Pd and Ag partitioning between liquid Fe metallic sulfide and liquid silicate under plausible magma ocean conditions constrains potential core 107Ag content and the origin of observed Pd and Ag mantle abundances. DPdmetallic sulfide/silicate (element concentration in metallic liquid/concentration in silicate liquid) in our experiments is insensitive to S content and temperature, but increases with total Pd content. DPdmetallic sulfide/silicate at low Pd concentration ranges from approximately 150-650. Metallic sulfide Pd content and silicate Pd content anticorrelate in our study. A curved silicate saturation surface in the Fe sulfide-silicate Pd ternary can explain both the metallic sulfide-silicate Pd anticorrelation and interstudy differences in DPdmetallic sulfide/silicate behavior. The size and shape of the curved silicate phase volume may respond to physical and chemical conditions, reducing the general applicability of D calculations. Ag becomes decreasingly siderophile as S increases: DAgmetallic sulfide/silicate decreases from 144 at 0 wt% S to 2.5 at 28 wt% S added to the starting metal sulfide liquid. Model calculations indicate that 1% core material incorporated into the Hawai'ian plume would yield a 107Ag signature on the surface smaller than detectable by current analytical techniques. Observed Pd and Ag mantle depletions relative to bulk Earth are consistent with depletions calculated with the data from this study for a magma ocean scenario without additional accretionary input after core formation.
ASJC Scopus subject areas
- Space and Planetary Science