Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites
Abstract Zinner and Göpel ( , ) found clear evidence for the former presence of 26 Al in the H4 chondrites Ste. Marguerite and Forest Vale. They assumed that the 26 Al‐ 26 Mg systematics of these chondrites date “metamorphic cooling of the H4 parent body.” Plagioclase in these chondrites can have ve...
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crwiley:10.1111/maps.12304 2023-12-03T10:20:13+01:00 Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites Telus, M. Huss, G. R. Nagashima, K. Ogliore, R. C. National Aeronautics and Space Administration National Aeronautics and Space Administration 2014 http://dx.doi.org/10.1111/maps.12304 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmaps.12304 https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.12304 en eng Wiley http://onlinelibrary.wiley.com/termsAndConditions#vor Meteoritics & Planetary Science volume 49, issue 6, page 929-945 ISSN 1086-9379 1945-5100 Space and Planetary Science Geophysics journal-article 2014 crwiley https://doi.org/10.1111/maps.12304 2023-11-09T14:16:49Z Abstract Zinner and Göpel ( , ) found clear evidence for the former presence of 26 Al in the H4 chondrites Ste. Marguerite and Forest Vale. They assumed that the 26 Al‐ 26 Mg systematics of these chondrites date “metamorphic cooling of the H4 parent body.” Plagioclase in these chondrites can have very high Al/Mg ratios and low Mg concentrations, making these ion probe analyses susceptible to ratio bias, which is inversely proportional to the number of counts of the denominator isotope (Ogliore et al. ). Zinner and Göpel ( ) used the mean of the ratios to calculate the isotope ratios, which exacerbates this problem. We analyzed the Al/Mg ratios and Mg isotopic compositions of plagioclase grains in thin sections of Ste. Marguerite, Forest Vale, Beaver Creek, and Sena to evaluate the possible influence of ratio bias on the published initial 26 Al/ 27 Al ratios for these meteorites. We calculated the isotope ratios using total counts, a less biased method of calculating isotope ratios. The results from our analyses are consistent with those from Zinner and Göpel ( ), indicating that ratio bias does not significantly affect 26 Al‐ 26 Mg results for plagioclase in these chondrites. Ste. Marguerite has a clear isochron with an initial 26 Al/ 27 Al ratio indicating that it cooled to below 450 °C 5.2 ± 0.2 Myr after CAI s. The isochrons for Forest Vale and Beaver Creek also show clear evidence that 26 Al was alive when they cooled, but the initial 26 Al/ 27 Al ratios are not well constrained. Sena does not show evidence that 26 Al was alive when it cooled to below the Al‐Mg closure temperature. Given that metallographic cooling rates for Ste. Marguerite, Forest Vale, and Beaver Creek are atypical (>5000 °C/Myr at 500 °C) compared with most H4s, including Sena, which have cooling rates of 10–50 °C/Myr at 500 °C (Scott et al. ), we conclude that the Al‐Mg systematics for Ste. Marguerite, Forest Vale, and Beaver Creek are the result of impact excavation of these chondrites and cooling at the surface of the parent ... Article in Journal/Newspaper Beaver Creek Wiley Online Library (via Crossref) Marguerite ENVELOPE(141.378,141.378,-66.787,-66.787) Meteoritics & Planetary Science 49 6 929 945 |
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Open Polar |
collection |
Wiley Online Library (via Crossref) |
op_collection_id |
crwiley |
language |
English |
topic |
Space and Planetary Science Geophysics |
spellingShingle |
Space and Planetary Science Geophysics Telus, M. Huss, G. R. Nagashima, K. Ogliore, R. C. Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
topic_facet |
Space and Planetary Science Geophysics |
description |
Abstract Zinner and Göpel ( , ) found clear evidence for the former presence of 26 Al in the H4 chondrites Ste. Marguerite and Forest Vale. They assumed that the 26 Al‐ 26 Mg systematics of these chondrites date “metamorphic cooling of the H4 parent body.” Plagioclase in these chondrites can have very high Al/Mg ratios and low Mg concentrations, making these ion probe analyses susceptible to ratio bias, which is inversely proportional to the number of counts of the denominator isotope (Ogliore et al. ). Zinner and Göpel ( ) used the mean of the ratios to calculate the isotope ratios, which exacerbates this problem. We analyzed the Al/Mg ratios and Mg isotopic compositions of plagioclase grains in thin sections of Ste. Marguerite, Forest Vale, Beaver Creek, and Sena to evaluate the possible influence of ratio bias on the published initial 26 Al/ 27 Al ratios for these meteorites. We calculated the isotope ratios using total counts, a less biased method of calculating isotope ratios. The results from our analyses are consistent with those from Zinner and Göpel ( ), indicating that ratio bias does not significantly affect 26 Al‐ 26 Mg results for plagioclase in these chondrites. Ste. Marguerite has a clear isochron with an initial 26 Al/ 27 Al ratio indicating that it cooled to below 450 °C 5.2 ± 0.2 Myr after CAI s. The isochrons for Forest Vale and Beaver Creek also show clear evidence that 26 Al was alive when they cooled, but the initial 26 Al/ 27 Al ratios are not well constrained. Sena does not show evidence that 26 Al was alive when it cooled to below the Al‐Mg closure temperature. Given that metallographic cooling rates for Ste. Marguerite, Forest Vale, and Beaver Creek are atypical (>5000 °C/Myr at 500 °C) compared with most H4s, including Sena, which have cooling rates of 10–50 °C/Myr at 500 °C (Scott et al. ), we conclude that the Al‐Mg systematics for Ste. Marguerite, Forest Vale, and Beaver Creek are the result of impact excavation of these chondrites and cooling at the surface of the parent ... |
author2 |
National Aeronautics and Space Administration National Aeronautics and Space Administration |
format |
Article in Journal/Newspaper |
author |
Telus, M. Huss, G. R. Nagashima, K. Ogliore, R. C. |
author_facet |
Telus, M. Huss, G. R. Nagashima, K. Ogliore, R. C. |
author_sort |
Telus, M. |
title |
Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
title_short |
Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
title_full |
Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
title_fullStr |
Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
title_full_unstemmed |
Revisiting 26 Al‐ 26 Mg systematics of plagioclase in H4 chondrites |
title_sort |
revisiting 26 al‐ 26 mg systematics of plagioclase in h4 chondrites |
publisher |
Wiley |
publishDate |
2014 |
url |
http://dx.doi.org/10.1111/maps.12304 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fmaps.12304 https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.12304 |
long_lat |
ENVELOPE(141.378,141.378,-66.787,-66.787) |
geographic |
Marguerite |
geographic_facet |
Marguerite |
genre |
Beaver Creek |
genre_facet |
Beaver Creek |
op_source |
Meteoritics & Planetary Science volume 49, issue 6, page 929-945 ISSN 1086-9379 1945-5100 |
op_rights |
http://onlinelibrary.wiley.com/termsAndConditions#vor |
op_doi |
https://doi.org/10.1111/maps.12304 |
container_title |
Meteoritics & Planetary Science |
container_volume |
49 |
container_issue |
6 |
container_start_page |
929 |
op_container_end_page |
945 |
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1784267639985537024 |