The Geologic Features And Tectonic Implications Of Lower Cretaceous In Alashan Area, Inner Mongolian Autonomous Region

The subjects of this study is Baogeqi Basin and Wuliji Basin which are respectively located in Alashan Right Banner area and Alashan Left Banner area of Inner Mongolian Autonomous Region. The two basins are Mesozoic sedimentary basins belonging to North Asia Orogenic Belt which is suituated at the suture zone between Kazakhstan plate and Huabei plate.Based on the achievements of former research, the study uses the theory of stratigraphy, sedimentology and rock geochemistry to analyze the characteristics of outcrops and samples which are eventually serve to study the geologic features and tectonic implications of lower Cretaceous in the study area. The geologic features of lower Cretaceous are as follows: the Bayingebi Formation in Baogeqi Basin deposited in piedmont-lake environment, which can be divided into three parts——the lower part and the upper part are of Alluvial fan facies while the middle part is of lake facies; the Suhongtu formation in Wuliji Basin is basaltic andesite- andesite combination. This thesis also studies the subfacies and microfacies of Bayingebi Formation and analyzes the rock geochemistry of Suhongtu formation. Finally, based on the works mentioned above, the thesis drows following conclutions: the sedimentary facies of Baogeqi Basin in early Cretaceous reflect the formation of rift basin; the volcanic rocks of Suhongtu formation in Wuliji Basin formed in continental stable massif instead of orogenic belt. The two formations reflect the retrogradation and volcanic activities in intermontane basins at North Asia Orogenic Belt after orogenic movements in late paleozoic.