雅鲁藏布江大峡谷的形成

通过对雅鲁藏布大峡谷流域地貌形成响应时间域的定量估算，大峡谷与上游河道特征的对比，以及大峡谷入口处河湖阶地的沉积分析和定年研究，结合构造研究的新进展和数值地貌分析成果，系统论证了雅鲁藏布大峡谷的形成。研究结果表明，现今的雅鲁藏布大峡谷与大峡谷上游的河道在大峡谷形成之前分属不同的河流体系，大约在距今30ka BP前后，原属于帕隆藏布江水系支流的扎曲—直白河段因溯源侵蚀，袭夺了位于现今直白河段上游的古雅鲁藏布江水系，使得此前向南经南伊沟（纳伊普曲）流出高原的古雅鲁藏布江与帕隆藏布江合二为一，雅鲁藏布大峡谷得以贯通和强烈的侵蚀下切，形成现今著名的大峡谷和大拐弯式样的流域结构。

Formation of the Yarlung Zangbo Grand Canyon, Tibet, China

The authors have quantitatively estimated the time scale of the geomorphologic response of the Yarlung Zangbo Grand Canyon, correlated the features of the Grand Canyon and the river courses of its upper reaches and performed sediment analysis and dating of terraces at the entrance of the Grand Canyon. On that basis, combined with the recent progress in tectonic study and numerical analysis of geomorphologic features, the authors have demonstrated systematically the formation of the Yarlung Zangbo Grand Canyon. The study shows that the present-day Yarlung Zangbo Grand Canyon and the river courses in its upper reaches belonged to two different river systems before the formation of the Grand Canyon. About 30 ka BP, the Za Qu-Zhibai River—a tributary of the Parlung Zangbo system—captured the paleo-Yarlung Zangbo (which is presently located in the upper reaches of the Zhibai River) due to head erosion; as a result, the paleo-Yarlung Zangbo River, which originally flowed southward through the Nanyi valley (Nayipu Qu) out of the ancient highland, joined the Parlung Zangbo and then the Yarlung Zangbo Grand Canyon came to being and eroded downward intensely, thus forming the drainage structure of the present famous Grand Canyon and big bend.