Abstract: The Zhalantun area is located in the center of the Hegenshan-Heihe structural belt.Indosinian granites with superimposed ductile deformation are developed in the area.Based on the detailed studies on petrology, lithochemistry and zircon dating of the Indosinian mylonitized monzonitic granite in the northwestern Zhalantun area, its petrogenesis and regional dynamics background are discussed.LA-ICP-MS zircon dating yields the crystallization age of 242.1±1.8 Ma for the mylonitized monzonitic granite, indicating it was formed in the Middle Triassic.Geochemical studies show that it is of quasi-aluminum-weak peraluminous high-potassium calcium-alkaline granites with high silicon, high alkali, low calcium and magnesium.It is enriched in large ion lithophile elements(Rb, U, Th, K), depleted in high field strength elements(Nb, Ta, Ti), with positive Zr and Hf anomalies, and in general, incompatible elements are gradually enriched.The increasingly depletion of Sr, P and Ti and the moderate negative Eu anomaly were observed.Based on the regional data, it is suggested that the Indosinian monzonitic granite was formed in the compression-extension transition stage of the tectonic environment after the Paleo-Asian Ocean closed collision orogeny.