Numerical Modeling On The Formation Of The Dabashan Thrust Nappe Structure,South Qinling

The Dabashan thrust nappe structure is suggested as the result of the subduction collision along Mianlue Suture between North China Block and Yangtze Block,combined Mesozoic-Cenozoic intracontinental orogeny of Qinling orogenic belt.It is a key factor for understanding the formation of Mianlue Suture Zone.In this work,several geometrical and rock mechanics numerical models are constructed to simulate the collisional and intracontinental orogeny movements,and the key factors that may control the formation of the Bashan Arc fault are analyzed.Additionally,3D visualization,high performance numerical modeling algorithms are developed which we hope to be helpful in later and others numerical modeling researches.A few two-dimensional plan-view models are firstly constructed that based on horizontal and geometrical view sight.The modelling results show that the compressive stress produced by the plate collision along both north and south boundaries is the main driving force;the dextral shearing derived from the inconsistent shape on the block margins is the main controller;rigid tectonic units such as Bikou and Hanan-Micangshan terranes,Foping and Wudang dome,as well as Shennongjia-Huangling anticline also contribute as "anchor" effects.Furthermore,the rheology properties of rock material in the Dabashan area affect the shape of the arc.The shortening rate in North and South Dabashan are calculated respectively,which is consistent with that from regional geological analytic.Plan-view models have limitations due to lack of varies pressure and temperature that depends on depth of rocks.To resolve this,we developed a cross-section model that based on Dabashan geological equilibrium profile.The cross-section model is more focus on rock mechanics properties,mainly simulates rock plastic deformation with a weak interlayer(slip layer)inside the model.The modeling results show that irreversible localized plastic deformation forms multiple,highly deformed shear belts that separated relatively undeformed blocks.These shear belts exist in the wide area that close to the boundary of North and South Dabashan,possibly caused by the deference of plastic deformation between strong and weak rock layers.These separated relatively undeformed blocks extruded upward,may be one of formation condition of Dabashan overthrust.We also integrated space insertion,multi-/varies deference grid,3D visualization,developed a OpenGL based software EarthEye,with NASA DEM data as input,EarthEye successfully built real 3D surface model for Dabashan area.Meanwhile,EarthEye also functioned to quickly and visually build 3D terrane model,seamless integrated with FLAC(2D/3D)for modeling solving and visualizing results.Even further,considering limitation of FLAC 3D,we setup open source project PyFlac that we hope to be a free alternative tool to Itasca FLAC 3D.