The petrogeochemical characteristics and tectonic setting of Mesozoic intrusive rocks in Chabaqi area of the Da Hinggan Mountains

Abstract：The Mesozoic intrusive rocks in Chabaqi area are located in the west of Nenjiang fault zone, and the east side of the study area is the joint between apophysis and graben basin. Hence the study of the structure of the study area can provide the information for the orogenic uplift of the Da Hinggan Mountains. The result of SHRIMP U-Pb zircon dating shows that the intrusive rocks were mainly formed in the early Jurassic and late Jurassic period, and the petrogeochemical characteristics show that the intrusive rocks are high-potassium and Si-saturated rocks, belonging to calc-alkaline series. Discrimination diagrams show that the intrusive rocks belong to I-type granite of crust-mantle miscibility，and they were formed in a prolonged stable environment but under different formation conditions. The early Jurassic quartz diorite and tonalite have the characteristics of extrusion type, so that they should be formed in a relatively high pressure environment, whereas the late Jurassic monzonitic granites belong to the transition type of extension-extrusion, and hence they should be formed in a high differentiation environment of relative low pressure. The spatial and temporal granite evolution heterogeneity was probably existent in the formation process. Therefore, the relationship between the formation of Jurassic granites and the thickness of the earth's crust can serve as the supporting evidence for the thinning of the earth's crust and lithosphere as well as the stretching orogenic process of the Da Hinggan Mountains.