Tungsten Isotopic Constraints on the Nature of Earth's Accreting Materials

Tungsten isotope is a powerful tracer for the Earth’s accreting materials because of the distinct W isotope compositions of the non-carbonaceous meteorites and carbonaceous meteorites.To better understand the evolution of the early Earth,here we calculated the expectedμ^(183)W of the bulk silicate Earth for different assumed compositions of the proto-Earth’s mantle,the Moon-forming giant impactor,and the late veneer using a Monte Carlo approach.The result shows that the proto-Earth likely has a non-carbonaceous composition,while the carbonaceous chondrite-like materials were delivered to the Earth at the late stages of accretion.The predicted difference inμ^(183)W values between the bulk silicate Earth and the non-carbonaceous meteorites of the scenarios assuming a pure carbonaceous composition for the giant impactor is slightly bigger than that of the scenarios assuming either a pure non-carbonaceous or a mixed carbonaceous-non-carbonaceous composition for the giant impactor(~5 ppm versus~2 ppm).The ancient mantle reservoir that partially lacks the late veneer with carbonaceous composition should have a negativeμ^(183)W value(from-3 to 0).Uncertainties introduced by the cosmogenic effects and mass-independent fractionation should be concerned during the high precision measurement ofμ183W for meteorites and ancient terrestrial samples in further work.