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The Tibetan Plateau was formed by intense Cenozoic shortening (up to 1,100 km) of a composite "proto‐Tibet," itself the product of a long Paleozoic and Mesozoic history of accretion of Gondwana‐derived continental fragments and volcanic arcs against the Asian continental margin. The difficult access and the scarcity of outcrops have long limited the possibilities of studying these Mesozoic suture zones in the heart of the Plateau. In this work, we present new U‐Pb and 40Ar/39Ar ages from the highly deformed units of the Yushu mélange, along the Jinsha Suture in the northeastern Qiangtang terrane. Early Triassic (c. 253 Ma) to Middle Jurassic ages (c. 165 Ma) complement the existing data set and help to refine the chronology of the Paleo‐Tethyan oceanic subductions which have structured the northeastern part of the Qiangtang terrane. The Yushu mélange records at least three successive tectono‐magmatic events. The opening of a back‐arc basin during the northward Paleo‐Tethyan subduction along the Longmu Co‐Shuanghu Suture during Early to Middle Triassic; then its closure during the southward subduction of the Songpan‐Ganze Ocean along the Jinsha Suture in Late Triassic. Finally, a shortening phase related to the continental collision of the Songpan‐Ganze and Qiangtang blocks from Late Triassic to Early‐Middle Jurassic. No evidence for any high‐ or mid‐temperature Cenozoic reactivation of the Jinsha suture in our study area is recorded. Plain Language Summary: The north‐eastern part of the Tibetan Plateau, called the Qiangtang terrane, has a long‐lasting geological history: not only it records the collision of the Indian continent with Asia, but also a much older history: during Mesozoic times (∼250–165 Ma), this area was made of continental islands separated by oceanic realms called "Paleo‐Tethyan" basins. The oceans disappeared by subduction, and the continents were accreted together to form the southern Asian margin. This part of the geological history of the Tibetan Plateau is not so well‐known, because of the scarcity of outcrops. In this work, we date rock samples with two methods (using argon and uranium isotopes) which give complementary results and allow a greater degree of precision concerning the timing of the deformation of the rocks. Our results contribute to refine the chronology of the tectonic events which have structured the northeastern part of the Tibetan Plateau, long before the India‐Asia collision. Key Points: The Jinsha Suture in the Yushu area (NE Tibet) recorded three main tectono‐metamorphic eventsDeformed samples yield Early Triassic to Middle Jurassic ages, related to the closure of the Songpan‐Ganze basin of the Paleo‐TethysThe Jinsha suture was not reactivated at >200°C during Cenozoic post‐collisional regional shortening [ABSTRACT FROM AUTHOR]

Numerous studies dated glacial deposits within the Himalayan‐Tibetan orogen. While most focus on young deposits, i.e., younger than the Last Glacial Maximum (LGM or Marine oxygen Isotope Stage (MIS)‐2, ∼20 ka), older moraines such as those from MIS‐6 (∼130–191 ka) are much harder to date and interpret due to the less well‐preserved nature of their surfaces and boulders, as well as their scattered and continuous age distribution due to long‐lived erosion since deposition. Here, we dated with 10Be, two imbricated moraines near Yadong in southern Tibet, as MIS‐2 and 6, showing that the most extensive, smooth surfaces were abandoned during MIS‐6. Compiling published data from 54 MIS‐6 moraines on the Tibetan Plateau reveals that they exist in most regions, dry or humid. They are particularly well‐preserved (sharp crests) in eastern and northern Tibet, while in southern and central Tibet, their crests are rounded to sub‐rounded. Because both MIS‐2 and 6 were equally cold, and because MIS‐6 moraines are much more extensive than those from the LGM, we conclude that MIS‐6 glacial advances were controlled by more abundant precipitation than during MIS‐2. This would be consistent with the peak in Asian monsoon during MIS‐6, revealed by sediments from the South China Sea. [ABSTRACT FROM AUTHOR]

More accurate normal fault mapping and more recently constrained extension rates in southern and central Tibet allow to better discuss the mechanical processes responsible for the distribution of extension in Tibet. First, we show that the location of the rifts in southern Tibet south of the Karakorum‐Jiali fault zone (KJFZ) does not exactly correspond to that of the rigid Indian lower lithosphere flattening below southern Tibet (underthrusting) inferred by P‐waves global tomography, thus suggesting an absence of mechanical coupling between the two processes. Instead, E‐W extension south of the KJFZ appears primarily due to divergent, orthogonal thrusting along the curved Himalayan arc, as proposed earlier. North of the KJFZ however, lower amplitude extension, distributed on numerous scattered normal faults in the western Qiangtang terrane, absorbs distributed eastward extrusion, while eastern Qiangtang is extruded more rigidly by the Xianshuihe fault, following a slip‐line resulting from in‐plane forces due to the collision/indenter, visible as a major discontinuity in the GPS velocity field. [ABSTRACT FROM AUTHOR]

The Xianshuihe (XSH) fault in eastern Tibet is one of the most active faults in China, with the next large earthquake most likely to occur along its SE part, where the fault splits into three parallel branches: Yalahe, Selaha and Zheduotang (ZDT). Precisely quantifying their slip rates at various timescales is essential to evaluate regional earthquake hazard. Here, we expand our previous work on the Selaha fault to the nearby ZDT and Moxi (MX) faults, and add observations on the Yalahe fault and on the newly discovered Mugecuo South fault zone. Using tectonic-geomorphology approaches with 10Be dating, we had previously determined average late Quaternary slip rates of 9.75 ± 0.15 and 4.4 ± 0.5 mm/yr along the NW and SE Selaha fault, respectively. Using the same methods here, we determine a slip rate of 3.4-4.8 mm/yr on the ZDT fault and of 9.6--13.4 mm/yr on the MX fault. This is consistent with the southeastward slip rate increase we had proposed along the XSH fault system from 6-8 mm/yr (Ganzi fault) to ~10 mm/yr (Selaha fault), and >9.6 mm/yr (MX fault). We propose a new model for the SE XSH fault, where the large-scale Mugecuo pull-apart basin lies within an even larger scale compressive uplift zone in a restraining bend of the XSH fault, where the highest peak in eastern Tibet is located (Gongga Shan, 7,556 m). Our slip rate determination helps to constrain a relatively high regional Mw ~7 earthquake hazard at present on the SE XSH fault. [ABSTRACT FROM AUTHOR]

The Three Rivers Region in south-east Tibet represents a transition between the strongly deformed zone around the Eastern Himalayan Syntaxis (EHS) and the less deformed south-east Tibetan Plateau margin in Yunnan and Sichuan. In this study, we compile and model published thermochronometric ages for two massifs facing each other across the Mekong River in the core of the Three Rivers Region (TRR), using the thermo-kinematic code Pecube to constrain their exhumation and relief history. Modelling results for the low-relief (< 600 m), moderate-elevation (∼ 4500 m) Baima Xueshan massif, east of the Mekong River, suggest regional rock uplift at a rate of 0.25 km/Myr since ∼ 10 Ma, following slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma. Estimated Mekong River incision accounts for 30 % of the total exhumation since 10 Ma. We interpret exhumation of the massif as a response to regional uplift around the EHS and conclude that the low relief of the massif was acquired at high elevation (> 4500 m), probably in part due to glacial "buzzsaw-like" processes active at such high elevation and particularly efficient during Quaternary glaciations. Exhumation of the Baima Xueshan is significantly higher (2.5 km since ∼ 10 Ma) than that estimated for the most emblematic low-relief "relict" surfaces of eastern Tibet, where apatite (U–Th) / He (AHe) ages > 50 Ma imply only a few hundreds of metres of exhumation since the onset of the India–Asia collision. The low-relief Baima Xueshan massif, with its younger AHe ages (< 50 Ma) that record significant rock uplift and exhumation, thus cannot be classified as a relict surface. Modelling results for the high-relief, high-elevation Kawagebo massif, to the west of the Mekong, imply a similar contribution of Mekong River incision (25 %) to exhumation but much stronger local rock uplift at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. We show that the thermochronometric ages are best reproduced by a model of rock uplift on a kinked westward-dipping thrust striking roughly parallel to the Mekong River, with a steep shallow segment flattening out at depth. Thus, the strong differences in elevation and relief of two massifs are linked to variable exhumation histories due to strongly differing tectonic imprint. [ABSTRACT FROM AUTHOR]

Constraining the long‐term exhumation history of the Gangdese magmatic arc is critical for understanding the coupled evolution of orogenic exhumation and accumulation of basin sediments on the southern Tibetan Plateau. We present new zircon fission‐track (ZFT) data from sandstones in the Mt. Kailas area, western Tibet, to decipher the relation between source rock exhumation and sediment deposition in the basin. Two sedimentary members were recognized in the Kailas Basin which are the Eocene conglomerates in the hanging wall of the Great Counter Thrust and the Oligocene–Miocene Kailas Formation in the footwall. The Eocene conglomerates were mostly derived from the Lhasa Terrane to the north with recycling of pre‐Cenozoic sediments, containing zircons that experienced post‐magmatic cooling after the Indian–Asian collision and buried deeply later by the Oligocene–Miocene Kailas Formation. The ZFT analysis from the Kailas Formation illustrates significant cooling during the Oligocene (ca. 32 Ma) in the source region, indicating that the Gangdese magmatic arc rocks were eroded rapidly during that time. The alternate increasing and decreasing of the southernmost Gangdese magmatic arc progresses are linked to dynamic topography deflection induced by the northward subduction of the Indian Plate since the Oligocene and subsequent southward overturning of the Indian mantle slab. Basin subsidence and formation of the Kailas Formation seems also be driven by dynamic topography since the Oligocene. [ABSTRACT FROM AUTHOR]

The Three Rivers Region in Southeast Tibet represents a transition between the strongly deformed zone around Eastern Himalayan Syntaxis and the less deformed southeast Tibetan plateau margin in Yunnan and Sichuan. In this study, we compile and model published thermochronologic ages for two massifs facing each other across the Mekong River in the core of the Three Rivers Region, by using the thermo-kinematic code Pecube to constrain their exhumation and relief development history. Modelling results for the low-relief, mean-elevation BaimaXueshan massif, east of the Mekong River, suggest regional rock uplift at a rate of 0.25 km/Myr since ~ 10 Ma, following slow exhumation at a rate of 0.01 km/Myr since at least 22 Ma. River incision accounts for only 15 % of the total exhumation in the BaimaXueshan. Exhumation since ~ 10 Ma is significantly higher (2.5 km) than that estimated (~ 0.23 km) for the most emblematic low-relief or relict surfaces of Eastern Tibet, which are characterized by apatite (U-Th)/He ages older than the collision age (> 50 Ma). We conclude that the BaimaXueshan massif, which shows younger ages (< 50 Ma) that record significant rock uplift and exhumation during the Neogene, cannot be classified as a relict surface despite its low relief. Modelling results for the high-relief, high-elevation Kawagebo massif, to the west of the Mekong, imply a similar contribution of Mekong River incision (20 %) to exhumation, but much stronger local rock uplift at a rate of 0.45 km/Myr since at least 10 Ma, accelerating to 1.86 km/Myr since 1.6 Ma. We show that the age-elevation profiles for three thermochronometers are best modeled by rock uplift on a kinked westward-dipping thrust striking roughly parallel to the Mekong River, with a steep shallow segment flattening out at depth. Thus, the strong differences in elevation and relief that characterize these massifs are linked to variable exhumation histories due to a strongly differing tectonic imprint. [ABSTRACT FROM AUTHOR]

The timing and mechanism of formation of the Tibet Plateau remain elusive, and even the present‐day structure of the Tibetan lithosphere is hardly resolved, due to conflicting interpretations of the geophysical data. We show here that significant advances in our understanding of this orogeny could be achieved through a better assessment of the composition and rheological properties of the deepest parts of the Tibetan lithosphere, leading in particular to a reinterpretation of the global tomographic cross sections. We report mantle phlogopite xenocrysts and carbonate‐bearing ultramafic cumulates preserved in Eocene potassic rocks from the Eastern Qiangtang terrane, which provide evidence that the lithospheric mantle in Central Tibet was enriched in H 2O and CO 2 prior to the India‐Asia collision. Rheological calculations and numerical modeling suggest that (1) such metasomatized mantle would have been significantly weaker than a normal mantle but buoyant enough to prevent its sinking into the deep mantle; (2) the slow seismic anomalies beneath Central Tibet may image a weakened lithosphere of normal thickness rather than a lithosphere thinned and heated by the convective removal of its lower part; and (3) melting of such soft and fusible metasomatized mantle would have been possible during intracontinental subduction, supporting a subduction origin for the studied Eocene potassic magmatism. These results demonstrate that the inheritance a soft and buoyant precollisional Tibetan lithosphere may have conditioned the growth and the present‐day structure of the Tibet Plateau. Plain Language Summary: The Tibetan Plateau is the largest relief on the Earth's surface, but also one of the least understood geodynamic phenomena, due to the lack of constrain on its growth evolution and mechanism. Here we have discovered, enclosed in Eocene (35‐Ma‐old) lavas from Central Tibet, hydrous and carbonated minerals derived from the underlying upper mantle, which reveal an unsuspected abundance of water and CO2 in this upper mantle. We show that, consequently, the upper mantle beneath Central Tibet has been anomalously weak since before the collision of India with Asia. It was previously thought to have disappeared, foundered in a process called "delamination," but we demonstrate here that this was an artifact: Most of the tibetan mantle is still there, but it is very weak and therefore does not appear on the seismic images. This implies that models expecting the Tibet Plateau to be a result of a delamination process are probably wrong; instead, we propose a model in which the weak upper mantle beneath our study area was easily indented by the strong adjacent continental block; this model manages to explain both Eocene magmatism and uplift in our study area. Key Points: Magmatic carbonates and mantle phlogopite have been found in 35 Ma lavas from Eastern QiangtangH 2O‐CO 2 metasomatism resulted in a very soft and fusible Tibetan subcontinental mantle lithosphereThis allowed intracontinental subduction magmatism and accounts for the upper mantle low VP anomaly [ABSTRACT FROM AUTHOR]

The incision history of the Three Rivers (Salween, Mekong, and Yangtze) region in the Southeast Tibetan Plateau has been linked to both tectonic and climatic controls. In this study, we report new apatite (U‐Th)/He and fission‐track thermochronology data from the >6,000‐m‐high Kawagebo massif, which forms the edge of the high plateau on the western flank of the steepened knickzone reach of the middle Mekong River valley. Thermal‐history modeling of a thermochronological age‐elevation profile shows rapid cooling since ~1.5 Ma and suggests a mean Quaternary exhumation rate of >1 km/Myr at the valley bottom. The amount of Quaternary exhumation is too high to be caused by fluvial incision alone and requires additional tectonic uplift. Comparing our data from the western flank of the Mekong River valley with published data from the eastern flank shows differential exhumation across the valley in the late Miocene, with the western flank undergoing more exhumation, but relatively uniform exhumation in the Quaternary. We relate rapid exhumation since the late Miocene on the western flank of the Mekong valley and the high topography of the Kawagebo massif to localized tectonic uplift associated with a restraining (left stepping) overstep between the still‐active right‐lateral Parlung and Zhongdian strike‐slip faults. The pattern of river steepness index across the knickzone also indicates that it results from locally focused uplift. Our results demonstrate the importance of detailed thermochronologic studies in this very active region to constrain the complex multiphase tectonic history before invoking any potential climatic forcing of river incision. Key Points: New low‐temperature thermochronology data show rapid Quaternary exhumation in the Mekong River knickzone, Southeast TibetBoth the amount of Quaternary exhumation and the pattern of river steepness point to a tectonic origin of the knickzoneThe exhumation history and topography around the knickzone are related to localized tectonic uplift associated with a restraining overstep between the Zhongdian and Parlung faults [ABSTRACT FROM AUTHOR]

The timing and mechanisms of uplift in southeastern Tibet remain disputed. To address this debate, we conducted structural and morphological analyses of the Yulong thrust belt; we also reconstruct the cooling and exhumation history of the Jianchuan basin in the hanging wall of the thrust system using inverse thermal modeling of apatite fission‐track and (U‐Th)/He thermochronology data. Our results provide evidence for 2.3–3.2 km of rapid exhumation in the Jianchuan basin between ~28 and ~20 Ma, followed by limited exhumation of less than 0.2 km since then. The magnitude of basin exhumation is consistent with the present‐day topographic step of 1.8–2.4 km across the Yulong and Chenghai thrust belts, as shown by morphometric analysis. We thus infer that the present‐day morphology of the southeastern margin of Tibet results partly from thrusting along the Yulong thrust belt during the Late Oligocene‐Early Miocene. This structure may be the southwest continuation of the Longmen Shan thrust belt, offset by the Xianshuihe fault in the Late Miocene. On a regional scale, the approximate synchronicity of exhumation in the hanging walls of the Yalong‐Yulong and Longmen Shan thrust systems indicates that widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene‐Early Miocene. Plain Language Summary: The timing and mechanisms for the high‐elevation, low‐relief landscape in southeastern Tibet remain at the center of debate. Using apatite fission track and apatite (U‐Th)/He thermochronology and thermal modeling, this study sheds new lights on this issue by reconstructing the cooling and exhumation history of the Jianchuan basin, western Yunnan. One major finding is that the Jianchuan basin experienced rapid exhumation during ~28–20 Ma at a rate of 0.57–0.80 km/Myr, coinciding with the absence of coeval sedimentation within the basin. Furthermore, morphometric and structural analyses point out a reasonable causal link between production of the topographic relief in the SE Tibet, exhumation of the Jianchuan basin, and thrusting of the Yalong thrust belt. These results allow us to propose a regional‐scale tectonic scenario of widespread crustal shortening and thickening took place in southeastern Tibet during the Late Oligocene‐Early Miocene. Key Points: The Jianchuan basin experienced 2.3‐3.2 km of exhumation at a rate of 0.57‐0.80 km/Myr at ~28‐20 MaExhumation of the Jianchuan basin was accomplished prior to ca. 20 MaTopographic relief in southeastern Tibet is partly produced by thrusting along the Yulong thrust belt during the Oligocene‐Early Miocene [ABSTRACT FROM AUTHOR]

The Litang fault system that crosses the Litang Plateau, a low relief surface at high elevation (∼4200-4800m above sea level) that is not affected by regional incision, provides the opportunity to study exhumation related to tectonics in the SE Tibetan Plateau independently of regional erosion. Combining apatite and zircon fission track with apatite (U-Th)/He thermochronologic data, we constrain the cooling history of the Litang fault system footwall along two transects. Apatite fission track ages range from 4 to 16 Ma, AHe ages from 2 to 6 Ma, and one zircon fission track age is ∼99 Ma. These data imply a tectonic quiet period sustained since at least 100 Ma with a slow denudation rate of ∼0.03 km/Ma, interrupted at 7 to 5 Ma by exhumation at a rate between 0.59 and 0.99 km/Ma. We relate that faster exhumation to the onset of motion along the left-lateral/normal Litang fault system. That onset is linked to a Lower Miocene important kinematic reorganization between the Xianshuihe and the Red River faults, with the eastward propagation of the Xianshuihe fault along the Xiaojiang fault system and the formation of the Zhongdian fault. Such strike-slip faults allow the sliding to the east of a wide continental block, with the Litang fault system accommodating differential motion between rigid blocks. The regional evolution appears to be guided by the strike-slip faults, with different phases of deformation, which appears more in agreement with an "hidden plate-tectonic" model rather than with a "lower channel flow" model. [ABSTRACT FROM AUTHOR]

The Béarn range, located to the north of the Axial Zone in the Western Pyrenees, is affected by numerous small-magnitude seismic events. These events overlap an area characterized by specific geological structures which are interpreted to have resulted from multistage extensional and compressional deformation. An analysis of surface geology draped over digital elevation model, together with field investigations, allow identification of two main shortening episodes with differing direction of contraction: D1 represents the inversion of the North Pyrenean Basin, whose Mesozoic infill was detached from highly extended crust and transported southward over the necking zone and the northern margin of the Iberian plate; D2 corresponds to the collision stage and is characterized in the study area by backfolding and backthrusting deformation coeval with uplift in the axial part of the chain due to thickening of the Iberian plate. The microseismicity appears to concentrate along the basal part of the inverted basin units (D1) where this initially low angle thrust has been tilted and steepened during collision (D2). We propose that local steepening of this ancient inversion structure, which should not be named 'North Pyrenean Fault,' provided the suitable dip for extensional solicitation in association with the present uplift of the Axial Zone, whatever the driving mechanism of this uplift could be. [ABSTRACT FROM AUTHOR]

The present work investigates the formation of curved ranges and syntaxes with scaled laboratory experiments. We simulated subduction and collision processes comparable to India-Asia configuration involving a continental upper plate and a subducting plate composed of an oceanic lithosphere and a continental indenter. The experiments reveal that the shape of the mountain range (concave, straight, or convex) and the development of syntaxes are controlled by the subduction interface, the buoyancy number ( Fb) of the upper plate (i.e., thickness and viscosity), and the boundary conditions. Four end-members regimes of indentation can be defined depending on the range shape and dynamics of the upper plate. The curvature of the range is convex toward the subducting plate with syntaxes for a weak subduction fault and concave without syntaxes for a strong subduction fault. Convex curvature and syntaxes form by overthrusting of upper plate material on the subducting plate, which is faster at the center than at the extremities. They are associated with a rather flat slab (underthrusting) during continental collision. Low- Fb experiments show less pronounced curvatures associated to thickening comparable to the early stages of the India-Asia collision. In contrast, a thick and weak upper plate (high Fb) leads to gravity collapse that increases the amplitude of the curvature and lateral escape, similar to the late evolution of the Himalaya-Tibet system. Important lateral decoupling on the sides of the indenter enhances the indentation and produces sharper syntaxes. [ABSTRACT FROM AUTHOR]

Terra Nova, 22, 290–296, 2010 High wavespeed seismic anomalies in the transition zone and uppermost lower mantle beneath the India-Asia collision zone, imaged by body-wave seismic tomography, have been interpreted as subducted fragments of continental material. In this study, we focus on the prominent anomaly located beneath India between depths of about 450 and 900 km. By combining the location of this anomaly with palaeogeographical positions of India, we constrain the timing of the subduction event probably related to this anomaly. We infer that a large portion of the north-western margin of India initiated subduction at 35 ± 5 Ma along a 1500-km-long WNW–ESE striking zone and ended with a progressive slab break-off process. This break-off started most probably around 25 Ma at the western end of the slab and propagated eastwards until complete break-off around 15 Ma. This study helps to constrain better the amount of convergence between India and Asia absorbed by continental subduction. [ABSTRACT FROM AUTHOR]