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

Abstract

SIMS analyses of ²⁶Al–²⁶Mg, ⁶⁰Fe–⁶⁰Ni, and ⁵³Mn–⁵³Cr systems in unequilibrated enstatite chondrites provide evidence for the former existence of ²⁶Al, ⁶⁰Fe, and ⁵³Mn 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 ²⁶Al–²⁶Mg characteristics similar to their counterparts in other types of chondrites. Assuming its homogenous distribution, fine-scale ²⁶Al relative chronology can be obtained for different components in meteorites. Well-defined isochrons yield initial ⁶⁰Fe/⁵⁶Fe ratios of (0.3−1) × 10⁻⁶ in sulfides from enstatite chondrites. The former presence of ⁶⁰Fe suggests a stellar source and its possible high abundance points to a supernova origin. ²⁶Al and ⁶⁰Fe could be important heat sources for the early planetary processes. The large variations of initial ⁶⁰Fe/⁵⁶Fe and ⁵³Mn/⁵⁵Mn ratios and the discordance between ⁶⁰Fe–⁶⁰Ni and ⁵³Mn–⁵³Cr 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.

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