Abstract:

Abstract:  The uppermost tectonic feature of the northwestern margin of Junggar Basin is a group of thrusts there. Disputes over these thrust structures are mainly about their formation time and attributes, and the relevant debate of whether the Junggar Basin is a faulted depression or a foreland basin. At the northwestern margin, granite and dyke swarms developed, suggesting that the studied area underwent an extension from 314 Ma to 255 Ma. The facts that the sedimentary scope of Jurassic is wider than that of Triassic and the alkali basalt developed in the early Jurassic indicate that the Junggar Basin underwent an extension and kept expansion in  Jurassic. The late Triassic strata unconformably overlying the granite indicates that the formation time of these thrust structures might be from the late Permian to the early Triassic, no later than the Late Triassic. The seismic profile of northwestern margin shows gentle and stable Permian strata in thrust fronts. As to Permian sedimentation, its major characteristics include volcanic development, positive cycle fining up in the long term, higher depositional rate, a steeptogentle pattern of subsidence curve, as well as higher paleogeothermal gradient and heat flow values. The main hydrocarbon traps are nonstructural traps, like lithostratigraphic traps, while the tectonolithological traps are the minority. Based on the analysis above, we believe that the thrust structures are short term inversion structures occurring between 314255 Ma extension and Jurassic extension, rather than large scale thrust belts associated with orogeny.

Key words: Key words: northwestern margin of Junggar Basin; late Permian to Triassic; thrust structures; inversion structures