The large scale (1∶1000) field mapping in the Beipiao area, western Liaoning Province shows that, the “Xinglonggou Formation” exposed in here is not a monoclinic stratum, but a suit of strongly deformed volcanic rocks, and intruded by some small stocks. Consequently, two kinds of igneous rocks are identified in the "Xinglonggou Formation" exposed in the Beipiao area, based on the field occurrence, lithology, crystallization age and geochemical characteristics of these rocks. The 144 Ma highmagnesium dacitic plugs belong to the first group, and they intrude into the deformed MidJurassic volcanic rocks. The first group igneous rocks exhibit characteristics of low potassium (K2O < 2%), high magnesium ( Mg# > 60) and calcium (CaO > 5%) content, low Rb content, but high Sr/Y ratio (> 60). Among these rocks, most of them have high Cs but low Li content. The second group igneous rocks are volcanic rock and have been strongly deformed. Compared with the rocks of first group, they have high potassium (K2O > 2%) and Rb content, but low magnesium ( Mg# < 60) and calcium (most samples CaO > 4%) content; meanwhile, they have lower Sr/Y ratios (in general < 60), and low Cs and high Li contents. The first group highMg dacites are typical adakite. They might result from partial melting of the mafic lower crust of Xing'anMongolian orogenic belt, and assimilated with mantle peridotite during ascending. The partial melting might be related to the subduction of Xing'anMongolian orogenic belt beneath North China Craton, or to the delamination of thickened lower crust of Xing'anMongolian orogenic belt, but not to the delamination of thickened lower crust of North China Craton. The second group belongs to highpotassium calcalkaline volcanic rocks, and may not be related to the delamination of lower continental crust, and this suit may belong to a longtraveled southvergent thrusting sheet from the southern segment of Xing'anMongolian orogenic belt.