Mn-Cr isotope systematics of the D'Orbigny angrite

• Published in: Meteoritics & planetary science Vol. 39; no. 5; pp. 693 - 700
• Main Authors: Glavin, D. P., Kubny, A., Jagoutz, E., Lugmair, G. W.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-05-2004
• ISSN: 1086-9379; 1945-5100
• DOI: 10.1111/j.1945-5100.2004.tb00112.x

— 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. 53Cr excesses in these samples correlate well with their respective Mn/Cr ratios and define an isochron with a slope that corresponds to an initial 53Mn/55Mn ratio = (3.24 ± 0.04) × 10−6 and initial 53Cr/52Cr ratio of ɛ(53) = 0.30 ± 0.03 at the time of isotopic closure. The 53Mn/55Mn ratio of the D'Orbigny bulk rock is more than two‐fold the 53Mn/55Mn 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.