Evolutionary sequence of faults and the formation of inversion structural belts in the northern Songliao Basin

On the basis of regional seismic interpretation of the northern Songliao Basin and the analysis of fault geometry characteristics and the formation and evolution of faults, this paper analyses fault deformation mechanisms at different stages, which reveal the formation mechanism of inversion structures and their role for oil and gas migration and accumulation. Studies show that the faults in the northern Songliao Basin have experienced the following stages of evolution: a continued extensional deformation in the faulted phase, continuous transtensional deformation in the depression phase and continuous extrusion inversion tectonic deformation in the inversion phase. The late tectonic inversion and deformation evolved on the basis of huge rifts in the basement of the Songliao Basin, grabens formed in a NW-SE tensile stress field during the faulted period, and multi-orientation fault-dense zones formed in a nearly EW tension stress field during the depression period. The sinistral compresso-shear deformation field, half grabens and huge basal faults jointly control the formation of subprime anticlines and inversion structural belts during the reversal period. The Daqing Placanticline area is controlled by both the NNE half grabens and NNE huge basal faults, so that it has a high reversal degree, which turns NE subprime anticlines into NNE structural inversion belts. Meanwhile, it turns fault dense zones from nearly SN into NW-NNW. Key words: fault evolution, faulted tectonic framework, fault-dense zone, inversion structural belt, formation mechanism, northern Songliao Basi