The anataxis of accretionary complexes is critical for crustal differentiation in orogenic belts. To clarify how anataxis in accretionary complexes drives crustal differentiation, this study examines Late Carboniferous granitoids from the Dunhuang orogenic belt using whole-rock geochemistry, zircon U-Pb geochronology, and zircon Lu-Hf isotopes. Zircon U-Pb dating indicates that the granitoids were emplaced between 323 and 312 Ma. Their negative igneous zircon εHf (t) values suggest derivation from ancient crustal materials. Geochemical correlations and field relationships between the granitoids and their wall rocks suggest that the magmatic sources were dominated by meta-sedimentary rocks with minor meta-mafic rocks. The systematic whole-rock Rb-Sr-Ba variations are attributed to water-fluxed melting of muscovite in a metasedimentary source. Given the continued activity of the Dunhuang subduction zone during the Late Carboniferous, we infer that elevated temperature combined with fluid-rich conditions in the deeper accretionary wedge triggered anataxis of the accreted materials. The segregation and upward migration of granitic magmas leave a residue within the deeper accretionary wedge that resembles the lower continental crust in composition. This process enhances vertical differentiation within the orogenic belt crust and likely plays an important role in transforming loose accreted materials into more mature continental crust.