THE STRUCTURAL CHARACTERISTICS AND EVOLUTION OF THE WESTERN ORDOS THRUST_ BELT

The western ordos thrust belt located among the Ordos block-Qinqi fold belt and Alashan block. It is a pivotal district，Connecting the western and eastern different tectonic units in northern China. This is a quasi- foreland thrust belt, structures are very complicated. Its formation and evolution have great significances to understand the structure transformation between the east and west China and the deformation of internal plate.

According to the characteristics of structural geology, the western ordos thrust belt was further separated into 6 sections from north to south. The structure character is mainly thick construction in Taole-Hengshanpu section in north. Thrust block cut through Shanxi formation of the early Permian, developing imbricate thrust structure, burst structure and hedging structure. Majiatan section in central developed eastward thrust nappes, and these main faults merged into a unified deep slip surface. The main structures include fault propagation fold and burst structure. In Shajingzi section and Pengyang section in south, the structure character is high and steep thrust faults which are mostly imbricated thrust structure.

The western ordos thrust belt was controlled by the evolution of the Qinghai-Tibet Plate and the Pacific Plate, and the tectonic evolution had gone through two major stages: Paleozoic platform evolution stage and Mesozoic - Cenozoic foreland basin evolution stage. In the first stage the Paleozoic sedimentary system and distribution characteristics of lithofacies paleogeography were structured. In the second stage the Mesozoic - Paleozoic burial history of strata was transformed under intense tectonic movements, and reservoirs were developed. The ancient reservoirs was formed in Triassic initial phase; ancient reservoirs had transformed in Jurassic - Early Cretaceous massive tectonic movement phase; and secondary reservoirs were finally structured in Late Cretaceous-Tertiary adjustment phase.