Tectonic Framework And Its Evolution In The Moxizhuang Area Of The Junggar Basin,Northwest China

The overlapped basins developed in the northwest China are characterized by overlapment of different prototype basins vertically at different stages and have undergone multistages of uplifting and denudation.As a result,the tectonic framework and the structural style are complicated and the faults have been formed and reactivated at different stages.It is only by understanding the tectonic evolution that we can have better understanding of the hydrocarbon migration and accumulation and thus improve the efficiency of hydrocarbon exploration.The Moxizhuang area is chosen as an example to study its tectonic framework and reconstruct its tectonic evolution.The following conclusions can be drawn:(1)The structure style is complicated as both compressional and rifting structure can be recognized.The thrust faults can be recognized underlying the Triassic and formed by the inversion of the boundary faults of the early rifting.The strike-slip faults can be recognized to have formed along the boundary of the depression and the uplift zone.They lined in parallel or in an echelon style in plain view and are characterized by the flower structure in seismic profiles.Isolated faults can be recognized in the depression that are away from the boundary.They are most confined in the Jurrassic-Cretacous Formation and with limited vertical throw and lateral extension.(2)Tectonic reconstruction of the four regional profiles have reconstructed the tectonic evolution of the Mosuowan anticline and the Chepaizi-Mosuowan(Chemo)paleo-uplift zone.The axial plane of the Chemo paleo-uplift zone has been tilted toward the south ever since its forming and its angle of plunge has been increasing till the Pleogene to the east,but inversion happened in the Neogene and its angle of plunge has changed for more than 20? to the west.Concurrently,almost the same happened to the Mosuowan anticline.Its axial plane tilted continusly toward the south and the plungeangle increased toward the southeast.As a result,the anticline has migrated toward the northwest and the Mosuowan anticline changed to be a monocline.(3)Tectonic evolution of the Mosuowan anticline has been reconstructed to show how it has changed from an anticline to a monocline.Reconstruction of the tectonic framework before the Jurassic indicates a division between the north and the south.The Mosuowan anticline is well shaped and lines in NW-SE direction and has divided the Shawan sag in the south with the sag that lies to the west of the well Pen1 in the north.The Chepaizi-Mosuowan paleo-uplift zone was linked to the Mosuowan anticline at that time.The tectonic framework is almost stable from the Jurassic to the Paleogene except the linkage of the Shawan sag in the south and the sag in the north due to the continuous tectonic subsidence of the foredeep and the continuous northwestward migration of the anticline.At the end of the Neogene,the anticline disappeared and a monocline has formed.