The Wei River, the largest tributary of the Yellow River, drains a catchment characterized by diverse geological, climatic, and geomorphic settings, yet the seasonal variability and controls on catchment-scale chemical weathering remain poorly constrained. This study integrated basin-wide seasonal hydrochemical data with climatic, land-use, and geomorphic characteristics to quantify the spatial and temporal variations in silicate (SWR) and carbonate (CWR) weathering rates and associated CO2 consumption fluxes in the Wei River basin. Major ion concentrations increase downstream and are higher in the lower reaches than in the upper mainstream, reflecting intensified anthropogenic influence. In contrast, concentrations are lower in southern sub-tributaries than in northern ones, highlighting strong lithological and geomorphic controls. Source apportionment indicates that atmospheric deposition and anthropogenic inputs contribute minimally to major cations, whereas evaporite dissolution (similar to 55%) is dominant, followed by carbonate (similar to 39%) and silicate (similar to 5%) weathering. Chemical weathering rates exhibit pronounced seasonality, with higher values in summer than in winter, primarily driven by temperature contrasts. Both SWR and CWR are 2.5-5.4 and 1.8-2.2 times higher, respectively, in northern sub-tributaries than in southern ones, attributable to gentler slopes that enhance water-rock interaction. The silicate- and carbonate-derived CO2 consumption fluxes repsresent about 15-20% and 7-9%, respectively, of the total fluxes in the Yellow River. These results demonstrate that climate and geomorphology jointly exert strong controls on chemical weathering and riverine CO2 consumption, underscoring substantial spatial heterogeneity in weathering processes across the Wei River basin.