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

A 3.95-Gyr-old trondhjemitic gneiss from eastern Hebei, North China Craton, records mantle-depleted source signatures and high-pressure melting, with parental magma from 8–16% melting at >1.6 GPa and 740–820°C.

• Why it matters: Few rocks older than 3.9 Gyr limit tests of when continental crust and plate tectonics began, leaving early Earth evolution uncertain.
• What they did: The team analyzed primary magmatic zircon for elevated δ18O (+6.77 ± 0.23‰) and positive εHf(t) (+1.45 ± 0.27), then used thermodynamic and trace-element modeling to infer melting conditions and source alteration.
• The result: The data indicate low-temperature altered basaltic crust from a Hadean-depleted mantle and imply rapid burial to mantle depths, most likely via a transient subduction event.

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