(53) Mn-(53) Cr Dating of Fayalite Formation in the CV3 Chondrite Mokoia: Evidence for Asteroidal Alteration.
Hutcheon, Ian D.; Krot, Alexander N.; Keil, Klaus; Phinney, Douglas L.; Scott, Edward R. D.
[Report] Science. 282(5395):1865-1867, December 4, 1998.

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Fayalite grains in chondrules in the oxidized, aqueously altered CV3 chondrite Mokoia have large excesses of radiogenic chromium-53. These excesses indicate the in situ decay of short-lived manganese-53 (half-life = 3.7 million years) and define an initial53 Mn/(55) Mn ratio of 2.32 ( /- 0.18) x 10-6. This ratio is comparable to values for carbonates in CI and CM chondrites and for several classes of differentiated meteorites. Mokoia fayalites formed 7 to 16 million years after Allende calcium-aluminum-rich inclusions, during hydrothermal activity on a geologically active asteroid after chondritic components had ceased forming in the solar nebula.

Copyright (C) 1998 by the American Association for the Advancement of Science