Highly siderophile elements were stripped from Earth's mantle by iron sulfide segregation

摘要

Highly siderophile elements (HSEs) are strongly depleted in the bulk silicateEarth (BSE) but are present in near-chondritic relative abundances. Theconventional explanation is that the HSEs were stripped from the mantle by thesegregation of metal during core formation but were added back innear-chondritic proportions by late accretion, after core formation had ceased.Here we show that metal-silicate equilibration and segregation during Earth'score formation actually increased HSE mantle concentrations because HSEpartition coefficients are relatively low at the high pressures of coreformation within Earth. The pervasive exsolution and segregation of ironsulfide liquid from silicate liquid (the "Hadean matte") stripped magma oceansof HSEs during cooling and crystallization, before late accretion, and resultedin slightly suprachondritic palladium/iridium and ruthenium/iridium ratios.