宽沟地区奥陶纪祁漫塔格群火山岩的SiO2含量在46.74％～53.35％之间,Na2O+K2O为3.71％～7.63％,K2O/Na2O为0.07～4.16,属于过铝质的低钾钙碱性—碱性系列火山岩.稀土元素特征:∑REE为96.19×10-6～119.37×10-6,LREE/HREE为2.97～6.07,δEu为0.70～0.86,(La/Yb)N为2.23～7.2,球粒陨石标准化曲线为右倾的弱铕正异常的轻稀土富集型平滑曲线.微量元素研究结果:La/Nb比值在1.57～3.08之间,Zr/Hf比值为35.28～48.23,相对富集大离子亲石元素(K、Rb、Ba、Th、LREE),亏损高场强元素(Nb、P、Ti),表现出类似于岛弧环境的地球化学特征.综合分析认为,该区火山岩具有洋岛玄武岩的特征,岩浆源于较富集地幔的部分熔融,形成于与大洋俯冲有关的洋内岛弧环境中.%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)Nof 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.
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