The Xiaohongshan granite on the southern margin of the Dunhuang block intrudes the Dunhuang rocks, and consists mainly of e biotite monzonitic granite and biotite granodiorite. LA- ICP- MS zircon U- Pb isotopic dating yielded a weighted 206Pb/238U average age of 289.6±3.9Ma for the Xiaohongshan biotite monzonite, indicating that the emplacement age was Early Permian. The geochemical analyses show that the granite is characterized by high silicon, high aluminum, alkali- rich and low magnesium. The rare earth elements show a LREE- enriched right- dipping pattern and weak negative Eu anomaly in the chondrite- normalized REE distribution patterns. Enrichment of large ion lithophile elements (such as Rb, Cs, Th, K, Pb), depletion of high field- strength elements (such as Nb, Ta, P, Ti, etc), especially enriched Sr and depleted Yb and Y, as well as relatively high Sr/Y raito, suggest that the rock has the same geochemical characteristics as that of Adakite was should be the product of partial melting of the thickened lower crust. The 87Sr/86Sr values of whole rock of the Xiaohongshan granite range from 0.706622 to 0.707778, 143Nd/144Nd values range from 051212 to 0512264 with εNd(t)=-4.093 to -6.887, indicating characteristic of the crust source. The Nd model age TDM2 of 1.39~1.62Ga (ave. 1.49 Ga) indicates that its source area may be related to the Proterozoic Dunhuang rocks. Combined with the diagenetic age and regional tectonic evolution characteristics, it can be concluded that the southern margin of the Dunhuang block might have involved into in a series of Paleozoic orogenic events related to closure of the paleo- Asian ocean in a tectonic setting from the collisional orogeny to the intracontinental extensional environment during the Carboniferous to Early Permian.