Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites
Abstract In the CR (Renazzo‐like) chondrite group, many chondrules have successive igneous rim (IR) layers, with an outer layer that contains a silica mineral and/or silica‐rich glass (silica‐rich igneous rims, SIRs). Models for SIR formation include (1) accretion of Si‐rich dust onto solid chondrul...
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Online Access: | http://dx.doi.org/10.1111/maps.14051 https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.14051 |
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crwiley:10.1111/maps.14051 2024-06-23T07:46:25+00:00 Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites Smith, Aimee Jones, Rhian H. Science and Technology Facilities Council 2023 http://dx.doi.org/10.1111/maps.14051 https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.14051 en eng Wiley http://creativecommons.org/licenses/by/4.0/ Meteoritics & Planetary Science volume 59, issue 4, page 685-718 ISSN 1086-9379 1945-5100 journal-article 2023 crwiley https://doi.org/10.1111/maps.14051 2024-06-04T06:48:11Z Abstract In the CR (Renazzo‐like) chondrite group, many chondrules have successive igneous rim (IR) layers, with an outer layer that contains a silica mineral and/or silica‐rich glass (silica‐rich igneous rims, SIRs). Models for SIR formation include (1) accretion of Si‐rich dust onto solid chondrule surfaces, followed by heating and cooling and (2) condensation of SiO (gas) onto the surface of partially molten chondrules. We evaluate these models, based on a petrographic study of five Antarctic CR chondrites that have undergone minimal secondary alteration. We obtained electron microprobe analyses of minerals and glass with quantitative wavelength‐dispersive spectroscopy mapping, and identified silica polymorphs with Raman spectroscopy. Common SIRs contain silica, low‐Ca pyroxene, Ca‐rich pyroxene, Fe,Ni metal, ± glass ± plagioclase ± rare olivine. We also describe near‐monomineralic SIRs where a narrow zone of cristobalite occurs at the outer edge of the chondrule. All crystalline silica is cristobalite, except for one SIR that consists of tridymite. Some rims contain silica‐rich glass (>80 wt% SiO 2 ) but no silica mineral. Features such as sharp interfaces and compositional boundaries between chondrules and SIRs indicate that SIRs were formed from solid precursors. Consideration of the stability fields of silica polymorphs and computed liquidus temperatures indicates that SIRs were heated to >1500°C for limited time periods, followed by rapid cooling, similar to conditions for chondrule formation. We infer that in the CR chondrule formation region, the same heating mechanism was repeated multiple times while the chemical composition of the nebular gas evolved to highly fractionated silica‐rich compositions. Article in Journal/Newspaper Antarc* Antarctic Wiley Online Library Antarctic Meteoritics & Planetary Science 59 4 685 718 |
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English |
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Abstract In the CR (Renazzo‐like) chondrite group, many chondrules have successive igneous rim (IR) layers, with an outer layer that contains a silica mineral and/or silica‐rich glass (silica‐rich igneous rims, SIRs). Models for SIR formation include (1) accretion of Si‐rich dust onto solid chondrule surfaces, followed by heating and cooling and (2) condensation of SiO (gas) onto the surface of partially molten chondrules. We evaluate these models, based on a petrographic study of five Antarctic CR chondrites that have undergone minimal secondary alteration. We obtained electron microprobe analyses of minerals and glass with quantitative wavelength‐dispersive spectroscopy mapping, and identified silica polymorphs with Raman spectroscopy. Common SIRs contain silica, low‐Ca pyroxene, Ca‐rich pyroxene, Fe,Ni metal, ± glass ± plagioclase ± rare olivine. We also describe near‐monomineralic SIRs where a narrow zone of cristobalite occurs at the outer edge of the chondrule. All crystalline silica is cristobalite, except for one SIR that consists of tridymite. Some rims contain silica‐rich glass (>80 wt% SiO 2 ) but no silica mineral. Features such as sharp interfaces and compositional boundaries between chondrules and SIRs indicate that SIRs were formed from solid precursors. Consideration of the stability fields of silica polymorphs and computed liquidus temperatures indicates that SIRs were heated to >1500°C for limited time periods, followed by rapid cooling, similar to conditions for chondrule formation. We infer that in the CR chondrule formation region, the same heating mechanism was repeated multiple times while the chemical composition of the nebular gas evolved to highly fractionated silica‐rich compositions. |
author2 |
Science and Technology Facilities Council |
format |
Article in Journal/Newspaper |
author |
Smith, Aimee Jones, Rhian H. |
spellingShingle |
Smith, Aimee Jones, Rhian H. Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
author_facet |
Smith, Aimee Jones, Rhian H. |
author_sort |
Smith, Aimee |
title |
Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
title_short |
Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
title_full |
Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
title_fullStr |
Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
title_full_unstemmed |
Petrographic constraints on the formation of silica‐rich igneous rims around chondrules in CR chondrites |
title_sort |
petrographic constraints on the formation of silica‐rich igneous rims around chondrules in cr chondrites |
publisher |
Wiley |
publishDate |
2023 |
url |
http://dx.doi.org/10.1111/maps.14051 https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.14051 |
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Antarctic |
geographic_facet |
Antarctic |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_source |
Meteoritics & Planetary Science volume 59, issue 4, page 685-718 ISSN 1086-9379 1945-5100 |
op_rights |
http://creativecommons.org/licenses/by/4.0/ |
op_doi |
https://doi.org/10.1111/maps.14051 |
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Meteoritics & Planetary Science |
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59 |
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4 |
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685 |
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718 |
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1802645820365864960 |