53Mn-53Cr Dating of Fayalite Formation in the CV3 Chondrite Mokoia: Evidence for Asteroidal Alteration
Ian D. Hutcheon,
*
Alexander N. Krot,
Klaus Keil,
Douglas L. Phinney,
Edward R. D. Scott
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 initial
53Mn/55Mn ratio of 2.32 (±0.18) × 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.
I. D. Hutcheon and D. L. Phinney, Lawrence Livermore
National Laboratory (LLNL), Livermore, CA 94551, USA. A. N. Krot, K. Keil, E. R. D. Scott, Hawai'i Institute of
Geophysics and Planetology, School of Ocean and Earth Science and
Technology, University of Hawai'i at Manoa, Honolulu, HI 96822, USA.
*
To whom correspondence should be addressed.
