Formation of broad-valley morphology triggered by uplift of Yulong-Haba Snow Mountains in the First Bend reaches of the Jinsha River, upper Yangtze River, SE Tibet Plateau

The southeast Tibetan Plateau (SETP) was marked with strong neotectonics due to the collision of Asia-Europe plate and Indian plate. However, different from the SETP morphology characterized by high mountains and deep-narrow valleys, broad-valley was developed in the First Bend (Shigu Town) reaches of the Jinsha River, uppermost Yangtze River. Simultaneously, an ancient channel was filled and buried with thick gravel layer in broad-valley area. Based on the geological and geomorphic investigation of the Jinsha River broad-valley, combined with its sedimentary geochronology and river bedrock profile variation, as well as the activities of the adjacent faults and uplift style and rate of the Yulong-Haba Snow Mountains, the comprehensive results showed that the broad-valley formation and thick sedimentary development were controlled by the eastern piedmont fault of Yulong-Haba Snow Mountains: the Deqin-Zhongdian-Daju-eastern piedmont fault of Yulong Mountains (DZDYF). The DZDYF was the west border of the Sichuan-Yunnan Rhombic Block with strong activities. Since the early Pleistocene, the rapid continuously asymmetric uplift of the Yulong-Haba Snow Mountains (YHSM) changed the hydrologic condition of the Jinsha River, formed a subsidence center in west Jinsha River channel of the YHSM. In this area, the current slows down and the valley becomes broad, the ancient channel was filled and buried by accumulated sedimentary. At east area of the YHSM, with the trenching incision of the Jinsha River, the knickpoint of the eastern piedmont fault of Yulong-Haba Snow Mountains migrated to west continuously. Affected by lithology of the YHSM, seven knickpoints were developed in Tiger Leaping Gorge.