In contrast to the eastern North China craton, limited progress has been made on Mesozoic lithospheric thinning in the central North China craton. This study presents detailed LA- ICP- MS zircon U- Pb dating, major and trace element geochemical, and Sr- Nd- Hf isotopic data for the Ketou syenite within the Huyanshan alkaline complex in central North China craton. LA- ICP- MS zircon U- Pb dating shows that the Ketou syenite was emplaced in the late stage (111 Ma) of Early- Cretaceous. These samples are all potassic- ultrapotassic and alkaline rocks, which have distinct positive Euanomalies. They also have high initial 87 Sr/ 86 Sr ratios of 0. 7058~0. 7062, lower ε Nd ( t ) values of -11. 1 to -10. 4, and zircon ε Hf ( t ) values of -12. 2 to -5. 2. Detailed research suggests that the primitive magmas of the Ketou syenite were derived from partial melting of the enriched lithosphere mantle with phlogopite- bearing lithosphere mantle at spinel lherzolite zone. The primitive magmas have gone through the process of assimilation and fractional crystallization (AFC). Integrating these results with the published data of magmatism in the central North China, we infer that the late- Mesozoic magmatism in the central North China can be subdivided into two stages: an early one at 123~135Ma for the peak magmatism and a later one at 114Ma for the last weak magmatism. Together with the source region for the late- Mesozoic magmatic rocks in the central North China, the results indicate that the lithosphere mantle in central North China was enriched and heterogeneous and began thinning at least between 138 to 111 Ma.