Eastern Himalayan Syntaxis Research Articles

New Late Cretaceous Paleomagnetic Results From the Eastern Qiangtang Terrane: Implications for the Postcollisional Extrusion and Convergence of the Southeastern Tibetan Plateau

AbstractTo refine the postcollisional extrusion and convergence history of the southeastern Tibetan Plateau, we report a quality paleomagnetic data set from Upper Cretaceous redbeds of the eastern Qiangtang Terrane (QT), where is situated at the front edge of eastern Himalayan Syntaxis. The 32 site‐mean directions provide a mean pole at 75.4°N, 176.8°E (A95 = 2.4°) and a paleolatitude of 31.8 ± 2.4°N for the Mangkang area. Comparison with reliable Late Cretaceous paleomagnetic data from the eastern QT and East Asia indicates that the eastern QT experienced a southward extrusion of 940 ± 310 km after the Late Cretaceous. Comparing Late Cretaceous paleolatitudes estimated from the eastern QT and Lhasa terrane (LT) reveals a paleolatitude difference of 2,390 ± 620 km. Such a great latitudinal convergence can be attributed to the fact that some continental terranes originally located between the eastern LT and QT were laterally extruded after the Late Cretaceous.

Cenozoic faulting of the Ganzi-Yushu (Xianshuihe) fault from apatite (U-Th)/He ages and its implications for the tectonic reorganization in the southeastern Tibetan plateau

The Ganzi-Yushu-Xianshuihe fault that lies along the northeastern boundary of the Chuan-Dian crustal fragment provides the opportunity to study the tectonic evolution and geodynamic mechanisms of the southeastern Tibetan Plateau. Apatite (U-Th)/He data from an elevation transect provide robust evidence for the initiation of the Ganzi-Yushu fault. The consistent AHe ages of the lower samples constrain the onset of fault activity to 9.4 ± 1.5 Ma. Moreover, the zircon U-Pb dating and rare earth element (REE) analysis confirm that the Queer Shan and Gaogong granitic plutons were emplaced as a whole and then displaced by the Ganzi-Yushu fault. Combining the total offset of these two plutons and the onset timing of the fault activity yields a long-term average left-lateral strike-slip rate of 7.3–10.8 mm/yr for the Ganzi-Yushu fault. Based on the summarized synchronous deformation in the southeastern Tibetan Plateau, including the initiation of fault activity along the whole Ganzi-Yushu-Xianshuihe fault, the slip reversal of the Red River fault, and the fault activity along a series of left-slip faults in the Indochina block, we suggest that the southward extrusion of the Chuan-Dian crustal fragment and clockwise rotation around the Eastern Himalayan Syntaxis initiated at the middle-late Miocene (15-10 Ma).

Contemporary crustal strain rates derived from GPS measurements in southwestern China

Surface strain rates in southwestern China can provide constraints on tectonic evolution of the Tibetan Plateau. Unfortunately, different strain rate fields were obtained from different authors although almost the same GPS data were exploited. Based on updated GPS data, in this paper, we calculate the strain rates in southwestern China using the method proposed by Zhu et al. (2005, 2006). The results confirm that the strain rates in the Sichuan Basin and the South China Block are very small, and the high values are largely concentrated along the Xianshuihe-Anninghe-Xiaojiang fault system and the Sagaing Fault. Furthermore, the highest principal strain rates are located around the eastern Himalayan syntaxis (EHS), with compressive orientations perpendicular to the strike of the Main Thrust Belt. The basic characteristic of the strain rate distribution is in accordance with the tectonic structures from the geological and geophysical investigations. In particular, the two calculated extensive deformation regions basically match the locations of normal-faulting earthquakes in the Sichuan-Yunnan Rhombic Block (SYRB), with one in N-S extension trending in the northern SYRB, and the other nearly E-W orientation in the southern SYRB. We suggest that the extensive deformation and the normal faulting earthquakes in southwestern China is mainly controlled by the lower crustal channel flow with a bend direction, rather than by gravitational spreading alone, as previous authors proposed.

Crust and Mantle Flow From Central Tibetan Plateau to the Indo‐Burma Subduction Zone

AbstractThe extremely oblique Indo‐Burma subduction zone exhibits dextral strike‐slip faulting along the Sagaing, Kabaw, and Churachandpur‐Mao Faults as well as east‐west shortening between the Sagaing Fault and Bengal Basin. Through regional stress analysis, considering areas from central Tibet, around the eastern Himalaya Syntaxis, to Burma, it has been determined that the principal compressive stress directions align with the principal strain rates. The northeast‐southwest oriented compressive stress direction from the western Shan Plateau continues into Burma. Notably, P axes align with the topographic gradients, and T axes are sub‐parallel to the topographic contours in the Shan Plateau region south of 27°N. These stress patterns are consistent with a gravitational potential energy induced crustal and mantle flow. The alignment of the fast shear wave with the maximum strain rate and the colinear NW‐SE to E‐W fast direction of the SKS wave and T axis determined from focal mechanisms in the Shan Plateau suggest that the mantle lithosphere deforms in concert with the crust. We suggest crust and mantle flow south of the Red River Fault has resulted in widening of the lithosphere in the Shan Plateau in an east‐west direction. Therefore, the Sagaing Fault has bowed approximately 50–100 km westward if we assume that the Sagaing Fault was originally straight. Our results of regional stress inversion are consistent with late Miocene to present E‐W shortening in the Indo‐Burma subduction zone resulting from the release of gravitational potential energy from the central Tibetan Plateau.

Dynamic Characteristics of the Long Runout Rock‐ice Avalanche at High Altitude—A Case from the Zelongnong Basin, Eastern Himalayan Syntaxis, China

AbstractRock‐ice avalanches have frequently occurred in the Eastern Himalayan Syntaxis region due to climate change and active tectonic movements. These events commonly trigger catastrophic geohazard chains, including debris flows, river blockages, and floods. This study focuses on the Zelongnong Basin, analyzing the geomorphic and dynamic characteristics of high‐altitude disasters. The basin exhibits typical vertical zonation, with disaster sources initiating at elevations exceeding 4000 m and runout distances reaching up to 10 km. The disaster chain movement involves complex dynamic effects, including impact disintegration, soil‐rock mixture arching, dynamic erosion, and debris deposition, enhancing understanding of the flow behavior and dynamic characteristics of rock‐ice avalanches. The presence of ice significantly increases mobility due to lubrication and frictional melting. In the disaster event of September 10, 2020, the maximum flow velocity and thickness reached 40 m/s and 43 m, respectively. Furthermore, continuous deformation of the Zelongnong glacier moraine was observed, with maximum cumulative deformations of 44.68 m in the distance direction and 25.96 m in the azimuth direction from March 25, 2022, to August 25, 2022. In the future, the risk of rock‐ice avalanches in the Eastern Himalayan Syntaxis region will remain extremely high, necessitating a focus on early warning and risk mitigation strategies for such basin disasters.

Hydrochemical appraisal and suitability for irrigation and portable purposes in eastern Himalayan syntaxis of Tibet Plateau

The formation mechanism and quality evaluation of surface water and groundwater have provided valuable information on water management of alpine catchment, such as Tibet Plateau. However, scarce knowledge of surface water and groundwater has been achieved from Eastern Himalayan syntaxis in eastern Tibet due to harsh and complicated natural and geological conditions. This study collected 60 water samples from the Layue alpine catchment within Eastern Himalayan syntaxis, including 35 samples of groundwater and 25 of surface water. A combination of multivariate statistical analysis, ion ratio analysis, geochemical modeling, hydrogen and oxygen isotope analysis, and water quality index (WQI) analysis was employed to explore hydrochemical processes and irrigation and portable suitability. Results indicate that the groundwater types identified include bicarbonate-calcium, sulfate·chlorine-sodium, and mixed bicarbonate-calcium·sodium, while surface water are sulfate·chlorine-sodium, mixed bicarbonate-calcium·sodium, and mixed chlorine-calcium·magnesium types. Groundwater recharge primarily originates from meteoric precipitation, with recharge elevations ranging from 2216 to 3698 m, while surface water receives both precipitation and groundwater recharge in a proportion of 50.51%–87.96%. Silicate weathering and carbonate dissolution predominantly control the hydrochemical compositions. Sodium adsorption ratios (0.75–88.55) and electrical conductivity (85.20–1686.12 μs/cm) indicate water resource are mostly suitable for irrigation. The entropy-weighted water quality index (97% in total <100) denotes the suitability for portable use. These achievements would provide substantial support for the sustainable water management in alpine areas, especially for Tibet Plateau.

Abrupt topographic descent at the eastern end of the Himalayan orogen: Insights from geodetic analyses

The Indian-Eurasian convergence has formed the Himalayas, one of the most youthful and dynamic orogeny on Earth, which is characterized by a unique “perfect arc” observed by seismicity, crustal deformation, and topographic relief. However, the presence of a significant topographic descent at the eastern end of the Himalayas, near the Eastern Himalayan Syntaxis (EHS) challenges the existing paradigm. The reason behind such significant topographic difference compared to other regions along the Himalayan mountains is still unclear. Based on the GPS velocity field, we determined the clockwise rotation of the North Indian Block (NIB) relative to the stable India plate with a Euler pole estimation of (89.566 ± 0.06°E, 26.131 ± 0.05°N, 1.34 ± 0.11°/Myr), implying that the NIB has broken away from the stable India plate. By reconstructing the position of the Northeast Indian Block (NIB) based on the Euler pole, we found that the collisional boundary between India and Eurasia is moving southward. Subsequently, a coupled fault model that accounted for continuous motion of fault can effectively match the topographic descent. Our result underscored the significant impact of the NIB rotation on regional geological evolution, an aspect that has received less attention in previous studies.

Responses of geomorphic indices to the northward migration of the Eastern Himalayan syntaxis

The Eastern Himalayan Syntaxis (EHS), featured by an exceptionally intense compression orogeny and an extremely rapid surface erosion rate, stands out as a prime area for investigating surface processes and landscape evolution. Understanding the formation of the EHS holds significant importance in advancing our comprehension of the evolutionary dynamics within the Tibetan Plateau and the complex interplay between endogenic and exogenic geological processes. Currently, two models, namely the tectonic aneurysm and the syntaxis expansion model, have been proposed to explain the formation and evolution of this syntaxis. In this study, we employ a multi-disciplinary approach, integrating geomorphic indices such as slope, relief, hypsometric integral (HI), normalized channel steepness (Ksn), river slope-basin area integration (χ), Gilbert metric, combined with erosion rates on long-medium-short term timescales obtained from thermochronology, cosmogenic nuclides 10Be and landslide disaster probability data. Our findings suggest a relatively high tectonic activity in the confluence of the Yigong and Parlung Rivers in the northern end of the syntaxis. Moreover, our data reveals that spatial variability of tectonic activity is the primary driver of regional geomorphologic features and the spatial-temporal characteristics of erosion observed in the EHS, with lithology and climatic precipitation playing a lesser role. Furthermore, the northward migration of the EHS appears to elucidate the shift of tectonic activity and rapid erosion from the core of the syntaxis near the Namche-Barwa towards the confluence of the Yigong and Parlung Rivers. This northward migration of the EHS underscores the need for increased attention to the high geological hazard risk in the northern part of the EHS.

Single‐Stage Synchronous India‐Asia Collision Model Revealed by Himalayan High‐Pressure Metamorphic Rocks

AbstractDespite a half‐century of intense research, the timing and diachroneity of initial collision between India and Asia remain highly debated, largely due to different definitions of “initial collision” and correspondingly different methods adopted. This study focuses on high‐pressure pelitic granulites of the Eastern Himalayan Syntaxis (EHS) to elucidate their metamorphic evolution and provide new constraints on the timing of initial India‐Asia collision. Petrological examination and phase equilibria modeling show that high‐pressure pelitic granulites have undergone four metamorphic stages, with the peak assemblage of garnet + K‐feldspar + kyanite + biotite ± plagioclase ± rutile + ilmenite + quartz at P‐T conditions of 13.1–15.7 kbar and 790–850°C. Clockwise P‐T paths suggest that the Indian continent underwent tectonometamorphic processes of initial collision and subsequent continent subduction. Zircon and monazite dating results indicate that the metamorphic ages of pelitic granulites range from 60 to 15 Ma, with the oldest ones clustered at 60–58 Ma. The oldest metamorphic ages of high‐ to ultrahigh‐pressure Himalayan metamorphic rocks can provide an upper age limit of the initial collision. Therefore, the initial India‐Asia collision must have occurred before 60–58 Ma in the EHS, roughly consistent with ca. 57 Ma in the western Himalaya and 63–60 Ma in the central Himalaya. Collectively, we conclude that the northern margin of India most likely underwent a single‐stage synchronous collision with the southern margin of Asia initially at around 60 Ma along the entire Yarlung‐Tsangpo suture zone.

Spatial distribution law of landslides and landslide susceptibility assessment in the eastern Himalayan syntaxis region

The eastern Himalayan syntaxis region is located on the eastern edge of the Qinghai–Tibet Plateau, and it is one of the regions with the most intense geological tectonic activity in the world. There have been many large-scale landslides in the eastern Himalayan syntaxis region and the distribution of these landslides is of great significance for the inversion of regional tectonic activity strength, major engineering construction and urban–rural planning. However, no researchers have systematically studied all these landslides of this area. In this study, based on Google Earth satellite imagery, landslides were identified using artificial visual interpretation. Then, we analysed 11 landslide-influencing factors were selected, comprising topographic factors (elevation, slope, aspect, curvature), geological environmental factors (strata, distance to faults, distance to water, distance to roads, normalized difference vegetation index), inducing factors (peak ground acceleration, rainfall), the relationships between the distribution law of landslides and influencing factors. Finally, we used the logistic regression model, the weight of evidence model and the weight of evidence–logistic regression coupled model to evaluate the landslide susceptibility.

Slab Tear of Subducted Indian Lithosphere Beneath the Eastern Himalayan Syntaxis Region

Slab Tear of Subducted Indian Lithosphere Beneath the Eastern Himalayan Syntaxis Region

Onset of Mid-Pleistocene glaciation in the Eastern Himalayan syntaxis

The Tibetan Plateau contains the largest numbers of glaciers outside the polar regions, yet the initiation times of glacial advances remain unclear. The potential relics of original moraines might be preserved in the sedimentary basins. Here, we present sedimentological and geochronological data from five boreholes located upstream of the Tsangpo Gorge, Eastern Himalayan Syntaxis. Our findings reveal that fluvial sediment accumulation began over 2.5 million of years ago due to enhanced rock uplift downstream, and extensive glacial advances occurred after ~0.75 million of years. Notably, the earliest extensive glacial advance (~0.75 million of years) is considerably younger than the formation of the Tsangpo Gorge (>2.5 million of years). Following the initiation of this glacial advance, the Eastern Himalayan Syntaxis experienced rapid exhumation of approximately 1.3–1.6 kilometers. Such geomorphological processes and exhumation history suggest that rock uplift, rather than glacial damming, played a pivotal role in maintaining the stability of the knickpoints on the southeastern margins of the Tibetan Plateau.

Structural features and Holocene activity of the Motuo fault zone, eastern Himalaya syntaxis

The Motuo Fault zone (MTF), the southeast boundary of the eastern Himalaya syntaxis, is an important information carrier to understand the present-day kinematics and geodynamics of the Tibetan Plateau. However, little knowledge has been obtained about its Holocene activity and structural features of the MTF due to the ubiquitous vegetation covering. Interpretations of satellite imageries, outcrop and trench observations, together with the radiocarbon and Optically Stimulated Luminescence (OSL) dating results reveal that (1) the MTF consists of multiple NE–SW-trending branch faults, forming a wide fault system that could be generally divided into the western segment, central segment and eastern segment; (2) the drainage systems, mountain ridges and alluvial fans have been systematically left-laterally deflected or offset along the MTF; (3) two surface-rupturing earthquakes occurred close to or slightly earlier than 9.41 ± 0.94 ky BP and after ∼1540 yr BP, respectively, indicating that the MTF is an Holocene active fault. Due to the very limited exposure, it is quite possible that many paleoseismic events have not been revealed by this study and previous publications. For a better understanding and assessment of the seismogenic behavior of the MTF, a complete paleoseismic sequence and reasonable earthquake recurrence model need to be set up, especially considering the complex geometry of the fault system that probably suggests intricate fault rupturing.

The Dynamics of the India‐Eurasia Collision: Faulted Viscous Continuum Models Constrained by High‐Resolution Sentinel‐1 InSAR and GNSS Velocities

AbstractThe distribution and magnitude of forces driving lithospheric deformation in the India‐Eurasia collision zone have been debated over many decades. Here we test a two‐dimensional (2‐D) Thin Viscous Shell approach that has been adapted to explicitly account for displacement on major faults and investigate the impact of lateral variations in depth‐averaged lithospheric strength. We present a suite of dynamic models to explain the key features from new high‐resolution Sentinel‐1 Interferometric Synthetic Aperture Radar as well as Global Navigation Satellite System velocities. Comparisons between calculated and geodetically observed velocity and strain rate fields indicate: (a) internal buoyancy forces from Gravitational Potential Energy acting on a relatively weak region of highest topography (&gt;2,000 m) contribute to dilatation of the high plateau and contraction on the margins; (b) a weak central Tibetan Plateau (∼1021 Pa s compared to far‐field depth‐averaged effective viscosity of at least 1022–1023 Pa s) is required to explain the observed long‐wavelength eastward velocity variation; (c) localized displacement on fault systems enables strain concentration and clockwise rotation around the Eastern Himalayan Syntaxis. We discuss the tectonic implications for rheology of the lithosphere, distribution of geodetic strain, and partitioning of active faulting and seismicity.

Assessing geological hazard susceptibility and impacts of climate factors in the eastern Himalayan syntaxis region

Assessing geological hazard susceptibility and impacts of climate factors in the eastern Himalayan syntaxis region

Landscape modelling of the Yalong River catchment during the uplift of Southeast Tibet

Southeast Tibet is characterized by low-relief surfaces at high-elevation, showing very little exhumation during the India–Asia collision, as well as deeply incised rivers valleys. Understanding how these low-relief surfaces adjacent to the plateau's edge survived from regressive fluvial erosion is still an enigma, which is key to understanding the formation of the plateau. In the Three Rivers Region around the Eastern Himalayan Syntaxis, the squeezing of the Salween, Mekong and Yangtze rivers’ drainage basins in their middlestream, where numerous thrusts parallel to the river channels are observed, has been invoked as the key factor driving the river evolution. More to the east, in the Great Bends Region, no such squeezing of the drainage basins has been observed; the Yalong and Yangtze rivers flow perpendicularly across northeast-trending thrust belts, generating huge (>100 km) river course bends with steep channel slopes. These faults have significantly contributed to construct the high plateau margin, including the Yalong Thrust Belt (YTB), active during the Eocene (∼35–25 Ma) and reactivated in the Miocene (15–12 Ma). By applying state-of-the-art landscape modelling (FastScape) to the Yalong River catchment, with simplified rock uplift scenario deduced from fault activities, we show that strong monsoonal precipitation on the plateau (∼1 m/yr), even during only a short period such as the Mid–Miocene Climatic Optimum (17–14 Ma), produces wide rivers and destroys the plateau edge. In contrast, modelling the orographic effect with weak net precipitation (∼0.2 m/yr) above ∼2700 or 4000 m, preserves the plateau edge and reproduces the slope of the Yalong River, but with a width larger than in nature. To reproduce both the slope and narrowness of the Yalong gorge just upstream of the YTB, a combination of a rapid Miocene rock uplift leading to a regional surface uplift, which creates a significant orographic effect and preserves interfluve low-relief surfaces close to the plateau edge, and a water inflow in upstream, which deeply incises downstream river valleys, is necessary. Such an amount of upstream water is collected from the flat and expansive headwater, inherited from the inland endorheic zone of the plateau interior, on which the hillslope processes dominate the landscape evolution.

Moderate magnitude clockwise rotation of the Yunlong Basin: Implications for synchronous Eocene rotation of the southeastern Tibetan Plateau

The clockwise rotation and southeastward extrusion of the southeastern Tibetan Plateau have played important roles in accommodating the uplift and deformation of the plateau. Numerous paleomagnetic studies have suggested post−late Eocene clockwise rotation of the southeastern Tibetan Plateau along the eastern Himalaya syntaxis, whereas few researchers have addressed the specific Eocene deformation, leading to ambiguous interpretations of the tectonic evolution in the region. Herein, we conducted a paleomagnetic study of the Yunlong Formation in the Yunlong Basin, which is Late Cretaceous to early Paleocene in age. In total, 386 oriented samples were collected. Rock magnetic, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) analyses revealed detrital carriers, such as hematite and some magnetite. In thermal demagnetization processes, 332 characteristic remanent magnetizations were isolated, which yielded positive reversals and tilt tests, providing a site-mean direction of declination (Ds) = 56.0° ± 2.6°, inclination (Is) = 34.3° ± 3.8°, α95 = 2.7°, k = 91.0, and N = 31 after tilt correction. Magnetostratigraphic analysis was performed, and a depositional age of 79−61 Ma for the section was obtained, which is consistent with the previous paleontological and detrital zircon ages. Compared with the Eurasia reference pole of the period, the data revealed a 45.2° ± 5.1° clockwise rotation of the Yunlong area since 79−61 Ma. The integrated regional paleomagnetic results suggest the occurrence of ∼20° of clockwise rotation of the Lanping-Simao terrane during the Eocene, which is similar (in terms of magnitude and time of occurrence) to that of the Gonjo Basin in the eastern Qiangtang terrane. Integrated with other lines of geologic evidence, we propose a new deformation model in which the entire southeastern Tibetan Plateau experienced ∼20° of rigid clockwise rotation during the Eocene, followed by subsequent oroclinal bending.

Crustal Deformation in Eastern Himalayan Syntaxis Constrained by Ambient Noise Tomography

ABSTRACT As the leading edge of the Indian–Asian collision, the eastern Himalayan syntaxis region has experienced extensive tectonic activities, resulting in complex crustal uplift and deformation in the corner area of the southeastern pathway for the extrusion of Tibetan plateau materials. Despite considerable efforts, the corresponding deformation mechanisms remain uncertain. This study presents a new 3D high-resolution azimuthal anisotropic shear-wave velocity model in the crust and uppermost mantle derived from ambient noise dispersion data. Results show that the upper crustal anisotropy aligns with the geological boundaries and major faults nearby, suggesting shape-preferred orientations. The upper crustal low velocity and weak anisotropy beneath the core of the eastern Himalayan syntaxis (EHS) are closely associated with the high fragmentation of shallow rocks and the upwelling of hot materials during the ongoing subduction of the Indian plate. Our model also reveals relatively complex anisotropic patterns in the midlower crust. The eastern Lhasa terrane, in particular, exhibits low velocity and strong anisotropy with a northwest–southeast-oriented fast axis, supporting the local scale midlower crustal “channel flow” model. In addition, a conspicuous, elongated low-velocity zone along the northwest–southeast direction is observed in the midlower crust and uppermost mantle beneath the Bangong–Nujiang suture. The anisotropy in this region increases with depth, and the fast directions are consistently parallel to the northeast subduction of the Indian plate. We infer that this low-velocity zone may result from partial melting under local compression driven by the Indian–Asian collision. On the basis of newly revealed anisotropic model and previous studies, we construct a new dynamic model, which reveals that the migration of mechanically weak material in the midlower crust and the significant contribution of the northeast subduction of the Indian plate jointly control the crustal deformation of the EHS region.

Three‐Dimensional Density Distribution and Seismic Activity along the Guxiang–Tongmai Segment of the Jiali Fault, Tibet

AbstractThe Guxiang–Tongmai segment of the Jiali fault is situated northeast of the Namche Barwa Syntaxis in northeastern Tibet. It is one of the most active strike‐slip faults near the syntaxis and plays a pivotal role in the examination of seismic activity within the eastern Himalayan Syntaxis. New study in the research region has yielded a 1:200000 gravity dataset covering an area 1500 km2. Using wavelet transform multiscale decomposition, scratch analysis techniques, and 3D gravity inversion methods, gravity anomalies, fault distributions, and density structures were determined across various scales. Through the integration of our new gravity data with other geophysical and geological information, our findings demonstrate substantial variations in the overall crustal density within the region, with the fault distribution closely linked to these density fluctuations. Disparities in stratigraphic density are important causes of variations in the capacity of geological formations to endure regional tectonic stress. Earthquakes are predominantly concentrated within the density transition zone and are primarily situated in regions of elevated density. The hanging wall stress within the Guxiang–Tongmai segment of the Jiali fault exhibits a notable concentration, marked by pronounced anisotropy, and is positioned within the density differential zone, which is prone to earthquakes.

Formation of the Great Bend and Enhanced Quaternary Incision of the Upper Yangtze River: New Insights from Low-Temperature Thermochronology and Tributary Morphology

Abstract The occurrence of a sharp turn along the upper course of the Yangtze River is referred to as the “Great Bend” and represents a large-scale drainage reorganization in response to the surface rise of the Tibetan Plateau. However, the timing and mechanism of the formation of the Great Bend remain disputed. In this paper, we report new (U–Th)/He and apatite fission track thermochronological data from the deep river valley in the Great Bend area of the southeastern margin of the Tibetan Plateau. Compared with the adjacent Jianchuan Basin, two phases of younger rapid cooling for the Great Bend area are identified based on thermal-history modeling, namely, Miocene (ca. 17 to 11–8 Ma) and Quaternary, with the former phase being contemporaneous with the formation of the anticline in the Tiger Leaping Gorge. Progressive increases in the normalized channel steepness (ksn) and the degree of river-valley incision with increasing distance downstream for tributaries of the Yangtze River in the Tiger Leaping Gorge indicate that river rerouting and formation of the Great Bend occurred during the Miocene. Samples located at the bottom of the Tiger Leaping Gorge also reveal a phase of rapid cooling since ca. 1.9 Ma, with an exhumation rate of 1.5 ± 0.2 mm/year. We hypothesize that enhanced Quaternary exhumation in the southeastern margin of the Tibetan Plateau occurred mainly within the narrow region between the Sichuan Basin and the Eastern Himalayan Syntaxis, corresponding to an episode of widespread extensional deformation superimposed above middle- to upper-crustal flexure in this region.