Half-life and initial Solar System abundance of 146 Sm determined from the oldest andesitic meteorite - Archive ouverte HAL Access content directly
Journal Articles Proceedings of the National Academy of Sciences of the United States of America Year : 2022

Half-life and initial Solar System abundance of 146 Sm determined from the oldest andesitic meteorite

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Linru Fang
Maud Boyet
Audrey Bouvier
Jean-Alix Barrat

Abstract

The formation and differentiation of planetary bodies are dated using radioactive decay systems, including the short-lived 146 Sm-142 Nd (T1 =2 = 103 or 68 Ma) and long-lived 147 Sm-143 Nd (T1 =2 = 106 Ga) radiogenic pairs that provide relative and absolute ages, respectively. However, the initial abundance and half-life of the extinct radioactive isotope 146 Sm are still debated, weakening the interpretation of 146 Sm-142 Nd systematics obtained for early planetary processes. Here, we apply the short-lived 26 Al-26 Mg, 146 Sm-142 Nd, and long-lived 147 Sm-143 Sm chronometers to the oldest known andesitic meteorite, Erg Chech 002 (EC 002), to constrain the Solar System initial abundance of 146 Sm. The 26 Al-26 Mg mineral isochron of EC 002 provides a tightly constrained initial δ 26 Mg* of 20.009 ± 0.005 ‰ and (26 Al/ 27 Al) 0 of (8.89 ± 0.09) × 10 26. This initial abundance of 26 Al is the highest measured so far in an achondrite and corresponds to a crystallization age of 1.80 ± 0.01 Myr after Solar System formation. The 146 Sm-142 Nd mineral isochron returns an initial 146 Sm/ 144 Sm ratio of 0.00830 ± 0.00032. By combining the Al-Mg crystallization age and initial 146 Sm/ 144 Sm ratio of EC 002 with values for refractory inclusions, achondrites, and lunar samples, the best-fit half-life for 146 Sm is 102 ± 9 Ma, corresponding to the physically measured value of 103 ± 5 Myr, rather than the latest and lower revised value of 68 ± 7 Ma. Using a half-life of 103 Ma for 146 Sm, the 146 Sm/ 144 Sm abundance of EC 002 translates into an initial Solar System 146 Sm/ 144 Sm ratio of 0.00840 ± 0.00032, which represents the most reliable and precise estimate to date and makes EC 002 an ideal anchor for the 146 Sm-142 Nd clock. meteorite j Sm-Nd j early Solar System j Erg Chech 002
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Origin : Publication funded by an institution

Dates and versions

hal-03859727 , version 1 (24-11-2022)

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Linru Fang, Paul Frossard, Maud Boyet, Audrey Bouvier, Jean-Alix Barrat, et al.. Half-life and initial Solar System abundance of 146 Sm determined from the oldest andesitic meteorite. Proceedings of the National Academy of Sciences of the United States of America, 2022, 119 (12), ⟨10.1073/pnas.2120933119/-/DCSupplemental⟩. ⟨hal-03859727⟩
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