关键词: 黄河, 河流阶地纵剖面, 活动地块, 构造隆升, 主夷平面

Abstract: The middle-upper reach of the Yellow River is a flowing water system passing through the whole "Qaidam-Qilianshan active block". We systematically investigated the river terraces of the Yellow River of about 1 800km length from Gonghe of Qinghai to Shizuishan of Ningxia, measured about 73 cross sections of terraces and obtained 88 age data in total. In addition, we have compiled the vertical profiles of river terraces on this river segment, and carried out the comprehensive analyses of the number, heights, ages and deformation features of the terraces. The following conclusion can be drawn from the obtained results: 1.These drainage areas can be divided into several secondary active blocks; they are Gonghe, Lanzhou, Haiyuan, Weining basin (Alashan) and Yinchuan basin (Ordos) secondary blocks, each of which is bounded by regional active faults and is independent of the others. The amplitudes and rates of uplift of the terraces in each block are significantly different, while those in the southern block are larger than those in the northern. For example, the relative elevation above river level of terrace planes of 1.60Ma age from south to north are: 400m in Gonghe block, 105～200m in Lanzhou block, 200～265m in Haiyuan block, 135～147m in Weining basin block, and -842m in Yinchuan basin block, respectively. 2. The interiors of the secondary active blocks are to some extent rigid, so the number, altitudes and ages of the terraces within the blocks are about the same, while the vertical profiles are relatively continuous and smooth. However, folding deformation is also obvious in local zones due to thrusting and other reasons. 3. Vertical profiles of river terraces reflect that the uplift amplitude of the Qaidam-Qilianshan active block since 1.6Ma B.P. is greater than that during 3.6～1.6Ma B.P. 4. Vertical profiles of terraces from Gonghe to Shizuishan segment of the Yellow River indicate that the rate of crustal uplift during 0.15～0.20 Ma B.P. is 2～6 times as high as that in the other periods, and the rate in the past 10 000 years is 4～10 times as high as that in the other periods, or 2～5 times even after deducting half of the amount that was caused by climatic effect. It indicates that there have been at least two intensive tectonic movements since 1.6 Ma B.P. These two events are comparable to the "Gonghe Movement" and "the Latest Movement" proposed by Li Ji-jun et al (2001).

Key words: Yellow River, vertical profile of river terraces, active block, uplifting rates, main planation surface