GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF THE ORDOVICIAN VOLCANIC ROCKS IN KUANGOU AREA, QINGHAI PROVINCE

Study on the geochemical characteristics of the Ordovician volcanic rocks in Kuangou area, Qinghai Province, shows that the content of SiO₂ is 46.74%-53.35%, with Na₂O+K₂O of 3.71%-7.63% and K₂O/Na₂O of 0.07-4.16, belonging to peraluminous low potassium calc-alkaline-alkaline series. The REEs are characterized by ∑REE of 96.19×10^-6-119.37×10^-6, LREE/HREE of 2.97-6.07, δEu of 0.70-0.86 and (La/Yb)_N of 2.23-7.2. The chondrite-normalized REE patterns are right-dipping smooth curves with weak positive Eu anomaly and enriched LREEs. The study on trace elements indicates that the La/Nb value is 1.57-3.08, Zr/Hf 35.28-48.23, with enrichment of LILEs such as K, Rb, Ba, Th and LREE and depletion of HFSEs(Nb, P and Ti), which are similar to the geochemical characteristics of island-arc environment. Based on the comprehensive analysis, it is considered that the volcanic rocks in Kuangou area, showing the characteristics of oceanic island basalt, with magma derived from the partial melting of enriched mantle, are formed in the intra-ocean island arc settings associated with oceanic plate subduction.