Mechanical Instability of the Crustal Thickness Transition Zone beneath the Taihang Mountains in Relation to the Tectonic Compression of the Frontal Cenozoic Basin

Abstract

AbstractBeneath the Taihang Mountains of China there is a large crustal thickness transition zones (CTZ). Since the late Cenozoic, deformation has occurred on the both sides of the Taihang Mountains CTZ, which is featured by NWW‐SEE extension on the west and NWW‐SEE compression on the east. Coexistence of extension and compression in the same direction on the both sides of the Taihang Mountains CTZ can not be interpreted by the regional stress field. To reveal the mechanism of the special deformation ,this study makes numerical modeling based on the viscoelastic proprieties of crustal rocks. Result indicates that under the gravitational loading of the Shanxi plateau, the crust beneath the Taihang Mountains is mechanically instable due to initiation of the lower‐crust ductile flow. The ductile flow of lower crust causes the mechanic de‐coupling between the lower and the upper crust, and favors to induce basal shear along the brittle‐ductile transition belt. Since the ductile flow is from the plateau side to the basin side, this basal shear will weaken the compression in the plateau and enhance the compression in the basin within the middle and upper crust. From the numerical result, it is concluded that the mechanics of tensile‐compression coupling in the North China block is probably not initiated by regional stress field associated with plate‐boundary interactions, but mainly by local stress variation caused by the crust ductile flow.