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

The authors studied zircon U-Pb age and geochemical data of Baicaogou tuff in Yanji, Jilin Province. The results indicate that the rocks formed in Early Cretaceous (125. 6±2. 3 Ma). Geochemically, these tuffs have high SiO₂ and total Na₂O + K₂O, low MgO and FeO, and they belong to metaluminous series, the rock are enriched in LREEs and LILEs, depleted in HREEs and HFSEs such as Nb, Ta, Ti, and P, exhibiting an affinity to I-type granite. All these characteristics implied that the volcanic rocks were derived from partial melting of lower crust. Combined with the geochronology and geochemical features of the coeval igneous rocks within NE China, it is concluded that Yanji area was in a back-arc extensional setting in response to the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.