Deformation Analyses and Their Geological Implications of Carboniferous-Permian Tectonic Transformation Period in Northwest Margin of Junggar Basin

Detailed deformation analyses of the Zaire-Hala'alate Mountains show the following three different directional trends of regional structural features developed in the northwest margin of the Junggar basin: the south-north (S-N), northeast to southwest (NE-SW) and east-west (E-W) directions. The deformation sequences demonstrate that nearly S-N fold-thrust structures were developed during the early Late Carboniferous. During the late Late Carboniferous, nearly S-N tectonic orientation was transformed into the NE-SW direction by dragging. Meanwhile, the Darbut and Karamay ophiolitic mélanges were emplaced into the overlying Carboniferous strata by pulling-out under the control of dextral strike slip shearing or lateral wedge extrusion. Subsequently, NE-SW extensional faults, represented by the Darbut fault, were developed during the late Late Carboniferous to Permian, accompanied by extensive intrusion of intermediate to mafic dykes and granites. Between the end Permian and the Early Triassic, widespread E-W cleavages and thrust nappes in the Hala'alate Mountains were developed, and the Darbut sinistral strike slip fault was activated. From the Carboniferous to the Permian, the western Junggar underwent complicated evolutional processes including subduction, collision and intra-continental deformation, with multiphase tectonic overprints of compression and extension. The tectonic evolution history in the study area fully exhibits the regional geodynamic processes in the tectonic transformation deformation.