Relationship Between The Cenozoic Minshan Uplift And Boundary Faults In The NE Tibet Plateau-Evidences From Sandbox Modeling

The Minshan uplift zone is the result of the escape of the Tibet Plateau to the East since the Cenozoic,as well as a component of the North-South seismic belt,and is also the key part of the discontinuous attenuation and transformation of the GPS velocity field.The Minshan Mountain Uplift Belt,near the Minjiang fault zone,developed Minjiang thrust nappe structures,its fold axis tracks to NE10-20 °degrees,intersecting with the fault to the small angle.The fold and fault patterns in the Minjiang fault belt are integrated,which conforms to the related fold characteristics of the thrust nappe structure system.and the East side of the Minshan uplift belt is the Huya fault,which also shows relatively strong tectonic activity at present,and it is closely related to the occurrence of many large earthquakes.The strong uplift of the Minshan uplift belt since the Cenozoic is controlled by the Minjiang fault zone and the Huya fault,and the late Cenozoic is characterized by NW-SE thrust thrust.Therefore,the comprehensive analysis of the tectonic style,spatial distribution characteristics and evolution process of the Minshan uplift and its boundary faults,it is the basis for understanding the uplift mechanism of the northern East plateau and the related seismogenic structures of the moderate strong earthquakes.In this paper,based on the previous data,a preliminary regional tectonic model is established through the field measured profiles,and the structural evolution of the Minshan uplift zone and its boundary fault zone since the Cenozoic era is simulated,and the Minjiang nappe structure,the Huya fault zone and the Minshan uplift belt structure are clarified.The evolution period and its structural styles are discussed to discuss the rapid uplift mechanism of Minshan uplift.Based on the deep structural features of the Minshan uplift area and adjacent areas,sand box simulation experiments are carried out.From Experiment 1,the evolution process of the Cenozoic Minshan uplift and the development sequence of the boundary faults were determined,that is,the Minjiang nappe structure was formed by the extrusion of NW-SE direction since the Cenozoic.With the eastward extrusion of the Songpan Ganzi plateau,the East Branch of the Minjiang fault zone is strongly active and eastward thrust.During the thrusting process,the material of low resistivity layer in the middle upper crust keeps moving to the bottom of Minshan uplift,and upward thrust along the "ramp" which is the lower part of the uplift zone.When the Minshan uplift rises to a certain height,forming a reverse thrust fault of the West Branch of Minjiang fault,and the direction of fault thrust is opposite to the East Branch of the Minjiang fault.The West Branch fault may cross the East Branch fault and become a strong fault in the new phase.Due to the blocking effect of the Pikou block,the Huya fault is eastward thrust to the East under the action of East extrusion pressure during the uplift of Minshan uplift.The comparison between experiment 1and experiment 2 suggests that the Minshan uplift may have the preexisting thrust belt,which causes the mechanical properties of the Minshan uplift to have the weak characteristics,The weak area is the first to uplift in the Cenozoic era when it is under the pressure of East extrusion.The comparison between the experiment 1 and the experiment 3 shows that the low resistivity layer of the middle and upper crust plays a vital role in the formation of the Minshan uplift,which controls the activity of the Minshan uplift boundary fault,and simultaneously transfers the squeezing pressure to the Minshan uplift zone and promotes its deformation and uplift.