Abstract:

The study of the tectonic deformation and evolution of the eastern section of North Qaidam is comparatively weak, particularly the paleotectonic stress characteristics and its transformation mechanism is not clear. In this paper, systematic observation and analysis on stressresponse structures (e.g. folds, joints, slickensides) and profile measurements were carried out in Olongbluke. Results indicate that compressive stress direction in the Caledonian was NE. There were two phase of compressional tectonic events in the late HercynianIndosinian, of which the early stress direction was SN and the late stress direction was NW. During the Early to Middle Jurassic, the stretching direction was approximately EW. Then, compressive stress direction changed into NE after the Late Jurassic. Based on balanced crosssection and the strata extension ratio of Ounan depression, the tectonic evolution of Northeast Qaidam can be divided into four stages. During Cambrian to Early Ordovician, the Ounan sag was under retroarc extensional environment and turned into retroarc extrusion, which resulted in the formation of the NW trending anticline. During the Permian to the Triassic, the whole uplifting of Olongbluke area resulted in the stratigraphic missing. Intracontinental extention within the Early to Middle Jurassic and extrusion inversion within the Cretaceous, the Olongbluke area was in an inherited uplifting and had not fully deposited. In Late Himalayan Epoch, tectonic deformation was intensified and surrounding mountain was uplifted rapidly caused by reverse faulting. Basement curled structural pattern was widely distributed within this phase.

Key words: Olongbluke area, structural character, structural evolution, Paleozoic