Crustal evolution and tectonic history of the Trans-North China Orogen during early Paleoproterozoic: evidence from ca. 2.47–2.45 Ga potassic granites in the Xuanhua complex, North China craton

Archaean and Paleoproterozoic potassic granitoids occur in several cratons worldwide and are commonly linked to crustal differentiation and stabilization processes. The northern segment of the Trans-North China Orogen (TNCO) in the North China Craton (NCC) preserves ~2.5–2.45 Ga magmatic rocks that provide important constraints on early crustal evolution. In this study, we present results from field, petrological, geochemical, and geochronological investigations on a suite of potassic granites in the Xuanhua terrane. Zircon U-Pb dating indicates emplacement at ~2.47–2.45 Ga and a subsequent metamorphic overprint at ~1.83 Ga. The granitoids can be subdivided into high-Sr/Y I-type granites and S-type garnet-bearing granites. The I-type granites are characterized by high SiO2, K2O, and Sr contents, high Sr/Y (10–131) and (La/Yb)N (91–193) ratios, depletion in Nb – Ta, and predominantly positive zircon εHf(t) values (+2.5 to +7.8), with two-stage Hf model ages of 2.45–2.84 Ga, indicating derivation from partial melting of juvenile arc-related intermediate – felsic crust in a moderately thickened lower crustal domain. In contrast, the ~2.46 Ga garnet-bearing granites show lower Sr/Y (3.6–5.9) and (La/Yb)n (2.4–5.1) ratios, weakly fractionated REE patterns, slightly negative zircon εHf(t) values (−5.7 to −1.6), and older Hf model ages (2.63–2.95 Ga), low Sr/Y ratios (3.61–5.90), and (La/Yb)N ratios (2.39–5.08) suggesting magma generation by partial melting of the older sedimentary crustal materials at relatively shallower crustal levels, such as felsic pelites or greywacke. Comparison with coeval granitoids from other segments of the TNCO indicates broadly similar arc-related geochemical affinities but variable source compositions and melting depths, implying vertical compositional and thermal heterogeneity within the crust at ~2.5 Ga. These ~2.47–2.45 Ga magmatic rocks record intracrustal reworking of the thickened arc-related crust during regional crustal assembly in the northern NCC, and were later modified by Paleoproterozoic metamorphism associated with final craton amalgamation.