The Duerji Granite Characteristics And Tectonic Significance In Inner Mongolia

Duerji granite in the Inner Mongolia is located in the middle-south section of the Great Hinggan Mountains and extends in NE direction.The area is under the jurisdiction of the Right-wing Central Banner of Horqin,Inner Mongolia Autonomous Region.Based on the 1:50,000 regional mineral survey in Xinaile area,Inner Mongolia,this paper makes a detailed study on the granitic intrusion characteristics in this area and discusses its tectonic significance.The granite intrusion occur in the batholith and stocks,and are divided into three superunits:Duerji,Mudetu and Titege,in which the lithologies are mainly granite,monzonitic granite?porphyry?and granodiorite,respectively.According to the analysis of 6 K-Ar dating samples from different units of granite,the Duerji granite was intruded during 111.9-120.29 Ma in the Early Cretaceous.Geochemical studies show that the granite bodies are characterized by high silicon,high potassium,alkali-rich,peraluminium,calcium-poor,magnesium and iron,and belong to the series of Al-supersaturated alkaline rocks.The chondrite normalized curve pattern of rare earth element is gentle and right inclined,and the fractionation of light and heavy rare earth elements is not strong.The large ion lithophile element Rb in trace elements is enriched and Sr and Ba elements are poor.The high field strength elements Nb and Ta are relatively enriched.The cobweb diagrams of trace elements are W-shaped with obvious negative Sr,Ba and Ti anomalies.Duerji granite is identified as A-type granite in the K₂O-Na₂O diagramr andA2-type granite.Considering the granite characteristics and regional tectonic background of the Daxing'anling area in the same period,the formation of the granite body in this area may be simultaneously subjected to the extension of the Mongolia-Okhotsk Ocean after closed orogeny and subduction of the Paleo-Pacific Ocean.