Tectonic Transition from the Neoarchean to Paleoproterozoic in the Northern North China Craton: Constraints from Geochemistry and Zircon U–Pb–Hf Isotopes of the Daxigou Granitoids in a Greenstone Belt

The greenstone belt of the North China Craton (NCC) records the crustal evolution from the Neoarchean to the post-Archean period, offering critical insights into the ancient tectonic background. This study focuses on the late Paleoproterozoic granitoids in the Daxigou area, located within the greenstone belt of the Qianhuai Block along the northern margin of the NCC. Zircon U–Pb dating indicates that two representative samples (H1 and HZK97-2) were emplaced at 1849 ± 2.1 Ma and 1852 ± 2.0 Ma, respectively (ca. 1.85 Ga). Both samples are characterized by high K2O (3.99–6.55 wt%) and Na2O + K2O contents (4.12–7.92 wt%), high 10,000 × Ga/Al ratios, zircon saturation temperatures (>800 °C), and seagull-type REE patterns, and are identified as A2-type granitic rocks. The Daxigou granitoids show LREE enrichment, negative Eu anomalies (δEu = 0.45–0.63), LILE enrichment, and Nb–Ta–Ti depletion, defining the arc-like trace-element signatures. Integrated with their low Mg# (0.15–0.20), Cr (12–21 ppm), and Ni (0.8–2.5 ppm) contents, negative zircon εHf(t) values (−4.25 to −0.17), Neoarchean Hf model ages (2.5–2.7 Ga), near-chondritic to slightly subchondritic Nb/Ta ratios (15.4–18.3), and high Zr/Hf ratios (41.2–44.1), these features indicate an inheritance from warm subduction-generated Neoarchean TTG protoliths. We propose that the arc-like signatures of the Daxigou granitoids reflect the source inheritance from Neoarchean TTG protoliths. At ca. 1.85 Ga, under an extensional setting, the ancient lower crust (TTG) underwent decompression melting, producing A2-type granitic rocks. They record a transition of the tectonic setting from Neoarchean warm subduction to late Paleoproterozoic post-orogenic extension.