Abstract:

The coexistence of two groups of thrust faults (N E faults and N W faults) and the complication of structure deformation history make structure analysis and interpretation very difficult in Dachaidan area, Qaidam Basin. In order to solve the problem, field geological investigation, seismic, well logging and drilling data were used to identify key fault systems and their distribution patterns. By integrating the features of surface and subsurface structures, shallow and deep structures, seismic and nonseismic data, we carried out studies of the structure modeling and analysis. As results of our effort, two systems of thrust faults (N W faults and W E faults) were identified. Also, we found that those faults could be categorized into three systems as: basin margin thrust system, and intro basin thrust system, introbasin compression and strikeslip fault system. Those structure systems show different features in different areas and zones. We also constructed interpretation models of different deformation mechanisms in the basin and on basin margins. Three tectonic systems(compression, extension and strike slip) were identified, which can be further divided into eight structure styles. We also established structure coexistence patterns as well as their distribution patterns. The overall structure characteristics in the area can be summarized as ‘North part and south part belong to different zones; west part and east part belong to different systems’. By analyzing the SW NE tectonic evolution sections, we defined the back propagation structure evolution sequence of thrust nappes(on basin margin or in the basin) and back thrust structures (in the basin), as well as their influence on residual strata of the Mesozoic.

Key words: tectonic deformation, structure modeling, fault combination, Dachaidan area, north margin of Qaidam Basin