Trace element partitioning between sulfide-, metal- and silicate melts at highly reduced conditions: Insights into the distribution of volatile elements during core formation in reduced bodies

E. S. Steenstra*, V. T. Trautner, J. Berndt, S. Klemme, W. van Westrenen

*Corresponding author for this work

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Chalcophile and siderophile element abundances are used to provide important constraints on the interior compositions of planetary bodies as well as the pressure (P) - temperature (T) conditions that prevailed during core formation. The oxygen fugacity (fO2) during core formation varied considerably between the various terrestrial planets and asteroidal bodies in our solar system. Mercury, the aubrite parent body (AuPB) and some terrestrial precursor bodies may have differentiated at highly reduced conditions. 

At present knowledge about how the metal liquid-silicate melt and sulfide liquid-silicate melt partitioning behavior of major and trace elements are affected by high S concentrations in the silicate melt at highly reducing conditions is incomplete. Here, we experimentally study the metal-silicate and sulfide-silicate partitioning behavior of trace elements in reduced silicate melts over a wide range of S contents as a function of redox state at 1 GPa and 1833–1883 K. Silicate melt S contents ranged between ~0.5 and ~20 wt%, with a corresponding silicate FeO range of ~0.4 to ~17.5 wt%, in a fO2 range between 1 and 9 log units below the iron-wüstite buffer. Our results reproduce the decrease of the S concentration at sulfide saturation (SCSS) with decreasing FeO contents down to ~3 wt%, as well as its strong increase at <3 wt% FeO. At S contents exceeding >6–9 wt% S, the FeO contents increase again. 

Results show that most elements (Mg, Ti, V, Cr, Mn, Cu, Zn, Se, Nb, Cd, Sb, Te, Ta, Tl, Pb and Bi) are more chalcophile than siderophile at reducing conditions, whereas Si, Co, Ni, Ga, Ge, Mo and W preferentially partition into Fe-rich melts instead of sulfide liquids. Silicon, Ti, Se, and Te preferentially partition into Fe-S over (Fe,Mg,Ca)-S liquids, whereas Mn, Zn and Cd are more compatible in the latter. As proposed by Wood and Kiseeva (2015), chalcophile elements such as Cu, Se and Te behave less chalcophile with increasing S concentrations of the silicate melt, whereas the opposite is observed for nominally lithophile elements such as Mg, Ca and Ti. 

The results can be used to improve interpretations of the observed trace element systematics of aubrites and other reduced achondrites. All of the volatile elements considered here behave chalcophile at the reducing conditions inferred for differentiation of the AuPB. A significant degree of the observed volatile element depletions in aubrites may therefore reflect their preferential partitioning into sulfide liquids, rather than degassing during or after differentiation of the AuPB. These results suggest that, depending of the extent of core merging, precursor body differentiation and the efficiency of sulfide liquid segregation, reduced precursor bodies that were incorporated in the early Earth were likely more rich in volatile elements than currently assumed.

Original languageEnglish
Article number113408
Pages (from-to)1-20
Number of pages20
Early online date9 Aug 2019
Publication statusPublished - 1 Jan 2020


This work was supported by a Carnegie Postdoctoral Fellowship to E.S.S, a Netherlands Organisation for Scientific Research (N.W.O.) Vici award to W.v.W and by SFB TRR-170 . The majority of the experiments presented in this study were performed by V.T. as part of an undergraduate research project supervised by E.S.S. and W.v.W. We thank Klaus Mezger and an anonymous reviewer for their constructive comments that significantly improved the quality of this manuscript. Appendix A

FundersFunder number
Nederlandse Organisatie voor Wetenschappelijk Onderzoek


    • Aubrites
    • Chalcophile
    • Mercury
    • Siderophile
    • Sulfide
    • Volatiles


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