| The northwest margin of Junggar Basin is located in the key area of the Central Asian orogenic belt,and it is a hot spot of current tectonic geology and even the whole geological research.Previous studies on the evolution of the Mesozoic basin have been carried out,but there are still many divergences on the evolution of the Mesozoic basin.The Mesozoic is an important turning point of the Late Paleozoic continental assemblage and Mesozoic-Cenozoic intracontinental basin-mountain system in northern Xinjiang.Studying the Mesozoic tectonic deformation characteristics in the northwest margin and the uplifting process of orogenic belt is of great significance to understand the overall evolution history of Junggar Basin and the basin-mountain coupling mechanism.Through detailed interpretation of seismic profiles and analysis of structural features and styles of faults,this paper identifies multi-stage angular unconformity contacts between Permian and Triassic,Triassic and Jurassic,Jurassic and Cretaceous,and strike-slip Retrofitting in Late Triassic,and defines the starting time of tectonic movement.The high precision zircon LA-ICP-MS U-Pb isotope dating method was used to determine the age spectrum of clastic zircons of the Middle and Lower Jurassic in Baicongshan and Tiechanggou areas of the Heshtorogai Basin and the Karamay Depression in the southern part of the Zaire Mountains.The age spectrum was matched with that of the surrounding orogenic belt and ophiolite.（1）The stratigraphic ages of the Upper Triassic Bailiangshan Formation（T3b）in the Shitorogai Basin are 290-330Ma（Bailiangshan）,280-330 Ma（Tiechanggou）,and the age peaks of the samples of the Xiaoquangou Formation（T3x）in the Karamay Depression are mainly 290-330 Ma.According to the similar age characteristics of the three groups,it is inferred that the Zaire Mountains are the main provenance areas in the three study areas.（2）Sample ages of the Lower Jurassic Badaowan Formation（J1b）in Baicongshan（310-338 Ma）,Tiechanggou（310-338 Ma）and Karamay Depression（269-340）all indicate that the Zaire uplift at this time provided sediments for three areas at the same time.In addition,the 261-290 Ma age peaks of the Baicongshan samples and the 269-290 Ma age peaks of the Karamay Depression samples indicate the Hara’a’a.Latshan uplift is the common secondary source area of the two regions at this time.（3）During the sedimentary period of the Lower Jurassic Sangonghe Formation（J1s）,the 278-409Ma age range of Tiechanggou area samples and the 262-352Ma and 365-419Ma age range of Karamay depression all came from the source area of Zaire Mountain and ophiolitic melanges in the source area.At this time,secondary provenance area of Hashan still exists in Karamay depression.（4）The samples of the Middle Jurassic Xishanyao Formation（J2x）in Bailiangshan contain two main age peaks,272-356 Ma and 384-461 Ma,respectively,corresponding to the provenance areas of the Zaire and Shemistai Mountains,and it is presumed that Hashan still provides fillers for the Heshtorogai Basin at this time.Based on the analysis of provenance area and seismic profile,combined with the geological literature of sedimentary facies and paleocurrent,the uplifting process of Mesozoic and Mesozoic mountain bodies in the source area was restored and the specific time limit of tectonic activity was determined.A period of intense compressive tectonic activity from Late Triassic to Early Jurassic resulted in the significant uplift of Zaire and Hashan,and the northwest margin entered the stage of fault basin development after that.Early Middle Jurassic is an important period of tectonic background transformation.During this period,tectonic compression triggered the uplift of the Shemistai Mountains.Therefore,this period of compressive tectonic activity is likely to be influenced by Yanshan movement,making the northwest margin enter the stage of compression depression. |
