Origin of moderately volatile element depletion on differentiated bodies: insights from the evaporation of indium from silicate melts

1Deze Liu,1Frédéric Moynier,1,2Julien Siebert,1,3Paolo A.Sossi,1Yan Hu,1Edith Kubik
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.09.043]
1Université Paris Cité, Institut de Physique du Globe de Paris, 1 Rue Jussieu, 75005 Paris, France
2Institut Universitaire de France, Paris, France
3Institute of Geochemistry and Petrology, ETH Zürich, Sonneggstrasse 5, CH-8092 Zürich, Switzerland
Copyright Elsevier

In comparison with the Sun and CI chondrites, moderately volatile elements (MVEs) are depleted in terrestrial planets and other small, rocky differentiated bodies in the inner solar system. The abundances of most MVEs in the bulk silicate Earth (BSE) fall on a trend that defines a near log-linear decrease with their 50% nebular condensation temperature (). This temperature scale has traditionally been used to infer elemental volatility during planetary formation and accretion, however, indium (In) deviates from this correlation. Despite being a siderophile element that could have been depleted by core formation, In is overabundant for its calculated in the BSE, as well as in the silicate portions of other small bodies (e.g., Moon and Vesta). This overabundance of In indicates that , calculated under nebular conditions, may not be applicable to planetary evaporation that occurs at much higher oxygen fugacity (fO2) and pressure than nominal nebular conditions. Here, we conduct a series of evaporation experiments for basaltic melts to quantify the volatility of In under conditions relevant to planetary evaporation. Our results show that, when using the evaporation temperature , refers to the temperature at which 1% of element i has evaporated from liquid to gas phase under equilibrium) as the volatility scale, the abundances of volatile elements, including In, of the Moon and Vesta display a progressive depletion with increasing volatility (decreasing ). This smooth depletion pattern contrasts with the overabundance of In shown on the scale, suggesting that volatile depletion on small bodies occurred under non-nebular environment instead of during nebular condensation. On the other hand, the volatile element composition of the BSE (including In) could be explained by integrating i) early accreted precursor materials of the proto-Earth that underwent volatile loss under conditions more oxidizing than those of the solar nebula with ii) late added volatile-rich materials.


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