Tectonic Characteristics Of The Altun Tagh Fault In Cenozoic And Its Influence Of Evolution Of The Western Qaidam Basin

Altun Tagh Fault is a famous giant strike-slip fault in the western China.As the northwest boundary of the Tibetan Plateau,it has extremely important geological boundary significance.Since the Cenozoic,the movement of strike-slip and uplift of the Altun Tagh Fault has jointly controlled the evolution of the western Qaidam Basin.Based on the field geological investigation,and combined with comprehensive analysis of seismic data and drilling data,this paper studied for the tectonic characteristics of the Altun Tagh Fault and its influences on the basin evolution in the western Qaidam basin in Cenozoic.The characteristics of faults development in the western Qaidam basin are very complicated.Combining with previous studies,the faults in the western Qaidam basin are generally divided into the NW trending Fault System and the near EW trending Fault System.The NW trending faults are distributed in the western Qaidam basin,and their formation is mainly controlled by the compressibility of the East Kunlun and South Qilian tectonic belt.The near EW trending faults are adjacent to the Altun Tagh Fault and distributed in an aragonite pattern,which belongs to the associated strata of the Altun Tagh Fault.According to the tectonic characteristics of the near EW trending Fault System,the tectonic evolution of the Altun Tagh Fault in Cenozoic was divided into four stages:in the Paleocene-Late Eocene,the activity intensity of the Altun Tagh Fault was weak;in the Late Eocene-Middle Miocene,the thrust of the Altun Tagh Fault was dominated,which led to the initial uplift of the Altun Mountains;in the Middle Miocene-Pliocene,the thrust of the Altun Tagh Fault weakened,and the magnitude of uplift of the Altun Mountains gradually decreased;since the Quaternary,the Altun Mountains uplifted and became the present form.The activity of the Altun Tagh Fault makes the basin-mountain contact relationship appear as two forms of contact with hemi-flower-shaped faults and the super contact on the under-cut faults,and it controls the formation of a series of anti-"S" structures in the transitional belts of the basin,and initial uplift of the Altun Mountains controlls the sedimentary characteristics and the distribution of sedimentary systems.After comprehensive analysis,there are six major tectonic movements in the Cenozoic in the western Qaidam Basin.The evolution of the western Qaidam basin has mainly experienced the stage of the weak extensional faulting in the Paleocene-Eocene,the stage of compressive depression in the Oligocene-Middle Miocene,and the stage of squeeze-slip in the Middle Miocene-Holocene.In the Paleogene-Neogene,the slip-thrust action of Altun Tagh Fault controled the staged uplift of the Altun Mountains,but the scale of the Altun Mountains uplift was not very large.The sedimentary range of the original basin may spread to the north of the Altun Tagh Fault.Since the Quaternary,the Altun Mountains has become the western boundary of the Qaidam Basin.