Kinematic analysis of the Ordos block and surrounding area based on GPS data: an initiative–passive vortex structure model

Abstract

The counterclockwise rotation of the Ordos block has a complex geodynamic background. The fracture zone around the Ordos block also has complex stress and strain fields. We propose an initiative–passive vortex structure model (I–P model) to explain the geodynamics of the Ordos block and the surrounding fracture zone. We analyze the relative velocity of the fracture zone around the Ordos block based on the GPS velocity field and use a multiple kernel function to calculate the strain field in the study area. According to the fault distribution and tectonic activity, we divide the fracture zone around the Ordos block into seven sections and use the I–P model to analyze the relative motion state and strain variation in these sections. The results show that the north and south margins of the Ordos block exhibit sinistral strike–slip movement, primarily because the eastward movement of the Ordos block is faster than the movement of the Yanshan block and slower than that of the Southern China block. The east and west margins of the Ordos block exhibit dextral strike–slip movement, mainly due to the counterclockwise rotation of the block. The NE extrusion force from the Tibetan Plateau increases the strike–slip rate of the eastern Ordos block. The I–P model perfectly explains the change in strain around the block. It also systematically explains the regional dynamic background of the area around the Ordos block. According to the I–P model and the surface strain characteristics inside the Ordos block, we find that a tensile belt runs from the southwest to the northeast. This means that the block will probably disintegrate in the future, and the length-to-width ratio of the block will be seriously unbalanced. Therefore, the Ordos block will no longer rotate counterclockwise. The I–P model agrees with the kinetic characteristics of the present vortex structure and will provide a reference for further research on the Ordos block.