Ni isotopes provide a glimpse of Earth's pre-lateveneer mantle (original) (raw)

Moderately siderophile (e.g., Ni) and highly siderophile elements (HSEs) in the bulk silicate Earth (BSE) are believed to be partly or near-completely delivered by late accretion after the depletion caused by metallic core formation. However, the extent and rate of remixing of late-accreted materials that equilibrated with Earth's prelate-veneer mantle have long been debated. Observing evidence of this siderophile element-depleted pre-lateveneer mantle would provide powerful confirmation of this model of early mantle evolution. We find that the mantle source of the~3.8-billion-year-old (Ga) Narssaq ultramafic cumulates from Southwest Greenland exhibits a subtle 60 Ni/ 58 Ni excess of~0.05 per mil and contains a clear HSE deficiency of~60% relative to the BSE. The intermediate Ni isotopic composition and HSE abundances of the~3.8-Ga Narssaq mantle mark a transitional Eoarchean snapshot as the poorly mixed 3.8-Ga mantle containing elements of prelate veneer mantle material transitions to modern Earth's mantle.