Abstract: The monzonitic granite in Erguying forest farm is located in the northeast area of Lesser Khingan Mountaines,it is the important part of the Yichun-Yanshou magma belt.Based on analyzing the regional geological background,combing with the related test results,the petrogeochemistry characteristics and genesis of the monzonitic granite in Erguying forest farm are discussed in detail.The results show that:①the monzonitic granite with the characteristics of high silica (w(SiO₂) 65.23%~71.20%),alumina (w(Al₂O₃) 13.46%~17.07%) and rick alkali (w(Na₂O+K₂O)6.56%~8.27%),it belongs to the partial aluminum calc-alkalic rock series with high potassium;②the monzonitic granite is enriched in large ion lithophile elements (such as K、Rb、Ba) and incompatible elements with lively chemical properties (such as U, Th), it is relatively depleted in high field strength elements (such as Nb、Sr、Ti) and heavy rare earth elements (such as Y、Yb、Lu ),the petrogeochemistry characteristics of the monzonitic granite is similar to the ones of I type granite;③the monzonitic granite is formed in volcanic arc tectonic environment related to the Pacific plate subduction.

Key words: Monzonitic granite, Petrogeochemistry characteristics, Genesis, Volcanic arc tectonic environment