Zircon U-Pb ages and geochemical characteristics of volcanic rocks in Baiyin-gaolao Formation of Suolun area within central Da Hinggan Mountains and their tectonic implications

The volcanic rocks in Baiyingaolao Formation are located in Suolun area of Horqin Right Wing Front Banner within central Da Hinggan Mountains.Lithologically, the Baiyingaolao Formation is composed mainly of rhyolites and rhyolitic tuffs.Three groups of zircon samples yielded U-Pb ages of 127±2Ma, 133±2Ma and 123±1Ma respectively.The results of LA-ICP-MS zircon U-Pb dating indicate that the volcanic rocks in the Baiyingaolao Formation of the study area were formed during the Early Cretaceous period with ag-es of 133~123Ma.Petrological and geochemical characteristics of these volcanic rocks suggest that they are all highly fractionated rocks similar to I-type granite rocks, and their parental magmas were likely derived from the partial melting of lower crustal materials with pla-gioclase and a little hornblende as the residual phases.In addition, the volcanic rocks sampled in this paper, tectonically located in the Xing'an terrain, have high initial ¹⁷⁶Hf/¹⁷⁷Hf ratios (0.282854~0.283026) and positive ε_Hf(t) values (+5.5~+11.5).These data, combined with young Hf two-stage model ages of 828~439Ma, suggest that the crustal growth of the Xing'an terrain occurred during Neopro-terozoic and Phanerozoic periods.The above results, combined with previous studies of the contemporaneous magma-tectonic activi-ties in Northeast China, imply that the generation of the Early Cretaceous volcanic rocks in the central Da Hinggan Mountains was relat-ed to the extensional environment caused by the subduction of the Paleo-Pacific plate beneath the Eurasian continent.