The Longmen Shan (LMS) fold-and-thrust belt in the eastern Tibetan plateau marks the boundary between the Songpan-Ganze terrane and the Sichuan basin. Deformation mechanisms and the mountain building process in the LMS remain unclear. Here we conducted field mapping, structural analysis, Ar-40/Ar-39 geochronology of biotite, and re-interpretation of the Wenchuan Earthquake Fault Scientific Drilling borehole data and a seismic reflection profile across the LMS. Our results indicate that a gently dipping LMS extruded wedge overlies the reactivated Yangtze craton. This wedge consists of several rigid Neoproterozoic complexes, bounded by the NW-dipping LMS detachment above and the Yingxiu-Beichuan thrust below. The Yingxiu-Beichuan thrust extends northwestwards to a depth of c. 8 km beneath the Songpan-Ganze terrane. Coeval activation of the top-to-the-NW LMS detachment and the top-to-the-SE Yingxiu-Beichuan thrust in the Early Cretaceous resulted in the extrusion of the LMS wedge from a depth of 10-15 km. The wedge rapidly exhumed through imbricated thrusting along low-strength series since 40-30 Ma. This Cretaceous basement wedge extrusion bridges the time gap between the Late Triassic-Early Jurassic crustal shortening and the Cenozoic rapid exhumation in the LMS, representing a transformation from north-south compression in the Late Triassic-Early Jurassic to east-west compression in the Cenozoic.

Global warming leads to drastic glaciers shrinkage worldwide, hence affecting the global water balance. Small mountain glaciers are the most widespread types of glaciers but have received less attention compared to larger ones, despite their importance for the regional hydrological cycle. To better understand the forcing underlying their dynamics, we investigated the glacial activity in the Hengduan Mountains in the SE Tibetan Plateau over the last 2000 years by analysing sediments from the Yunzhu proglacial lake. Five sediment cores were retrieved and dated using short-lived radionuclides, 14C, and analyses of Earth's magnetic field palaeosecular variations. A multiproxy analysis was performed on sediment cores, including geochemical, sedimentological, and hyperspectral analyses. As the sediment was relatively homogeneous and poor in organic material, geochemical ratios and pigment analysis were used to track the evolution of terrigenous inputs and lake photosynthetic activity. Sedimentation is dominated by clastic inputs, which are traced by K flux, while the authigenic components are traced by chlorophyll pigments. During the Little Ice Age (LIA), anoxic conditions prevailed at the bottom of the lake, leading to the preservation of millimetric laminae in the sediment and a bloom of purple sulphur bacteria, visible through abundant bacteriochlorophyll a pigment. We attribute this to persisting ice cover preventing water column mixing over most of the year. During cold periods such as the LIA or the Dark Ages, the relative amount of terrigenous inputs increased at the expense of lake bioproductivity. We interpret the observed erosion increases during cold periods as the consequence of glacial activity, consistent with other sparse glacial records available on the Tibetan Plateau. We show that glacial extent was mainly controlled by temperature in the past two millennia rather than by precipitation, yielding potential widespread melting in the next decades as well as more irregular water supply downstream.

While the Xianshuihe fault displays continuous creeping behavior, it is also the most seismically active fault in the eastern Tibetan Plateau, and its earthquake mechanisms remain unclear. Here, we aim at the stick‐slip portion of the creeping Qianning segment of the Xianshuihe fault to determine the characteristics of fault rocks and how fluids at depth influence fault behavior. Field survey, optical and scanning electron microscope observations, X‐ray diffraction and fluorescence analyses, as well as carbon and oxygen isotope analyses were performed on the collected samples. The fault core consists of 3–5 cm‐thick black fault gouge and ∼2.5 m‐thick breccia, surrounded by ∼12 m damage zone. In contrast to fault breccia (1–8 cm in diameter), the black fault gouge, which represents the principal slip zone of repeated seismic events, contains angular quartz particles (∼10 μm on average) and clays dominated by illite. The fluid‐rock interactions altering silica minerals into illite, and the thermal decomposition of carbonate minerals, passively increase the relative content of quartz and feldspar (total 63%–73%) in the fault gouge. The deeply sourced CO 2 (from mantle and metamorphic degassing) within the hydrothermal fluids causes carbonate precipitation in breccias (21%–53%), composed of calcite, dolomite, and aragonite. These fluid‐assisted reactions lead to more abundant strong mineral phases (quartz, feldspar, and carbonates, 64%–87%) than weak clays (12%–36%) within the fault core, and locally strengthen the fault, which inhibits slow release of stress at shallow depth and promotes seismic rupture of the fault.

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.

Determining the timing of E-W extension across the NS-trending rifts in southern Tibet is key to test the mechanical models of the latest evolution in the collision between India and Asia. We focus on the southern half of the largest of the seven main rifts, the Yadong-Gulu rift (YGR), which, despite being the focus of numerous studies thanks to its easy access, still lacks direct time constraints. Using illite K-Ar ages of fault gouge from the active Yadong normal fault of the YGR, we directly constrain its onset timing at 9 ± 1 Ma. (U-Th)/He dating of the footwall leucogranite reveals a rapid exhumation of the southern YGR since ∼9 Ma, attesting to its onset activity. Such timing is similar to that estimated for the northern half of the YGR at 8 ± 1 Ma, suggesting that the entire YGR formed at approximately the same time. Our synthesis of published initiation ages of the other main rifts in southern Tibet shows that they mostly fall between ∼23 and 8 Ma, suggesting a clear spatial and temporal pattern of old initiation ages to the west and young to the east. In this case, the formation of rifts in southern Tibet is unlikely caused by slab tearing of the underthruting Indian plate or orogenic collapse. Our study supports that E-W extension in Tibetan Plateau is triggered by a combination of eastward propagation of the Karakorum-Jiali fault zone and divergent thrusting along the curved Himalayan arc.

Large earthquakes are among the most dangerous natural disasters with potentially devastating effects on society and infrastructure across the globe. In order to better understand earthquakes, research in active tectonics aims at quantifying crustal deformation throughout the active fault's earthquake cycles by studying geomorphic and stratigraphic evidence of recent and past earthquakes. The underlying assumption in this approach is that a fault's current and previous seismic behavior is representative of its future behavior. Constraining a fault's seismic behavior in such a manner requires high-resolution geomorphic and stratigraphic records that enable us to resolve the spatial and temporal characteristics of co-, post-, and interseismic phases, ideally over multiple earthquake cycles. Recent technological developments have dramatically increased not only the amount and resolution of topographic and geophysical survey data sets but also our ability to date stratigraphic units and geomorphic surfaces. These technological advances have enabled us to better understand the interplay between crustal deformation, earthquake ruptures, and their signature in geomorphic and stratigraphic records. In particular, the availability of high-resolution data sets from LiDAR, SfM, or geophysical surveys and the use of accurate dating methods such as cosmogenic or OSL dating allow us to quantitatively study surface deformation at high spatial resolution over large areas and at multiple time scales-from a few years to millions of years. In this special issue, we focus on the tectonic activity of active faults and the geomorphic processes in various tectonic regimes worldwide. It covers active tectonics, earthquake geology, remote sensing, tectonic geomorphology, Quaternary geochronology, geohazard, and seismology.

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.

2022年1月8日01时45分,青海省海北州门源县发生了Ms6.9级强烈地震,震中位于青藏高原东北缘海原断裂带中西段的冷龙岭断裂附近.震后的野外现场考察表明,这次地震在海拔3500～4100 m的高原北部祁连山区形成了一系列由张裂隙、张剪裂隙、剪切裂隙、挤压鼓包和裂陷等多类型破裂雁行状组合而成的同震地表变形带,表现为左旋走滑运动性质,总长约27 km.破裂带呈NWW SEE走向,可分为南北两支,北支沿冷龙岭断裂西段分布,南支沿托莱山断裂东端分布,与北支间隔3 km呈左阶雁行排列.根据破裂带的走向变化和阶区特征,可将破裂带分为三段:西段、中段和东段,与地表同震位移分布特征较为吻合.西段为破裂带的南支,呈N93°E走向,长约4.5 km,最大左行水平位错约85 cm;中段为北支破裂带西侧部分,主要呈N102°E走向,长约7.5 km,最大左行水平位错约3.7m;东段为北支破裂带东侧部分,走向呈N110～120°E走向,长约15 km,最大左行水平位错约3.0m.门源地震震级与地表破裂带分布规模和变形强度的对比,表明本次地震的震源深度较浅,可能远小于10 km深.这次门源地震的发震断裂为海原断裂带呈挤压弯曲部分的冷龙岭断裂,具有花状构造特征.由于本次地震余震向SE方向扩展,表明具有应力向东迁移趋势,因此,冷龙岭断裂东侧处在海原断裂带上1920年海原大地震与2022年门源地震之间地震空区的金强河、毛毛山和老虎山断裂未来强震危险性升高,需要重点关注.

We report detailed field measurements of the 2021, Mw7.4 Maduo earthquake surface rupture south of the Kunlun fault, near the northern boundary of Tibet's Bayan Har block. In the field, the dominantly left-lateral surface rupture length was ∼151 km, along the poorly known Jiangcuo fault, with maximum horizontal and vertical displacements of ∼2.1±0.2 to 2.9±0.2 m (up to 3.6±0.2 m at one site) and ∼1.2±0.2 to 1.8±0.2 m, respectively. The rupture, which propagated bilaterally from a roughly central epicenter, terminated in well-defined, ∼20 km-long horsetail splays, as predicted by Coulomb stress failure, consistent with the very young age of the still growing Jiangcuo fault, which may be trying to bypass the Anyemaqen restraining bend in order to connect directly the Kokoxili and Maqen segments of the main Kunlun fault. 14C dating at one site (Cuoerjiala) implies long return times (≥6500 years) for M7+, Maduo-type earthquakes, in keeping with a slow horizontal slip rate of ∼0.55±0.03 mm/yr and the subdued geomorphic expression of the fault. In the broader Tibetan tectonics framework, the Jiangcuo fault may be better interpreted as a kinematic streamlining of the Kunlun fault bend, rather than a result of diffuse deformation across the Bayan Har terrane.

Magnetic mineral assemblages record physical and chemical changes that occur during and after seismic events with large slips. For example, previous studies have reported that siderite, a common phase in carbonate rocks and a cement in noncarbonate rocks, breaks down to neoformed magnetite due to seismic friction or fluid related to earthquakes and high-velocity activities. Seismic magnetic mineral transformation of siderite to hematite, while also possible, is less common. Here, we present new rock magnetism and X-ray diffraction data to assess the magnetic mineral assemblage and mineral reactions along the East Yibug Chaka Fault, Tibetan Plateau. These data from well-exposed outcrops document the presence of siderite, magnetite and hematite. We show that abundant magnetite is neoformed during historic seismic fluid processes due to the breakdown of siderite at similar to 300-400 degrees C and that hematite forms from magnetite and siderite through subsequent interaction with interseismic fluids and/or Earth surface weathering.

Thrusting implication in the crustal thickening history of eastern Tibet is highly debated. The ∼250 km‐long Muli thrust of the Yalong thrust belt in SE Tibet is a major Miocene structure with a pronounced topographic step (∼2,000 m). Using thermo‐kinematic modeling based on thermochronology data, we constrain the crustal geometry of the thrust as being steep (>70°) at the surface, in agreement with field observations, and flattening at depth (≥20 km) on an intra‐crustal décollement. Thrusting motion on the fault shows a velocity of 0.2 ± 0.06 km/Ma since 50 Ma, followed by an acceleration at a rate of 0.6 ± 0.08 km/Ma starting at 12.5 ± 1 Ma, yielding a total of ∼15 km of exhumed crust. Deeper, deformation may be localized through a ductile shear zone, and be related to the ∼15 km Moho step and shear wave velocity contrast imaged by tomography beneath the Yalong thrust belt.

The geometry and kinematics of first-order structural systems on the Tibetan Plateau (TP) are key to understanding how the continental crust and lithosphere deformed during the India-Asia collision. The Altyn Tagh Fault (ATF), which is a large-scale fault bounding the northern edge of the Tibetan Plateau (NTP), absorbed as much as one-third of the total convergence in the collision between India and Eurasia. The Baiganhu Fault, in the western Qimen Tagh Mountains on the NTP, is recognized as belonging to the ATF and has played an important role in the development of its adjacent region. Due to the high elevation and harsh working conditions, this fault has received little attention, and the timing of its activation has not been thoroughly researched. In this study, we collected granite samples from close to the Baiganhu Fault in the Qimen Tagh Mountains, and used zircon and apatite fission track dating to constrain the timing of activation for this fault. The fission track ages and HeFTy modeling results reveal two rapid cooling stages along the Baiganhu Fault: one during the Jurassic-cretaceous (similar to 180-120 Ma) and the second since the mid-Miocene (similar to 15-10 Ma), consistent with other regions on the NTP. The first fast exhumation event was a far-field response to the Lhasa-Qiangtang collision, and the second stage most likely resulted from crustal thickening, with a connection to the ATF occurring at around similar to 15-10 Ma.

The global and systematic coverage of Sentinel-1 radar images allows characterizing, by radar interferometry (InSAR), surface deformation on a continental scale. Our study focuses on the eastern part of the Tibetan plateau, where a combination of major strike-slip and thrust fault systems accommodates part of the deformation related to the collision between the Indian and Eurasian plates. We use an automated Sentinel-1 InSAR processing chain based on the NSBAS approach (Doin et al., 2011, Grandin, 2015) to measure the interseismic deformation across these fault systems. Processing is made on the CNES high-performance computer center in Toulouse in the FLATSIM project framework (ForM@Ter LArge-scale multi-Temporal Sentinel-1 Interferometric Measurement, Durand et al., 2019). We perform a time series analysis of the 2014-2020 Sentinel-1 InSAR data set, for 1200 km-long tracks (acquired along 7 ascending and 7 descending orbits), covering a 1 700 000 km2 area, with a 160 m spatial resolution. From about 130 acquisitions per track, we perform about 600 interferograms, with short, three months, and one-year temporal baselines. After inversion, we obtain time series of line-of-sight (LOS) delay maps, including residual atmospheric delay and network misclosure measurements. The time series are fitted by a seasonal signal plus a velocity trend. The velocity field on overlap areas agrees within less than 1~mm/yr. Finally, we decompose the LOS velocity maps into a vertical and a horizontal contribution. InSAR velocity maps highlight surface deformation patterns mostly localized on known major faults, short-wavelength patterns attributed to slope instabilities phenomena, and hydrological signals. The seasonal signal combines residual atmospheric phase delays and widespread hydrological phenomena in sedimentary basins, which we interpret in parallel with the regional geological map. Masking areas affected by dominant gravitational slope or hydrological deformation allows to better focus on tectonic deformation. We finally discuss slip partitioning on the various fault systems from the velocity maps and 2D profiles’ analysis.

大陆内部构造变形和地震活动往往突显出复杂的、区域性的特征,很难用板块构造理论来解释.青藏高原是大陆构造变形的典型实例,具有不同构造变形的分区特征,不仅表现在物质组成、地形地貌和断裂组合等方面的不同,而且还表现出不同的地震活动特征.东昆仑断裂带以北的青藏高原北部地块,主要发育一系列挤压环境下的盆岭构造,表现为以连续变形为特征的上地壳挤压缩短变形;高原中北部巴颜喀拉地块,具有整体向东运动的特点,变形主要集中在其边缘,表现为刚性块体运动特征.在东部,由于稳定的四川盆地(扬子地块)的阻挡,位于龙日坝和龙门山断裂带之间相对坚硬的龙门山地区受到东西向强烈挤压,西部边界为伸展变形;在高原中央腹地羌塘地块西部,由于上地壳物质在向东挤出的驱动下不断变形,沿一系列小型正断层和走滑断层以伸展变形为主,表现为弥散型变形特征.相比之下,羌塘地块的东部向东-南东方向挤出,在大型走滑断层之间形成一个刚性块体;高原南部地块以东西向伸展的南北向裂谷系为主要变形特征,高原南缘以南北向挤压的大型逆冲断裂系为特征.历史地震和仪器记录的大地震(M≥8)只发生在高原东北和东南部的大型走滑带,以及东部和南部边缘的大型逆冲断裂上,沿后者更为频发.到目前为止,高原其他地区只发生了8级以下地震.青藏高原这种分区域的地壳变形形式和地震活动分布是大陆构造变形的重要特征.

Southern Tibet is characterized by seven main N-S trending rifts bounded by normal faults which accommodate E-W extension. Quantifying the throw and extension rates along these rifts is essential to understand their activity, onset timing, regional seismic hazard and kinematic role in the tectonic evolution of the Tibetan Plateau. The Yadong-Gulu rift (YGR), near Lhasa, is the longest and most prominent rift in southern Tibet, and one of the few that crosses the Himalayas, however it remains poorly studied and understood. Here, we focus on the Yadong rift, i.e., the southern section of the YGR, south of the Yarlung Zangbo suture. We determine the late Quaternary/Holocene throw rates at four sites, where the active Yadong normal fault vertically offsets glacial and fluvial geomorphic surfaces. Using terrestrial LiDAR, UAV and kinematic GPS, we precisely measured vertical offsets (up to 17 m) and constrained the age of abandoned surfaces using 32 Be-10 cosmogenic surface-exposure ages (similar to 10-20 ka), one optically stimulated luminescence age and two travertine samples dated using U-series dating. The offset-age reconstructions yield uniform throw rates of 0.9 +/- 0.3 mm/yr along the entire Yadong rift. Taking a fault dip of 50 degrees as measured in the field, we obtain late Quaternary E-W extension rates of 0.8 +/- 0.3 mm/yr, which is similar to but at the lower end of those along other rifts in southern Tibet (similar to 1-2 mm/yr).

The presence of similar to NS-trending rifts within the Tibetan Plateau attests that it is undergoing similar to EW extension. In southern Tibet, the total extension rate, distributed across seven main rifts over a distance of similar to 1,000 km, has been inferred to amount to about half of the shortening rate across the Himalayas. Quantifying the late Quaternary extension rates across the largest rift (Yadong-Gulu rift [YGR]) is important to understand Tibetan deformation and to discuss the high plateau evolution during the later stages of continental collision. We performed Be-10 surface-exposure cosmogenic nuclide dating of 57 samples from three fluvial surfaces and two moraines that are vertically offset by the normal faults bounding the northern YGR. After carefully assessing individual ages at each site, to elucidate scatter in the age distributions, we obtained similar to EW extension rates of up to 3-6 mm/yr near the northern end of the rift (Gulu) and of only 1.3 +/- 0.3 mm/yr in the south (Yangbajing). The fast rates in the north may be influenced by dextral slip along the Beng Co fault, whose rate ought to be at least 6.0 +/- 1.8 mm/yr. The total late Quaternary extension rate of 9 +/- 2 mm/yr we infer across southern Tibet between similar to 81 degrees E and 92 degrees E, assuming similar rates across each rift, is similar to earlier, qualitative inferences and consistent with recent geodetic results. Distinct deformation rates north and south of the Bangong-Nujiang suture may reflect significant differences between the extensional kinematics and mechanisms across the Qiangtang and Lhasa blocks.

The South Tibetan Detachment System (STDS) and the Yadong-Gulu Rift (YGR) are important extensional structures in the southern Tibet, which are closely related to the uplift of the Tibetan Plateau. The chronological information of the tectonic uplift in southern Tibet since the Cenozoic is of great significance for the discussion of the uplift mechanism of the Tibetan Plateau and the dynamics of continental deformation. We conducted zircon U-Pb dating and low-temperature thermochronology analysis of apatite fission tracks on the Chumba Yumco leucogranite in the Yadong area of the southern Tibet. The results show that the Chumba Yumco leucogranite have gone through five different uplift-cooling stages within 22Ma : the cooling rate during 18 similar to 15. 6Ma is 125 degrees C/Myr; during 15. 6 similar to 11Ma, the average cooling rate was about 94 degrees C/Myr; 11 similar to 7Ma, the average cooling rate is about 24 degrees C/Myr; the average cooling rate of 7 similar to 3Ma is about 5 degrees C/Myr; after 3Ma, the average cooling rate was about 14 degrees C/Myr. Because the studied pluton is located in the STDS and has been cut by the Yadong fault, we conclude that the activity time of the STDS is 22 similar to 11Ma and the onset time of the Yadong rift is 11Ma. Thermal history modeling results indicate a fast cooling stage at similar to 3Ma, which represent strong activity of the Yadong rift.

喀喇昆仑断裂系(KF)位于青藏高原西缘,具有右旋走滑性质,从帕米尔高原至尼泊尔西部延绵1000多km.长期以来,对于喀喇昆仑断裂活动的起始时间、总位移量、在不同时间尺度上的滑移速率以及断层两端的精确位置等问题,都存在较大争议.为了更好的了解喀喇昆仑断裂现今的运动学特征及其与喜马拉雅—青藏高原陆内碰撞造山带的关系,确定喀喇昆仑断裂的滑移速率历史以及它随时间和/或空间的变化规律是极其重要的.目前研究表明,从现今的大地测量学尺度到几个百万年的地质学尺度,喀喇昆仑断裂走滑速率的变化范围为3～10 mm/yr.本论文对断裂各段的分布情况进行了详细描述,阐述了获得晚第四纪以来走滑速率的方法,回顾了喀喇昆仑断裂在大地测量学、晚第四纪以及地质学等不同时间尺度的走滑速率,并重点讨论了晚第四纪以来断裂的走滑速率.然后,确定了喀喇昆仑断裂北端的精确位置、讨论了其运动学意义和地震灾害效应.鉴于喀喇昆仑断裂具有长期的活动历史、规模巨大、运动速率较高,我们认为即使板块内部小尺度的似连续变形非常发育,板块模型依然可以很好的解释由于印度-亚洲板块碰撞造成的喜马拉雅北部的岩石圈变形.喀喇昆仑断裂、阿尔金断裂、昆仑断裂及龙木错—郭扎错断裂等青藏高原周缘的主要走滑断裂对青藏高原向东的挤出起着重要的调节作用.