College of Earth Sciences, Jilin University, Changchun 130061, China

The testing results of chronology and geochemistry of rhyolites in Baiyingaolao Formation from Jiyuan area in northern Da Hinggan Mountains indicate that the LA-ICP-MS zircon U-Pb crystallization age is (112.84±0.81)Ma, which belongs to Early Cretaceous. The rhyolites are characterized by high SiO₂(75.74%~82.87%)and K₂O+Na₂O(6.65%~8.71%)and low MgO(0.01%~0.03%).They are enriched in LREE, with high LREE/HREE fraction[(La/Yb)_N=1.13~5.46],obvious negative Eu anomalies.They are characterized by the enrichment of large ion lithophile elements (such as Rb,Th and U),depletion in Ba, Sr and Ti. The value of Rb/Sr is 20.29~74.89, Ti/Y is 2.52~14.53, Nb/Ta is 12.25~14.7.Comprehensive studies show that the rhyolites of Baiyingaolao Formation in Jiyuan area are similar to A-type granite. The magma originates from partial melting of basic rocks in the lower crust in an extensional background after the closure of Mongolia-Okhotsk Ocean.