Magnetite in the unequilibrated <scp>CK</scp> chondrites: Implications for metamorphism and new insights into the relationship between the <scp>CV</scp> and <scp>CK</scp> chondrites

Abstract

Abstract Bulk isotopic and elemental compositions of CV and CK chondrites have led to the suggestion that both originate from the same asteroid. It has been argued that magnetite compositions also support this model; however, magnetite has been studied almost exclusively in the equilibrated (type 4‐6) CK s. Magnetite in seven unequilibrated CK s analyzed here is enriched in MgO, TiO 2 , and Al 2 O 3 relative to the equilibrated CK s, suggesting that magnetite compositions are affected by metamorphism. Magnetite in CK s is compositionally distinct from CV s, particularly in abundances of Cr 2 O 3 , NiO, and TiO 2 . Although there are minor similarities between CV and equilibrated CK chondrite magnetite, this is contrary to what we would expect if the CV s and CK s represent a single metamorphic sequence. CV magnetite should resemble CK 3 magnetite, as both were metamorphosed to type 3 conditions. Oxygen fugacities and temperatures of CV ox and CK chondrites are also difficult to reconcile using existing CV ‐ CK parent body models. Mineral chemistries, which eliminate issues of bulk sample heterogeneity, provide a reliable alternative to techniques that involve a small amount of sample material. CV and CK chondrite magnetite has distinct compositional differences that cannot be explained by metamorphism.