Abstract: In tectonically active regions, geomorphic features such as fluvial terraces can be interpreted as the consequence of tectonic and climatic forcing. However, deciphering and distinguishing tectonic impacts and climate changes remain a challenge. In this study, we examine the terraces along the Hongshuiba river and Maying river, which flow across the Fudongmiao-Hongyazi fault in the northern margin of the Qilian Mountains. Our purpose is to analyze the relative roles of tectonics and climate in shaping orogenic topography in this area. 8~9 levels of river terraces were identified through field observations, interpretation of satellite images and using DEMs. According to relative heights and ages of T₅ of the Hongshuiba river and T₆ of the Maying river, the incision rates are calculated to be (10.2±2.0)mm/a and (12.2±2.8)mm/a, respectively. Furthermore, the thrust rate along the Fodongmiao-hongyazi fault was determined based on offset terraces and OSL dating, which are ten times less than river incision rates approximately. Comparing the uplift rate and incision rate in the northern margin of the Qilian Mountains and adjacent areas, we inferred that climate change is the most plausible controlling factor in the evolution of the river terraces, while tectonics plays a minor role in this process.

Key words: Fluvial terraces, Tectonics, Climate change, Holocene, Northern margin of the Qilian Mountains

摘要： 河流阶地作为构造和气候作用的载体，记录了活动造山带地区的构造活动和气候变化之间的相对变化信息。文中以穿过祁连山北缘活动断裂带的洪水坝河和马营河为例，探讨河流地貌发育与构造和气候之间的关系。基于遥感影像解译识别出8—9级河流阶地，并对其期次进行划分。根据洪水坝河T₅和马营河T₆阶地的相对拔河高度和年龄，分别计算出2条河流15ka和11ka以来的平均下切速率为（10.2±2.0）mm/a和（12.2±2.8）mm/a。再利用差分GPS分别对2条河流的T₅和T₆阶地面上的断层陡坎进行精确测量，结合测年结果，计算出佛洞庙-红崖子活动断裂的垂直滑移速率比河流下切速率低1个量级。对比研究区内活动断裂两侧阶地发育序列的差异性，构造抬升和河流下切速率数量级的差别，并结合祁连山北缘区域上已发表的研究结果，初步认为构造活动与气候变化共同影响祁连山北缘河流阶地的发育，其中气候变化是控制该区全新世河流阶地发育的主要因素。更深入的活动构造调查和阶地年龄约束有助于更好地揭示祁连山北缘的活动构造特征和河流演化历史。

关键词: 河流阶地, 构造活动, 气候变化, 全新世, 祁连山北缘