The role of Bells in the continuous accretion between the CM and CR chondrite reservoirs

1Elishevah van Kooten,2Larissa Cavalcante,3Daniel Wielandt,3Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1111/maps.13459]
1Institut de Physique du Globe de Paris, Université de Paris, CNRS, UMR 7154, 1 rue Jussieu, 75238 Paris, France
2Institute of Chemistry, University of São Paulo, 03178 São Paulo, Brazil
3Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK‐1350 Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

CM meteorites are dominant members of carbonaceous chondrites (CCs), which evidently accreted in a region separated from the terrestrial planets. These chondrites are key in determining the accretion regions of solar system materials, since in Mg and Cr isotope space, they intersect between what are identified as inner and outer solar system reservoirs. In this model, the outer reservoir is represented by metal‐rich carbonaceous chondrites (MRCCs), including CR chondrites. An important question remains whether the barrier between MRCCs and CCs was a temporal or spatial one. CM chondrites and chondrules are used here to identify the nature of the barrier as well as the timescale of chondrite parent body accretion. We find based on high precision Mg and Cr isotope data of seven CM chondrites and 12 chondrules, that accretion in the CM chondrite reservoir was continuous lasting <3 Myr and showing late accretion of MRCC‐like material reflected by the anomalous CM chondrite Bells. We further argue that although MRCCs likely accreted later than CM chondrites, CR chondrules must have initially formed from a reservoir spatially separated from CM chondrules. Finally, we hypothesize on the nature of the spatial barrier separating these reservoirs.

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