Neoarchean prolonged subduction-related magmatism and multistage metamorphism in the Zunhua area: implications for the cratonization of the eastern North China Craton

The late Neoarchean crustal accretion and ultimate cratonization of the North China Craton (NCC) were fundamentally dictated by the continuous evolution of subduction-accretion systems. In this study, we present comprehensive petrological, whole-rock geochemical, and zircon U-Pb geochronological data for the metavolcanic sequences (amphibolites and felsic gneisses) from the Zunhua area on the northern margin of the eastern NCC. SIMS (Secondary Ion Mass Spectrometry) zircon U-Pb dating identifies three distinct magmatic episodes at ∼2.59 Ga, 2.54–2.53 Ga, and 2.52–2.50 Ga. The mafic volcanic rocks (now metamorphosed as amphibolites) of different episodes exhibit pristine arc-like geochemical signatures without significant crustal contamination. They were derived from partial melting of mantle wedge metasomatized by fluids within a supra-subduction zone, representing the progressive construction of an isolated intra-oceanic island arc built upon juvenile oceanic lithosphere. Conversely, the felsic gneisses display diagnostic adakitic (or Tonalite-Trondhjemite-Granodiorite-like) affinities and originated from the profound partial melting of the thickened mafic lower crust within the garnet stability field. The adakitic magmatism marks the climax of sub-arc vertical thickening and the paramount volumetric accretion of the early continental crust. Synchronized with this magmatism, metamorphic zircon overgrowths, as revealed by SIMS zircon U-Pb dating, record a multistage tectonothermal evolution capturing a fundamental geodynamic transition. The sustained subduction convergence and magma underplating drove an early thermal event (∼2.55 Ga) and a subsequent regional metamorphic peak (∼2.52–2.51 Ga) coeval with maximum crustal thickening. Following this climax, late-stage thermal pulses (∼2.49–2.45 Ga) document post-peak retrograde re-equilibration and extensional overprinting triggered by sub-arc crustal delamination. Collectively, our results provide a complete petrogenetic archive for the continuous operation of a subduction-accretion system, deciphering the transition from subduction to accretion and lower crustal delamination. This process on the northern margin of eastern NCC took place before the final amalgamation of the eastern and western blocks, providing geological constraints on Neoarchean cratonization and lithospheric rigidification in the eastern NCC.