Abstract: The 3D seismic information from Structure 4 and Structure 5 in northern margin of Qaidam basin are fine interpreted,integrated with data of surface geological survey and drilling.By determining the structural elements,its tectonic model is developed.Structure 4 and Structure 5 occur as fault-complicated anticlines of S-N trend,with slight difference in structural depth to some extent.Structure 4 is a box-like anticline and Structure 5 an oblique one,but they have different deformation styles in overlying and underlying zones,which shape complex structural superimposition.The transition zone between Structure 4 and Structure 5 occur as faulted and oblique anticline.The study shows that the belt of Structure 4-5 is controlled by both folding and X-style faulting,and the structural style lies on the faulting development.Based on the unconformity and the fault assemblage,the period of forming these structures should be in late Himalayan movement when Lower Youshashan formation was deposited,with compression of SW-NE direction.The formation of these structures is also related with the Jurassic distribution in this area.

Key words: Qaidam basin, Structure 4-5 belt, structural evolution, structural mechanism, structural model