Geochronology And Geochemistry Of The Early Permian Volcanic Rocks In The Yitong Area,jilin Province And Its Tectonic Implications

In this paper,petrology,zircon U-Pb geochronology,whole-rock geochemistry and zircon Hf isotope studies were carried out on the Early Permian volcanic rocks in the Yitong area,central Jilin Province.The rock assemblage,formation age and mantle source properties of the volcanic rocks were identified,and the tectonic setting of the formation of the Early Permian volcanic rocks in the Jilin province was discussed.The Early Permian volcanic rocks in the Yitong area,central Jilin Province,are mainly composed of basaltic andesite and andesite.The phenocrysts are mainly plagioclase,and plagioclase is also visible in the matrix.Zircon U-Pb dating results show that zircons in basaltic andesite and andesite samples have clear oscillation rings and high Th/U ratio,indicating that they are all of magmatic origin.The weighted mean ages of the two samples are 283±2 Ma and 280±2 Ma,respectively,i.e.,the Early Permian.Petrogeochemical studies show that the volcanic rocks in the Yitong area have low Si O₂ contents and relatively high Mg^#values,belonging to the tholeiitic series.These volcanic rocks have low Rb/Sr ratios（0.10-0.16）and Lu/Yb ratios（0.15-0.16）,indicating that they are not products of partial melting of lower crustal material.The higherεHf（t）values（12.47-14.24）,enrichment in LREEs and LILEs,and depletion in HREEs and HFSEs,suggest that the primary magma should have originated from the partial melting of the depleted mantle wedge metasomatized by fluids from the subducting slab.Combined with the existing regional research results,it is believed that the Early Permian volcanic rocks in the Yitong area,central Jilin province were formed in the active continental margin,associated with the southward subduction of the Paleo-Asian Ocean Plate t under the North China Plate.