| Since the late Cenozoic,there have been many controversies on the dynamic mechanism of the propagation of Pamir arcuate tectonic belt.Different scholars put forward many interpretation models,which can be divided into strike slip model,radial thrusting model,composite model and tear fault model.However,the previous explanations are almost single endmember models,which can not match the activity characteristics of Pamir arcuate tectonic in the late Cenozoic well.Therefore,what is the dynamic mechanism of the northward propagation of Pamir arcuate tectonic belt? Is it controlled by single factor or multiple factors? How do these factors affect the propagation of Pamir arcuate tectonic belt? These problems are worth exploring.As for the Pamir arcuate tectonic belt,since late Cenozoic,it has produced an important response to the surrounding area during the process of northward propagation.For example,a series of complex fold-thrust systems and great thickness of Cenozoic sediments were formed in the piedmont of the eastern margin of Pamir.Conversely,the Cenozoic tectonic deformation and deposition recorded the propagation of Pamir arcuate tectonic belt.Studying the spatial-temporal development characteristics of fold-thrust belts deformation in the piedmont of eastern Pamir margin,analysis of the variation law of the deformation rate of these Piedmont fold-thrust belts,which will help to reveal the dynamic mechanism of the propagation of Pamir arcuate tectonic belt.In this paper,the piedmont in the eastern margin of Pamir is taken as the research object,base on the latest research results of magnetostratigraphic age in Southwest Tarim from Zheng et al(2015)and Wei et al(2018),established a new stratigraphic age framework and combined with field geological data,drilling data,logging data and seismic data,made fine interpretations of seismic profile data of fold-thrust belts in the piedmont of eastern Pamir,these revealed the geometric characteristics of fold-thrust belts deformation.By identifying and tracing the growth strata in these seismic profiles,then combine them with the new stratigraphic age framework,the deformation time of fold-thrust belts of piedmont can be obtained.On this basis,use the 2D MOVE software to restore the equilibrium of these fold-thrust belts of piedmont in the eastern margin of Pamir,and recover the deformation process of each tectonic segment,so as to establish the spatial-temporal development characteristics of fold-thrust belts deformation of Late Cenozoic in the piedmont of eastern Pamir margin and obtain the variation law of the deformation rate in different stages.Combining with paleo-magnetic of Pamir area,numerical simulation of Kongur Extension System and thermochronology,etc,this paper discussed the propagation mode and controlling factors of Pamir arcuate belt.The main results are as follows:(1)The Late Cenozoic tectonic deformation of piedmont in eastern Pamir is characterized by sections.Along strike,it can be divided into Wupoer tectonic section,Qimeigan-Yengisar tectonic section and Qibei-Kekeya tectonic section.Wupoer tectonic section is characterized by piggyback basin of shallow part and stacking structure formed by involvement faults of deep part.QimeiganYengjisar tectonic section is mainly characterized by structural wedges: structure wedges of piedmont are composed of a series of basement thrust faults,roof thrust faults of Paleogene and the thrust slices between them.Continuous stacking of these thrust slices results in large monoclinic in Cenozoic strata;Anticlines developed in baisn are formed by branch faults of deep faults,which slide to basin along the lower slip surface,then recoil to piedmont along the upper slip surface.Qibei tectonic section of Qibei-Kekeya tectonic section also is mainly characterized by structural wedges.while the Kekeya tectonic is characterized by the high angle thrust nappe structure and flower structure in the piedmont,toward basin,mainly develop thin-skinned detachment structure.(2)The deformation of fold-thrust belts in the piedmont of eastern margin of Pamir is generally phased.?15-13 Ma,the first row of tectonic of the southern piedmont in eastern margin of Pamir,Fusha and Damus anticlines began to develop;?11.5-8Ma,the second row of tectonic of piedmont in the eastern margin of Pamir began to develop,Kekeya anticline,Qimeigan anticline,Suget anticline and Wupoer piggyback basin began to develop;?5.7-3.5Ma,the third row of tectonic of piedmont in the eastern margin of Pamir,Qibei and Guman anticlines began to developed;?2.5-1.0Ma,the front deformation segments of the eastern Pamir mainly developed,Jiede anticline,Yengjisar anticline,Aktao anticline,Mushi anticline and Mingyaolu anticline began to develop.(3)The deformation rate of fold-thrust belts in the piedmont of eastern margin of Pamir shows migration in space and time.Spatially,the deformation rate of each row of fold-thrust belts in piedmont increase from SE to NW,and decrease from the piedmont to the inner basin.In terms of time,at?11-8 Ma,the deformation rate of the second row of fold-thrust belts in piedmont increase sharply,which reach to 4.4-5.8km/Ma,and the deformation rate of NW section is higher than that of NE section.At ?2.5 Ma,the deformation rate of Yengjisar anticline and Aktao anticline in the front deformation belt also increased sharply,which is much higher than that of other anticlines in the front deformation belt,reach to 2.5-3km/Ma.(4)The accelerated deformation of 11-8Ma and 2.5Ma-present in the piedmont of eastern Pamir may be related to the initiation activity of Kongur Extension System and the rapid extension in the later stage,there is a spatiotemporal correlation between them.In terms of time,Kongur Extension System started at 10-5Ma and accelerated at 2.5Ma.While the second row of fold-thrust belts in piedmont of eastern margin of Pamir was formed in 11-8Ma,and the deformation of front tectonic belt in piedmont also accelerated at 2.5Ma;Spatially,the deformation rate of Kongur Extension System was 4-5km/Ma,and the extension rate of the northern part was higher than that of the southern part and the extension rate of the north part is higher when accelerat extension.While the deformation rate of the second row of fold-thrust belts in Piedmont is 4.4-5.8km/Ma,and the deformation rate of NW segment is higher than that of NS segment,when the front tectonic belt accelerates deformation,the deformation rate of NW segment is also higher.(5)The northward propagation of Pamir arcuate tectonic belt since Late Cenozoic can be divided into two stages,and it is controlled by many factors.About 15-5Ma,the eastern margin of Pamir is controlled by the dextral strike slip of Kashi-Yecheng Transform System,Kongur Extension System in northeastern of Pamir began to form during 10-5Ma.The deformation rate of the second row of fold-thrust belts in the Piedmont increases sharply due to the compression caused by the extensional collapse of Kongur Extension System;Since 5Ma,under the background of the northward propagation of Pamir arcuate tectonic belt,Kongur Extension System began to extend rapidly at about 2.5Ma,and the compression of the piedmont zone by gravity collapse in the northern part of the footwall of Kongur Extension System is increased,which resulted in a sharply increase of the deformation rate of Yengjisar anticline and Aketao anticline in the front tectonic belt of the piedmont zone. |
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