Abstract:

The western part of northern Qilian Mountains marginHexi Corridor basin, situated at the northeastern margin of the QinghaiXizang plateau, is one of the areas where the neostructural activity occurs most strongly in our country. By means of the field investigation and chronologic measurement of the main active faults in the area and analysis of other materials, the authors reached a new conclusion as follows. The HanxiaDahuanggou fault, the Yumen fault, the Yinwashan fault and the Xinminbao fault were all active during the late Quaternary (late Pleistocene and Holocene epoch). The HanxiaDahuanggou fault developed during the late Miocene epoch and has been being active till the present. The Yumen fault developed during the early period of Pliocene epoch, and there were twice strong neostructural activities (paleoearthquakes) taking place at about 76 ka BP and 32 ka BP. The fault was also the causative structure of Yumen earthquake in 2002. The Yinwashan fault developed during the late period of Pliocene epoch (about 3 Ma), and there were three strong neostructural activities (paleoearthquakes) occurring at about 199210 ka BP, 86100 ka BP and 4150 ka BP. The Yinwashan fault probably was the causative structure of the Huiminbao (now Xinminbao) earthquake in 1785. However, the forming age of the Xinminbao fault is much younger than those of above three faults, the fault developed during the late period of middle Pleistocene epoch (about 017 Ma) and three strong neostructural activities (paleoearthquakes) took place there at about 283 ka BP, 44 ka BP and 12 ka BP. The sense of the movement of all the four faults is unanimously trusting from the southwestern side (upside) to the northeast. The feature of the movement of the Xinminbao fault is the creeping deformation, but other faults move mainly in stickslip mode. On the section, the thrust faults of western part of northern Qilian Mountains marginHexi Corridor developed on a composite model of progressive and retrogressive development. In other words, the youngest fault is the Xinminbao fault near the centre of the basin. The faults on the section south of the centre of the Western Jiuquan basin developed on a progressive developing model and the forming age of fault is becoming younger and younger from the hinterland of Qilian Mountain to the centre of the basin. While the faults on the section to the north of the centre developed on a retrogressive developing model and the forming age of fault is becoming older and older from the centre to the northern margin of the Western Jiuquan basin.

Key words:

active fault; late Quaternary; thrust; developing model; western part of northern Qilian Mountains marginHexi Corridor