Granites serve as critical indicators of crust-mantle material cycling. Their genetic evolution provides essential constraints for deciphering continental crustal accretion-differentiation processes, unraveling the dynamics of orogenic mechanisms, and elucidating the evolution of deep-seated geochemical reservoirs. To constrain the Late Mesozoic tectonic evolution of the Yanshan Fold Belt along the northern margin of the North China Craton, we conducted systematical investigations of the Shayukou granites in Beijing. These investigations included petrographic analysis, zircon U-Pb geochronology, whole-rock major and trace element geochemistry, and Lu-Hf isotopic analyses. Zircon U-Pb concordant ages from the Shayukou monzogranite yield 134±1, 132±1, 132±1, 131±3, 130±4 and 133±2 Ma, respectively, constraining the pluton emplacement to the Early Cretaceous. Geochemical analyses reveal the following characteristics: the Shayukou monzogranites possess high silica (SiO₂ = 63.70%～69.13%), alkali enrichment (Na₂O+K₂O = 9.48%~10.81%), and peraluminous composition (A/CNK=1.05~1.13 and A/NK=1.26~1.29), classified as high-K calc-alkaline I-type granites. The rocks exhibit pronounced enrichment in large-ion lithophile elements (LILEs; e.g., Rb, K, Ba) and light rare earth elements (LREEs), coupled with depletion in high-field-strength elements (HFSEs; e.g., Nb, Ta, Ti). Diagnostic features, including elevated K₂O, Sr, (La/Yb)_N ratios, and suppressed MgO, Y, and Yb contents, collectively characterize them as C-type adakites. Zircons from the Shayukou monzogranites exhibit εHf(t) values ranging from -23.84 to -19.76, with two-stage Hf model ages (t^C_DM) of 3 768~3 408 Ma, indicating derivation from the partial melting of Paleoarchean crust. The low zircon saturation temperatures, ranging from 637°C to 699℃, classify the monzogranite as a low-temperature granite, suggesting the generation of magma involved infiltration of external fluids. Integrated with regional tectonic evolution, the Shayukou granite formed in a setting associated with the subduction of the Paleo-Pacific Plate. The underplating of mantle-derived magma, along with fluid fluxing, initiated the partial melting of thickened Archean igneous lower crust. Subsequently, the magma underwent limited fractional crystallization and crystallized at low temperatures.