites and that of rocks in the upper zones of the Skaergaard intrusion (Greenland), the Am phenomenon may be seen to result from a precipitation of large geochemically differentiated planetoids onto a star. Such planetoids (including the Moon) condense in the cooled envelope of the primary component of a close binary stellar system.  相似文献   

17.
Sorption of Heavy Metals from Acetic Acid Extracts by Ferric Phosphate Colloids A conceivable procedure to remedy heavy metal contaminated soil materials is given with extraction of organic acids, i. e. by the use of a biological degradable extraction agent. The following concentration step of heavy metal extracts should be carried out to a great extent without a change of the low pH values. A conventional precipitation of the heavy metals by rising the pH should be avoided in order to introduce no large amounts of salts into the wastewaters of the process and furthermore, to reduce the amount of sludge to be deposited. The process scheme developed with the objective of heavy metals recycling consists of the following steps: the extraction of the heavy metal contaminated soils with weak organic acids like acetic acid or citric acid, the electrolysis of the extract, and a concentration step in order to treat metal concentrations not fully removed by electrolysis. This third step, e.g. could contain sorption on iron phosphate colloids and precipitation within the acidic environment. It has been examined whether a removal of the heavy metals Pb, Cd, Cu, Sb, Cr, Ni and Zn from acetic aqueous solutions of pH between 2 and 3 can be carried out.  相似文献   

18.
The removal of heavy metals such as Ni(II), Zn(II), Al(III), and Sb(III) from aqueous metal solutions was investigated using novel, cost effective, seaweed derived sorbents. Studies with a laboratory scale fixed‐bed sorption column, using a seaweed waste material (referred to as waste Ascophyllum product (WAP)) from the processing of Ascophyllum nodosum as biosorbent, demonstrated high removal efficiencies (RE) for a variety of heavy metals including Ni(II), Zn(II) and Al(III), with 90, 90 and 74% RE achieved from initial 10 mg/L metal solutions, respectively. The presence of Sb(III) in multi component metal solutions suppressed the removal of Ni(II), Zn(II) and Al(III), reducing the RE to 28, 17 and 24%, respectively. The use of Polysiphonia lanosa as a biosorbent showed a 67% RE for Sb(III), both alone and in combination with other metals. Potentiometric and conductometric titrations, X‐ray photoelectron and mid‐infrared spectroscopic analysis demonstrated that carboxyl, alcohol, sulfonate and ether groups were heavily involved in Sb(III) binding by P. lanosa. Only carboxyl and sulfonate groups were involved in Sb(III) binding by WAP. Furthermore, a greater amount of weak acidic groups (mainly carboxylic functions) were involved in Sb(III) binding by P. lanosa, compared to WAP which involved a greater concentration of strong acidic groups (mainly sulfonates).  相似文献   

19.
The ion microprobe has been used to analyse olivine in seven pallasites for Ni. The results are in the range 22–41 μg/g and are significantly lower than published electron probe analyses. The olivine-metal equilibrium temperatures deduced from thermodynamic calculations are correspondingly lower, and it is likely that equilibrium between olivine and metal was maintained to somewhat below the temperature of the γ-α transformation in metal (～700°C). The results appear to be consistent with cooling rates of ～1K/Ma derived from metal phase compositions, and certainly more so than the previous electron probe data. A Ni profile across an olivine grain in Eagle Station shows a decrease from 40 μg/g at the centre to 25 μg/g at the edge, illustrating the effect of limited diffusion of Ni in olivine during cooling. A correlation between grain size and central Ni content was also observed in Eagle Station, the smallest grains having the lowest Ni content.  相似文献   

20.
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.  相似文献   

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