Hadean mantle depletion and 3.95-Gyr subduction implied by North China rocks

Abstract The scarcity of terrestrial rocks older than 3.9 billion years (Ga) has hindered our understanding of Earth’s early evolution, fueling persistent debates on how and when the first continental crust formed and plate tectonics started. Currently, the only unequivocally documented >3.9 Ga rocks are from the Acasta Gneiss Complex, Canada 1–3. Here we report a newly discovered 3.95 Ga trondhjemitic gneiss from eastern Hebei, North China Craton, where 3.95 Ga magmatic zircon records elevated δ18O values (average +6.77 ± 0.23‰) and positive εHf(t) (weighted mean +1.45 ± 0.27), indicating a low-temperature altered basaltic source that originated from a Hadean depleted mantle. In contrast to the low-pressure origin inferred for the ca. 4.0 Ga Acasta rocks 2, the 3.95 Ga trondhjemitic gneiss reported here exhibits geochemical signatures attributed to a high-pressure origin 4. Thermodynamic and trace element modelling demonstrates that its parental magma formed via low degree (8–16%) melting of basaltic crust at >1.6 GPa and 740–820 ℃, suggesting rapid burial of (near-)surface‑altered oceanic crust to mantle depths along a cool thermal gradient. We propose that this rapid burial was most likely achieved through a transient subduction event.