YANSHANIAN MOVEMENT IN ORDOS BASIN AND ITS RELATIONSHIP WITH DISTRIBUTION OF OIL AND GAS

Ordos basin is one of the important oil and gas bearing basins in the mid-western part of China. Yanshanian period is the main stage for migration and accumulation of oil and gas in this basin. Based on the analyses of the late Mesozoic sedimentary framework, structural deformation, and of late Jurassic-early Cretaceous magmatic and thermal events in the basin and its adjacent regions, it is suggested that the basin prior to the late Jurassic was mainly controlled by Tethys tectonic domain, whereas influence of Paleo-Pacific plate on the Ordos basin seems to appear until late Jurassic. The possible mechanism of change in paleo-thermal field in the basin was caused by deep mantle dispersion which not only led to drastic raising of the geothermal gradient in the basin, but influenced on late shallow level structural deformation in surrounding regions of the basin. In addition, the mantle dispersion was a dominant factor controlling the migration and accumulation of oil and gas in the basin, and alse an important element for the difference in late Mesozoic between Shanxi region and Ordos basin. In general, the characteristics of paleo-stress field , paleo-geothermal and structural deformation in Yanshan period reflect that the Yanshan movement was playing the most important role for distribution of oil and gas in the basin.