Process And Mechanism Of The Interaction Between Surface Erosion And Structural Deformation In Fold-and-thrust Belts

Tectonic deformation affects surface processes,which in turn have feedback on the distribution of tectonic stress and the pattern of structural deformation through crustal isostasy.Progress has been made in the influence of surface erosion and sedimentation on tectonic development in large scale.However,the tectonic differentiation in the mesoscale fold-and-thrust belts will lead to complex river morphology and sediment distribution and react on the structural development.So it is an important place to study the interaction between surface erosion and crustal deformation.In this study,we designed a series of sandbox modeling experiments using water-saturated materials to investigate the response of surface processes to crustal shortening and its influence on structural development in fold-and-thrust belts,considering whether the plastic detachment exists,the thickness of plastic detachment and different crustal shortening rates.The modeling results show that the existence and thickness of the plastic detachment layer affect the wedge shape and structural deformation pattern.Single-taper critical wedge and thick-skinned structures develop without the presence of plastic detachment.With the presence of plastic detachment layer,double-taper critical wedge develops due to the different strength of detachments between the piedmont and basin.Thin-skinned structures and duplex structures develop which amplifies the role of surface processes and influences the development of new structure.When the plastic detachment layer is thick,duplex structure is inhibited.As a detachment layer,it decouples the deformation between the upper and lower strata.As strata,it also accommodates part of the crust's shortening,inhibiting the transfer of deformation from deep to shallow layers.Different shortening rates affect the structural propagation distance and arrangement by affecting the relative strength between the plastic detachment and the brittle layer.The lower shortening rate leads to longer intervals between structures.In addition,the structures propagate farther into the foreland.In terms of geomorphic,the shortening rate also leads to diverse drainage system and different erosion and sedimentation processes.Under a low shortening rate,the channels have more opportunities to undergo lateral erosion and capture with more sediment eroded and deposited.Long and dendritic drainage system develops.Large alluvial fans and fluvial terraces are formed.Under a high shortening rate,less sediment is eroded and deposited without undergoing lateral erosion and capture processes.Dense and short parallel drainage system mainly develops.In turn,erosion and sedimentation affect the location,morphology,amplitude,lateral propagation and connection of new structures with the presence of plastic detachment.The distribution of sediments controls the location of new structures.The axial planes of the new folds usually intersect tips of the alluvial fans.By compaction and gravity loading,sediment thickness has negative correlation with fault slip in different degrees.Especially,when the size of alluvial fans varies greatly,the fault will be segmented in the initial development,showing an en-échelon distribution and no linkage mode.Then the detachment linkage forms through the fault growth and lateral propagation,and hard linkage tends to form.These results indicate that structural development is controlled by both endogenic forces and surface erosion and deposition processes.The physical properties of detachments play an important role in linking deep tectonic activity and surface processes.Meanwhile,the drainage system,the surface fault trace and the lateral propagation and connection of structures in our modeling are highly comparable with the natural examples in the Longmenshan,the southern and northern Tianshan Mountains.These demonstrate that our modeling can provide a dynamic 3D evolution of medium-scale fold-and-thrust belt under subtle surface processes.Our modeling also provides some insights for the study of structural geometry and kinematics under the influence of surface processes,as well as earthquake hazards in Tianshan,Longmenshan,and other regions.