Petrogenesis of late Neoarchean tonalite-trondhjemite-granodiorite and dioritic gneisses in Eastern Hebei: Implications for coexisting vertical and horizontal geodynamic regime in the eastern North China Craton

The Archean continental crust is dominated by tonalite-trondhjemite-granodiorite (TTG) rocks, which are commonly accompanied by dioritic rocks during late Neoarchean time. An integrated study of coeval TTG and dioritic rocks is crucial for constraining the tectonic regime of the Archean cratons. In this contribution, we report a systematic geochronological, geochemical, and zircon Hf-O isotopic study for the late Neoarchean TTG and dioritic gneisses in Eastern Hebei, North China Craton. Zircon U-Pb dating reveals that the TTG and dioritic gneisses have protolith crystallization ages of 2.55-2.52 Ga and record two stages of metamorphism at 2.51-2.47 Ga and ~2.45 Ga. The TTG gneisses show similar geochemical affinity to adakitic rocks and can be divided into two groups. The first group has low concentrations of MgO, Cr, and Ni, coupled with positive zircon ε_Hf(t) values (+3.0 to +7.3) and δ¹⁸O values of 5.36‰-6.59‰, indicating its magmatic source of juvenile thickened lower crust. The second group exhibits relatively high concentrations of MgO, Cr, and Ni, as well as a wide range of zircon ε_Hf(t) values (-2.6 to +5.7) and δ¹⁸O values of 5.58‰-7.47‰, suggesting that it was derived from partial melting of subducted oceanic crust, with some inputs of ancient crust material. The dioritic gneisses have geochemical affinity akin to the Archean sanukitoids. They show positive zircon ɛ_Hf(t) values of +4.0 to +6.4 and δ¹⁸O values of 5.99‰-6.42‰, probably derived from partial melting of depleted lithospheric mantle metasomatized by subducted fluids and slab-derived melts. In combination with our new data and available regional geological data, we propose that the tectonic evolution of the eastern NCC in the late Neoarchean was jointly controlled by vertical mantle plume activity and horizontal slab subduction.