Abstract
Part of the transition from active crustal shortening and strike-slip faulting in northwestern China to active extension in northeastern China takes place within the Ningxia Autonomous Region. Four arcuate zones of both strike-slip faults and thrust faults with associated ramp anticlines dominate the structures in southern Ningxia. Deformation in these zones indicates that a component of left-slip displacement is transferred into crustal shortening on north-south-trending folds and thrust faults. The average Quaternary slip rate along the Haiyuan-Liupan Shan fault zone is 5-10 mm/yr, and that along the Tianjin Shan-Mibo Shan fault zone is about 1.5-2.7 mm/yr. The amount of offset and rate of slip along the Yanton Shan and the Niushou Shan-Daluo Shan fault zones are unknown, but the topography of the mountains suggests that the rates of slip along these zones is lower than that of the Haiyuan-Liupan Shan fault zone. Deformation in northern Ningxia is dominated by normal faulting and extension. The Helan Shan rise about 2,000 m above the Yinchuan basin, reportedly filled with a few kilometers of Cenozoic sediments. The average rate of vertical separation in Quaternary time along the East Helan Shan fault is estimated to be at least 0.5-0.8 mm/yr. Opening of the Yinchuan graben is probably partly related to left-lateral slip on the Niushou Shan and Daluo Shan fault zone. The northeastern margin of Tibetan Plateau is probably being elevated by the irregular growth of convergent and left-slip structural zones. The evolution of deformation along the Haiyuan-Liupan Shan structural zone probably foreshadows the future deformation in the ranges north of it. Left slip and shortening within the Ningxia region appears to accommodate less than 20-25 km of east or northeast displacement of crustal fragments of the northern Tibetan Plateau. Large-magnitude lateral transport of crust with respect to the area to the east has not taken place within the part of the Ningxia region covered by this study.
