摘要:

Sulphur contents and δ34S values have been determined for metallic spheroids collected from the vicinity of Meteor Crater, Arizona. Large spheroids with diameters ∼ 1.3 mm contain about 20% more sulphur than do small spheroids with diameters ∼ 0.5 mm. The mean δ34S value for large spheroids is + 0.23°/∞, while that for small spheroids is + 0.4°/∞, both measured relative to Canyon Diablo troilite. Abrasion experiments on large spheroids show that δ34S varies radially within them, with values of ∼ 1.9δ/∞ at their surfaces, falling to zero at their centres. The favoured explanation for the observed sulphur content and δ34S patterns is low temperature oxidation during post‐

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00819.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Our survey of type 4–6 ordinary chondrites indicates that gas‐poor, melt‐rock and/or exotic clast‐bearing fragmental breccias constitute 5%, 22% and 23%, respectively, of H, L and LL chondrites. These abundances contrast with the percentages of solar‐gas‐rich regolith breccias among ordinary chondrites: H (14%), L (3%) and LL (8%) (Crabb and Schultz, 1981). Petrologic study of several melt‐rock‐clast‐bearing fragmental breccias indicates that some acquired their clasts prior to breccia metamorphism and others acquired them after metamorphism of host material. In general, the melt‐rock clasts in gas‐poor H chondrite fragmental breccias were acquired after breccia metamorphism and were probably formed by impacts into boulders or exposed outcrops of H4‐6 material in the H chondrite parent body regolith. In contrast, most of the melt‐rock clasts in gas‐poor L and LL fragmental breccias were acquired prior to breccia metamorphism. The low abundance of regolith breccias among L chondrites and evidence that at least two‐thirds of the L chondrites suffered a major shock event 0.5 Gyr ago, suggest that the L parent body may have been disrupted by a major collision at that time and that the remaining parent body fragments were too small to develop substantial regoliths (e.g., Heymann, 1967; Crabb and Schultz, 1981). Such a disruption would have exposed a large amount of L chondrite bedrock, some of which would consist of fragmental breccias that acquired melt‐rock clasts very early in solar system history, prior to metamorphism. The exposed bedrock would serve as a potential target for sporadic meteoroid impacts to produce a few fragmental breccias with unmetamorphosed melt‐rock clasts. The high proportion of genomict brecciated LL chondrites reflects a complex collisional history, probably including several episodes of parent body disruption and gravitational reassembly. Differences in the abundances of different kinds of breccias among the ordinary chondrite groups are probably due to the stochastic natu

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00820.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Bulk and trace lithophilic elements (Al, Ca, Fe, Mn, Ti, Cr, Sr, V and Zn) have been determined in individual chondrules and in other constituents of the H‐4 Mafra chondrite by means of flameless A.A. microanalysis. Twenty‐four large sized (>1 mg) chondrules, composite samples of minor‐sized (0.1 and 0.2 mg) chondrules and fine‐grained “interchondrular” material have been examined. Data on the large‐sized chondrules exhibit large compositional variations among cosmochemically coherent groups of elements. A weak anti‐correlation was found between the geochemically coherent refractory V and volatile Zn. A possible mass‐composition relationship is suggested by the apparent concentration of lithophile high‐temperature condensing elements (Ca, Al, Ti) in the minor‐sized chondrules. Compositional features tend to support the hypothesis that chondrules originate from a large number of precursor components constituting a distinct grain population in the solar nebula. Melting through a sudden heating of random mixtures of these precursor grains was possibly followed by further condensation of vo

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

The isotopic compositions of noble gases in the solar wind show high enrichments of light isotopes. When corrected for mass fractionation all five noble gases there can be resolved in terms of the two primitive noble gas components that have been identified in planetary solids. Reasons are presented for assigning the fractionation to a solar process that selectively enriches lighter nuclei at the surface of the Sun. When abundances of the elements at the Sun's surface are corrected for this fractionation, it is shown that atomic abundances for major elements in the bulk Sun are (in decreasing order): Fe, Ni, O, Si, S and Mg. Solar elements at about the 1% atomic abundance level include He, C, Ne, Ca and Cr. These results suggest that fusion of hydrogen is probably not the Sun's primary energy source.

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Ustí nad Orlici (Kerhartice), a meteorite which fell on June 12, 1963 in Czechoslovakia, is classified as a L6 chondrite. Compositions of olivine (Fa 23.4), orthopyroxene (Fs 20, Wo 1.3), plagioclase (Ab85An10Or5) along with the bulk composition of the meteorite support this classification. Chromite compositions vary with grain size. Large chromites are higher in TiO2and lower in Fe3than small chromites. This may indicate that either these two chromites formed initially under different fO2conditions, or that this difference resulted from different equilibration behaviors of both chromites as a function of grain size. The meteorite contains three distinct sulfide assemblages: 1) troilite‐pentlandite, 2) troilite, pentlandite‐cubanite‐chalcopyrite‐pyrrhotite‐mackinawite, 3) troilite‐tetrataenite‐(Fe, Cu, Ni)1***.02S. These assemblages indicate equilibration down to temperatures c

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Shatter cones were discovered at Glover Bluff, Wisconsin. Coordinates are: N 43° 58.2′ W 089° 32

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Delaney et al. (1983) propose to redefine howardites as basaltic achondrites containing more than 10% of magnesian orthopyroxenite (diogenite) component. Since the 10% requirement is arbitrary and of no genetic significance this redefinition should be rejected and the earlier definition of Score et al. (1982) “Howardites are polymict pyroxene‐plagioclase achondrites containing magnesian orthopyroxene” — in any amount — should be

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

ISSN:0026-1114    

DOI:10.1111/j.1945-5100.1983.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY