Sandbox Physical Simulation Of The Dabashan Arc Structure Formation And The Stress Boundary Effect

The Dabashan arc structural belt is the east-west tectonic belt in central China intracontinental multiphase orogeny in the process of one of the most representative construct,the arc structure evolution process and dynamic mechanism have been obsessed by many scholars both here and abroad.In this paper,the evolution process and its deformation mechanism are studied by combining the methods of field structure analysis and sandbox physical simulation.based on the previous research results and the outcrop structures of different typical observation sites in Dabashan arc tectonic belt,the analysis shows : the Dabashan arcs are formed from the complex arcs that formed during the period of the indo-yanshan period and evolved over a long period of time,along the whole arc belt there are three different kinds of deformation,over thrust,dextral and levorotatory,the main structure of the west section of Dabashan arc tectonic belt is near north south direction,The kinematics is characterized by thrust from east to west,accompanied by strong dextral strike slip characteristics;kinematic characteristics are thrust from north west to east,with obvious dextral strike slip component,And show the trend of slipping away eastward;the eastern tectonic movement toward the main body is near east-west,the kinematic characteristics are obvious near South North extrusion,and the strike slip component is relatively weak.Based on the regional characteristics of the study area,choose the right scale,design the physical simulation boundary conditions of the sandbox;based on the material similarity principle,using dry quartz sand to simulate a capable layer,glass beads and silicone to simulate the weak layer;based on the principle of geometry and kinematic similarity,design the slide-the extruded sandbox physical model.In the experiment,SLR cameras were used to take a top view at regular intervals of sliding / extrusion displacement;PIV real-time recording sand box material particle kinematics vector,and the vector data vector is calculated by the computer;at the end of the experiment,the whole sand box model was subjected to pour water consolidation,Slice it every certain radian(to observe the profile characteristics).In order to investigate whether the decollement layer controls the arc structure,The physical simulation experiment of homogeneous and heterogeneous sand box is designed;study the superimposed directions of thrust structures,design low angle and high angle stacking experiment.The existence of the slippage layer makes the tectonic deformation gradual,the formation stage of arc structure,in the formation arc of the prerequisites,The homogeneous sand box physical model shows an arc tectonic belt pattern,almost no difference from north to south,the heterogeneous sand box physical model shows : As the experiment goes on,the surface of the slide formed by the slide of the base is carried along the arc of the arc along the curved path and then into the south.the comparison between the homogeneous sand box physical model and the heterogeneous sand box physical model reveals the importance of the detachment layer to the Dabashan tectonic activity,in homogeneous sand box model sections are found in the profile,the upper part of silica gel layer(middle and lower three series)has strong deformation,the lower part of the silicone layer is weaker,the physical model of a homogeneous medium sand box is mainly controlled by the bottom slip layer.the arc tectonic boundary has obvious control effect on stress transmission,the physical stress model of heterogeneous sand box is different from the boundary of the arc boundary and the front edge of the arc boundary,the structural stress at the trailing edge of the arc boundary is mainly subjected to the action of the extrusion stage,when the arc boundary is encountered,the stress direction is changed due to the influence of the arc boundary.The high and low angle compressional deformation stage of inhomogeneous media reveals that the low angle inhomogeneous medium agrees most well with the actual geological body,in the low angle heterogeneous sand box model,the deformation zone of the west extension deformation zone is the smallest,the middle section is the middle,and the west section is the biggest,however,the extended deformation zone of the west side of the deformation zone of the high angle heterogeneous sand box model is the largest,and the middle section and the eastern section are approximately equal,compared with previous studies,it is concluded that the low angle heterogeneous sand box model has the highest similarity with the actual geological conditions.Therefore,the formation of the arcs of the dabashan is controlled by the early curved tectonic boundary,and to be subjected to the strong landlord movement of the yangzi plot,which leads south to the north Dabashan nappe passive low angle,and so the pku was passively pushed south,It is formed by the combined detachment of the lower cambrian decollement layer and the middle lower permian composite gypsum decollement.rather than the focus of the precambrian basement "the pillar".