River terrace and Quaternary tectonic uplift in the Qilian Mountain

River terrace series in Qilian Mountain and its adjacent areas is a significant landform symbol reflecting the regional tectonic uplift. In this paper, the authors conducted a comparative study of the amplitude and time of the terrace uplift in the Shagou River in the northeast and the Hongshuiba River terrace in the northwest of the Qilian Mountain, the southeast of the Yellow River in Gonghe and the Weihe River in Longxi as well as the east of the Yellow River in Lanzhou, and analyzed the features of Quaternary tectonic uplifting of the Qilian Mountain and its adjacent areas and its response to Tibetan Plateau uplifting. As shown by the comparative study, there have been at least five phases of tectonic activities in the Qilian Mountain and its adjacent areas since 1.6Ma:the first tectonic activity occurred at 1.6Ma, the second at 1.2~0.6Ma with its second-rate tectonic activities at 1.2Ma, 0.8Ma and 0.6Ma, the third tectonic activity at 0.45~0.25Ma, the fourth tectonic activity at 0.2~0.08Ma with two times of tectonic activities respectively at 0.15Ma and 0.1Ma, and the last tectonic activity since 0.08Ma, respectively. Studies reveal that there existed synchronous uplifting in the first, second, fourth and fifth tectonic activities in the Qilian Mountain and its adjacent areas, whereas the third tectonic activity displayed difference in uplifting time. In combination with the tectonic activity in Qilian orogenic belt, it is held that the strongest activity that occurred in eastern Qilian Mountain was caused by the second tectonic activity. Tectonic activity intensity of the third tectonic activity in 0.45~0.25Ma exhibited the feature that the intensity of the north area was stronger than that of the south area, and the intensity became stronger from west to east on the northern margin of the Qilian Mountain. Since 0.2Ma, the tectonic activity intensity in south and north direction became gradually weak in east-north direction, and the tectonic activity in the west part of the northwest side of the Qilian Mountain is stronger than that in the northeast section. The average amplitude of uplift since 1.80Ma is 0.25mm/a and 450m in the Qilian Mountain. A rough calculation shows that the region has been uplifted by about 600m since 2.60Ma. River terraces show that the tectonic uplift in the west of the Qilian Mountain and its adjacent areas is stronger than that in the east. Therefore, it is considered that the west of the Qilian Mountain and its adjacent areas have been uplifted by 600m since Quaternary.