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

摘要： 黄河中上游河段是横贯整个"柴达木-祁连山活动地块"的贯流水系.通过对青海共和至宁夏石嘴山段长约1 800km的黄河中上游阶地的系统考察、阶地剖面实测和年代测定,绘制了该河段的阶地纵剖面图.综合分析各段的阶地级数、高度、年代及变形特征得到以下认识:该流域可划分为若干个次级活动地块,表现在不同地块之间的阶地抬升幅度和速率存在较大差别;活动地块内部在较大程度上具刚性特征,表现在块体内部阶地级数、高度和形成年代基本相当;阶地纵剖面反映的本区活动地块自1.6Ma B.P.以来的抬升量大于3.6～1.6Ma B.P.的抬升量;柴达木-祁连山活动地块距今1万年以来和15～20万年间存在2次强烈的构造抬升运动.

关键词: 黄河, 河流阶地纵剖面, 活动地块, 构造隆升, 主夷平面