Situated between the Altyn Tagh and Eastern Kunlun ranges, the western Qaidam Basin records Cenozoic sediment-routing changes associated with the growth of the northern Tibetan Plateau. However, the provenance of post-Miocene strata in this region remains debated, and the role of sediment recycling has not yet been quantitatively constrained. Here, we integrate field observations, sandstone petrography, quantitative detrital zircon U-Pb analysis, and inverse Monte Carlo modeling to compare Late Cenozoic strata in the Qigequan area with nearby Mesozoic strata and basement sources in the Altyn Tagh and Eastern Kunlun ranges, thereby assessing direct versus recycled sediment supply. Sandstones of the Qigequan and Shizigou formations are poorly sorted and contain angular to subangular quartz and feldspar grains and identifiable sandstone and mudstone lithic fragments, indicating erosion of pre-existing sedimentary rocks. Their detrital zircon age spectra are dominated by 300–600 Ma grains (57.9%–69.0%), followed by subordinate < 300 Ma grains (18.4%–21.1%) and minor 600–1000 Ma (6.9%–13.2%), 1000–1500 Ma (1.3%–3.9%), and >1500 Ma (1.3%–3.9%) components. Similarity metrics and multidimensional scaling (MDS) analyses show that the Cenozoic age distributions are substantially more similar to the composite Mesozoic proxy than to the Altyn Tagh or Eastern Kunlun basement endmembers. Inverse Monte Carlo modeling further shows that a three-endmember model incorporating the composite Mesozoic proxy provides a better fit than the two-endmember Altyn Tagh–Eastern Kunlun model. Across the three optimization metrics, the composite Mesozoic proxy contributes approximately 36%–68% and 61%–72% to the modeled detrital zircon age distributions of the Shizigou and Qigequan formations, respectively. Together, these results support a substantial role for recycled Mesozoic material in the Late Cenozoic sediment-routing system of the western Qaidam Basin, providing new provenance constraints on basin–range coupling along the northwestern margin of the Tibetan Plateau.