CV chondrites: More than one parent body

Abstract

CV chondrites are one of the most studied group of carbonaceous chondrites. Based on a number of mineralogical features, they have been divided into three sub-groups: CVOxA, CVOxB, and CVRed. These sub-groups are classically interpreted as coming from a single parent body, with a common protolith affected by significant parent body fluid-assisted metasomatism occurring at different temperatures and/or redox conditions. In this work, we studied a set of 53 CV chondrites. We classified them into the three sub-groups, measured their apparent chondrule sizes and their matrix modal abundance. We measured the triple oxygen isotopic composition for 17 of them. The distributions of chondrule size and matrix abundances in CVOxA and CVOxB cannot be statistically distinguished. Conversely, CVRed and CVOx have distinct distributions. These two robust and simple petrographic indicators combined with the previous knowledge of the peak metamorphic temperatures experienced by these meteorites show that CVOx and CVRed originate from two distinct parent bodies. On the other hand, CVOxA and CVOxB likely originate from the same parent body, with CVOxA representing deeper, more metamorphosed levels. For clarification of the chondrite classification scheme, in which one group should ultimately represent a single parent body, we propose to divide the CV group into two proper groups (and not subgroups as in the current scheme), keeping the names CVRed and CVOx. These two groups can be readily separated by estimating the average nickel content of their sulfides.