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

The volcanic rocks in Baiyingaolao Formation of Wenbuqi area of Da Hinggan mountains are composed of a series felsic volcanic rocks such as rhyolite and rhyolitic lithic crystal tuff. LA-ICP-MS zircon U-Pb dating results show the rhyolite formed in the Early Cretaceous, aged in (131±1.5)Ma. The geochemical study suggests that the rhyolite is characterized by high SiO₂(72.43%~78.64%), Al₂O₃(11.48%~14.24%), and K₂O(4.09%~5.05%), and low MgO(0.14%~0.34%) in contents. Samples are significant in fractionation of HREE and LREE[(La/Yb)_N=8.22~13.68], with negative Eu anomalies (��Eu=0.39~0.90). The trace element are characterized evidently by enrichment of Rb, Ba, K, depletion of Nb,P,Ti. The ratios of ¹⁷⁶Hf/¹⁷⁷Hf vary in 0.282 830~0.282 983 and the corresponding ��_Hf(t) values are positive ranging from 6.02 to 10.19. Above characteristics indicate that the volcanic rocks derived from the basic lower crust accreted from depleted mantle during Neoproterozoic. Tectonic setting is related to the extensional setting.