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Mn‐Cr isotope systematics of the D'Orbigny angrite
Author(s) -
Glavin D. P.,
Kubny A.,
Jagoutz E.,
Lugmair G. W.
Publication year - 2004
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2004.tb00112.x
Subject(s) - pyroxene , isochron , geology , mineralogy , olivine , closure temperature , geochemistry , analytical chemistry (journal) , chemistry , environmental chemistry , metamorphic rock
— We have conducted a detailed study of the Mn‐Cr systematics of the angrite D'Orbigny. Here, we report Cr isotopic abundances and Mn/Cr ratios in olivine, pyroxene, glass, chromite, and bulk rock samples from D'Orbigny. 53 Cr excesses in these samples correlate well with their respective Mn/Cr ratios and define an isochron with a slope that corresponds to an initial 53 Mn/ 55 Mn ratio = (3.24 ± 0.04) × 10 −6 and initial 53 Cr/ 52 Cr ratio of ɛ(53) = 0.30 ± 0.03 at the time of isotopic closure. The 53 Mn/ 55 Mn ratio of the D'Orbigny bulk rock is more than two‐fold the 53 Mn/ 55 Mn ratio of the angrites Lewis Cliff 86010 (LEW) and Angra dos Reis (ADOR) and implies an older Mn‐Cr age of 4562.9 ± 0.6 Ma for D'Orbigny relative to a Pb‐Pb age of 4557.8 ± 0.5 Ma for LEW and ADOR. One of the most unusual aspects of D'Orbigny is the presence of glass, a phase that has not been identified in any of the other angrites. The Mn‐Cr data for glass and a pyroxene fraction found in druses indicate that they formed contemporaneously with the main phases of the meteorite. Since the Mn‐Cr age of D'Orbigny is ˜5 Ma years older than the angrites LEW and ADOR, D'Orbigny likely represents an earlier stage in the evolution of the angrite parent body.