Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes
Carbonaceous chondrites of the Ornans-type (CO3) form a well-documented metamorphic series. To investigate the conditions under which metamorphism took place, whole rock oxygen and carbon isotope analysis has been carried out on 10 CO3 chondrites (ALH A77307 [3.0], Colony [3.0], Kainsaz* [3.1], Feli...
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ftunivarizonaojs:oai:journals.uair.arizona.edu:article/15047 2023-05-15T13:42:28+02:00 Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes Greenwood, R. C. Franchi, I. A. 2004-01-01 application/pdf https://journals.uair.arizona.edu/index.php/maps/article/view/15047 eng eng Meteoritics & Planetary Science Archives https://journals.uair.arizona.edu/index.php/maps/article/view/15047/15018 https://journals.uair.arizona.edu/index.php/maps/article/view/15047 Meteoritics & Planetary Science Archives; Vol 39, No 11 (2004); 1823-1838 1945-5100 1086-9379 Oxygen isotopes;Terrestrial alteration;Carbon isotopes;CO3 Chondrites info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Peer-reviewed Article 2004 ftunivarizonaojs 2020-11-14T17:53:01Z Carbonaceous chondrites of the Ornans-type (CO3) form a well-documented metamorphic series. To investigate the conditions under which metamorphism took place, whole rock oxygen and carbon isotope analysis has been carried out on 10 CO3 chondrites (ALH A77307 [3.0], Colony [3.0], Kainsaz* [3.1], Felix* [3.2], Ornans* [3.3], ALH 82101 [3.3], Lanc* [3.4], ALH A77003 [3.5], Warrenton* [3.6], and Isna [3.7] [*denotes a fall]). Whole rock oxygen isotope analysis was carried out by laser-assisted fluorination, whole rock carbon isotope analysis by continuous flow mass spectrometry. The results of this study indicate that the oxygen and carbon isotopes in CO3 finds have been significantly disturbed by terrestrial weathering processes. Conclusions based on the isotopic composition of such weathered finds may be significantly flawed. In particular, the Antarctic meteorite ALH A77307 (3.0), suggested as being close in composition to CO-CM chondrite precursor material, has experienced significant terrestrial contamination. Oxygen isotope data for CO3 falls indicates that there is a subtle increase in ?17O values with increasing metamorphic grade for sub-types 3.1 to 3.4. This increase does not persist to higher sub-types, i.e., Warrenton (3.6). These relationships are explicable in terms of the progressive formation of phyllosilicates, coupled with loss of primary phases such as melilite, and suggest that an aqueous fluid phase was present during metamorphism. Carbon abundance and 13C values of CO3 falls decrease with increasing metamorphic grade. These trends reflect progressive changes in the nature of the organic macromolecular component during metamorphic heating and lend additional support to the evidence that CO3 chondrites are part of a metamorphic series. The most likely setting for metamorphism was on the CO3 parent body. The "Ornans paradox," whereby Ornans (3.3) should belong to a higher sub-type based on chemical compared to petrographic evidence, may result from local-scale redox differences on the CO3 parent body. A wide variety of classification schemes have been proposed for CO3 chondrites. In view of its simplicity and applicability, the scheme of Scott and Jones (1990) is regarded as the most useful in assigning sub-types to new CO3 samples. Article in Journal/Newspaper Antarc* Antarctic Journals at the University of Arizona Antarctic The Antarctic |
institution |
Open Polar |
collection |
Journals at the University of Arizona |
op_collection_id |
ftunivarizonaojs |
language |
English |
topic |
Oxygen isotopes;Terrestrial alteration;Carbon isotopes;CO3 Chondrites |
spellingShingle |
Oxygen isotopes;Terrestrial alteration;Carbon isotopes;CO3 Chondrites Greenwood, R. C. Franchi, I. A. Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
topic_facet |
Oxygen isotopes;Terrestrial alteration;Carbon isotopes;CO3 Chondrites |
description |
Carbonaceous chondrites of the Ornans-type (CO3) form a well-documented metamorphic series. To investigate the conditions under which metamorphism took place, whole rock oxygen and carbon isotope analysis has been carried out on 10 CO3 chondrites (ALH A77307 [3.0], Colony [3.0], Kainsaz* [3.1], Felix* [3.2], Ornans* [3.3], ALH 82101 [3.3], Lanc* [3.4], ALH A77003 [3.5], Warrenton* [3.6], and Isna [3.7] [*denotes a fall]). Whole rock oxygen isotope analysis was carried out by laser-assisted fluorination, whole rock carbon isotope analysis by continuous flow mass spectrometry. The results of this study indicate that the oxygen and carbon isotopes in CO3 finds have been significantly disturbed by terrestrial weathering processes. Conclusions based on the isotopic composition of such weathered finds may be significantly flawed. In particular, the Antarctic meteorite ALH A77307 (3.0), suggested as being close in composition to CO-CM chondrite precursor material, has experienced significant terrestrial contamination. Oxygen isotope data for CO3 falls indicates that there is a subtle increase in ?17O values with increasing metamorphic grade for sub-types 3.1 to 3.4. This increase does not persist to higher sub-types, i.e., Warrenton (3.6). These relationships are explicable in terms of the progressive formation of phyllosilicates, coupled with loss of primary phases such as melilite, and suggest that an aqueous fluid phase was present during metamorphism. Carbon abundance and 13C values of CO3 falls decrease with increasing metamorphic grade. These trends reflect progressive changes in the nature of the organic macromolecular component during metamorphic heating and lend additional support to the evidence that CO3 chondrites are part of a metamorphic series. The most likely setting for metamorphism was on the CO3 parent body. The "Ornans paradox," whereby Ornans (3.3) should belong to a higher sub-type based on chemical compared to petrographic evidence, may result from local-scale redox differences on the CO3 parent body. A wide variety of classification schemes have been proposed for CO3 chondrites. In view of its simplicity and applicability, the scheme of Scott and Jones (1990) is regarded as the most useful in assigning sub-types to new CO3 samples. |
format |
Article in Journal/Newspaper |
author |
Greenwood, R. C. Franchi, I. A. |
author_facet |
Greenwood, R. C. Franchi, I. A. |
author_sort |
Greenwood, R. C. |
title |
Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
title_short |
Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
title_full |
Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
title_fullStr |
Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
title_full_unstemmed |
Alteration and metamorphism of CO3 chondrites: Evidence from oxygen and carbon isotopes |
title_sort |
alteration and metamorphism of co3 chondrites: evidence from oxygen and carbon isotopes |
publisher |
Meteoritics & Planetary Science Archives |
publishDate |
2004 |
url |
https://journals.uair.arizona.edu/index.php/maps/article/view/15047 |
geographic |
Antarctic The Antarctic |
geographic_facet |
Antarctic The Antarctic |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_source |
Meteoritics & Planetary Science Archives; Vol 39, No 11 (2004); 1823-1838 1945-5100 1086-9379 |
op_relation |
https://journals.uair.arizona.edu/index.php/maps/article/view/15047/15018 https://journals.uair.arizona.edu/index.php/maps/article/view/15047 |
_version_ |
1766168213367816192 |