Abstract: A set of intermediate volcanic rock assemblages dominated by pyroxene andesite is exposed in the Ulanhot area. The LA-ICP-MS zircon U-Pb dating results show that the volcanic rocks have two zircon U-Pb ages of 130.0 ±1.5 Ma and 129.9 ±1.4 Ma, suggesting that the volcanic rocks were formed in the Early Cretaceous. Pyroxene andesite has SiO2 content of 57.84%～60.86%, Al2O3 of 16.49%～17.76%, A/CNK> 1.1, suggesting that the rock belongs to peraluminous rock. ALK value is 11.19%～11.87%, σ is 1.08～1.98. ∑REE of(128.69～145.06)×10-6,(La/Sm)N of 4.64～5.24 and(La/Yb)N of 6.58～8.09 show enrichment of light rare earth elements and distinct fractionation of light and heavy rare earth element. Weak Eu anomaly, enrichment of large ion lithophile elements(Rb, Ba, K and Sr)and depletion of high field strength elements(Nb, Ti, P and Ta)suggest that its formation is related to the lithospheric extension which followed continental crust thickening after closure of the Mongolian-Okhotsk Ocean.