Chemical composition of Mars     

John W Morgan  Edward Anders 《Geochimica et cosmochimica acta》1979,43(10):1601-1610

The composition of Mars has been calculated from the cosmochemical model of Ganapathy and Anders (1974) which assumes that planets and chondrites underwent the same 4 fractionation processes in the solar nebula. Because elements of similar volatility stay together in these processes, only 4 index elements (U, Fe, K and Tl or Ar³⁶) are needed to calculate the abundances of all 83 elements in the planet. The values chosen are U = 28 ppb, K = 62 ppm (based on $\text{K}\text{U}\text{= 2200}$ from orbital γ-spectrometry and on thermal history calculations by Toksöz and Hsui (1978) Fe = 26.72% (from geophysical data), and Tl = 0.14 ppb (from the Ar³⁶ and Ar⁴⁰ abundances measured by Viking).The mantle of Mars is an iron-rich [Mg/(Mg + Fe) = 0.77] garnet wehrlite (ρ = 3.52?3.54 g/cm³), similar to McGetchin and Smyth's (1978) estimate but containing more Ca and Al. It is nearly identical to the bulk Moon composition of Morgan et al. (1978b). The core makes up 0.19 of the planet and contains 3.5% S—much less than estimated by other models. Volatiles have nearly Moon-like abundances, being depleted relative to the Earth by factors of 0.36 (K-group, T_cond = 600–1300 K) or 0.029 (Tl group, T_cond < 600 K). The water abundance corresponds to a 9 m layer, but could be higher by as much as a factor of 11.Comparison of model compositions for 5 differentiated planets (Earth, Venus, Mars, Moon, and eucrite parent body) suggests that volatile depletion correlates mainly with size rather than with radial distance from the Sun. However, the relatively high volatile content of shergottites and some chondrites shows that the correlation is not simple; other factors must also be involved.  相似文献   

Mass spectrometric isotope dilution analyses of palladium,silver, cadmium and tellurium in carbonaceous chondrites     

Robert D. Loss  Kevin J.R. Rosman  John R. De Laeter 《Geochimica et cosmochimica acta》1984,48(8):1677-1681

The mass spectrometric isotope dilution technique was used to measure the elemental abundances of Pd, Ag, Cd and Te in Orgueil (C1), Ivuna (C1), Murray (C2) and Allende (C3) chondrites. The Pd abundance of 554 ppb for the C1 chondrites is almost identical to the recommended value of Anders and Ebihara (1982); that for Cd (712 ppb) is approximately 5% higher, whereas that for Ag (198 ppb) is approximately 10% lower than the recommended values. A smooth distribution for the abundances of the odd-A nuclides between65 ≦ A ≦ 209 have been observed except for small irregularities in the Pd-Ag-Cd and the Sm-Eu mass regions (ANDERS and Ebihara, 1982). The results from the present work have the effect of smoothing out the dip in the Pd-Ag-Cd region and indicate that there is no systematic fractionation of cosmochemical element groups in this mass region.A Te abundance of 2.25 ppm has been determined for the C1 chondrites Orgueil and Ivuna in agreement 2+with the value of Smith et al. (1977). This value is some 30% lower than the value of Krähenbühl et al. (1973) but is in good agreement with the more recent measurements from Chicago. The Krähenbühl et al. value causes ¹²⁸Te and ¹³⁰Te to lie approximately 30% above the r-process peak at A = 130 (Käppeler el al., 1982), whereas the new value fits smoothly into the general trend.  相似文献   

Chemical studies of L chondrites—II. Shock-induced trace element mobilization     

Thomas M. Walsh  Michael E. Lipschutz 《Geochimica et cosmochimica acta》1982,46(12):2491-2500

Previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock-heated collisional debris indicate that Au, Co, Se, Ga, Rb, Cs, Te, Bi, In, Ag, Zn, Tl and Cd progress in mobility. We report data for these 13 trace elements in 14 L4–6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier. Trace element contents vary with petrologic type, $\text{S}\text{Fe}$ sub-group and shock history, the last dominating strongly. Absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock-loading (i.e. residual temperatures) established from mineralogic/petrologic study. A tertiary process, shock-heating, previously known to have affected radiogenic ⁴⁰Ar and/or ⁴He in meteorites but not other elements, apparently was at least as effective as other open-system processes (secondary [parent body] and primary [nebular and/or accretionary] episodes) in establishing mobile trace element contents of L chondrites and probably others. If conditions during early genetic episodes are to be deduced from compositional information, shocked meteorites should be avoided or effects of later processes should be compensated for.  相似文献   

Light element geochemistry of the Apollo 16 site     

J.F Kerridge  I.R Kaplan  C Petrowski  S Chang 《Geochimica et cosmochimica acta》1975,39(2):137-162

Pronounced variations in abundances and isotopic compositions of some light elements in soils from the Apollo 16 site are interpreted in terms of differing degrees of solar wind exposure for an originally, and approximately, homogeneous regolith. Carbon abundances in soils are compatible with a model in which equilibrium is established, after 10⁴-10⁵ yr, between solar wind input and loss by H stripping. However, this model does not explain the observed C isotopic distribution, suggesting that other sources of C or other processes, or both, are also important. Carbon abundances in rocks from Apollo 16 are higher (average 40 ppm) than at other landing sites although their isotopic compositions, ?35 < δ¹³C < ?16%. PDB, are normal. Abundances of N and, to a less extent, He and H in soils correlate with C as does a fraction of metallic Fe attributed to in situ reduction of indigenous Fe²⁺ by solar wind H.Fillet soil 67461 apparently contains solar wind C and N in a relatively unfractionated form, yielding an upper limit to solar wind (δ¹³C of ?16%., PDB and a value of 3.4 for $\text{C}\text{N}$ in the solar wind.Sulfur at the Apollo 16 site represents a paradox in that, although abundances in soils are apparently controlled by local rock S contents, they also correlate, for all but one sample, with δ³⁴S, which itself is apparently controlled by surface exposure age. A complex lunar S cycle is suggested.  相似文献   

Are C1 chondrites chemically fractionated? a trace element study     

Mitsuru Ebihara  Rainer Wolf  Edward Anders 《Geochimica et cosmochimica acta》1982,46(10):1849-1861

Six C1 chondrite samples and a C2 xenolith from the Plainview H5 chondrite were analyzed by radiochemical neutron activation for the elements Ag, Au, Bi, Br, Cd, Ce, Cs, Eu, Ge, In, Ir, Lu, Nd, Ni, Os, Pd, Pt, Rb, Re, Sb, Se, Sn, Tb, Te, Tl, Yb, and Zn. The data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in C1 chondrites.A number of elements (Br, Rb, Cs, Au, Re, Os, Ni, Pd, Sb, Bi, In, Te) show small but correlated variations. Those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body, whereas those of Sb, Bi, In, and Te may at least in part involve nebular processes. Br and Au show systematic abundance differences from meteorite to meteorite, which suggests hydrothermal transport on a kilometer scale. The remaining elements vary from sample to sample, suggesting transport on a centimeter scale.There is no conclusive evidence for nebular fractionation affecting C1 's. Though C1 chondrites have lower $\text{Zr}\text{Hf}$ and $\text{Ir}\text{Re}$ ratios than do other chondrite classes, these ratios vary in other classes, suggesting that those classes rather than C1's are fractionated. Three fractionation-prone REE—Ce, Eu, and Yb have essentially the same relative abundances in C1's and all other chondrite classes, and hence apparently are not fractionated in C1's. We did not confirm the large Tb and Yb variations in C1's reported by other workers.We present revised mean C1 abundances for 35 elements, based on the new data and a critical selection of literature data. Changes are generally less than 10%, except for Br, Rb, Ag, Sb, Te, Au, and the REE.The Plainview C2 xenolith has normal trace element abundances, except for 3 elements falling appreciably above the C2 range: Rb, Cs, and Bi. Hydrothermal alteration may be the reason for all 3, though nebular fractionation remains a possibility for Bi.  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   

The abundances of titanium,zirconium and hafnium in stony meteorites     

Masako Shima 《Geochimica et cosmochimica acta》1979,43(3):353-362

The concentrations of Ti, Zr and Hf have been determined, by a stable isotope dilution method, in 27 chondrites, seven achondrites and standard rock samples BCR-1 and W-1.Among all chondrites investigated, enstatite chondrite Abee is lowest in Ti atomic ratio compared with Si while all carbonaceous chondrites show higher values. The Zr contents are higher in CII and CIII chondrites, relative to the other groups of chondrites. There is a clustering of Ti and Zr within each group. The $\text{Zr}\text{Hf}$ ratios in CII, CIII. E and H chondrites are essentially the same, while that in the CI chondrite is lower and in L, LL and unequilibrated chondrites are higher.The concentrations of Ti, Zr, Hf and $\text{Ti}\text{Zr}$, $\text{Zr}\text{Hf}$ ratios in achondrites are variable, even among members of the same group.Based on these results, condensation models for these elements are discussed. The variable results for Ti, Zr and Hf in achondrites may be due to the reheating recrystallization and metamorphic processes.‘Cosmic atomic abundances’ of Ti, Zr and Hf are calculated as 2470, 11.2 and 0.185. respectively for Si = 10⁶ atoms.  相似文献   

The role of carbon and oxygen in cosmic gases: some applications to the chemistry and mineralogy of enstatite chondrites     

John W Larimer  Mary Bartholomay 《Geochimica et cosmochimica acta》1979,43(9):1455-1466

A new condensation sequence appears if the $\text{C}\text{O}$ ratio in a gas of otherwise solar composition is increased by less than a factor of two. As the ratio increases from the solar value of 0.6 to ? 1 the gas becomes extremely reduced, the condensation temperatures of silicates and oxides are depressed markedly ～ 400 K and a new suite of refractory minerals appears: AIN, CaS, MgS, SiC, TiN, graphite, Si₂N₂O and probably metastable (Fe,Ni)³C. Many of these minerals are unique to enstatite chondrites and may be analogues of the refractory silicates and oxides found in more oxidized meteorites such as Allende.The change in chemistry is related to the stability of CO, the most stable C or O compound at high T. Since the elements occur in a 1:1 ratio in CO, only the element which is in excess is free to form other compounds. But as T decreases CO reacts with H₂ to form graphite, CH₄ or other hydrocarbons thereby freeing O to form H₂O. If equilibrium is maintained oxides and silicates form at about 1000 K ($\text{C}\text{O}\text{> 1}$, P_τ = 10^?4atm) as products of reactions among the carbides, nitrides, sulfides and the gas. The possibility that equilibrium was not maintained among the C-bearing species was also investigated. If either graphite or CH₄ does not form as predicted the stability fields of the reduced minerals expands to lower temperatures. If neither graphite nor CH₄ form as predicted, CO remains stable and the nebular gas is highly reduced at all temperatures.Enstatite chondrites appear to have originated in a region of the nebula where the $\text{C}\text{O}$ ratio was somewhat higher than the solar value. Various fractionation mechanisms are considered. An interesting possibility is that graphite, which is quite refractory under a wide range of conditions, survived the collapse of the solar nebula.  相似文献   

Isotopic studies of Mg,Fe, Mo,Ru and W in Fremdlinge from Allende refractory inclusions     

《Geochimica et cosmochimica acta》1987,51(12):3175-3192

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Isotopic anomalies of noble gases in meteorites and their origins—IV. C3 (Ornans) carbonaceous chondrites     

Leo Alaerts  Roy S Lewis  Edward Anders 《Geochimica et cosmochimica acta》1979,43(9):1421-1432

The C3O chondrites Kainsaz, Lancé and Ornans were studied by an acid dissolution technique, to characterize the noble-gas components in 3 mineral fractions: HF, HCl-solubles (99% of the meteorite), chromite and carbon (0.3–0.9%), and ‘phase Q’, a poorly characterized trace mineral (0.05–0.4%) containing most of the Ar, Kr, Xe. For all fractions, gas contents decline in the order Kainsaz > Lancé > Ornans; this trend parallels volatile contents but not heterogeneity of olivine composition or degree of metamorphism and seems to reflect progressively higher condensation temperatures from the solar nebula.Solubles contain nearly unfractionated Xe, and show ${}^{136}\text{Ar}{}^{132}\text{Xe}$ ratios up to 850. Hence the high $\text{Ar}\text{Xe}$ ratios (200–400) of bulk C3O chondrites must be due to an HF-soluble mineral (possibly magnetite). Phase Q contains ordinary planetary gases and a Ne component of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 10.3 ± 0.4.}$Chromite and carbon contain Ne of ${}^{20}\text{Ne}{}^{22}\text{Ne}\text{= 8.6 ± 0.1}$ and ‘CCF’ xenon (a peculiar component of possibly fissiogenic origin, enriched in the heavy isotopes but accompanied by a component enriched in the light isotopes).In all primitive chondrites, both the amount and the chemical separability of CCFXe parallel the abundance of promordial noble gases and other volatiles, such as C, N, Tl, Bi and In. The close correlation of CCFXe with various properties of undoubtedly local origin (volatile content, petrologic type, presence of ferrichromite and carbon, etc.) is more consistent with a local than with an extrasolar origin of this component. A volatile superheavy element seems to be the most plausible source, but the evidence is not conclusive.  相似文献   

“Mysterite” : a late condensate from the solar nebula     

H. Higuchi  R. Ganapathy  John W. Morgan  Edward Anders 《Geochimica et cosmochimica acta》1977,41(7):843-852

We have attempted to clarify the nature of “mysterite”, a material that had been postulated to explain the overabundance of Tl, Bi and Ag in certain chondrites. Four dark clasts and a vein sample from the H6 chondrite Supuhee were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Rb, Re, Sb, Se, Te, Tl and Zn. One of the clasts is enriched in all volatile elements, while the other 4 samples are enriched only in the siderophile volatiles Ag, Bi and Tl. The enrichments range up to 100 times typical H6 chondrite abundances. The proportions of Ag, Bi, Tl suggest the presence of at least two, Tl-rich and Tl-poor, varieties of mysterite ($\text{Tl}\text{Bi}\text{= 7.2}$ and <0.1). The former seems to dominate in Supuhee and Krymka, and the latter in Mezö-Madaras. Apparently mysterite is a late condensate from the solar nebula that collected volatiles left behind by earlier generations of chondrites. It was incorporated in Supuhee and perhaps in other chondrites (mainly of low petrologic types) during brecciation events.  相似文献   

Absolute isotopic abundances of Ti in meteorites     

F.R Niederer  D.A Papanastassiou  G.J Wasserburg 《Geochimica et cosmochimica acta》1985,49(3):835-851

The absolute isotope abundance of Ti has been determined in Ca-Al-rich inclusions from the Allende and Leoville meteorites and in samples of whole meteorites. The absolute Ti isotope abundances differ by a significant mass dependent isotope fractionation transformation from the previously reported abundances, which were normalized for fractionation using ${}^{46}\text{Ti}{}^{48}\text{Ti}$. Therefore, the absolute compositions define distinct nucleosynthetic components from those previously identified or reflect the existence of significant mass dependent isotope fractionation in nature. We provide a general formalism for determining the possible isotope compositions of the exotic Ti from the measured composition, for different values of isotope fractionation in nature and for different mixing ratios of the exotic and normal components. The absolute Ti and Ca isotopic compositions still support the correlation of ⁵⁰Ti and ⁴⁸Ca effects in the FUN inclusions and imply contributions from neutron-rich equilibrium or quasi-equilibrium nucleosynthesis. The present identification of endemic effects at ⁴⁶Ti, for the absolute composition, implies a shortfall of an explosive-oxygen component or reflects significant isotope fractionation. Additional nucleosynthetic components are required by ⁴⁷Ti and ⁴⁹Ti effects. Components are also defined in which ⁴⁸Ti is enhanced.Bulk samples of carbonaceous meteorites (C2 and C3 types) show distinct excesses at ⁵⁰Ti but no nonlinear effects at the other Ti isotopes. Other chondrites, including Orgueil (Cl), show no nonlinear effects. Relative to terrestrial Ti, a small isotope fractionation is found for only an enstatite chondrite. The Ti absolute compositions in Ca-Al-rich inclusions show significant isotope fractionation effects corresponding to an enhancement in the heavier isotopes relative to the lighter isotopes as compared to Ti in a TiO₂ standard and in chondrites. The absence of a correlation of Ti isotope fractionation effects with those for Ca and Mg is indicative of multiple processes of condensation, volatilization and recondensation; however, the mechanisms causing the isotope fractionation are not well understood.  相似文献   

Unequilibrated ordinary chondrites: A tentative subclassification based on volatile-element content     

Edward Anders  M.G. Zadnik 《Geochimica et cosmochimica acta》1985,49(5):1281-1291

For unequilibrated ordinary chondrites (= UOC), two measures of primitiveness are available: volatile content, in principle reflecting accretion conditions from the solar nebula, and metamorphism, reflecting reheating in the parent bodies. These two measures do not always correlate, and we have therefore developed a tentative classification scheme based on volatile content that complements the Searset al. (1980) scheme based on metamorphism. Like the latter, it subdivides type 3 chondrites on a scale of 3.0 to 3.9; the notation 3.4/0 indicates a meteorite that is subtype 3.4 according to metamorphism and 3.0 according to volatile content.The classification is based mainly on C and Xe—two elements that are little affected by shock-induced reheating—and to a lesser extent on Ar³⁶,Bi,In, and Tl. Of 22 meteorites considered, the majority have concordant classifications (±0.2) on the two scales. However, 5 meteorites are richer in volatiles than their metamorphic grade indicates: Sharps 3.4/0, ALHA 77011 3.5/0, Ngawi 3.6/3, ALHA 77299 3.7/4, and Mezö-Madaras 3.7/3. It remains to be seen whether these differences indeed denote a more primitive nature.Some new clues to the formation of chondrites may eventually come from Xe and C. Their concentrations in UOC's vary by more than 5×, but the $\text{Xe}\text{C}$ ratio remains nearly constant at 3.4 × 10^?3 of the solar-system ratio. Even the ratios for other chondrite classes differ only slightly from that for UOC's, e.g., C3O (1.5×) and E3,4 (0.4×). Either the 4 factors determining this ratio (T, t, P, and internal surface area of the carbon) varied in complementary fashion, or—more probably—they varied only slightly in the entire source region of chondrites.  相似文献   

Al-Sm-Eu-Sr systematics of eucrites and Moon rocks: Implications for planetary bulk compositions     

Paul H Warren 《Geochimica et cosmochimica acta》1983,47(9):1559-1571

Analysis of the Eu and Sr “anomalies” of eucrites and lunar rocks allows constraints to be placed on the bulk compositions of the eucrite parent body (EPB) and the Moon. The elements Al, REE, and Sr, all are essentially incompatible with the major minerals of these small, low-?(O₂) bodies, except for plagioclase, into which Al, Sr, and Eu tend to concentrate. Therefore, the hypothesis that Al, REE, and Sr in the EPB and the Moon are all in proportions close to those in the bulk solar system (i.e., chondrites) leads to certain predictions about the concentrations of these elements in samples affected by plagioclase fractionation. The predictions are almost ideally fulfilled by eucrites and lunar samples. For the EPB, the ratios $\text{REE}\text{Al}$, $\text{Sr}\text{Al}$, and $\text{Sr}\text{REE}$ are constrained to be probably within 10%, almost certainly within 20%, of the chondritic ratios. For the more complicated Moon, the constraints are less precise: $\text{REE}\text{Al}$ is very probably within 25% of chondritic; $\text{Sr}\text{Al}$ and $\text{Sr}\text{REE}$ are probably within 35% of chondritic. These findings are proof that there is a strong similarity between the bulk compositions of the planets and the compositions of chondritic meteorites.The eucrites' Sm-Eu-Sr systematics are also valuable sources of constraints on the distribution coefficients for Eu and Sr into plagioclase, at low ?(O₂). From the slope of data for noncumulate eucrites on a Eu-Sm plot, D(Eu,pl/liq) can be inferred to be 1.1_?0.1^0.2. From the slope on a Sr-Sm plot, D(Sr,pl/liq)) can be inferred to be 1.5 ± 0.3. In the case of D(Eu), this is in excellent agreement with experimental data. In the case of D(Sr), the empirical result is probably more appropriate for eucritic systems than most experimental data, which, due to compositional effects, scatter widely.  相似文献   

陨石学及天体化学研究某些新进展     

王道德  王桂琴 《矿物学报》2012,32(3):321-340

陨石是来自含气体-尘粒的太阳早期星云盘凝聚和吸积的原始物质,大多数原始物质因吸积后的作用过程而改变（如月球、地球及火星样品）,但有一些却完整的保存下来（如球粒陨石或球粒陨石中的难熔包体）。这些原始的物质通常依据同位素丰度特征来识别,依据其矿物-岩石学特征和成因可将已知的陨石划分许多更小的类型。陨石学及天体化学的新近进展包括：新近识别的陨石群;发现新类型球粒陨石及行星际尘粒中发现前太阳和星云组分;利用短寿命放射性核素完善了早期太阳系年代学;洞察宇宙化学丰度、分馏作用及星云源区及通过次生母体的作用过程阐释星云和前星云的记录。本文概述了早期太阳系内从星云到陨石的演化过程。依据这些资料,对早期太阳系所经历的多种核合成的输入、瞬时加热事件与星云动力学有一些新的认识,以及认识到小星子和行星体系的演化比以前预期的更快速。  相似文献   

Elemental fractionations among enstatite chondrites     

Philip A Baedecker  John T Wasson 《Geochimica et cosmochimica acta》1975,39(5):735-765

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Isotopic anomalies of noble gases in meteorites and their origins—VII. C3V carbonaceous chondrites     

Jun-Ichi Matsuda  Roy S. Lewis  Hiroshi Takahashi  Edward Anders 《Geochimica et cosmochimica acta》1980,44(11):1861-1874

Noble gases were measured in bulk samples of the C3V chondrites Grosnaja, Vigarano, and Leoville, and in HF,HCl-insoluble residues before and after etching with HNO₃. The residues were characterized by INAA and SEM. Gas components were determined, directly or by subtraction, for the following fractions: HF,HCl-solubles (?98% of the meteorite), ‘sphase Q’, a poorly characterized trace mineral that is insoluble in HCl-HF but soluble in HNO₃, and an insoluble residue, consisting of ferrichromite, carbonaceous matter, and spinel.Bulk meteorites show some correlation of the noble-gas pattern with McSween's subclasses: two ‘oxidized’ C3V's—Allende (LEWIS et al, 1975) and Grosnaja— have lower Ar/Xe but higher Ne/Xe ratios than the ‘reduced’ C3V's—Vigarano and Leoville—which are transitional to LL3's and C3O chondrites in both respects. An HCl-soluble mineral of high Ar/Xr ratio seems to be responsible. In other respects, the 3 C3V's of this study resemble Allende, with only moderate differences. Phase Q contains most of the Ar, Kr, Xe, but only small amounts of Ne; the etched residues contain planetary Ne ($\text{Ne}{}^{20}\text{Ne}{}^{22}\text{? 8.5}$) and the controversial CCFXe component, enriched in the heavy Xe isotopes ($\text{Xe136}\text{Xe132 ? 0.4–0.5}$). The CCFXe is accompanied by an ‘L-Xe’ component that is enriched in the light Xe isotopes. The proportion of the two is virtually constant in C3V's. as in all other C-chondrites. in contrast to the ~ 2-fold variation in ordinary chondrites.C3V's have systematically higher $\text{Xe}{}^{136}\text{Xe}{}^{132}$ ratios, and hence higher ratios of CCFXe to planetary Xe, than do other chondrite classes. This may reflect some peculiarity in their formation conditions, favoring uptake of CCFXe.  相似文献   

Electron microprobe study of a ‘mysterite’-bearing inclusion from the Krymka LL-chondrite     

Lawrence Grossman  John M. Allen  Glenn J. MacPherson 《Geochimica et cosmochimica acta》1980,44(2):211-216

The black inclusion from the Krymka LL3 chondrite previously found to contain ‘mysterite’ by Lewiset al. (1979) belongs to a hitherto unknown class of carbonaceous chondrites. Its olivine and pyroxene compositions. Fo 97–99 and En 96, respectively, are characteristic of carbonaceous chondrites and its plagioclase composition. An 100, is characteristic of C3's. It contains a peculiar group of Co-, Cr-rich metal grains whose compositions are similar, but not identical, to those in C2 chondrites and which also bear some similarities to those in Renazzo. Its weight ratios of total $\text{Fe}\text{SiO}{}_2$ and $\text{solSiO}{}_2\text{MgO}$ are 0.74 and 1.43, respectively, and its atomic ratio of $\text{Si}\text{Al}$ is 10.7, exactly the same as in carbonaceous chondrites. Its bulk chemical composition is very close to that of the Murchison C2 chondrite. The association of mysterite with a special type of carbonaceous chondrite material suggests that mysterite formed by low-temperature condensation in a different region of the nebula from other carbonaceous chondrites.  相似文献   

Nitrogen isotopes in the solar system     

Johannes Geiss  Peter Bochsler 《Geochimica et cosmochimica acta》1982,46(4):529-548

Measurements of the isotopic composition of nitrogen in the solar system are summarized. We show that the 30% change, during the last 3 to 4 billion years, of ${}^{15}\text{N}{}^{14}\text{N}$ in solar-wind-bearing lunar soils and breccias probably does not reflect changes in this ratio at the solar surface. Such changes, whether by spallation or thermonuclear reactions are ruled out by comparing the yields of ¹⁵N with those of other rare isotopes such as ⁹Be, ¹¹B, ³He or ¹³C, even if an arbitrary degree of solar mixing is introduced. Moreover, we calculate that the solar activity required for producing significant amounts of ¹⁵N by spallation at the solar surface should have resulted in a particle bombardment of the Moon of an intensity that would have produced amounts of spallation isotopes (e.g.¹⁵N, ²¹Ne, ³⁸Ar, ¹³¹Xe) several orders of magnitude in excess of what is actually found in the whole regolith.We argue that accretion of interstellar matter also does not work as a cause for a significant change of the photospheric ${}^{15}\text{N}{}^{14}\text{N}$ ratio. Evidence is presented that the mixing depth at the solar surface on a time scale of ?10⁹ years is (10^?2 ?10^?1) M_⊙ Mixing to this depth renders accretion of interstellar matter as a source of compositional changes at the solar surface inefficient, even if allowance is made for the expected large difference in the accretion rates of condensed and gaseous matter. A quantitative treatment of several alternatives of solar accretion leads to serious contradictions (e.g. with the low Ne abundances in planetary atmospheres or with the amounts of nitrogen that should have been directly accreted by the Moon), and we conclude that accretion during the main sequence life of the Sun is an unlikely source of changes in ${}^{15}\text{N}{}^{14}\text{N}$ at the solar surface.A ratio of ${}^{15}\text{N}{}^{14}\text{N}\text{= (4.0 ± 0.3) × 10}{}^{\mathrm{?3}}$ is our best estimate for average solar system material and for the Sun. We propose that a rare, very light nitrogen component (called LPN) is admixed in varying amounts to planetary matter. Undiluted LPN has not been found in meteorites or planetary atmospheres, but we show that the combined effects of LPN admixture and isotope fractionation can in principle account for the variability of ${}^{15}\text{N}{}^{14}\text{N}$ observed in the planetary system. Determination of the Jovian ${}^{15}\text{N}{}^{14}\text{N}$ ratio with an accuracy of ~10% would crucially test our interpretation of the nitrogen isotope observations.  相似文献   

Oxygen and bulk element abundances in Luna 20 fines     

Morteza Janghorbani  David E Gillum  William D Ehmann 《Geochimica et cosmochimica acta》1973,37(4):905-908

Abundances of O, Si, Al and Mn have been determined in Luna 20 fines sample 22001,9 by instrumental neutron activation analysis. The abundances of O, Si and Al are among the highest we have observed in lunar samples and reflect a highlands origin for much of this regolith sample. The Luna 20 abundances reported here most closely resemble those we have determined in four samples of two Apollo 16 fines, rock 14310, and a clast from breccia 15459. The Luna 20 $\text{O}\text{Si}$ ratio of 1.96 ± 0.05 is similar to that in most other lunar samples, but the $\text{Al}\text{Si}$ ratio of 0.532 ± 0.024 is exceeded only by our data on the Apollo 16 fines. This $\text{Al}\text{Si}$ ratio is in agreement with the value of 0.55 ± 0.06 determined by the remote X-ray fluorescence experiment for the highlands between Mare Crisium and Mare Smythii which lie near the Luna 20 site (Adleret al., 1972).  相似文献