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

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