53Mn‐53Cr ages of Kaidun carbonates

Abstract– We report the ⁵³Mn‐⁵³Cr systematics of three dolomite grains from two different CI1 clasts contained within the Kaidun meteorite breccia. Three internal isochrones result in initial ⁵³Mn/⁵⁵Mn ratios of (4.2 ± 0.4) × 10^?6, (4.6 ± 1.3) × 10^?6, and (5.2 ± 1.1) × 10^?6. These initial values are consistent with those measured for dolomite in the Orgueil CI1 chondrite ( Hoppe et al. 2007 ; Petitat et al. 2009 ) but significantly lower than the initial ratio determined by Hutcheon et al. (1999) from a combination of different carbonate types within various lithologies of the Kaidun meteorite. We construct an accretion scenario for the Kaidun breccia by comparing the mineralogy and formation time scales of carbonates in the Kaidun CI1 lithologies to the analogous ones of the CI1 chondrite Orgueil. In Orgueil, dolomite precipitation precedes the formation of the first bruennerite grains by a few million years ( Hoppe et al. 2007 ; Petitat et al. 2009 ). As the CI1 clasts in Kaidun lack breunnerite grains, and considering that aqueous alteration occurred prior to reaccretion of the various clasts onto the Kaidun parent body (e.g., MacPherson et al. 2009 ), we hypothesize that after rapid accretion and early aqueous alteration occurring within the first approximately 4 Myr after solar system formation, impact disruption of several asteroids and their reassembly into the Kaidun parent asteroid was complete within an additional approximately 2 Myr. This confirms that aqueous alteration, impact, and reaccretion of material in the asteroid belt were early processes that began contemporaneously with chondrule formation.