Redox and hydration evolution of Archean felsic magmatism in the North China Craton

The North China Craton (NCC) preserves geological records from the Eoarchean to the Neoarchean, providing a window into the secular evolution of Earth's early continental crust. By integrating zircon U-Pb-Hf-O isotopes, whole-rock geochemistry, and calculated magmatic physicochemical parameters (oxygen fugacity, fO₂; water content, H₂O) for felsic rocks from the NCC, we identify three distinct evolutionary stages marked by fundamental shifts in magmatic characteristics. The Paleo–Mesoarchean (~3.8–3.2 Ga) felsic rocks are dominated by sodic tonalite-trondhjemite-granodiorite (TTG) suite characterized by low K₂O/Na₂O ratios and high positive ε_Hf(t) values. Their low magmatic fO₂ (ΔFMQ –3 to 0) and H₂O content (4–8 wt%) reflect partial melting of low-K juvenile sources under reduced and relatively dry conditions. A pivotal transition occurred during the mid-Mesoarchean (~3.0 Ga), with high K₂O/Na₂O ratios, elevated zircon ε_Hf(t), increased whole-rock Nb/Ta ratios and a subtle rise in both magmatic fO₂ and H₂O. We attribute these signatures to an early pulse of crustal growth and recycling of subduction-related fluids. By the Neoarchean, the zircon ε_Hf(t) values dropped significantly, indicating extensive crustal reworking, while zircon δ¹⁸O, magmatic fO₂ and H₂O rose dramatically (fO₂:ΔFMQ -1.5 to +3; H₂O: 6–16 wt%), comparable to modern arc magmas. These Neoarchean oxidized and hydrous felsic magmas were likely generated through effective water-fluxed melting of early-formed, underplated crust derived from the metasomatized mantle wedge. Notably, the redox and hydration evolution of the Archean crust in the NCC deviates from that of the global detrital zircon or TTGs records, suggesting that the onset of plate subduction could be diachronous across different cratons. Meanwhile, the convergence of these magmatic parameters at ~2.5 Ga marks a globally synchronous tectonic transition. Our findings also demonstrate that magmatic oxidation and hydration evolution could provide critical constraints on crust-mantle interactions.