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| GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF THE ORDOVICIAN VOLCANIC ROCKS IN KUANGOU AREA, QINGHAI PROVINCE |
| LI Cheng-fu, CHANG Ge-hong, ZHAO Juan, SHI Lian-chang, LI De-biao, ZHAO Ming-fu, XU Bo |
| Qinghai Bureau of Geological Survey, Xining 810001, China |
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Abstract 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.
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Received: 24 March 2017
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2017, Vol. 26 
