Ni isotopes provide a glimpse of Earth’s pre-late-veneer mantle

• Published in: Science Advances
• Main Authors: Xu, Yong, Szilas, Kristoffer, Zhang, Lingyu, Zhu, Jian-Ming, Wu, Guangliang, Zhang, Jie, Qin, Bin, Sun, Yao, Pearson, D. Graham, Liu, Jingao
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Association for the Advancement of Science (AAAS) 2023
• Subjects: Greenland; Narssaq
• Online Access: http://dx.doi.org/10.1126/sciadv.adj2170; https://www.science.org/doi/pdf/10.1126/sciadv.adj2170

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 pre-late-veneer mantle have long been debated. Observing evidence of this siderophile element-depleted pre-late-veneer 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 pre-late-veneer mantle material transitions to modern Earth’s mantle.