Research On The Late Quaternary Activity Characteristics Of The Kuantanshan Fault

The Kuantanshan fault is located at the western end of the Hexi Corridor,and at the triple junction between the Tarim,Alxa and Qinghai-Tibet Plateau block.The Kuantanshan and its surrounding area have experienced complex tectonic deformation by developed active faults during late Quaternary.The Kuantanshan fault plays a key role in responding to the eastward extension of the Altyn tagh fault and the tectonic activities of the Qinghai-Tibet Plateau northeastern margin.Based detailed field investigation and geomorphological interpretation,we clarified the characteristics of the Kuantanshan fault,including the distribution movement properties,and slip rate.Then,we discussed the formation mechanism of the Kuantanshan fault and its tectonic effect on the Altyn tagh fault.The main findings of this work are summarized below as follows:Through satellite image interpretation and field geological survey,we find that the Kuantanshan fault is a strike-slip and thrust fault.The Kuantanshan fault extended the sinistral strike-slip of Altyn tagh fault,resulting in a series of faulted landforms,such as faulted ridges,faulted river systems,low-fault cliffs,etc.In addition,late Pleistocene and Holocene alluvial fans have been displaced to form obvious fault sacrp in the piedmont.The profiles across fault scarps revealed that several thrust branches thrusting Quaternary alluvial gravel beds.Based on the GF-7 three-dimensional satellite image and Unmanned Aerial Vehicle(UAV)photos,we quantitative measuring morphotectonic deformation of different geomorphic scarps and dating morphological surfaces.Of those,the horizontal and vertical displacement were measured by LaDicao＿v2 and Point Fit software,respectively.Therefore,the cumulative offset probability density analysis was performed to obtain two horizontal displacement peaks ～3.8 m,～10.4 m,and two vertical displacement peaks ～1.6 m,～5.4 m,corresponding to the two stages of alluvialproluvial fans in the piedmont.Besides,using cosmogenic nuclides dating method,the ages of the two faulted alluvial fans in the piedmont are 6.7(+1.8/-1.7)ka and 28.1(+3.6/-3.5)ka,respectively.The Monte Carlo analysis method was introduced to simulate the slip history of the fault,and 1000 possible fault slip paths were fitted by comprehensively considering the displacement-time envelop.Finally,the horizontal and vertical slip rates of the Kuantanshan fault since ～28 ka was calculated to be 0.37 +0.10/-0.07 mm/a and 0.19+0.04/-0.03 mm/a,respectively.Our results completes the velocity distribution of the eastern end of the Altyn fault.Considering fault geometry characteristics,movement properties and slip rates,we believe that the Kuantanshan fault is a branch of the flower-like structure formed by the transformation and extrusion of the Altyn tagh fault responding to the north-east expansion of the Qilian mountain.Therefore,the Kuantanshan fault is located at a structural transformation zone.In conclusion,with the Huoshaogou fold on the west side and the Heishan fold on the east side,the Kuantanshan fault absorbed the strikeslip component of the eastern end of the Altyn tagh fault through the arc-shaped extrusion structure.The kinetic property of the Kuantanshan fault have been adjusted and transformed from strike-slip to thrust.