A 4,565-My-old andesite from an extinct chondritic protoplanet

The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segreg...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2021-03, Vol.118 (11), p.1-7
Main Authors: Barrat, Jean-Alix, Chaussidon, Marc, Yamaguchi, Akira, Beck, Pierre, Villeneuve, Johan, Byrne, David J., Broadley, Michael W., Marty, Bernard
Format: Article
Language:English
Subjects:
Alkalis
Andesite
Crusts
Crystallization
Depletion
Deposition
Environmental Sciences
Iron meteorites
Magma
Melting
Meteorites
Meteors & meteorites
Photosphere
Physical Sciences
Planet formation
Protoplanets
Solar system
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Summary:The age of iron meteorites implies that accretion of protoplanets began during the first millions of years of the solar system. Due to the heat generated by 26Al decay, many early protoplanets were fully differentiated with an igneous crust produced during the cooling of a magma ocean and the segregation at depth of a metallic core. The formation and nature of the primordial crust generated during the early stages of melting is poorly understood, due in part to the scarcity of available samples. The newly discovered meteorite Erg Chech 002 (EC 002) originates from one such primitive igneous crust and has an andesite bulk composition. It derives from the partial melting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis relative to the Sun’s photosphere and at a high degree of melting of around 25%. Moreover, EC 002 is, to date, the oldest known piece of an igneous crust with a 26Al-26Mg crystallization age of 4,565.0 million years (My). Partial melting took place at 1,220 °C up to several hundred kyr before, implying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets covered by andesitic crusts were probably frequent. However, no asteroid shares the spectral features of EC 002, indicating that almost all of these bodies have disappeared, either because they went on to form the building blocks of larger bodies or planets or were simply destroyed.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.2026129118