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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. Plain Language Summary: 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. Key Points: 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 [ABSTRACT FROM AUTHOR]

The uplift and deformation styles of the Tibetan Plateau have been long debated on stepwise growth and crustal channel flow. Here, we offer new insight into this issue by constraining the pulsed exhumation history of the Yalong thrust belt in eastern Tibet, using apatite and zircon (U–Th)/He data from three ∼1 km vertical transects. The results revealed two rapid cooling pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35 °C/m.y.), respectively, which we ascribe to the staged‐thrusting faulting of this belt. These thrust faulting events indicated upward and eastward growth of the Tibetan Plateau, further suggested that the high topographic relief across the Yalong thrust belt mainly formed (at least) since the Late Oligocene. The available documents from paleoaltimetry, basin sediment accumulation, and thermochronometers and our new results reveal a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet. Plain Language Summary: The role of faulting in crust thickening has been one of the main controversies in the formation and evolution of the Tibetan Plateau. The Yalong thrust belt in eastern Tibet is a major Cenozoic structure with a 1.8–2.4 km topographic step, and its deformation processes are closely associated with the Cenozoic eastward plateau growth. In this study, we report 79 apatite and 78 zircon (U–Th)/He (AHe and ZHe) ages of 26 granitoid samples from three ∼1 km vertical transects. We suggest that the Yalong thrust belt underwent two rapid cooling (exhumation) pulses in the Late Oligocene (∼24 Ma, 50°C/m.y.) and the Middle Miocene (17–14 Ma, 35°C/m.y.), respectively. These pulses of exhumation and uplift along the Yalong thrust belt contributed to the development of the current morphology across eastern Tibet. Integrating previous findings and those reported in our study allow us to propose a regional‐scale stepwise propagation pattern of tectonic deformation during the Middle–Late Cenozoic in eastern Tibet. We suggest that the dynamic development of the deformation pattern may have been driven by the northward indentation of the Eastern Himalayan Syntaxis and the consequent lower crustal flow into southeastern Tibet. Key Points: The Yalong thrust belt underwent two rapid cooling pulses in the Late Oligocene (∼24 Ma) and Middle Miocene (17–14 Ma)The topographic relief across the Yalong thrust belt is mainly the result of pulsed thrusting at least since 24 MaA regional‐scale stepwise propagation pattern was proposed for the Middle–Late Cenozoic tectonic deformation in eastern Tibet [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP), often known as the "Asia Water Tower", is the source region of several continental-scale rivers. However, due to the extremely difficult access and harsh living conditions in the interior plateau, fluvial processes in the headwaters of these large rivers and their connections to global climate changes remain unknown. In this study, the luminescence (using both quartz and K-feldspar) and AMS 14C dating techniques were employed to date the four terraces of the Zado Basin in order to elucidate the aggradation and incision history of the initial intermontane basin in the headwater of the Mekong River. One sample from the upper part of T4 terrace (which features a 12 m thick gravel layer, the base of which is unexposed) provides a K-feldspar pIR 50 IR 225 age of 125 ± 10 ka, indicating that the initial deposition of this terrace could predate marine isotope stage (MIS) 5. Considering the margin of error, this age also suggests that the onset of incision on T4 terrace during the climate transition from MIS 6 (glacial) to early MIS 5 (interglacial). This incision likely occurred due to increased meltwater and precipitation, causing the Mekong carving into the bedrock for more than 50 m. Eight luminescence samples are collected from T3 terrace (26.5 m in thickness) with ages ranging from 83 ± 7.6 ka to 22.3 ± 1 0.2 ka, indicating T3 formation/aggradation from late MIS 5 to the Last Glacial Maximum (LGM), possibly owing to reduced precipitation and enhanced sediment supply from intensive glacial activities. At around 22 ka, the Mekong once again shifted towards incision, crafting the T3 terrace, situated roughly 28 m above the current floodplain. This incision event was recorded by two luminescence samples from a sandy lens located at the top of gravel layer of T3, with OSL ages of about 22 ka. Floodplain samples from T2 and T1, dated at 16 ka and 2.8 ka respectively, demonstrate that from the last deglaciation to the Holocene, the Mekong continued its downward incision. This erosion developed two cut and fill terraces at elevations of 22 m and 11 m above the present floodplain, likely due to increased precipitation and enhanced vegetation at that time. Overall, the glacial–interglacial climate changes were the most likely driving force behind fluvial processes in the upper Mekong basin since the Late Pleistocene, with aggradation occurring during the glacial period while incision in deglacial and interglacial periods, suggesting a close link between the fluvial geomorphic evolution and orbital-scale climate changes. • Four Mekong River terraces in the Zado Basin of Tibet were dated by luminescence. • At c. 125 ± 10 ka T4 incision (into bedrock by > 50 m) initiated due to global warming. • T3 has been deposited since 83 ka and began downcutting at ∼22 ka in deglacial. • These terraces generally accumulate during glacial and cut down since deglacial. [ABSTRACT FROM AUTHOR]

The Dadu River in the eastern Tibetan Plateau has the potential to record transient variations of tectonic uplift since the Late Cenozoic. In this study, we extracted bedrock channels of the Dadu River drainage basin from the 30 m ASTER digital elevation model. The longitudinal river profiles were then analyzed, and three generations of knickpoints were recognized via the slope area method. By solving the analytical solution of the linear transient stream power incision model, we determined a Late Cenozoic history of regional tectonic uplift. The results reveal slow pre–middle Miocene uplift rates (<0.1 mm/a) and then increased gradually to 0.33 ± 0.03 mm/a since 12–15 Ma until present. This increase of uplift rate from bedrock channel inversion is consistent with the regional findings of low‐temperature themochronology, emphasizing the potential and significance to utilize channel profiles to infer the tectonic uplift history. Plain Language Summary: Recently, numerous thermochronology studies have provided constraints on the timing of rapid denudation along the eastern Tibetan Plateau. However, the rates of denudation/uplift determined by thermochronological profiles are often given as an average since a certain time duration. Thus, it is difficult to quantify the history of the tectonic uplift and whether uplift has been uniform or varied through time. We used the linear simulation method and inverted the longitudinal river profiles to decipher the Late Cenozoic uplift history of the eastern Tibetan Plateau. The results reveal that before the middle Miocene, the uplift rate was slow (<0.1 mm/a), and it increased gradually to 0.33 ± 0.03 mm/a since 12–15 Ma until present. Key Points: Linear inversion of the longitudinal river profiles for Tibetan Plateau uplift historyIncrease of the uplift rate since 12-15 Ma, consistent with regional resultsNew evidence of the late Miocene tectonic uplift in eastern Tibet [ABSTRACT FROM AUTHOR]