Characteristics and Geological Significance of the Devonian Granitoids in Koktokay Area of Altay

The Koktokay area is located in the southern part of Altay, where Devonian granitoids were well developed and the ages of the granitiods are about 400 Ma. The SiO₂ content ranges from 62.36% to 77.41%, and σ from 0.43 to 1.88, A/CNK from 0.97 to 1.12, implying the granitoid belongs to mid-K, calc-alkaline, quasi-aluminous and weak peraluminous rocks. In addition, they are enriched in LILE(Rb, Th, U) and LREE, obvious depleted of HREE and HFSE(Nb, Ta, Ti), besides, they have island-arc magmatite features characterized by weak-medium negative Eu anomaly. Combined with the regional geological data, the Devonian granitoids is a product of Paleo-Asian Ocean subduction toward north, and generated in an island-arc setting of active continental margin.