Fe-Ni and Al-Mg isotope records in UOC chondrules: Plausible stellar source of 60Fe and other short-lived nuclides in the early Solar System

The short-lived now-extinct nuclide Fe-60, present in the early Solar System, is a unique product of stellar nucleosynthesis. Even though the first hint for its presence in the early Solar System was obtained more than two decades back, a robust value for Solar System initial (SSI) Fe-60/Fe-56 is yet to be established. A combined study of Al-26-Mg-26 and Fe-60-Ni-60 isotope systematics in chondrules from unequilibrated ordinary chondrites of low petrologic type, Semarkona (LL3.0), LEW 86134 (L3.0), and Y 791324 (L3.1), has been conducted to infer the value of SSI Fe-60/Fe-56. Seven of the analysed chondrules host resolved radiogenic excess in both Ni-60 and Mg-26 resulting from in situ decay of the short-lived nuclides Fe-60 and Al-26, respectively. The initial Al-26/Al-27 values for these chondrules range from (6.9 +/- 5.8) x 10(6) to (3.01 +/- 1.78) x 10(5) that suggest their formation between 2.1 and 0.6 Ma after CAIs. The initial Fe-60/Fe-56 at the time of formation of these chondrules ranges from (3.2 +/- 1.3) x 10(-7) to (1.12 +/- 0.39) x 10(-6) and show a good correlation with their initial Al-26/Al-27 values suggesting co-injection of the two short-lived nuclides, Fe-60 and Al-26, into the protosolar cloud from the same stellar source. Considering Al-26 as a reliable early Solar System chronometer, this data set yield a SSI Fe-60/Fe-56 value of (7.0 +/- 1.2) x 10(-7), if we adopt a half-life value of 2.6 Ma for Fe-60 reported in a recent study. Model stellar nucleosynthesis yields suggest that both a high mass (5-6.5 M-circle dot) Asymptotic Giant Branch (AGB) star or a supernova (SN) could be the source of Fe-60 and Al-26 present in the early Solar System. A high mass (similar to 25 M-circle dot) SN appears more plausible because of the much higher probability of its close association with the protosolar molecular cloud than a high mass AGB star. Such a SN can also account for SSI abundance of Al-26 and its correlated presence with Fe-60 in chondrules. (C) 2014 Elsevier Ltd. All rights reserved.