A Water-Rich Proto-Planet Inferred by Tridymite and Pyroxene in the Oldest Igneous Achondrite Northwest Africa 11119

A. Cernok, K. Tait, M. Anand, I. Nicklin, L. White, T. Kizovski, X. Zhao, I. A. Franchi

51st Lunar and Planetary Science Conference (2020), Abstract #1900


“The meteorite Northwest Africa (NWA) 11119 has been reported to be the oldest sample from a differentiated proto-planet, suggesting that volcanic activity on its parent body occurred 4563.3 ± 2.9 million years ago [1, 2]. It is a chemically evolved extrusive volcanic rock that has a silica-rich (andesite-dacite) bulk composition, with the highest modal abundance (~30 vol.%) of free silica of any known achondrite [1]. Intrigued by the fact that silicic volcanism on differentiated planets such as the Earth or Mars is promoted by abundant water dissolved in parental magmas, we investigated the water abundance and hydrogen isotope compositions of the phenocrysts in NWA. Understanding the water budget and isotopic composition of rare ancient achondrite samples like NWA 11119 can lend insight into important questions relating to the source(s) of water in the earliest stages of inner solar system formation.