The composition of metal phases in Bruderheim (L6) and implications for the thermal histories of ordinary chondrites —Erratum
| Autor: | D.G.W. Smith, S. Launspach |
|---|---|
| Rok vydání: | 1991 |
| Předmět: |
Lattice diffusion coefficient
Mineralogy chemistry.chemical_element Metamorphism Electron microprobe Silicate Metal chemistry.chemical_compound Nickel Geophysics chemistry Meteorite Space and Planetary Science Geochemistry and Petrology Chondrite visual_art Earth and Planetary Sciences (miscellaneous) visual_art.visual_art_medium Geology |
| Zdroj: | Earth and Planetary Science Letters. 102:79-93 |
| ISSN: | 0012-821X |
| DOI: | 10.1016/0012-821x(91)90019-e |
| Popis: | The compositions and textures of metal phases in Bruderheim have been examined in detail using Nomarski differential interference contrast techniques, backscattered electron imaging and quantitative electron microprobe analysis for Fe, Ni and Co. The results clearly demonstrate substantial inter- and intra-grain compositional variations, and that these persisted through the high-temperature thermal event which largely homogenised the silicate phases forming the bulk of the meteorite. These results are difficult to reconcile with prograde thermal metamorphism. Instead, accretion at high temperatures is envisaged with homogenisation of silicates occurring at these temperatures. Relatively sparse metal grains were largely unaffected at these temperatures because they did not form three-dimensional networks (and hence lattice diffusion of metallic Fe and Ni was ineffective), and because, at the temperature of accretion, most grains were present as homogeneous particles of the γ phase. The complexities now apparent in metal grains were established first during the decline of temperature and retrograde metamorphism after accretion and then later during relatively low-temperature burial metamorphism in asteroidal bodies. The reliability and significance of cooling rate calculations based on measurements of Ni concentrations in metal grains of such meteorites are questioned. |
| Databáze: | OpenAIRE |
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