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Formation and destruction of magnetite in CO3 chondrites and other chondrite groups
Rubin, Alan E.1,2; Li, Ye1,3,4
2019-12-01
Source PublicationGEOCHEMISTRY
ISSN0009-2819
Volume79Issue:4Pages:10
Corresponding AuthorRubin, Alan E.(aerubin@ucla.edu)
AbstractPrimitive CO3.00-3.1 chondrites contain similar to 2-8 vol.% magnetite, minor troilite and accessory carbide and chromite; some CO3.1 chondrites have fayalite-rich veins, chondrule rims and euhedral matrix grains. All CO3.00-3.1 chondrites contain little metallic Fe-Ni (0.4-1.2 vol.%). CO3.2-3.7 chondrites contain 1-5 vol.% metallic Fe-Ni, minor troilite, accessory chromite and 0-0.6 vol.% magnetite. Magnetite is formed in primitive CO3 chondrites from metallic Fe by parent-body aqueous alteration, resulting in decreased metallic Fe-Ni and an increase in the proportion of high-Ni metal grains. The paucity or absence of magnetite in CO chondrites of subtype >= 3.2 suggests that magnetite is destroyed during thermal metamorphism; thermochemical calculations from the literature suggest that magnetite is reduced by H-2 and reacts with SiO2 to form fayalite and secondary kamacite. Analogous processes of magnetite formation and destruction occur in other chondrite groups: (1) Primitive type-3 OC have opaque assemblages containing magnetite, carbide, Ni-rich metal and Ni-rich sulfide, but OC of subtype > 3.4 contain little or no magnetite. (2) Primitive R3 chondrites and clasts (subtype less than or similar to 3.5) contain up to 6 vol.% magnetite, but most R chondrites contain no magnetite. The principal exception is magnetite with 9-20 wt.% Cr2O3 in a few R4-6 chondrites. Magnetite grains with high Cr2O3 behave like chromite and are more stable under reducing conditions. (3) CK chondrites average similar to 4 vol.% magnetite with substantial Cr2O3 (up to similar to 15 wt.%); these magnetite grains also are stable against reduction during metamorphism. (4) The modal abundance of magnetite decreases with metamorphic grade in CV3 chondrites. (5) Chromite occurs instead of magnetite in those rare samples classified CR6, CR7 and CV7.
KeywordCO chondrites Magnetite Chromite Alteration Aqueous alteration Metallic Fe-Ni Metallic Cu
DOI10.1016/j.chemer.2019.07.009
WOS KeywordOXYGEN-ISOTOPE COMPOSITIONS ; CARBONACEOUS CHONDRITES ; METAMORPHIC HISTORY ; CV3 CHONDRITES ; COMPOSITIONAL CLASSIFICATION ; CHEMICAL-COMPOSITIONS ; PRIMITIVE CHONDRITES ; THERMAL HISTORIES ; ORGANIC-MATTER ; OLIVINE
Indexed BySCI
Language英语
WOS Research AreaGeochemistry & Geophysics
WOS SubjectGeochemistry & Geophysics
WOS IDWOS:000500465000004
PublisherELSEVIER GMBH
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Document Type期刊论文
Identifierhttp://libir.pmo.ac.cn/handle/332002/35172
Collection中国科学院紫金山天文台
Corresponding AuthorRubin, Alan E.
Affiliation1.Univ Calif Los Angeles, Dept Earth Planetary & Space Sci, Los Angeles, CA 90095 USA
2.Maine Mineral & Gem Museum, 99 Main St,POB 500, Bethel, ME 04217 USA
3.Chinese Acad Sci, Purple Mt Observ, Key Lab Planetary Sci, Nanjing 210034, Jiangsu, Peoples R China
4.Chinese Acad Sci Ctr Excellence Comparat Planetol, Beijing, Peoples R China
Recommended Citation
GB/T 7714
Rubin, Alan E.,Li, Ye. Formation and destruction of magnetite in CO3 chondrites and other chondrite groups[J]. GEOCHEMISTRY,2019,79(4):10.
APA Rubin, Alan E.,&Li, Ye.(2019).Formation and destruction of magnetite in CO3 chondrites and other chondrite groups.GEOCHEMISTRY,79(4),10.
MLA Rubin, Alan E.,et al."Formation and destruction of magnetite in CO3 chondrites and other chondrite groups".GEOCHEMISTRY 79.4(2019):10.
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