53Mn-53Cr dating of fayalite formation in the CV3 chondrite Mokoia: evidence for asteroidal alteration.

Hutcheon, I D; Krot, A N; Keil, K; Phinney, D L; Scott, E R · Science · 1998

basic_science · Level V

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Abstract

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) 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.

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