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

SIMS analyses of Al-26-Mg-26, Fe-60-Ni-60, and Mn-53-Cr-53 systems in unequilibrated enstatite chondrites provide evidence for the former existence of Al-26, Fe-60, and Mn-53 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 Al-26-Mg-26 characteristics similar to their counterparts in other types of chondrites. Assuming its homogenous distribution, fine- scale Al-26 relative chronology can be obtained for different components in meteorites. Well-defined isochrons yield initial Fe-60/Fe-56 ratios of (0.3 - 1) x 10(-6) in sulfides from enstatite chondrites. The former presence of Fe-60 suggests a stellar source and its possible high abundance points to a supernova origin. Al-26 and Fe-60 could be important heat sources for the early planetary processes. The large variations of initial Fe-60/Fe-56 and Mn-53/Mn-55 ratios and the discordance between Fe-60-Ni-60 and Mn-53-Cr-53 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. (C) 2004 Elsevier B.V. All rights reserved.