Petrology, Mineralogy, and Stable Isotopic Composition of NWA 13943 (CK5) Carbonaceous Chondrite

Abstract

Karoonda-like (CK) carbonaceous chondrites are highly oxidized meteorites, with metal-to-magnetite ratio close to zero. Unlike other carbonaceous chondrites (petrologic type: 1–3), most CK chondrites have undergone thermal metamorphism (550–1270 K) on their parent body with a petrologic type 4 or above. Lines of evidence suggest a genetic relationship between CK chondrites and Vigarano-like (CV) carbonaceous chondrites, which are predominantly type 3. However, observable petrographic distinctions persist between the two groups. Thus, a thorough reevaluation of their geochemical discrepancies is critical to test the CK-CV single parent body hypothesis. Northwest Africa (NWA) 13943, a newly discovered meteorite subjected to intense modification, was classified using scanning electron microscopy and electron microprobe techniques. High-precision measurements of the mass-independent chromium isotope compositions (${\epsilon }^{53}$Cr and ${\epsilon }^{54}$Cr) and the mass-dependent oxygen isotope compositions (${\delta }^{17}$O and ${\delta }^{18}$O) of NWA 13943 were reported for the first time. Integrating petrological, mineralogical, oxygen, and chromium isotopic data, it is legitimated to infer that CK and CV chondrites may originate from two proximal but distinct isotopic reservoirs within the protoplanetary disk.