Nature of the Eastern Boundary of the Mesozoic Ordos Basin and the Formation of the Lüliangshan Anticline

The Mesozoic to Cenozoic intraplate deformation of the North China Craton (NCC) is an intriguing phenomenon that led to different evolutions of the Ordos Basin and the eastern part of the NCC. Located in the central part of the NCC, the Lüliangshan is regarded as a boundary between the Ordos Basin and the eastern NCC, but the exact location of this boundary is still debated. Our field investigations suggest that the Lüliangshan anticline is a classical Mesozoic basement-involved anticline. The Lishi fault on the west of the southern part of the Lüliangshan anticline is argued to be a large fault and the east boundary of the Ordos Basin. However, our investigations show that it is not a continuous single fault but a deformation zone composed of several segments without connection along the strike. In front of the western Lüliangshan, this tectonic zone is a top-to-the-west breakthrough thrust placing the western Lüliangshan basement-involved anticline in the hanging wall with limited displacement. Field investigations show that the traditional view of the northern segment of the Lishi fault as a boundary between blocks is not clear. With a similar deformation style, the southern Lishi fault passes Lishi City, extends northeastward, connects to the Ximafang fault, and then extends to link with the Kouquan fault as the west boundary of the Datong Basin. All these faults show a map pattern of relay array. The eastern margin of the Ordos Basin was deformed by a series of thrusts that controlled the basement-involved folds. The Lüliangshan anticline and its boundary faults were formed in the Late Jurassic, and the driving force of the intraplate deformation is inferred to the westward low-angle subduction of the Paleo-Pacific plate from the east.