Tight bounds on missing late veneer in early Archean peridotite from triple oxygen isotopes

Abstract

Oxygen isotopes provide a unique possibility to study Earth’s late accretion phase from a lithophile element perspective, because most carbonaceous chondrites – meteorites that likely resemble the composition of the terrestrial late veneer – have markedly different Δ′17O values than the silicate Earth. Ultramafic rocks in the early Archean assemblage of southwest Greenland have not incorporated the full amount of late accreted materials, and therefore possibly record the Δ′17O of the mantle before late accretion. We measured 17O/16O and 18O/16O ratios of olivine from these ultramafic rocks and compared them with olivine from post-Archean mantle peridotite. A missing late veneer component was not resolved. The missing component from the early Archean mantle is therefore restricted to ≤0.12 % of Earth’s mass (M⊕) for most carbonaceous chondrite-like materials, unless the missing component resembles CI chondrites – the only carbonaceous chondrites with Δ′17O values similar to those of the silicate Earth. If the early Archean mantle had incorporated 60 % late veneer, the overall late accreted mass would be restricted to ≤0.3 % M⊕ for most types of carbonaceous chondrites, with a more massive late veneer only possible for CI-like chondrites.