Seismic Evidence and Geological Significance of Thrust‐Extension Structure in Upper Basement of North Songliao Basin

Abstract Near‐vertical seismic reflection stacked migration section study has proved that the distant stress field formed by the westward subduction of Pacific plate led to the detachment of upper crust. In the upper basement of Songliao basin in Binbei area, the thrust‐nappe fault system was controlled by middle‐distance Mongolia–Okhotsk suture zone and distant westward subduction of Pacific plate together. The fault system shows bidirection and asymmetric intensity in longitudinal and transverse directions. The thickness is 3~4 km and 1~2 km for the westward thrust‐nappe fault system and the eastward fault system, respectively. The structure of fault system is complex. According to the distribution of geophysical field along both sides of the Sunwu–Shuangliao fault which controlled the evolution of the basin, the thrust‐nappe fault system in the upper basement of Songliao basin was overlapped on the Sunwu–Shuangliao fault. As we know, the Mongolia–Okhotsk suture zone has formed the huge Yinshan–Yanshan thrust‐nappe zone more than 1000 km far away from the suture zone. Taking this and the regional tectonic environment of Songliao basin into account, a thrust‐nappe fault system should be formed in the south Songliao basin and the Binbei area beyond the Sunwu–Shuangliao fault system.