UC San Diego

This study aims to better characterize highly siderophile element (HSE; Re, Os, Ir, Ru, Pt and Pd) and incompatible trace element abundances in meteorite sample from the carbonaceous, ordinary and enstatite chondrite classes to better understand their origins and histories. The sample suite of thirty-two chondrites was analyzed for bulk sample major- and trace-element compositions, oxygen isotope systematics, HSE abundances, and Re-Os isotope systematics. Mineral chemical compositions were also obtained for the Chelyabinsk ordinary chondrite meteorite that fell on Februrary 15th, 2013. The HSE abundances and Os isotope systematics measured in this study are useful tracers for nebular formation conditions, secondary parent body processing and terrestrial alteration. The HSE data paired with the Re-Os isotope systematics and major- and trace-element data allows for a distinction of these processes and their effects on different chondrite classes and individual samples. All Northwest Africa (NWA) chondrite meteorites measured in this study show mobility of the HSE, Re and Os, from terrestrial alteration. The absolute abundances of the HSE vary considerably between and within the chondritic classes. However, some of these variations are shown to reflect heterogeneities within sample aliquots. HSE ratios (e.g., (Os, Ru, Pt, Pd, Re)/Ir) were therefore used as a means to distinguish nebular formation conditions for the chondrite classes. Mineral phases measured in Chelyabinsk give insights to parent body processing and its effects on sample mineral chemistry. Trace-element data on various phases suggest formation from ordinary chondrite precursors in the Chelyabinsk parent body, followed by equilibration, likely induced from shock metamorphism. Collectively, these results reveal significant differences in the degrees of terrestrial alteration, parent-body process and initial compositions within chondrite classes.