Complex Tectonic Deformation Characteristics, Formation and Evolution of the Mountain Front in the Middle Part of the Southern Margin of Junggar Basin

The middle part of the southern margin of the Junggar Basin is adjacent to the North Tianshan Mountain Front, and the tectonic deformation is intricate and complex. There are many differences in the understanding of the formation time of the three rows of structures developed in the mountain front, and there is a lack of systematic comparative analysis of the deformation superposition characteristics of folds and fractures during the evolution. In this paper, on the basis of previous studies, the research tools such as seismic data interpretation and equilibrium profile recovery are used, combined with the quantitative analysis methods of fault slip distance and extensional compressional rate, to make a systematic analysis of the tectonic deformation characteristics and superposition evolution process in the study area. The study concludes that: ① The three rows of structures in the middle section of the southern margin from south to north, the deformation intensity from strong to weak; the first−row anticlines are controlled by the basement−involved fault system, and the second−row and third−row anticlines are controlled by the bedding−decollement fault system. There is a progressive evolution relationship between the structures, and a variety of composite structural styles are superimposed. ② The fault slip distance gradually decreases from deep to shallow, with the characteristics of inheritance development; there is an obvious inflection point in the slip distance of the main fracture, which is a strong evidence of multi−stage activity. ③ The basement large−scale thrust fault is a pre−existing fault, and later inherited development; the basement−involved fold−thrust belt is characterized by fold while fault in the later period when fold occurs before thrust fault; the detachment fold−thrust belt is formed by thrust and fold at the same time or thrust before fold.④ The first row of anticlines formed in the late Jurassic, and the second row of anticlines formed a weak prototype in this period, and formed a clear outline in the late Paleogene; the third row of anticlines formed in the late Neogene; the strong extrusion effect since the Quaternary period has made the three−row anticline strongly modified by fracture.