Growth of continental crust and lithosphere subduction in the Hadean revealed by geochemistry and geodynamics.

The rates of continental crust growth and recycling on early Earth remain unclear due to the lack of information resulting from the extensive alteration of ancient rocks. Melt inclusions trapped and shielded from alteration in Archean high-Mg olivine crystals offer a solution to this problem. We report an unprecedented unradiogenic Sr mantle source component (Sr/Sr = 0.69932 ± 0.00024, 95% confidence interval) of melts included in olivine from 3.27 Ga komatiitic lava flows in the Barberton Greenstone Belt, South Africa. This component indicates a model age of 4.31 ± 0.19 Ga and significant chemical fractionation (Nb/U = 36.9 ± 1.5, Ce/Pb=16.7 ± 1.1), suggesting up to 80% ± 16% of the present-day continental crust's mass was extracted by the late Hadean from the whole mantle. Geodynamic models support this finding, explaining geochemical data by producing 40% to 70% of the present-day continental crust mass during the Hadean in a variable tectonic regime with tens of millions of years-long periods of massive impulsive subduction induced by mantle plumes.