Abstract: The most compelling phenomena for transverse drainage in active fold belt are lateral diversion of channels and development of water/wind gaps. This phenomenon is the result of competition between uplift and erosion, which is controlled by fault vertical/lateral propagation and segment linkage, fault geometry, climate condition and lithology. Previous studies found that the higher the uplift rate is, the greater number of wind gaps form, and the variation of the uplift rate is also critical to the sustainability of transverse rivers. Lateral propagation and linkage of several separate folds in fold-and-thrust belts will lead to defeat of streams and diversion into a trunk drainage; if the trunk is still unable to keep pace with uplift, water gap will be abandoned and left as a wind gap. For lateral propagation of an anticline associated with development of tear faults, the locations of wind/water gaps are likely to coincide with the trace of tear fault and it's not quite clear about the relation between tear faulting and stream deflection. Nonzero dip of the underlying detachment induces a lateral surface slope in the direction of fault propagation, which in turn makes rivers deflection more efficient. Climate and rock erodibility control the water/sediment discharge, and further influence river transport/incision capacity. The changing climate and rock erodibility conditions enable river to abandon the current waterway to create a wind gap unless they could down-cut through a growing fold. However, the role of climate cycle in the formation of wind gap is still controversial. In addition, wind gaps are commonly developed along the divides where parts of longitudinal river have been captured by transverse catchments. Generally, the development of transverse drainages and the formation of wind gaps in nature are result from a combination of tectonic and fluvial process. The wind gap pattern and transverse drainage evolution in fold-and-thrust belts contain plenty of information on fault growth, interaction between tectonic uplift and fluvial erosion, and development of sedimentary basin. Such researches have significant implications in geomorphology, seismic hazard assessment and hydrocarbon exploration. However, there are still many knowledge gaps on the study of transverse river evolution in active fold areas. First, adequate chronology and geomorphic/strata mark to quantify fold growth and erosion is commonly not available, which leads to a poorly constrained rate in both river incision and lateral propagation of growing folds. In addition, more geological and geomorphological processes could influence the evolution of transverse drainages. For examples, (1)during the formation of a young range or anticline, the mechanism of fault-related folding may change over time, e.g. from fault-propagation folding to surface breaking; (2)Besides the knickpoint retreat in downstream, efficient lateral planation and downstream sweep erosion are also important in understanding the erosion of folds by rivers flowing through it. These processes make the development of transverse drainage across folds more complex and should be considered in more comprehensive models. There are lots of rivers originating from the Tibetan plateau and cutting through young surrounding mountains. These surrounding mountains, such as Qilian Mountains, Tianshan Mountains and Longmen Mountains, are ideal areas for the study of transverse river evolution and wind gap formation. In the end, combining with the geological and geomorphological features of the Heli Shan-Jintanan Shan, north of Hexi Corridor, we propose that the Heihe River has experienced deflection, beveling and incision since Mid Pleistocene. These processes have led to 1)the formation of a wind gap on the western Heli Shan, 2)a layer of fluvial gravels from the Qilian Shan preserved on the top surface of the Jintanan Shan, and overlying angular unconformity upon older strata, and 3)the incision of the Heihe River to form the Zhengyi Gorge through the linked structure between Heli Shan and Jintanan Shan. Thus, we propose a general model for the development of transverse drainages in the central Hexi Corridor: deflection-beveling-incision.

Key words: fold growth, transverse drainage, wind gaps, Heihe River, Heli Shan, Jintanan Shan

摘要： 河流偏转和风口发育是横向河流域最显著的地貌现象, 其形成体现着区域抬升和河流侵蚀间的平衡, 并受控于断层侧向生长、 连接与几何形态等构造过程以及影响河流侵蚀的气候和岩性要素。 风口与横向河网的演化可用于评估相关断层活动的速率和方式, 探索河流侵蚀与构造抬升之间的相互作用以及复杂环境下沉积系统的形态, 研究成果对地貌学、 地震灾害、 油气储藏等学科领域具有重要的理论意义。 文中围绕影响风口形成与保存的地质地貌过程, 对过去20a活动褶皱区域的横向河演化研究案例进行了初步总结。 最后以河西走廊地区的合黎山-金塔南山为例, 探讨在褶皱隆起和水动力变化的条件下黑河在该区域的演化过程。 分析认为现代黑河约1.1Ma BP穿过合黎山, 而随着合黎山的生长、 黑河水动力条件的变化, 黑河偏转到达金塔南山区域; 由于合适的水沙比与抬升速率, 金塔南山区域早期抬升时处于夷平状态; 约0.23Ma BP以来, 大部分支流无法到达金塔南山区域, 黑河在金塔南山与合黎山连接的区域下切, 形成正义峡。

关键词: 活动褶皱, 横向河, 风口, 黑河, 合黎山, 金塔南山