The ~1.9 Ga syn-collisional granitic magmatism in the Sushui Complex: new evidence for the late Paleoproterozoic tectonic evolution of the southern North China Craton

The late Paleoproterozoic tectonic evolution of the southern North China Craton (NCC) remains controversial, largely due to its complex structural position and ambiguous magmatic-metamorphic records. This study presents an integrated petrology, whole-rock geochemistry, and in-situ zircon U-Pb-Hf isotopic investigation of newly identified monzogranites from the Sushui Complex. LA-ICP-MS zircon U-Pb dating yields emplacement ages of 1904 ± 37 Ma and 1895 ± 37 Ma. Geochemically, these rocks are high-K calc-alkaline I-type granites characterized by elevated SiO₂ and K₂O/Na₂O ratios, low A/CNK and Fe₂O₃^T/MgO values, and zircon saturation temperatures ranging from 635°C to 842°C. They exhibit a moderately fractionated REE patterns ((La/Yb)_N = 1.76–35.92) with significant negative Eu anomalies (δEu = 0.42–0.71). Zircons exhibit uniformly negative ε_Hf(<i>t</i>) values (−6.8 to −4.7) and Neo- to Mesoarchean two-stage Hf model ages (T_DM2 = 2.82–2.96 Ga). These geochemical and isotopic features, combined with regional correlations, indicate that the monzogranite rocks were likely originated from partial melting of pre-existing Neoarchean TTGs, and formed in a syn-collisional setting. Combined with regional magmatic, metamorphic, and sedimentary evidence, we propose that the southern NCC underwent a tectonic transition from compressional collision to extension between 2.1 and 1.8 Ga. We further interpret the ca. 1.94–1.90 Ga tectono-magmatic events as recording the assembly of the Columbia supercontinent, and the ca. 1.80–1.70 Ga extensional activities as corresponding to its subsequent break-up.