Geochronology of Zircon SHRIMP, Geochemistry and Its Implication of the Volcanic Rocks from Yingcheng Formation in Depression Area, North of Songliao Basin

A suite of intermediate or acidic volcanic rocks distributed widely in the Yingcheng Formation of the Xujiaweizi depression, north of the Songliao Basin, consist of basaltic trachyte andesite, andesite, dasite, rhyolite and rhyolitic volcaniclastic rocks, etc., which mostly belong to subalkaline and parapelite. Geochronological study through zircon SHRIMP UPb of the volcanic rocks shows that the volcanic eruption concentrates between 113Ma and 111Ma, which experienced from the early Aptian to the Albian of the early Cretaceous. Geochemical study and Nd isotopic data shows that the volcanic rocks of the Yingcheng Formation in the depression were from the same magma source, for the rhyolites are rich in such elements as Rb, Th, Zr, etc., and have obvious negative anomalies of Sr, Ba, P, Ti, Eu, etc., while the andesites have a notable loss of those elements, and the characteristics of dacites are between them. The tectonic discrimination diagrams of granite for the volcanic rocks indicate that they were formed in the extensional tectonic environment of intraplate and is the product of a largescale lithospheric thinning and magmatism in eastern China during the Early Cretaceous