The indium isotopic composition of the bulk silicate Earth

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Liu, Deze, Moynier, Frederic, Sossi, Paolo A., Pik, Raphael, Halldórsson, Sæmundur Ari, Inglis, Edward, Day, James M. D., Siebert, Julien
• Other Authors: Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Nordic Volcanological Center, Institute of Earth Sciences, Institute of Earth Sciences University of Iceland, University of Iceland Reykjavik -University of Iceland Reykjavik, Scripps Institution of Oceanography (SIO - UC San Diego), University of California San Diego (UC San Diego), University of California (UC)-University of California (UC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Indium isotopes; Bulk silicate Earth; Isotopic fractionation; MC-ICP-MS; Earth Science; [SDU]Sciences of the Universe [physics]; Iceland
• Online Access: https://insu.hal.science/insu-04155688; https://doi.org/10.1016/j.gca.2023.04.018

International audience Indium (In) behaves as a moderately volatile metal during nebular and planetary processes, and its volatility depends strongly on oxygen fugacity. The In isotopic composition of the bulk silicate Earth (BSE) could provide a critical constraint on the nature of Earth's building blocks and mechanisms that lead to its volatile depletion. However, accurately and precisely determining the isotopic composition of In of the silicate Earth is challenging due to its low abundance in igneous rocks and the presence of significant isobaric interferences on its isotopes (e.g., 113 Cd + on 113 In + and 115 Sn + on 115 In + ). Here, we present a purification procedure for In from rock matrices and report the first dataset of In isotopic compositions of 30 terrestrial igneous rocks, one biotite geostandard, and one carbonaceous chondrite (Allende) measured on a Nu Sapphire collision-cell equipped multi-collector inductively-coupled-plasma mass-spectrometer (CC-MC-ICP-MS) with an external reproducibility of 0.11‰ (2SD). At this level of precision, we find no statistically significant difference in the In isotopic compositions of mid-ocean-ridge basalts (MORB), oceanic island basalts (OIB), and continental flood basalts (CFB). Furthermore, Canary Islands, Iceland and Afar lavas display no analytically resolvable In isotopic variations from basalts to rhyolites. Therefore, In isotope fractionation during igneous processes is smaller than our analytical uncertainty and the In isotopic compositions of basalts are likely to be representative samples of their mantle sources. The twenty-one terrestrial basalts from diverse geological settings have an average δ 115 In of 0.35 ± 0.07 ‰ (2SD). This value represents the current best estimate of the In isotopic composition of the mantle as well as of the bulk silicate Earth, assuming limited In isotope fractionation during mantle partial melting, and due to the small contribution of the continental crust to the In budget (<5%). This isotopic composition provides ...