Abstract: The widely distributed Early Cretaceous volcanic rocks of Yingcheng Formation in northern Songliao basin are intermediate-felsic rocks, which are mainly rhyolites, characterized by high silicon, aluminum,rich alkali,and low magnesium and iron. The standard curve of rare earth elements reveals the deficiency of heavy rare earth elements,but the enrichment of light rare earth elements, and the rare earth elements are seriously differentiated in different kinds of volcanic rocks. The rhyolites are distinctly enriched in incompatible elements such as Pb, U, Th, Ta, Hf, Zr, and apparently loss of Sr, Ba, Eu, while in neutral andesite, trachyandesite and basic basalt they have no obvious loss, and in the intermediate-acid dacite they are in between. The results show that the magma of Yingcheng Formation originated form depleted mantle. Because the magma was contaminated by crust during evolution under magma plating and crust partial melting, forceful magmatic differentiation occurred before the eruption of acid magma. The volcanoes of Yingcheng Formation may erupt in an extensional background within plate according to the discrimination diagrams, and the volcanic rocks of Yingcheng Formation have the same evolutionary characteristics as those of the volcanic rocks developed in active continental margin or island arc associated with plate subduction. Taking the tectonic environment of Eastern China into consideration, the large-scale volcanic action in the Early Cretaceous may be associated with the lithospheric thinning and mantle upwelling under the subduction of the Pacific plate toward northwest in a high speed.

Key words: geochemistry, volcanic rock, Yingcheng Formation, Early Cretaceous, Songliao basin