Eastern Margin Of Tibetan Plateau Research Articles

Geophysical constraints on continental rejuvenation in central China: Implications for outward growth of the Tibetan Plateau

Continental rejuvenation results from the tectonic reactivation of crustal structures and lithospheric reworking by mantle flow. Geochemical observations and field mapping have traditionally provided the primary evidence for the secular evolution of crustal composition and tectonic processes during continental rejuvenation. Nonetheless, the impact of continental rejuvenation on the observed present-day strain rate and orogenic-scale lithospheric structure has not been well constrained. The pre-existing E-W−trending Central China Orogenic Belt has been overprinted by the N-S−trending Central Longitudinal Seismic Belt and constitutes the intracontinental West Qinling Syntaxis in central China, where the tectonic setting changes eastward from contraction to extension. Combining updated global positioning system data and high-resolution crustal seismic tomography, we reveal a modern continental rejuvenation process within the West Qinling Syntaxis in central China. The northward extrusion of the Tibetan Plateau’s weak lithospheric layer (middle-lower crust and lithospheric mantle) of southwestern China relative to the rigid Sichuan Basin/Ordos Block of the eastern West Qinling Syntaxis results in regional dextral shearing that shapes the Central Longitudinal Seismic Belt and defines the eastern Tibetan Plateau margin. The pre-existing E-W−trending Central China Orogenic Belt has been preserved above the brittle-ductile transition zone, and the northward movement of the deep lithospheric layer drives the deformation of the upper crust in the West Qinling Syntaxis. Our results, along with previous studies, suggest the presence of an intracontinental lithospheric interchange structure in central China. The continental rejuvenation of the West Qinling Syntaxis results from a combination of fault reactivation in the upper crust (Stage I, Eocene−Oligocene) and reworking of the deep lithosphere (Stage II, middle−late Miocene) related to the plateau-wide shift in stress accommodation ultimately driven by the redistribution of mass outward from the central Tibetan Plateau. At present, the transition zone between the high- and low-velocity anomalies along the Central Longitudinal Seismic Belt not only shapes the landscape boundary but controls the size and recurrence interval of earthquakes within the West Qinling Syntaxis in central China.

Channel Profiles Reveal Fault Activity along the Longmen Shan, Eastern Tibetan Plateau

Assessing fault activity in regions lacking Quaternary sedimentary constraints remains a global challenge. In this study, we used channel slope distribution to examine variations in rock uplift along faults. By comparing channel steepness with published low-temperature thermochronology and paleo-seismic data, we identified deformation changes both perpendicular to and along the Longmen Shan at various time scales. Our data revealed distinct fault segments displaying distinct thrust activities along the Longmen Shan’s strike. In the southern segment, the Dachuan fault exhibited the highest activity, and its movement had persisted for millions of years. In the central segment, the Wenchuan fault was active during theearly Quaternary but has become dormant since the late Pleistocene. Within the past millions of years, the Yingxiu and Pengguan faults displayed significant vertical displacement. Fault activity in the northern Longmen Shan was relatively weak, with the Qingchuan fault transitioning from thrust movement during the Neogene to pure strike-slip activity since the Pleistocene. Overall, the Dachuan and Huya faults exhibited deformation patterns similar to the Yingxiu fault during the Quaternary. Similar to the Yingxiu fault, which triggered the Wenchuan earthquake, the Dachuan and Huya faults possess the capacity to produce significant earthquakes in the future. The variations in deformation perpendicular to and along the Longmen Shan fault system underscore the importance of upper crustal shortening in shaping the rock uplift patterns and topography of the eastern Tibetan Plateau margin.

Post-seismic deformation of the 2008 Wenchuan earthquake reveals a misaligned rheological boundary in the lower crust along the eastern Tibetan Plateau margin

SUMMARY Along the margins of orogenic plateaus, the viscous Earth structure and fault geometries play a primary role in controlling the tectonic evolution and earthquake generation. After the 2008 Mw 7.9 Wenchuan earthquake, the long-standing debate regarding the tectonics producing and maintaining prominent topography across the Longmen Shan reignited. Post-seismic deformation, representing the surface strain history in response to lithospheric stress perturbations, provides important insights into the lithospheric rheology and active structures. Here, we construct a new 3-D post-seismic deformation model for the Wenchuan earthquake, invoking viscoelastic relaxation and afterslip. Our best-fitting model indicates that the steady-state viscosities of the lower crust in the region to the immediately west of the Songpan-Ganzi terrane and beneath the Songpan-Ganzi terrane are estimated to be 4.0 × 1018 and 1.0 × 1018 Pa s, respectively. Our results, combining geophysical and geodetic observations and model analyses, highlight the prevalent parallelism between the rheological and structural boundaries of the lower crust, which diverge northward away from the trend of the Longmen Shan fault at ∼20°. This diverging rheological structure and the partially coupled upper and lower crust have broad implications for the stress build-up, strain partitioning and deformation styles along the eastern Tibetan Plateau margin.

Pulsed counterclockwise rotation of the southwestern Sichuan Basin in response to the India-Asia convergence during 128-42 Ma

Deciphering the building history of the eastern Tibetan Plateau since the India-Asia convergence is crucial to understand geodynamic models of plateau formation. The Sichuan Basin adjacent to the eastern Tibetan Plateau margin potentially provides valuable records of when and how the Tibetan Plateau expanded eastward. In this study, we reconstruct ∼128–42 Ma rotation history of the southwestern Sichuan Basin using detailed paleomagnetic declination data from the Early Cretaceous to Eocene sedimentary sequence of ∼2400 m thick. A total of 78 sampling sites (774 samples) yield primary remanent magnetization confirmed by positive paleomagnetic tests. Our results show that the southwestern Sichuan Basin experienced a long-term clockwise rotation during 128–42 Ma which was interrupted by three transient and rapid counterclockwise rotation pulses. The earlier two pulses (86–82 Ma and 66–60 Ma) coincide with two India Plate acceleration episodes which are probably induced by the Marion and/or Réunion mantle plume upwelling, whereas the later pulse (53–46 Ma) temporally corresponds to the sudden slowdown of the India Plate caused by the India-Asia collision. Our findings indicate that the eastern Tibetan Plateau experienced prolonged and episodic building processes since the Late Cretaceous, long predating the traditional view of the late Miocene. The Tibetan Plateau was built synchronously from the Himalayas to its eastern margin. Lateral extrusion, block rotation, and strike-slip deformation collectively contribute to the mountain building in the eastern Tibetan Plateau region.

Cenozoic kinematics of the Wenchuan-Maoxian fault implies crustal stacking rather than channel flow extrusion at the eastern margin of Tibetan plateau (Longmen Shan)

The Longmen Shan, eastern and steepest margin of the Tibetan plateau, is often seen as the archetype example of an orogenic system built by crustal channel flow extrusion since the Miocene. This model is controversial as other studies propose an accretionary prism mechanism. A key difference between these models resides in the kinematics proposed for the Wenchuan - Maoxian (WM) fault zone, a major tectonic structure of the Longmen Shan. We constrain the Cenozoic kinematics of the WM fault zone by combining structural observations, fault gouge K/Ar dating and 40Ar/39Ar dating of syn-kinematic white mica. Normal / right lateral ductile deformation occurred at 28.0 ± 0.9 Ma while top-to-the-east reverse deformation at 15.4 ± 0.2 Ma. K/Ar ages of authigenic illite from two fault gouges show that brittle right-lateral / reverse deformation was active at 6.9 ± 2.9 Ma. These ages are consistent with the relative vertical motions across the fault zone deduced from thermochronology. Three deformation phases can be identified: right-lateral / normal in the Middle Oligocene (∼30–25 Ma), reverse in the middle Miocene (25–15 Ma), and right-lateral / reverse since the upper Miocene (since ∼6 Ma). The WM fault zone never experienced pure normal motion, and only shortening since the Oligocene, in contrast to predictions of lower crustal channel-flow extrusion models. These results are in favor of a crustal accretionary prism model for the Cenozoic building of the eastern Tibetan plateau.

Topography effect on ambient noise tomography: a case study for the Longmen Shan area, eastern Tibetan Plateau

SUMMARY Ambient noise tomography (ANT) is a widely used method to obtain shear wave velocity structure in the crust and upper mantle. Usually, the topography is assumed to have negligible effect on the resulting models. This, however, might not be proper in regions with large topographic variation, such as plateau edges, submarine slopes and volcanic islands. In this study, we use synthetics from waveform-based numerical simulation to quantify the topography effect on ANT in the Longmen Shan area, eastern Tibetan Plateau margin. Three kinds of models are used in forward simulation to obtain theoretical waveforms, including Case1: the layered model, Case2: the layered model with topographic variation and Case3: the flattened model of Case2. The final inversion results show that the bias of ANT is negligible in the blocks with relatively flat topography, such as the interior regions of the Tibetan Plateau and the Sichuan Basin. However, for the Longmen Shan boundary zone with significant topographic variation (∼4 km), the shear wave velocity image has an obvious negative bias that can reach up to −4 per cent. The maximum depth of bias is ∼5 km, which is mirrored with the maximum topographic elevation difference of the region, and the average bias disappears as the depth decreases to the surface (0 km) or increases to three times of the maximum influence depth (∼15 km). The horizontal distribution of the tomographic bias is almost linearly related to the topographic elevation difference with a slope of −1.04 and a correlation coefficient of 0.90 at maximum influence depth. According to this first-order correction formula and the decreasing trend of average bias with depth, the topography effect on ANT can be suppressed to a certain extent.

Thermochronological constraints on Eocene deformation regime in the Long-Men Shan: Implications for the eastward growth of the Tibetan Plateau

Understanding the spatio-temporal distribution of strain during Cenozoic growth of the Tibetan Plateau is important for constraining the geodynamic processes underpinning plateau formation. Offset Quaternary landforms and historic earthquake data suggest an along-strike change in deformation style for the eastern margin of the Tibetan Plateau, characterized by a transition from ESE-verging shortening to right-lateral shear from the southern to northern segment of the Long-Men Shan fault zone within a distance of ca. 500 km. When and how this along-strike deformation pattern formed is central to understanding the uplift history and spatio-temporal distribution of strain in the eastern margin of the Tibetan Plateau, and the underpinning geodynamics. To address this, we report a suite of low-temperature thermochronology data from the northern segment of Long-Men Shan fault zone that show a contrast in post late Cretaceous cooling and exhumation histories between the hinterland (west of the marginal Yingxiu-Beichuan fault) and foreland sides (east of the fault). Prior to the Eocene (ca. 40 Ma), the hinterland experienced significant exhumation in contrast to minor exhumation on the foreland side, but, post Eocene exhumation accelerated on the foreland side. This change reflects a switch in the deformation regime from shortening to strike-slip-dominated. This switch reduced hinterland rock uplift and tectonic and topographic loading over the foreland basin, leading to accelerated foreland exhumation through isostatic adjustments. A compilation of fault deformation history for the eastern Tibetan Plateau shows a second tectonic transition in the late Miocene, characterized by formation of the south-striking Huya and Minjiang faults. Our results highlight the importance of progressive late Eocene and late Miocene tectonic transitions in shaping the eastern margin of the Tibetan Plateau. • The hinterland and foreland sides of the eastern Tibetan Plateau margin experienced differential Eocene exhumation. • The differential evolution indicates a coeval tectonic transition from shortening-dominated to strike-slip-dominated. • A second tectonic transition is characterized by the late Miocene formation of the Huya and Minjiang faults. • The eastern margin of the Tibetan Plateau is shaped by progressive late Eocene and late Miocene tectonic transitions.

The elevation gradient of stable isotopes in precipitation in the eastern margin of Tibetan Plateau

The elevation gradient of stable isotopes in precipitation in the eastern margin of Tibetan Plateau

Multi-period formation and possible high-position hazards of Chada gully deposits on the eastern margin of Tibetan Plateau

High-position rockslides on Tibetan Plateau are usually characterized by multiple in-situ events and multi-period movement. Better understanding on the evolution process of high-position rockslide deposits can help to predict its development trend in the future. In this paper, taking the Chada high-position rockslide-debris avalanche as an example, a series of technical methods, including field investigation, drilling, remote sensing, isotopic dating and engineering geological analogy, are adopted to study the formation and evolution of the Chada gully deposits, and analyze the potential instability range of the jointed rock mass on the slope top. In view of the possible secondary hazards that may be induced by further movement of the top rock masses, the DAN3D software is adopted to simulate the dynamic processes and study the effects on the planning and construction of a railway station near the slope toe. The results show that the formation and evolution of the gully deposits can be divided into 4 periods as follows: 1) At around 43.5 ka BP ago, it was in a period of glacial deposition characterized by moraine deposits. 2) At around 17.5 ka BP, an earthquake induced a rockslide-debris avalanche in the gully. 3) At about 1.0 ka BP, an ice-rock avalanche occurred and formed a layer of purple-reddish boulders with a small thickness. 4) In modern times, during which some small-scale rock collapses were triggered by far-field earthquakes. The results also show that, no matter whether the entrainment effect is considered, the predicted rockslide-debris avalanche deposits cannot fully reach the gully outlet. When the entrainment effect is considered, only a small amount of debris or boulders will roll down and reach the proposed railway station site. Based on the simulation results, some monitoring and protective measures are proposed accordingly.

Subannual-to-biannual-resolved travertine record of Asian Summer Monsoon dynamics in the early Holocene at the eastern margin of Tibetan Plateau

In this study, we present a subannual–biannual-resolved (0.9–2 years) ASM intensity record spanning from 11.6 to 10.0 ka BP (before 1950 AD) inferred from a 230Th-dated travertine δ18O record at Zhangjia Ravine on the eastern margin of the Tibetan Plateau. The ZJG-1 δ18O sequence is characterized by high-frequency fluctuations at decadal to centennial scales. Fluctuating between −11.15‰ and −14.78‰ over the δ18O sequence, the fluctuation range gradually decreased from 11.6 to 10.0 ka BP. There are several abrupt changes in the δ18O sequence, which indicate that the ASM in the early Holocene was highly unstable. Comparison with marine records suggests that the Preboreal oscillation (PBO) event could be triggered by a freshwater outburst which led to/resulted in a sudden release of thousands of cubic kilometers of the meltwater to the North Atlantic Ocean. Furthermore, the climate oscillations during the PBO were associated with the complex interplay of solar activity and freshwater outburst, the freshwater outburst may amplify the effect of solar activity when it was in the minima. The rapid warming after the PBO event may be controlled by the common mechanism that induced the Dansgaard–Oeschger warming events during the last glacial period. The further pronounced increases of the travertine δ18O values occurred at about 10.3 ka BP, coinciding roughly with Bond 7 event, also caused by the freshwater outburst and solar activity. This study is not only important to understand the primary driving force of the ASM intensity in the early Holocene, but also essential for evaluate the probability of abrupt climate changes in the future.

Subannual-to-biannual-resolved travertine record of Asian Summer Monsoon dynamics in the early Holocene at the eastern margin of Tibetan Plateau

Subannual-to-biannual-resolved travertine record of Asian Summer Monsoon dynamics in the early Holocene at the eastern margin of Tibetan Plateau

Strong Seasonal Variations of Seismic Velocity in Eastern Margin of Tibetan Plateau and Sichuan Basin From Ambient Noise Interferometry

AbstractAmbient noise interferometry between seismic stations makes it possible to monitor temporal changes of the Earth's media continuously. Here, we examined seasonal changes of Rayleigh‐wave empirical Greens functions at 2–10‐s period from 8 years of continuous data of 200 seismic station pairs in Sichuan, China. We used a wavelet decomposition to extract the seasonal signals. We found that most station pairs show seasonal variations with velocity perturbations of up to 0.8%. The seasonality varies in strength, amplitude, phase, periods, and location, but the phase is remarkably consistent, with the largest changes mostly in summer or winter months. We believe that the cause of the seasonality is likely the elastic loading due to regional precipitation. The effect is greater in the tectonically active Tibetan Plateau margin than in the stable Sichuan basin and in the deeper crust than in the uppermost crust. The effect is also strongly influenced by local crustal structure. Our results indicate that studies of tectonic crustal changes need to consider non‐tectonic effects.

Crustal deformation in eastern margin of Tibetan Plateau from a dense linear seismic array

Crustal anisotropy beneath a dense broadband seismic array across the Longmenshan fault belt is measured based on P-to-S converted phases from the Moho and an intra-crustal interface. The crustal thickness and the average Vp/Vs values are also estimated by a new H-κ-c method. The crustal anisotropy in Aba sub-block mainly comes from the middle-lower crust and the NW-SE fast polarization directions (FPDs) may reflect the direction of the crustal flow. A sharp variation of FPDs is observed in the vicinity of the Longriba faults, combined with the Vp/Vs values and other geological and geophysical observations, we suggest the Longriba faults may block the eastward flow of crustal materials. East of the Longriba faults, the consistence between the FPDs and the direction of the maximum horizontal compression, and low Vp/Vs values indicated that the crustal thickening may be the dominant deformation mechanism in the Longmenshan sub-block. The crustal anisotropy in the Longmenshan fault belt is mainly manifested as fault-parallel FPDs, probably related to fluid-filled fractures in this area. The Sichuan basin is weakly anisotropic and the NE-SW FPDs may reflect the tectonic strike. Combined with previous observations, our results suggest that the crustal flow and crustal thickening are co-exist in the crustal deformation in eastern Tibet.

Late Quaternary activity of the Qingchuan Fault, eastern Tibetan Plateau margin: Insights from stream channel offsets and catchment erosion

The Qingchuan Fault (QCF) is the main fault of the northeastern segment of the Longmenshan Fault zone (LMSFZ) on the eastern Tibetan Plateau boundary. The QCF accommodates ongoing deformation in the eastern Tibetan Plateau; however, its fault motion and potential seismic risk are still debated. This study combines a systematic analysis of deflected stream channels along the fault using 10-m digital elevation models with field investigations and measurements of the cosmogenic 10Be-derived erosion rates. The degree of channel deflection due to the interaction between strike-slip motion and channel growth processes is analyzed, followed by a quantitative extraction of the actual tectonic offsets and a calculation of the erosion rates. The long-term average strike-slip rates calculated from channel offsets range from 0.4 ± 0.1 to 1.7 ± 0.1 mm/a along the fault, with those in the southwestern section lower than those in the central section. Such differences may be attributed to slip partitioning of the northeastern extension of the Yingxiu–Beichuan Fault. In addition, analysis of stream longitudinal profiles and along-fault topographic variations illustrate that the small thrust component of the QCF decreases to the northeast, and a minor normal component exists at its northeastern end. The distributions of strike-slip and vertical-slip motions of the QCF indicate that fault slip of the central LMSFZ propagates to the northeast across the Minshan uplift and continues to slip along the QCF. Moreover, thrusting of the southern-central segment of the LMSFZ and dextral strike-slip faulting of the QCF may both accommodate complex deformation related to eastward expansion of the Tibetan Plateau. These findings have implications for constraining potential seismic hazards and understanding characteristics of the regional tectonic deformation.

Photodegradation Characteristics of Dissolved Organic Matter (DOM) in Alpine Soils of the Eastern Margin of Tibetan Plateau

Photodegradation Characteristics of Dissolved Organic Matter (DOM) in Alpine Soils of the Eastern Margin of Tibetan Plateau

Synchronous Sedimentation in Gonjo Basin, Southeast Tibet in Response to India‐Asia Collision Constrained by Magnetostratigraphy

AbstractThe India‐Asia collision has been the object of vigorous debate for decades, with ages of the start ranging from Late Cretaceous to Oligocene. Sedimentary records preserved in both near‐field and far‐field settings provide critical evidence concerning the age and mechanism of the collision. Gonjo Basin, one of a series of fault‐controlled basins developed along the eastern margin of Tibetan Plateau, contains well‐exposed sedimentary successions, providing great potential for understanding depositional, tectonic‐geomorphological and climatic history associated with India‐Asia collision and plateau uplift. Lithofacies analysis reveals that the sequences consist of sandstone, mudstone and conglomerate, formed in fluvial‐lacustrine systems. High‐resolution magnetostratigraphy, constrained by U‐Pb dating of zircon from a volcaniclastic layer which has been found in the central Gonjo Basin for the first time, indicates that sedimentation started at 69 Ma and continued in this locality until 50 Ma. Anisotropy of magnetic susceptibility (AMS) interpretation based on the age framework reveals a post‐depositional compression after 50 Ma, responding simultaneously to the early uplift of southeast Tibetan Plateau driven by India‐Asia collision.

Three-dimensional resistivity structure in the hydrothermal system beneath Ganzi Basin, eastern margin of Tibetan Plateau

The Ganzi geothermal system located in the eastern margin of Tibetan Plateau, is found to distribute the strongly active surface manifestations, such as boiling springs, and fumaroles. The resistivity structure of high-temperature hydrothermal system beneath Ganzi Basin has been obtained from the three-dimensional (3-D) magnetotelluric inversion of 103 broadband MT stations in period range from 320 Hz to 1000s. The MT stations have an average spacing of 500 m and completely cover the Ganzi Basin. The detailed 3-D resistivity structure which the authors found has been described characteristics of the shallow and deep geothermal reservoirs as well as to correlate with the structural features present in the Ganzi Basin. The shallow geothermal reservoir is mainly composed of the sedimentary layer, with a depth of 300−800 m, while the deep geothermal reservoir mainly consists of the fault fracture zone with a depth of 1−5 km. The porosity of the geothermal reservoirs is in the range 5–10 %, estimated based on the resistivity model. The Ganzi fault provides the pathway for transport heat and the circulation of geothermal fluids. The possible heat source for the Ganzi geothermal system has been attributed to tectonic deformation heating in the crust, radiogenic heat production derived from the decay of U, Th and K, and heat from the mantle.

Upper crustal velocity and seismogenic environment of the <em>M</em>7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China. The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad. The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area; the complex tectonic background and the reason(s) for the frequent seismicity in the Jiuzhaigou earthquake region are unclear. In order to reveal the characteristics of the deep medium and the seismogenic environment of the <i>M</i>7.0 Jiuzhaigou earthquake region, and to interpret the tectonic background and genesis of the seismicity comprehensively, in this paper, we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale, dense mobile seismic array (China Array) for the northern section of the North–South Seismic Belt around Jiuzhaigou earthquake region. Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region, we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region, its deep tectonic environment, and the ongoing seismic risk in this region. We report that: the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity; the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology; the <i>M</i>7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust; the mainshock of the <i>M</i>7.0 earthquake occurred in the upper crust; the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence. The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB (Songpan–Garzê Block) stretches into MSM (Minshan Mountain), and migrates to the northeast, but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block. Our results reveal an uneven distribution of high- and low-velocity structures around the Tazang segment of the East Kunlun fault zone. Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault, it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu–Maqên segment of the East Kunlun fault zone.

Constraints on late cenozoic tectonics in the Southern Longmen Shan: evidence from low-temperature thermochronology

ABSTRACT The NE-trending Longmen Shan (LMS) thrust belt, located between the Songpan-Garze terrane and the Yangtze craton, is one of the steepest topographic margins around the Tibetan Plateau. However, the exhumation history and the fault activity of the southern segment of the LMS have remained poorly constrained, particularly in the range front, where little thermochronology ages have been reported. Herein, we report 17 apatites (U-Th)/He (AHe) ages from the southern LMS along the Qingyi River across the Dachuan–Shuangshi Fault (DSF), the Yanjing–Wulong Fault (YWF), and the Gengda–Longdong Fault (GLF). The AHe ages in the hanging-wall of the DSF are ca. 6–11 Ma, which increase to ca.19–23 Ma in the footwall of the DSF. New AHe ages reveal that exhumation rates across the DSF increased significantly from 0.05 to 0.1 km/Myr in the footwall to 0.2–0.4 km/Myr in the hanging-wall since the Late Miocene. The width of the high exhumation rate (0.4–0.6 km/Myr) belt concentrated between the DSF and the GLF, and towards DSF eastward and GLF westward, the exhumation rates decrease rapidly. The results show that continuous crustal shortening along the DSF. Our results support the upper crustal thrusting model that emphasizes crustal shortening deformation along the eastern Tibetan Plateau margin.

Glacial advances and stability of the moraine dam on Mount Namcha Barwa since the Last Glacial Maximum, eastern Himalayan syntaxis

The Tibetan Plateau and Indian Plain exhibit the largest altitudinal difference between two geographically contiguous areas on Earth, but the eastern margin of the Plateau has not experienced headward erosion of the Yarlung Zangbo River (YZR) since ~2.5 Ma. In the past, some scientists have argued that moraine dams on Mount Namcha Barwa (in the Eastern Himalayan syntaxis) frequently blocked the YZR, thus keeping the Plateau's margin intact at this point. In this study, three sets of moraines were identified in the Pai Valley alongside Namcha Barwa, and were dated using optically stimulated luminescence (OSL) and 10Be exposure dating. The resultant ages would suggest that three glaciations occurred at ~22.2, 4.7 and 1.3 ka, respectively. Comparison of OSL and 10Be ages for glacial advances with local paleoclimatic proxies would suggest that temperature was the dominant factor controlling glacial change. Because of the paleoglacial advance frequency, coupling with rapid fluvial incision, moraine dams were cut through by the YZR. Thus, any moraine dams that lost their efficacy in impacting upon knickpoint migration. Instead, similarities between rock uplift and fluvial incision, rather than moraine dams, might have been the main control impeding headward erosion of the YZR, thereby keeping this part of the eastern Tibetan Plateau margin intact.