SIMS analyses of Mg, Cr, and Ni isotopes in primitive meteorites and short-lived radionuclides in the early solar system

Abstract

SIMS analyses of 26 Al – 26 Mg , 60 Fe – 60 Ni , and 53 Mn – 53 Cr systems in unequilibrated enstatite chondrites provide evidence for the former existence of 26 Al , 60 Fe , and 53 Mn in this highly reduced meteorite group, suggesting the widespread of these short-lived radionuclides in the early solar system. Calcium–aluminum-rich inclusions and Al-rich chondrules in enstatite chondrites show 26 Al – 26 Mg characteristics similar to their counterparts in other types of chondrites. Assuming its homogenous distribution, fine-scale 26 Al relative chronology can be obtained for different components in meteorites. Well-defined isochrons yield initial 60 Fe / 56 Fe ratios of (0.3−1)×10 −6 in sulfides from enstatite chondrites. The former presence of 60 Fe suggests a stellar source and its possible high abundance points to a supernova origin. 26 Al and 60 Fe could be important heat sources for the early planetary processes. The large variations of initial 60 Fe / 56 Fe and 53 Mn / 55 Mn ratios and the discordance between 60 Fe – 60 Ni and 53 Mn – 53 Cr systems observed in sulfides indicate later disturbance of the two isotopic systems, and therefore, bear no strict chronological significance. SIMS isotopic analysis can be utilized to attain important information about the early evolution of the solar system.