Characteristics and origin of the components of the carbonaceous chondrite NWA 470

Abstract

For the first time, data are presented from a detailed investigation of all components of the NWA 470 CH-type carbonaceous chondrite. The meteorite’s major characteristics are a high metal content with a solar Co/Ni ratio, a majority of chemically-zoned metal grains, cryptocrystalline chondrules, grossite- and hibonite-bearing refractory inclusions, the presence of SiO2 objects and the lack of a fine-grained matrix. The bulk chemical and isotope composition of oxygen in the meteorite is typical for CH chondrites. However, among all CH chondrites, NWA 470 is the most enriched in iron. Notable among the chondrite’s components are refractory inclusions and chondrules of several different generations, which may have formed under either canonical nebular or dust-rich conditions. In general, the origin of refractory inclusions, SiO2 objects and zoned metal can be explained through fractional condensation with partial isolation of the condensates. Dark inclusions were probably included in the material of CH chondrites from a different parent body, similar in composition to CM chondrites. After mixing of these multiple types of material during accretion, the components of NWA 470 were not further affected by aqueous alteration or thermal metamorphic processes, and the components’ primary characteristics have been preserved.