STAGES OF THE NEOTECTONIC MOVEMENT IN THE MENYUAN BASIN, QINGHAI PROVINCE

The Menyuan Basin is a structural basin located inside the Qilianshan Mountains, the northern edge of Qinghai—Tibet Plateau, the surface of which is about 3000m ASL. To the south of this basin is the Dabanshan Mountain and to the north, the Lenglongling Mountain, which are 4000m ASL.. The neotectonic movement within this area is intense and can be divided into 6 stages.1 The basic data for identifying the stages of the neotectonic movement (1) Deformation of Tertiary deposit: Of the Tertiary system, only Baiyanghe Formation exists in the studied area, distributing at the boundary and under the bottom of the basin with Quaternary deposits discontinuously overlying it. Baiyanghe Formation has been intensely offset and folded, the folding dose not appear in Quaternary deposits. Its exact age remains unknown.(2) Deformation of Quaternary deposits: Most of Quaternary deposits belong to glacial and fluvial deposits, which have been offset and uplifted or sunk by neotectonic movement.(3) Deformation of the geomorphic surfaces: In the studied area exist many types and many orders of geomorphic surfaces, including 2 orders of planation surfaces, 3 orders of glacial platforms, 3 orders of river terraces and 2 orders of alluvial fans. Their ages are dated or comparatively estimated. All of them have been offset and uplifted or subsided by neotectonic movement. They are the time scales for dividing the stages of neotectonic movement.