Chondritic Mn/Na ratio and limited post-nebular volatile loss of the Earth

Siebert, Julien, Sossi, Paolo A., Blanchard, Ingrid, Mahan, Brandon, Badro, James, and Moynier, Frédéric (2018) Chondritic Mn/Na ratio and limited post-nebular volatile loss of the Earth. Earth and Planetary Science Letters, 485. pp. 130-139.

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Abstract

The depletion pattern of volatile elements on Earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. The processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the H2-rich nebular gas. Furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. With the notable exception of the Earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic Mn/Na ratios, taken as a signature of post-nebular volatilization. The bulk silicate Earth (BSE) is unique in that its Mn/Na ratio is chondritic, which points to a nebular origin for the depletion; unless the Mn/Na in the BSE is not that of the bulk Earth (BE), and has been affected by core formation through the partitioning of Mn in Earth’s core. Here we quantify the metal–silicate partitioning behavior of Mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. The experiments show that Mn becomes more siderophile with increasing pressure and temperature. Modeling the partitioning of Mn during core formation by combining our results with previous data at lower P–T conditions, we show that the core likely contains a significant fraction (20 to 35%) of Earth’s Mn budget. However, we show that the derived Mn/Na value of the bulk Earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a Mn/Na vs Mn/Mg plot, which tend to higher Mn/Na with increasing volatile depletion. This suggests that the material that formed the Earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization.

Item ID: 62754
Item Type: Article (Research - C1)
ISSN: 1385-013X
Keywords: volatile depletion, post-nebular volatilization, bulk Earth composition core formation, laser-heated diamond anvil cell
Copyright Information: © 2018 Elsevier B.V. All rights reserved.
Funders: French National Research Agency (ANR), Sorbonne Paris Cité (SPC), Paris-IdF region SESAME (PIS), European Research Council (ERC)
Projects and Grants: ANR project VolTerre, grant No. ANR-14-CE33-0017-01, SPC UnivEarthS Labex program, ANR-10- LABX-0023 and ANR-11-IDEX-0005-02, PIS grant No. 12015908, ERC European Community’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement No.207467, ERC H2020 framework program/ERC grant agreement #637503 (Pristine), ANR chaire d’excellence Sorbonne Paris Cité
Date Deposited: 28 Jun 2020 21:32
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040202 Inorganic Geochemistry @ 50%
04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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