Early Cenozoic Drainage Evolution and Surface Uplift of the Eastern Tibetan Plateau: Insights From the Ninglang Basin

The modern high topography of the eastern Tibetan Plateau is drained by several of the largest rivers on Earth, and exerts a prominent influence on the Asian monsoon pattern. However, when the high terrain was formed remains highly debated. Here, we present detrital zircon U-Pb ages that indicate a south-flowing drainage system with distal headwaters passed through the Ninglang Basin at ca. 45 Ma. We advocate for early-middle Eocene surface uplift in the Gonjo Basin and areas to the west creating a southeast tilted topography across eastern Tibet. The termination of sedimentation at ca. 40 Ma implies that the river system had deviated from the Ninglang Basin, which we interpret as a result of rise of the Yalong-Yulong thrust belt. Combined with other lines of evidence from previous studies, we support the establishment of moderate-high elevation topography of eastern Tibet by late Eocene time. The eastern Tibetan Plateau has been a hotspot for studying the interactions between tectonic uplift, monsoon evolution, Asian biodiversity, and topographic development during continental collision. However, the timing of high-elevation topography formation in eastern Tibet is a matter of debate, with age estimates ranging from middle Eocene to late Miocene. This directly leads to contradictory understanding of uplift processes and plateau growth mechanisms. Sedimentary basins are excellent recorders of past drainage pattern and tectonic process, while many Cenozoic basins in eastern Tibet have been understudied. Here we focus on the Ninglang Basin and carry out comprehensive research including stratigraphy, sedimentology, chronology, and provenance analysis. We indicate that the Ninglang Basin was mainly supplied by a south-flowing exterior drainage system during the middle Eocene, implying the existence of a regional, low-gradient landscape beveling to the southeast at that time. The extinction of this drainage system in late Eocene time likely means the initiation of the Yalong-Yulong thrust belt, a major boundary fault system in eastern Tibet. Our study thus support that the topography of eastern Tibet has been elevated in the late Eocene. A large-scale, south-flowing fluvial system drained through the Ninglang Basin during the middle EoceneThe demise of the Ninglang Basin in the late Eocene resulted from the uplift of the Yalong-Yulong thrust beltThe elevated terrain of eastern Tibet was initially formed in the late Eocene