The tectonics of the western Ordos Plateau, Ningxia, China: Slip rates on the Luoshan and East Helanshan Faults

摘要

Analysis of the locus, style, and rate of faulting is fundamental to understanding the kinematics of continental deformation. The Ordos Plateau lies to the northeast of Tibet, within the India-Eurasia collision zone. Previous studies have suggested that it behaves rigidly and rotates anticlockwise within a large-scale zone of ENE-WSW left-lateral shearing. For this rotation to be accommodated, the eastern and western margins of the Ordos Plateau should be undergoing right-lateral shearing and yet the dominant faulting style appears to be extensional. We focus specifically on the kinematics of the faults bounding the western margin of the Ordos Plateau and make new slip rate estimates for two of the major faults in the region: the right-lateral strike-slip Luoshan Fault and the normal-slip East Helanshan Fault. We use a combination of infrared stimulated luminescence dating of offset landforms with high-resolution imagery and topography from the Pleiades satellites to determine an average right-lateral slip rate of 4.3 0.4mm/a (1 sigma uncertainty) on the Luoshan Fault. Similarly, we use Be-10 exposure dating to determine a vertical throw rate on the East Helanshan Fault of <0.6 0.1mm/a, corresponding to an extension rate of <0.7 0.1mm/a (1 sigma uncertainty). Both of these results agree well with slip rates determined from the latest campaign GPS data. We therefore conclude that right-lateral shearing is the dominant motion occurring in the western Ordos region, supporting a kinematic model of large-scale anticlockwise rotation of the whole Ordos Plateau.