Abstract：The LA-ICP-MS zircon U-Pb dating for the Jianshetun volcanic rocks in Eastern Inner Mongolia yields an age of Early Triassic(248.4±4.8 Ma). According to the major element compositions, the volcanic rocks, with a high Na2O/K2O ratio (2.04), A/CNK of 0.81-1.40 and A/NK of 1.48-2.50, should be assigned to acidic-intermediate and intermediate calc-alkaline to high potassium calc-alkaline series. With respect to the features of Sr>300, Yb=1.37-2.91, δEu=0.62 (average), the rocks can be regarded as adakites, whose original magmas were most likely produced by the partial melting of granulite facies materials in the thickened lower crust. Considering the geochemical characteristics of the simultaneous Jianshetun granites and regional tectonic background, the volcanic rocks of this study should be the product of partial melting of the thickened newborn lower crust after the Late Permian closure of the Paleo-Asian Ocean along the Xar Moron suture zone.
2013, Vol. 22 
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