Characteristics of Early Cretaceous volcanic complexes in the Genhe area in the northern segment of the Da Hinggan Mountains：with a discussion of their genesis

Abstract：Early Cretaceous volcanic complexes in the Genhe area in the northern segment of the Da Hinggan Mountains may be divided into three types according to their petrological and geochemical characteristics. Type I is composed of rhyolitic rocks, which are characterized by higher Si and alkali contents and lower Al and Ti contents, Na2O/K2O＜1, a pronounced negative Eu anomaly (δEu=0.27–0.59), enrichment in Rb and depletion in Sr and Ba. Type II consists of trachydacitic rocks, which are enriched Al and Ti, with Na2O/K2O＞1 and a weak negative Eu anomaly (δEu=0.65–0.95), enriched in Sr and Ba and poor in Rb. Types I and II probably formed in an extensional to postorogenic extensional environment, accompanied by compressional uplift. Type III is composed of latite and benmoreite, which are enriched in Al and Ti, with Na2O/K2O≥1.1 and no negative Eu anomaly (δEu=0.93–1.06), and Th/Ta and Ta/Hf ratios indicate a continental intraplate extensional environment. Its formation is probably related to underplating of basaltic magma.