Uranium in the silicate inclusions of stony-iron and iron meteorites     

Ghislaine Crozaz  Scott F. Sibley  Douglas R. Tasker 《Geochimica et cosmochimica acta》1982,46(5):749-754

The microdistribution of U has been studied, using fission track techniques, in eleven mesosiderites, seven pallasites and four iron meteorites with silicate inclusions. When concentrated, U is usually found in phosphates: merrillite and/or chlorapatite. As in stony meteorites, the U concentrations in a given phosphate phase are highly variable from meteorite to meteorite and sometimes also exhibit variations in the same meteorite. Uranium is found to be concentrated in merrillite (0.25 to 1.43 ppm) in all the mesosiderites except Bondoc where none was observed. No U-rich phase was identified in six of the seven pallasites. In the seventh, Marjalahti, there are merrillite grains with concentrations ranging from 0.06 to 0.14 ppm. Where observed, the phosphates from silicate inclusions in the irons appear to have U concentrations similar to the mesosiderites.  相似文献   

The distribution of U and Pu in the St. Severin chondrite     

J.H. Jones  D.S. Burnett 《Geochimica et cosmochimica acta》1979,43(12):1895-1905

A detailed study of the U distribution of the St. Severin chondrite has been made by fission track radiography in order to clarify the interpretation of fission Xe thermal release data in terms of the mineralogical location of the fission Xe within the meteorite. This is of importance because the ${}^{244}\text{Pu}{}^{238}\text{U}$ ratio for St. Severin has been widely adopted as the average solar system value. The U contents of the constituent minerals cannot account for the total rock U which, instead, appears to be primarily localized on grain boundaries. The greatest localizations of U are in olivine-poor, orthopyroxene-rich ‘clasts’. Our data coupled with those of Podosek (1970a) show that ²⁴⁴Pu in St. Severin was also located on grain boundaries and that the bulk of Pu and U are unfractionated within this meteorite. Due to recoil, the ²⁴⁴Pu fission Xe is found in 10 micron surface layers on major phases. Assuming that the grain boundaries (on which the Pu was located) was formed during metamorphism, the ${}^{244}\text{Pu}{}^{238}\text{U}$ ratio for St. Severin applies to a time subsequent to the textural recrystallization of the meteorite. Our data support the interpretation of Podosek and our best estimate of the solar system ${}^{244}\text{Pu}{}^{238}\text{U}$ is 0.015.  相似文献   

The behavior of actinides,phosphorus, and rare earth elements during chondrite metamorphism     

M.T Murrell  D.S Burnett 《Geochimica et cosmochimica acta》1983,47(11):1999-2014

New data on the U, Pu, and P distributions in less metamorphosed H-chondrites (type 3–5), coupled with literature results, permit a provisional picture to be assembled of the chemistry of these elements and for the rare earth elements in ordinary chondrites and the changes brought about by chondritic metamorphism. Preferential associations of phosphates with metals and/or sulndes in all chondrites strongly indicate an “initially” siderophile or conceivably chalcophile character for P in ordinary chondrite precursor materials with phosphate subsequently formed by oxidation. This oxidation occurred prior to or during chondritic metal-silicate fractionation. Uranium is initially concentrated in chondrule glass at ~ 100 ppb levels with phosphates (primarily merrillite) in H-3 chondrites being essentially U-free (<20 ppb). As chondrule glass devitrified during metamorphism, U migrated into phosphates reaching ~ 50 ppb in Nadiabondi (H-5) merrillite and 200–300 ppb in merrillite from equilibrated chondrites but “froze out” before total concentration in phosphates occurred. Relative ²⁴⁴Pu fission track densities in the outer 5 μm of olivine and pyroxene grains in contact with merrillite and with chondrule mesostasis in Bremervörde (H-3) give Pu(mesostasis)/Pu(merrillite) <0.01, implying total concentration of Pu in phosphates. Similarly, no detectable Pu (<0.1 ppb) was found in chondrule mesostasis in Tieschitz and Sharps; whereas, direct measurements of tracks in phosphates in H-3 chondrites are consistent with high (?10 ppb) Pu concentrations. Thus, a strong Pu-P correlation is indicated for ordinary chondrites. There is variable Pu/U fractionation in all chondritic phosphates reaching an extreme degree in the unequilibrated chondrites; therefore, the Pu/U ratio in phosphates appears relatively useless for relative meteorite chronology. Literature data indicate that the REE are located in chondrules in unequilibrated chondrites, most likely in glass; thus there may also be strong Pu/Nd fractionation within these meteorites. Like U, the REE migrate into phosphates during metamorphism but, unlike U, appear to be quantitatively concentrated in phosphates in equilibrated chondrites. Thus relative ages, based on Pu/Nd, may be possible for equilibrated chondrites, but the same chronological conclusions are probably obtainable from Pu concentrations in phosphates, i.e., on the Pu/P ratio. However, Pu/P chronology is possible only for ordinary chondrites; so there appears to be no universal reference element to cancel the effects of Pu chemical fractionation in all meteorites. Available data are consistent with — but certainly do not prove-that variations in Pu/P represent age differences, but if these age differences do not exist, then it is conceivable that the solar system ${}^{244}\text{Pu}{}^{238}\text{U}$ ratio, important for cosmochronology, is still lower than the presently accepted value of 0.007.  相似文献   

Fission track studies of xenolithic chondrites: implications regarding brecciation and metamorphism     

Brajesh K. Kothari  R.Sundar Rajan 《Geochimica et cosmochimica acta》1982,46(10):1747-1754

We have studied fission tracks in phosphates from one gas-poor chondrite and three gas-rich chondrites to determine their thermal history and brecciation time scales. More than 70 percent of the tracks in whitlockites in these meteorites are due to the decay of extinct Pu²⁴⁴.Whitlockites separated from Bhola, a gas-poor chondrite, have $\text{ρ}{}_{\mathrm{Pu}}\text{ρ}{}_{\mathrm{U}}\text{= 2.6–5.2}$ and a model fission track age of 4.0 Gyr for a $\text{(}\text{Pu}\text{U}\text{)}{}_{\mathrm{4.55Gyr}}\text{= 0.045}$. Brecciation of the Bhola meteorite must have occurred at ?4.3 Gyr to account for the metal data (Scott and Rajan, 1981). A minimum cooling rate of $\text{0.9}{}_{\mathrm{–0.2}}{}^{0.3}\text{K}\text{Myr}$ in the temperature interval 800 to 300 K obtained from the track data is a factor of seven higher than the metallographic cooling rate ($\text{0.1}\text{K}\text{Myr}$).For the gas-rich chondrites, the $\text{ρ}{}_{\mathrm{Pu}}\text{ρ}{}_{\mathrm{U}}$ in whitlockites are: Weston, 32–148; Fayetteville, 21–227; and St. Mesmin, 26–137. Whitlockites from all these meteorites give model fission track ages of 4.4 Gyr assuming a $\text{(}\text{Pu}\text{U}\text{)}{}_{\mathrm{4.55\; Gyr}}\text{= 0.045}$. The final brecciation event definitely did not reset the track clock in phosphates of St. Mesmin. Our data suggest that it is also true for Weston and Fayetteville. We conclude that our observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites.  相似文献   

The compositional classification of chondrites: IV. Ungrouped chondritic meteorites and clasts     

Gregory W. Kallemeyn  John T. Wasson 《Geochimica et cosmochimica acta》1985,49(1):261-270

Six specimens of unusual chondritic materials were analyzed by neutron activation for 30 elements in order to assess their degree of chondritic compositional pristinity and to search for evidence of genetic links to other chondrites. Five have highly recrystallized textures; the other, the Cumberland Falls chondrite, has suffered minor metamorphic recrystallization. Acapulco and Allan Hills A77081, are closely related and have subpristine compositions; they are more distantly related to Enon which has an altered composition. Udei Station appears to be a IAB meteorite even though its $\text{FeO}\text{(FeO + MgO)}$ ratio is slightly above the IAB field. The highly weathered meteorite Tierra Bianca is closely related to IAB but has a δ¹⁸O value 5 standard deviations higher than the IAB mean and is designated ungrouped. Udei Station and Tierra Bianca have altered compositions; rare earth element patterns indicate loss of a phosphate phase. The elemental composition of the Cumberland Falls chondrite is virtually identical to that of LL chondrites and its O-isotope composition is closely similar to those of some unequilibrated ordinary chondrites including LL Semarkona. The $\text{FeO}\text{(FeO + MgO)}$ ratios in its olivine are generally much lower than those in pyroxene, a relationship we show to be indicative of in situ reduction resulting from exchange with the aubritic host. The names winonaites and forsterite chondrites have no taxonomic utility.  相似文献   

The significance of europium anomalies in the REE spectra of granites and pegmatites,Mont Laurier,Quebec     

A.D Fowler  Ronald Doig 《Geochimica et cosmochimica acta》1983,47(6):1131-1137

Negative Eu anomalies in the REE spectra of granitic rocks are usually interpreted as evidence of earlier separation of a mineral phase such as plagioclase. Our study of the behaviour of the REE, and of U and Th, during late stage alteration of granites and the formation of pegmatites, suggests an alternative means for producing Eu anomalies. Albitization of earlier-formed plagioclase has depleted the granites in Eu and enriched the pegmatites in this element. This process is linked to the mobilization of U in the granites which is dependent on the oxidation state of the fluids. A systematic correlation between the ratios $\text{Eu}\text{Ce}$ and $\text{U}\text{Th}$ leads us to suggest a similar explanation for irregularities in the abundances of Ce and other rare-earths in the REE spectra of these rocks.We suggest that anomalous behavior of Eu in other environments or processes such as the alteration of basalt and the formation of certain ore deposit types may be caused partly by this mechanism.  相似文献   

Actinide microdistributions in the enstatite meteorites     

M.T. Murrell  D.S. Burnett 《Geochimica et cosmochimica acta》1982,46(12):2453-2460

Oldhamite is a major Th and U bearing phase in the enstatite meteorites. Oldhamite from E-6 chondrites has mean Th and U abundances of 1550 ± 80 ppb Th and 410 ± 20 ppb U, with $\text{Th}\text{U}\text{= 3.8 ± .2}$. With the exception of ferroan alabandite which contains 25 ± 1 ppb U, no other Th or U enriched phases were located in the E-6 chondrites, and nearly all of the total rock Th and U can be accounted for by oldhamite. In Khairpur (E6), excess fossil fission tracks were observed in enstatite grains in contact with oldhamite which indicates the presence of ²⁴⁴Pu in oldhamite. Oldhamite from St. Mark's (E5) and Abee (E4) also shows actinide enrichments but at levels about half the E-6 results. Niningerite in Abee contains 45 ± 5 ppb U and due to its high reported modal abundance is an important U reservoir in Abee. The U content of oldhamite from the aubrite Peña Blanca Spring is 1920 ± 100 ppb. All $\text{Th}\text{U}$ values measured in this study cluster tightly around a value of 4 which indicates a lack of ThU fractionation in both oldhamite and in the enstatite meteorites, themselves. This lack of fractionation, along with the presence of ²⁴⁴Pu in oldhamite and reported rare earth enrichments also in oldhamite, suggests that the enstatite chondrites may be well-suited for PuU chronology and for providing the initial PuU value in the early solar system.  相似文献   

Storage of F and Cl in the upper mantle: geochemical implications     

J.V. Smith  J.S. Delaney  R.L. Hervig  J.B. Dawson 《Lithos》1981,14(2):133-147

Electron microprobe analyses yielded mean values of $\text{F}\text{0.43}\text{and}\text{Cl}\text{0.08}\text{wt.}\text{\%}$ for primary-textured phlogopites in coarse, depleted garnet-lherzolite xenoliths from kimberlites. Most secondary-textured phlogopites have too low Cl (0.01–0.08 wt.%) to be metamorphic precursors of primary-textured phlogopites. MARID-suite phlogopites and many megacrysts in kimberlites have low Cl ($\text{～ 0.02}\text{wt.}\text{\%}$), and some but not necessarily all secondary micas may result from infiltration of kimberlite into peridotite xenoliths. A good correlation between P and F in some oceanic basalts and gabbros might suggest that these elements are derived mainly from F-rich apatite inthe mantle, and that whitlockite is not present in the source region. Mantle-derived mica and amphibole have such low Cl that it is necessary to attribute Cl in oceanic basalts and gabbros either to substantial Cl in the source apatite, or to Cl from invading solutions, or both: three apatites from the mantle contain 0.8–1.0 wt.% Cl, and others contain lower amounts. The halogen contents of kimberlitic magmas can be explained by incorporation of Cl-bearing mica and F-rich apatite during melting of peridotites, but compositional constraints are weak.  相似文献   

Helium-uranium dating of corals     

Michael L. Bender 《Geochimica et cosmochimica acta》1973,37(5):1229-1247

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Isotopic anomalies of noble gases in meteorites and their origins—III. LL-chondrites     

Leo Alaerts  Roy S Lewis  Edward Anders 《Geochimica et cosmochimica acta》1979,43(9):1399-1415

Nine LL-chondrites were studied by a selective etching technique, to characterize the noblegas components in three mineral fractions: HF-HCl-solubles (silicates, metal, troilite, etc.; comprising ～ 99% of the meteorite), chromite and carbon (～ 0.3–0.7%) and Q (a poorly characterized mineral defined by its solubility in HNO₃, comprising ～ 0.05% of the meteorite but containing most of the Ar, Kr, Xe and a neon component of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 10.9 ± 0.8}$). The ${}^{20}\text{Ne}{}^{36}\text{Ar}$ ratio in Q falls wi petrologic type and rising ³⁶Ar content, as expected for condensation from a cooling solar nebula, but contrary to the trend expected for metamorphic losses. Chondrites of different petrologic types therefore cannot all be derived from the same volatile-rich ancestor, but must have formed over a range of temperatures, with correspondingly different intrinsic volatile contents.The CCFXe (carbonaceous chondrite fission) component varies systematically with petrologic type. The most primitive LL3s (Krymka, Bishunpur, Chainpur) contain substantial amounts of CCFXe in chromite-carbon, enriched relative to primordial Xe as shown by high ${}^{136}\text{Xe}{}^{132}\text{Xe}$ (0.359–0.459, vs 0.310 for primordial Xe). These are accompanied by He and by Ne with ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{≈ 8.0}$ and by variable amounts of a xenon component enriched in the light isotopes. The chromite in these meteorites is compositionally peculiar, containing substantial amounts of Fe(III). These meteorites, as well as Parnallee (LL3) and Hamlet (LL4) also contain CCFXe in phase Q, heavily diluted by primordial $\text{Xe}\text{(}{}^{136}\text{Xe}{}^{132}\text{Xe}\text{= 0.317–0.329)}$. On the other hand, LL5s and 6s (Olivenza, St. Séverin, Manbhoom and Dhurmsala) contain no CCFXe in either mineral. This deficiency must be intrinsic rather than caused by metamorphic loss, because Q in these meteorites still contains substantial amounts of primordial Ne.If CCFXe comes from a supernova, then its distribution in LL-chondrites requires three presolar carrier minerals of the right solubility properties, containing three different xenon components in certain combinations. These minerals must be appropriately distributed over the petrologic types, together with locally produced Q containing primordial gases, and they must be isotopically normal, in contrast to the gases they contain. On the other hand, if CCFXe comes from fission of a volatile superheavy element, then its decrease from LL3 to LL6 can be attributed to progressively less complete condensation from the solar nebula. Ad hoc assumptions must of the host phase Q, its association with ferrichromite and the origin of the associated xenon component enriched in the light isotopes.Soluble minerals in LL3s and LL4s contain a previously unobserved, solar xenon component, which, however, is not derived from the solar wind. Three types of ‘primordial’ xenon thus occur side-by-side in different minerals of the same meteorite: strongly fractionated Xe in ferrichromite and carbon, lightly fractionated Xe in phase Q, and ‘solar’ Xe in solubles. Because the first two can apparently be derived from the third by mass fractionation, it seems likely that all were trapped from the same solar nebula reservoir, but with different degrees of mass fractionation.  相似文献   

Ion microprobe measurements of O/O ratios of phosphate minerals in the Martian meteorites ALH84001 and Los Angeles     

James P. Greenwood  Ruth E. Blake 《Geochimica et cosmochimica acta》2003,67(12):2289-2298

Oxygen isotope ratios of merrillite and chlorapatite in the Martian meteorites ALH84001 and Los Angeles have been measured by ion microprobe in multicollector mode. δ¹⁸O values of phosphate minerals measured in situ range from ∼3 to 6‰, and are similar to Martian meteorite whole-rock values, as well as the δ¹⁸O of igneous phosphate on Earth. These results suggest that the primary, abiotic, igneous phosphate reservoir on Mars is similar in oxygen isotopic composition to the basaltic phosphate reservoir on Earth. This is an important first step in the characterization of Martian phosphate reservoirs for the use of δ¹⁸O of phosphate minerals as a biomarker for life on Mars. Cumulative textural, major-element, and isotopic evidence presented here suggest a primary, igneous origin for the phosphates in Los Angeles and ALH84001; textural and chemical evidence suggests that phosphates in ALH84001 were subsequently shock-melted in a later event.  相似文献   

The isotopic composition of silver and lead in two iron meteorites: Cape York and Grant     

J.H. Chen  G.J. Wasserburg 《Geochimica et cosmochimica acta》1983,47(10):1725-1737

Silver in the metal phases of Cape York (IIIA) and Grant (IIIB) has been determined after an extensive surface cleaning process. The ${}^{107}\text{Ag}{}^{109}\text{Ag}$ was found to be enriched over that found in terrestrial Ag by ~7%. to 19%., demonstrating the presence of excess ¹⁰⁷Ag (¹⁰⁷Ag¹) in this class of meteorites. An effort was made to find schreibersite with a distinctive ¹⁰⁸Pd/¹⁰⁹Ag ratio in order to establish a three-point isochron, but the results are not markedly different from those obtained for the bulk metal. The Ag isotopic ratio of sulfides from the same meteorites were nearly normal in composition. These results demonstrate correlations of ${}^{107}\text{Ag}{}^{109}\text{Ag}$ with ${}^{108}\text{Pd}{}^{109}\text{Ag}$ between coexisting phases of two iron meteorites that are associated with planetary differentiation processes. The ratios ${}^{107}\text{Ag}{}^1{}^{108}\text{Pd}$ were found to be 1.7 × 10^?5 and 1.2 × 10^?5 for Cape York and Grant, respectively. These observations are in support of the widespread presence of ¹⁰⁷Pd in the early solar system. The difference in isotopic composition between metal and sulfide phases demonstrates that silver diffusion was small (over 6.5 × 10⁶ y) indicating a cooling rate much greater than 150°C/my for meteorites which have been attributed to small planetary cores. Uranium determinations were carried out on the metal phases and concentrations of ~ $\text{1 × 10}{}^{12}$ g U/g and 2 × 10^?10g U/g were found for Cape York and Grant, respectively. The Pb in these meteorites was determined using the improved cleaning procedures and chemical separations with low blank levels. The results confirm the presence of variable proportions of radiogenic Pb in both the metal and sulfide phases of iron meteorites. No simple explanation for the presence of radiogenic lead is apparent; while terrestrial contamination may appear to be the obvious explanation, it is possible that this effect could result from relatively recent metamorphism in the meteorite parent body.  相似文献   

A carbonaceous inclusion from the Krymka LL-chondrite: noble gases and trace elements     

Roy S. Lewis  Leo Alaerts  Jan Hertogen  Marie-Josée Janssens  Herbert Palme  Edward Anders 《Geochimica et cosmochimica acta》1979,43(6):897-903

A black inclusion from the Krymka LL3 chondrite was analyzed for 20 trace elements and five noble gases, by radiochemical neutron activation and mass spectrometry. The trace element pattern somewhat resembles that of C1 or C2 chondrites, but with several unique features. Elements of nebular condensation T ? 1000 K (U, Re, Os, Ir, Ni, Pd, Au, Sb and Ge) are essentially undepleted, as in C1 chondrites, but $\text{Re}\text{Ir}$ is 1.49 × higher than the characteristic Cl value. Among elements condensing below 1000 K, Cs, Se, Te, and In are depleted to approximately C2 levels (~0.6 × C1), whereas Ag, Bi, Tl are enriched to ~ 1.6 × C1. Such enrichments are thought to be characteristic of late nebular condensates.The noble-gas pattern also is unique. Gas contents are higher than in C1s, by factors of 2.6 to 19 for Ne through Xe. The $\text{Ar}{}^{36}\text{Xe}{}^{132}$ ratio of 500 is higher than mean values for C1s or C2s (109 or 89) and exceeds even the highest value seen in C3Os, 420, whereas the $\text{He}{}^4\text{Ne}{}^{20}$ ratio of 62 is much lower than the values for C1s and C2s (200–370). The $\text{Xe}{}^{129}\text{Xe}{}^{132}$ and $\text{Xe}{}^{136}\text{Xe}{}^{\mathrm{l32}}$ ratios of 1.040 and 0.320 resemble those of C1 chondrites, and seem to imply typical proportions of radiogenic Xe¹²⁹ and ‘fissiogenic’ xenon.It appears that the inclusion represents a new primitive meteorite type, similar to C-chondrites, but probably a late condensate from a region of higher nebular pressure.  相似文献   

⁴⁰Ar-³⁹Ar ages and trace element contents of Apollo 14 breccias; an interlaboratory cross-calibration of ⁴⁰Ar-³⁹Ar standards     

E.Calvin Alexander  Paul K. Davis 《Geochimica et cosmochimica acta》1974,38(6):911-928

Rare gas data are presented from step-wise heatings of lunar breccias 14066 and 14318 and from an interlaboratory cross-calibration of five standards used in ⁴⁰Ar-³⁹Ar dating. Four samples of 14066 all show depressed ⁴⁰¹Ar/³⁹¹Ar ratios at high temperatures, thus making age interpretation uncertain. While different in detail, the Ar release patterns in the four samples yield indistinguishable plateau ages of $\text{3.93 ± 0.03}$ b.y. and > 400°C total ages of $\text{3.87 ± 0.06}$ b.y. Concentrations of K, Ca, Ba, Br, U and I are given for 14318 and 14066. We also present an updating of all of the ⁴⁰Ar-³⁹Ar ages and trace element concentrations previously published by this laboratory.⁴⁰Ar-³⁹Ar dating standards from Menlo Park, Pasadena, Stony Brook, Toronto and Berkeley are calibrated against each other and the internal homogeneity of their ⁴⁰¹Ar/K ratios is tested. The Berkeley standard (from the St. Severin meteorite) has an age of $\text{4.504 ± 0.020}$ b.y. from this intercalibration.⁸⁰Kr from capture of lunar neutrons is detected in 14318. A comparison of the release pattern of the ⁸⁰Kr produced by lunar neutrons with the ^80,82Kr produced by pile neutrons in 14318, indicates that 14318 has lost approximately 35 per cent of the ⁸⁰Kr produced by lunar neutrons.  相似文献   

A 33S Anomaly in the allende meteorite     

C.E Rees  H.G Thode 《Geochimica et cosmochimica acta》1977,41(11):1679-1682

The isotope ratios ³³S/³²S and ³⁴S/³²S have been measured in sulphur fractions extracted from samples of the meteorites Allende and Eagle Station by leaching at successively greater acid concentrations and higher temperatures. On a three isotope plot of δ³³S$\text{vs}$δ³⁴S most of the data lie on or close to the mass fractionation line. The last fraction of sulphur extracted from a bulk Allende sample lies off the line and has an approximately 1%. excess in the ³³/³²S ratio.Previous searches for anomalous abundance patterns of ³²S, ³³S, ³⁴S and ³⁶S have been reported by HULSTON and THODE (1965a,b), THODE and REES (1971), and REES and THODE (1972). No isotope abundance variations were found, in the meteorite and lunar samples studied, which could not be explained on the basis of either mass dependent isotope fractionation or, in the special case of iron meteorites, cosmic ray production of ³³S and ³⁶S. We report here preliminary results of a renewed search for isotopically anomalous sulphur in which we are concentrating on the Allende and Eagle Station meteorites, both of which contain anomalous oxygen (CLAYTON $\text{et}$$\text{al}$., 1973, 1976). In a first attempt to distinguish between normal sulphur and any possible anomalous sulphur, we have leached both bulk samples and hand separated components of these meteorites with hydrochloric acid.CLAYTON and RAMADURAI (1977) suggested that the presence of isotopically anomalous sulphur would be evidence for the existence of presolar grains which are relics of nucleosynthesis in certain zones of supernova expansion. In particular they suggested that sulphides of titanium are good candidates for isotopic analysis. These are not expected to exist in conventional solar equilibrium condensation sequences, but might be abundant in condensates from silicon burning shells of supernovae. Our chemical procedures were already completed when CLAYTON and RAMADURAI'S suggestions came to our attention and it must be stressed that so far, in all cases but one we have examined only sulphur from sulphides which are decomposed by HC1. Thus we may not have sampled sulphides of the type suggested by CLAYTON and RAMADURAI.All samples of the Allende meteorite were ground finer than 50μm before acid extraction of sulphur. Samples of sulphur were extracted from the various phases of the meteorites by using successively stronger hydrochloric acid leaches, longer times and higher temperatures of reaction. Sulphur initially released as H₂S was successively converted to CdS, Ag₂S and SF₆, this latter compound being analysed mass spectrometrically (THODE and REES, 1971). Analyses of nine SF₆ samples prepared from Ag₂S originally derived from Canyon Diablo troilite were also performed in order to monitor fluorination and mass spectrometry precision and to establish the zero points ofthe isotope variation scales. The results are shown in Table 1. The sulphur contents of the various samples were determined gravimetrically as Ag₂S. The bulk and matrix samples are probably a few percent low because of mechanical losses. The percentages of sulphur in each fraction of a sample extracted during each leaching stage are given in the table. The total sulphur content in the bulk and matrix samples of the Allende meteorite i.e., the sum of the sulphur contents of the individual fractions, varies from 1.8 to 2.08%, the highest percentage being in the matrix. These values compare with about 2 to 2.1% obtained by CLARKE $\text{et}$$\text{al}$. (1970).  相似文献   

Colloidally separated samples from Allende residues: Noble gases,carbon and an ESCA-study     

Ulrich Ott  Johann Kronenbitter  Jose Flores  Sherwood Chang 《Geochimica et cosmochimica acta》1984,48(2):267-280

A non-colloidal fraction separated by physical means from an $\text{HF}\text{HCl}$-resistant residue of the Allende carbonaceous meteorite exhibits a ratio of isotopically “normal” (Q-type) xenon to “anomalous” xenon (X-type) that is ~4 times larger than usually observed. Coincidentally this fraction contains carbon that is isotopically heavier by ~10%. than bulk Allende residue samples. ESCA analyses of companion colloidal separates show that the major portion of the S contained in our $\text{HF}\text{HCl}$-residues is elemental rather than a sulfide. They also confirm earlier observations that no elementally distinct surface coating is present, in accord with the absence of a surface-sited sulfur-bearing gas carrier, and that the oxygen content is increased after etching with nitric acid. For these separates noble gas data coupled with the ESCA data for nitrogen and the isotopic data for carbon point to the existence of heterogeneities among the noble gas-, carbon- and nitrogen-bearing phases and, thus, preservation of discrete components from the variety of source regions (or production mechanisms, or both) sampled by the Allende parent body. In sharp contrast to the success of physical and chemical methods in yielding samples in which one of the major noble gas components predominates to an extraordinary degree over the other, carbon isotopic compositions that have been inferred for the respective carrier phases in these same samples are strongly contradictory. Mass and isotope balance considerations lead us to conclude that a major fraction of the carbonaceous matter in Allende is noble-gas-poor, a result that could be confirmed by direct isolation of a sample, the carbon in which is dominated by this variety; and for that reason no simple relationship is discernable yet between observed isotopic compositions and either major noble gas component. Similar ambiguities may exist for nitrogen. The possible relationship between carbon-rich phases in ureilites and carbonaceous chondrites is considered.  相似文献   

Foreign inclusions in stony meteorites—III. Rare gases and oxygen isotopes in a carbonaceous chondritic xenolith in the Plainview gas-rich chondrite     

Laurel L. Wilkening  Robert N. Clayton 《Geochimica et cosmochimica acta》1974,38(6):937-945

Measurements of oxygen and rare gas isotopes in a carbonaceous xenolithic inclusion in the Plainview H5 chondrite indicate that the xenolith and Plainview host are of two distinct meteorite types, and that no isotopic exchange has taken place between the two materials since their juxtaposition. The oxygen isotope analysis of the xenolith yields δ-¹⁸O value of 6.5 ± 0.1 % relative to SMOW, a value similar to that of carbonaceous chondrites (C2). Rare gas contents of the xenolith are also similar to those of carbonaceous chondrites. The radiation ages of the xenolith ($\text{2.9 ± 0.4}\text{Myr}$) and the host ($\text{2.8 ± 0.4}\text{Myr}$) are identical.Analyses of the rare gases in a sample of the host material adjacent to the xenolith show that Plainview is gas-rich, i.e., it contains large amounts (52,300 ± 10^?8 cm³ STP/g ⁴He) of solar-type trapped gases.We speculate that carbonaceous chondritic material may be more prevalent in the asteroid belt than previously suspected.  相似文献   

Ries impact crater,southern Germany: search for meteoritic material     

John W. Morgan  Marie-josée Janssens  Jan Hertogen  Jacques Gros  Hiroshi Takahashi 《Geochimica et cosmochimica acta》1979,43(6):803-815

Twenty-three samples from the Ries crater, representing a wide range of shock metamorphism, were analyzed for seven siderophile elements (Au, Ge, Ir, Ni, Os, Pd, Re) and five volatile elements (Ag, Cd, Sb, Se, Zn). Taking Ir as an example, we found siderophile enrichments over the indigenous level of 0.015 ppb Ir occur in only eight samples. The excess is very modest; even the most enriched samples (a weakly shocked biotite gneiss and a metal-impregnated amphibolite) have Ir, Os corresponding to ~4 × 10^?4 C1 chondrite abundances. Of five flädle glasses analyzed only one shows excess Ir. Suevite matrix and vesicular glass have slight enrichment, but homogenous glass from the same rock does not. In flädle glasses, Ni and Se are strongly correlated and apparently reside in Ir, Os-poor Sulfides [pyrrhotite, chalcopyrite, pentlandite(?)]of terrestrial, probably sedimentary, origin. The Ir, Os and Ni enrichments of the metal-bearing amphibolite are compatible with chondritic ratios, but these are ill-defined because of uncertainty in Ni. In the other samples enriched in siderophiles Ir(Os), Ni and Se are mutually correlated; $\text{Ni}\text{Ir}$ and $\text{Ni}\text{Os}$ ~ 11 × C1 and are much higher than any chondritic ratios; $\text{Se}\text{Ni}\text{~ 2 × C1}$ and suggests a sulfide phase, rather than metal may be the host of the correlated elements. Lacking a plausible local source, this material is apparently meteoritic in origin. The unusual elemental ratios, coupled with the very low enrichments, tend to exclude chondrites and most irons as likely projectile material. Of the achondrites, aubrites seem slightly preferable. Ratios of excess siderophiles in Ries materiel match tolerably those of an aubrite (possibly atypical) occurring as an inclusion in the Bencubbin meteorite, Australia. The Hungaria group of Mars-crossing asteroids may be a source of aubritic projectiles.  相似文献   

Uranium in submarine metalliferous deposits     

Harold S Rydell  Enrico Bonatti 《Geochimica et cosmochimica acta》1973,37(12):2557-2565

Hydrothermal submarine metalliferous deposits, common in areas of the ocean floor with high heat flow, contain generally about 10 ppm U as an order of magnitude. The $\text{U}{}^{234}\text{U}{}^{238}$ ratio is in the majority of cases close to that of seawater; only in a few cases is it anomalously high. Anomalous $\text{U}{}^{234}\text{U}{}^{238}$ ratios are coupled with low U concentrations. These data are explained by a model where thermal water (essentially heated seawater) in its sub-bottom circulation often is unable to leach U from the basaltic oceanic crust; in fact, these thermal waters may in some cases lose U. When leaching of U from the basalt does take place, probably during shallow stages of the sub-bottom circulation, the resulting anomalous $\text{U}{}^{234}\text{U}{}^{238}$ ratio can be preserved in the hydrothermal deposit only if mixing with ‘seawater’ U is prevented.  相似文献   

Total nitrogen content of deep sea basalts     

Thomas L. Norris  Oliver A. Schaeffer 《Geochimica et cosmochimica acta》1982,46(3):371-379

Various models have been suggested concerning the origin and evolution of the earth's atmosphere. An estimate of the nitrogen content of the mantle could further constrain atmospheric models. Total nitrogen content was determined by thermal neutron activation analysis via ¹⁴N(n,p)¹⁴C. The ¹⁴C was converted to carbon dioxide and counted in miniature low level proportional counters. The total nitrogen content of U.S.G.S. standards BCR-1 and G-2 as determined by different laboratories is variable, probably due to atmospheric adsorption by the finely ground samples. Total nitrogen content was determined in deep sea basalt glasses from three regions: East Pacific Rise ($\text{15 ± 4, 18 ± 4}$, and $\text{7 ±}\text{ppm}\text{2 N}$), Mid-Atlantic Rift (FAMOUS Region:$\text{22 ± 5, 18 ± 3}$, and $\text{10 ± 2}\text{ppm}\text{N}$) and the Juan de Fuca Ridge ($\text{17 ± 4}\text{ppm}\text{N}$). Matrix material from the same samples as the glasses was available from the East Pacific Rise ($\text{37 ± 6, 26 ± 4}$, and $\text{34 ± 6}\text{ppm}\text{N}$) and the Mid-Atlantic Rift ($\text{39 ± 4}\text{ppm}\text{N}$) which are about 50 to 100% greater than the associated glasses. The increased matrix abundance may be due to incorporation of chemically bound nitrogen from sea water rather than dissolved molecular nitrogen. The nitrogen content of the FAMOUS samples are inconsistent with the model of Langmuir et al. (1977) for petrogenesis based on trace element data. Factors which can affect the observed nitrogen content in the basalts and the interpretation in terms of the mantle nitrogen abundance are discussed (e.g. partial melting and degassing of the basalts). A lower limit of about 2 ppm N in the mantle can be estimated.  相似文献