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In the southeastern Tibetan Plateau, region‐scale dextral strike‐slip shear zones, crucial for India‐Asia convergence, were investigated along the Dulongjiang shear zone near the Eastern Himalayan Syntaxis (EHS). Structural, kinematic, and geochronological data from Dulongjiang and Nabang regions in western Yunnan, China, reveal dextral strike‐slip shearing between 30 and 15 Ma. Various rocks were affected by moderate‐temperature shear deformation (∼450–550°C), inferred from microstructures and quartz CPO patterns, during dextral strike‐slip and exhumation of the shear zone. Combined with structures of pre‐, syn‐, and post‐shearing leucogranites, zircon U‐Pb dating indicates that the dextral shear along the shear zone began in the Early Oligocene (30–29 Ma) subsequent to the India‐Asia collision. Micas in mylonitic granites yield 40Ar/39Ar ages, suggesting that the principal dextral shear deformation occurred approximately between 18 and 15 Ma. The Dulongjiang shear zone is linked to the Parlung, Nabang shear zone, and Sagaing Fault, forming a regional Cenozoic dextral shear system around the EHS. The study, combined with tomographic anomalies beneath the India‐Asia collision zone, highlights distinct lithospheric‐scale evolution in southeastern and eastern Tibet. Continuous intracontinental strike‐slip shearing indicates a tectonic shift from Tibetan extension to block rotation around the EHS. From 30 to 15 Ma, slab tear, accompanied by clockwise rotation and dextral strike‐slip shearing, suggests a warmer geodynamic setting influenced by hot mantle flow associated with ongoing subduction of the Indian lithosphere. Oligocene‐Miocene dextral strike‐slip shearing around the EHS, linking southwards with the Sagaing Fault, may correspond to the rotation necessary for slab to bend, stretch, and eventually tear beneath the region. Plain Language Summary: The southeastern Tibetan Plateau undergoes active southeastward extrusion and rotation around the Eastern Himalayan Syntaxis (EHS) due to ongoing Indo‐Eurasian continent collision. N‐S, NW‐SE, and NE‐SW ductile strike‐slip shear zones/faults in Tibet and the Indochina Block reveal this tectonic activity. Understanding their kinematics, linkages, and developmental patterns is crucial for investigating the relationship between Cenozoic surface tectonics and Tibetan Plateau lithospheric evolution. This study focuses on the Jiali‐Dulongjiang‐Nabang dextral (relative rightward movement on both sides of the fault) strike‐slip ductile shear zone/fault system, revealing a curved regional‐scale dextral strike‐slip zone system influenced by continuum rotation deformation, driven by slab tear beneath the EHS region. Contrary to the concept of a conjugated strike‐slip shear/fault system dominating extension tectonics, these findings suggest a significant influence of continuum rotation deformation on the initiation, movement, and linkage of curved dextral strike‐slip shearing around the EHS. Key Points: A network of dextral strike‐slip shear zones formed a regional curved belt around the Eastern Himalayan Syntaxis from ∼30 to ∼15 MaSlab tear beneath the Eastern Himalayan Syntaxis induced unique asthenospheric flow pattern, causing the bending and interconnection of dextral shear zonesThe V‐shaped conjugate shear zones are related to indent‐driven system, marking northward penetration of the Indian plate into Eurasia [ABSTRACT FROM AUTHOR]

Tectonic research of the Tibetan Plateau has long focused on its deformation style and mechanisms. The 2008 Mw7.9 Wenchuan earthquake ruptured the Longmen Shan fault located at the eastern rim of the plateau and excited a viscoelastic response of the lithosphere. We infer a three‐dimensional (3D) rheological structure of eastern Tibet from modeling nine years of postseismic displacements observed by GPS. Our solution provides tight constraints on the lower‐crustal and upper‐mantle steady‐state viscosities of the Songpan‐Ganzi Terrane as (5.0 ± 0.7) × 1018 and (1.3 ± 0.3) × 1019 Pa s, respectively, consistent with a "jelly sandwich" model of Tibet, but not with some crustal channel flow models featuring much lower viscosities. The inferred lower‐crustal and upper‐mantle transient viscosities are (5.0 ± 1.3) × 1017 and (5.0 ± 1.5) × 1018 Pa s, respectively, suggesting nonlinear deformation mechanisms. The adjacent West Qinling and Sichuan blocks feature an order‐of‐magnitude higher rheological strength, which is consistent with the changes in the crustal material properties and interseismic deformation style across the East Kunlun‐Tazang and Longmen Shan faults. Our results enable us to propose a conceptual 3D tectonic deformation model, in which the eastward extrusion of Tibet is absorbed in the Songpan‐Ganzi crust mainly by E‐W shortening and N‐S extension, accommodated through faulting of conjugate strike‐slip faults in the upper crust and distributed shear in the lower crust. Plain Language Summary: One of the fundamental questions in Earth science is the deformation mechanism of the continents, which controls the topography of the land we live on, the distribution of the resources extracted to support our living, and the origins of natural hazards such as landslides and earthquakes. The Tibetan Plateau, arguably, is the best natural laboratory to study the deformation mechanism of the continents. In this study, we address two critically important and much debated problems in Tibetan Plateau dynamics; that is, the rheologic structure of the Tibetan lithosphere and how it deforms under tectonic loading. We use nine years of mostly unpublished three‐dimensional (3D) deformation data collected in the aftermath of the 2008 Mw7.9 Wenchuan earthquake to infer the rheological structure of the eastern Tibet lithosphere. Our results are consistent with a "jelly sandwich" model, with a relatively weak lower crust underlain by a stronger upper mantle. However, they do not support the very low viscosities envisioned by some of the channel flow models of lower crustal deformation in eastern Tibet. We also propose a conceptual 3D tectonic deformation model, in which the eastward extrusion of Tibet is absorbed in the Songpan‐Ganzi crust by E‐W shortening and N‐S extension, accommodated through conjugate faults in the upper crust and distributed shear in the lower crust. Key Points: A comprehensive GPS data set is provided to cover nine years of three‐dimensional (3D) postseismic displacements after the 2008 Wenchuan earthquakeGPS constrained eastern Tibet Lithospheric rheological structure agrees with a "jelly sandwich" model, not models of much lower viscositiesA conceptual 3D tectonic deformation model in eastern Tibet is proposed to characterize its dynamic deformation style and mechanisms [ABSTRACT FROM AUTHOR]

Rock slope failures are controlled by a complex interplay of geological structures and anthropogenic activities. In this study, data from structural geology, rock mass characterization, and ground-based monitoring networks are integrated into a numerical model. This model is used to explore the relationships among structural features, damages, anthropogenic activities, and slope failures occurring on the Tibetan Plateau in China. In particular, a model for the interpretation of brittle tectonic structures is illustrated, which characterizes the fracture patterns and explains the role of these features in the development of rock slope instability. Additionally, the relationships between tectonic structure-related fractures and slope failure mechanisms are investigated by characterizing the rock mass damage using the geological strength index. Finally, a numerical model is developed, which integrates the available data. It is found that the tectonic structure-related fractures controlled by an anticline are primarily responsible for slope failure, while an excavation was identified as its triggering mechanism. This research can serve as a reference for studies on excavation-induced rockslides. [ABSTRACT FROM AUTHOR]

Geodetic velocities and mantle seismic anisotropy provide relevant constraints to the dynamics of the Asian continent. Here, these are compared to numerical models of subduction, collision, and upper plate deformation, developing features similar to the present‐day India‐Asia region. Varying buoyancy and far‐field forces, the models provide coupled surface and mantle motions and deformation allowing a first‐order agreement to the observables in the Tibetan area. Observed trends are reproduced when the pull from the Indian slab vanishes and the neighboring southeast Asian slab drives extrusion in eastern Tibet, matching GPS rotation and convergence‐perpendicular component, and a far‐field force acts to increase the GPS convergence‐parallel component and lithospheric thickening observed in the Tian Shan‐Tibetan domain. The net force exerted on the Tibetan lithosphere is ~2.6 × 1012 N/m, mostly due to neighboring southeast Asian subduction, and raises to ~2.8 × 1012 N/m, when additional far‐field forces apply. Largest suction force exerted on the Sunda margin is ~2.4 × 1012 N/m, whereas the comparison to seismic anisotropy supports the idea that the mantle is passive. These are interpreted in the context of the differential along‐strike dynamics of the Indian‐southeast Asian subduction: The coupled indentation‐suction along the plate margin drives large‐scale extrusion, while the excess stress along the Indian margin is accommodated by Tibetan lithospheric thickening. The models constrain the boundary forces and lithospheric processes of the Asian tectonics and emphasize the role of large‐scale coupling of the Indian margin and the southeast Asian subduction. Key Points: Varying boundary forces in subduction models provide continental motions and deformation and mantle shearing end‐membersThese are compared to Tibetan Plateau GPS motions and seismic anisotropy in the India‐Asia regionThe match to observables constrains the boundary forces acting along the subduction margin [ABSTRACT FROM AUTHOR]

A number of large landslides, which have strongly affected fluvial processes in the upstream catchment of the Minjiang River along the eastern margin of the Tibetan Plateau, Sichuan, were investigated with regard to both geological structure and topographic development. Topographic analysis suggested that there is a major knickpoint that formed not as a result of landslides but via tectonic activity and that the knickpoint propagated upstream, forming an inner gorge and undercutting and destabilizing nearby slopes. The effects of the knickpoint propagation and inner gorge formation on slope stability are dependent on the geometrical relationships between the river and geological structures. When the geological trend is normal or highly oblique to the river axis, landslides generally do not occur, but gigantic rockslides have occurred on one side of the Minjiang valley, which can be attributed to a wedge structure consisting of bedding planes and joints with intersections dipping valleyward and tight folds with hinges plunging valleyward. When the beds are planar, moderately dipping, and strike nearly parallel to the river, buckling deformation commonly occurs on cataclinal slopes, often transforming into catastrophic failure. Landslide dams form another type of knickpoint on the river channel that gradually disappear from the downstream to upstream as a result of river erosion. Our findings strongly suggest that the study of slope development by river incision must consider geological structures and that an understanding of geological structures and river incision history can provide a conceptual model for the prediction and mitigation of geohazards in tectonically active drainage basins. [ABSTRACT FROM AUTHOR]

Abstract As the eastern margin of the Tibetan Plateau, the Longmen Shan fault zone (LMSFZ) is characterized by a complex structural style and strong seismicity, such as the 2008 Wenchuan Ms8.0 and 2013 Lushan Ms7.0 earthquakes. In order to better understand the subsurface geometry of the LMSFZ we inverted 391 focal mechanism solutions (FMS) of earthquakes (M ≥ 3.5) that occurred between 2009 and 2016 in the Longmen Shan region using seismic waveforms. Subsequently, we calculated the stress field based on the FMSs. The results show that the LMSFZ is dominated by a thrust faulting stress regime with subhorizontal NW-SE-trending maximum principal stress σ 1 and subvertical minimum principal stress σ 3 , indicating a lateral compression due to the southeastward movement of the Bayan Har block. Changes in fault dips at ~ 10 km depth are inferred as the result of a shallow level detachment layer, which may also promote shortening of the upper crust and uplift of the Longmen Shan. Based on differences in subsurface fault geometry, stress field and geomorphological evidence, we divide the LMSFZ into two segments by Beichuan County: the southwestern segment has a listric fault geometry, while the northeastern segment is dominated by subvertical transpressional strike-slip faults. According to the FMSs results, we suggest that the Lixian fault is a tear fault accommodating different thrusting rates in the eastern margin of the Bayan Har block. The normal faulting earthquakes in the Lixian area are caused by local extension resulting from the sinistral shear movement of Lixian fault in a strike-slip faulting stress regime. It is suggested that under the continuous southeastward movement of the Bayan Har block and the obstruction of the rigid Sichuan basin, stress is accumulating along the southwestern segment of the LMSFZ, to which accordingly a high seismic hazard is ascribed and which should be carefully monitored. Graphical abstract Unlabelled Image Highlights • 391 Focal mechanism solutions in the Longmen Shan fault zone are presented. • A shallow detachment layer at ~10 km depth is revealed by changes in fault dips. • Normal faulting earthquakes in the Lixian area are caused by local extension. • The Longmen Shan fault zone should be divided into two segments. • Seismic hazard in the southwestern segment is potentially high. [ABSTRACT FROM AUTHOR]

The Lenglongling fault (LLLF) is located along the northeastern margin of the Tibetan Plateau and forms a part of the Tianzhu seismic gap along the Qilian‐Haiyuan fault zone. Little is known about the recurrence of large earthquakes along the LLLF nor the associated seismic hazards of the gap. Here the six most recent surface rupturing paleoearthquakes of the LLLF are revealed by measurement of offset landforms, trench excavations, and radiocarbon dating. They are labeled E1–E6 from youngest to oldest, and their timings are constrained to the following time ranges: 636–498 to present, 2951–1155, 4016–3609, 5325–4476, 7284–6690, and 8483–7989 years BP, respectively. The LLLF displays evidence of fresh, recent surface rupture, and the trench sections reveal that the fault ruptured to the ground surface during the most recent event. Based on this fresh surface rupture and historical earthquake records, the latest event E1 was most likely the 1927 M8.0 Gulang earthquake. In conjunction with previous studies, Gulang earthquake might be a complicated event characterized by the combined rupture of both strike‐slip and thrust faults. The average recurrence interval of the six paleoearthquakes is 1643 ± 568 years, and the coefficient of variation is 0.34, indicating that the LLLF follows a quasiperiodic recurrence model. Based on this new understanding of the last event, the LLLF may not be a part of the Tianzhu seismic gap. However, an earthquake of up to MW7.6 could still rupture the gap sections composed of the Jinqianghe, Maomaoshan, and Laohushan faults. Key Points: Six recent surface rupturing paleoearthquakes of the Lenglongling fault were revealed by trench excavationsThe most recent event of the Lenglongling fault was most likely the 1927 M8.0 Gulang earthquakeThe Lenglongling fault may follow a quasiperiodic recurrence model [ABSTRACT FROM AUTHOR]

Magnitudes of differential stress in the lithosphere, especially in the crust, are still disputed. Earthquake-based stress drop estimates indicate median values <10 MPa whereas the lateral variation of gravitational potential energy per unit area (GPE) across significant relief indicates stress magnitudes of ca. 100 MPa in average across a 100 km thick lithosphere between the Indian lowland and the Tibetan plateau. These standard GPE -based stress estimates correspond to membrane stresses because they are associated with a deformation that is uniform with depth. We show here with new analytical results that lateral variations in GPE can also cause bending moments and related bending stresses of several hundreds of MPa. Furthermore, we perform 2-D thermomechanical numerical simulations (1) to evaluate estimates for membrane and bending stresses based on GPE variations, (2) to quantify minimum crustal stress magnitudes that are required to maintain the topographic relief between Indian lowland and Tibetan plateau for ca. 10 Ma and (3) to quantify the corresponding relative contribution of crustal strength to the total lithospheric strength. The numerical model includes viscoelastoplastic deformation, gravity and heat transfer. The model configuration is based on density fields from the CRUST1.0 data set and from a geophysically and petrologically constrained density model based on in situ field campaigns. The numerical results indicate that values of differential stress in the upper crust must be > ca. 180 MPa, corresponding to a friction angle of ca. 10° to maintain the topographic relief between lowland and plateau for >10 Ma. The relative contribution of crustal strength to total lithospheric strength varies considerably laterally. In the region between lowland and plateau and inside the plateau the depth-integrated crustal strength is approximately equal to the depth-integrated strength of the mantle lithosphere. Simple analytical formulae predicting the lateral variation of depth-integrated stresses agree with numerically calculated stress fields, which show both the accuracy of the numerical results and the applicability of simple, rheology-independent, analytical predictions to highly variable, rheology-dependent stress fields. Our results indicate that (1) crustal strength can be locally equal to mantle lithosphere strength and that (2) crustal stresses must be at least one order of magnitude larger than median stress drops in order to support the plateau relief over a duration of ca. 10 Ma. [ABSTRACT FROM AUTHOR]

Variation in the location of the South Asian High (SAH) in early boreal summer is strongly influenced by elevated surface heating from the Tibetan Plateau (TP) and the Iranian Plateau (IP). Based on observational and ERA-Interim data, diagnostic analyses reveal that the interannual northwestward-southeastward (NW-SE) shift of the SAH in June is more closely correlated with the synergistic effect of concurrent surface thermal anomalies over the TP and IP than with each single surface thermal anomaly over either plateau from the preceding May. Concurrent surface thermal anomalies over these two plateaus in May are characterized by a negative correlation between sensible heat flux over most parts of the TP (TPSH) and IP (IPSH). This anomaly pattern can persist till June and influences the NW-SE shift of the SAH in June through the release of latent heat (LH) over northeastern India. When the IPSH is stronger (weaker) and the TPSH is weaker (stronger) than normal in May, an anomalous cyclone (anticyclone) appears over northern India at 850 hPa, which is accompanied by the ascent (descent) of air and anomalous convergence (divergence) of moisture flux in May and June. Therefore, the LH release over northeastern India is strengthened (weakened) and the vertical gradient of apparent heat source is decreased (increased) in the upper troposphere, which is responsible for the northwestward (southeastward) shift of the SAH in June. [ABSTRACT FROM AUTHOR]

Highlights • Key parameters are calibrated in the shear-stress bedrock-incision model. • Differential rock uplift rates are inferred from bedrock channel longitudinal profiles. • Tectonic deformation pattern and controlling factors are explored in active orogen. Abstract Bedrock channel profile analysis is a robust reconnaissance tool for examining the rates and patterns of deformation in active orogens. Here, steepness and concavity indices were extracted from bedrock channels draining the northern Qilian Mountains based on the universal shear stress incision model. The profile analysis reveals a systematic spatial distribution of steepness and concavity indices. The average steepness index for channels draining the western part is approximately 1.6 times higher than that for the eastern part. Through empirical calibration of erosion coefficient K , the influence of channel width, rock strength, discharge and sediment flux are identified, and an approximately 1.1–1.2 times difference in K values is found between the west and east under the hypothesis that lithologic resistance and sediment flux have no contribution. Correlating profile analyses with parameter calibration, an approximate 2–3 times increase in the rock uplift rate is found from the eastern part to the western part of the orogen. The integration of this study with previous work in the eastern part of the mountains indicates that cross-strike (2–4 times) and along-strike (2–3 times) differential rock uplift both exist in the northeastern margin of the Tibetan Plateau. In addition, the abnormal values of concavity are apparently associated with the channels transecting large thrust fault zones. Thus, the shortening deformation may play a dominant role in controlling the differential rock uplift through folding and thrusting of the northeast-directed thrust faults across the northeastern margin of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

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Abstract The Cenozoic deformation history of the Qilian Shan, which is a reactivated fold-thrust belt in the northeastern region of the Tibetan Plateau, is poorly understood but features prominently in the geodynamic mechanism of the evolution of the plateau. The northeastern Qaidam Basin, which is located on the south flank of the Qilian Shan, provides a valuable record of the timing and pattern of the Cenozoic deformation of the Qilian Shan in its synorogenic sediments. This study analyzes the apatite fission-track (AFT) thermochronological signatures of the middle Miocene-Quaternary detrital sediments in the northeastern Qaidam Basin and modern stream sands draining the Qilian Shan as a proxy for the timing of tectonic deformation in the Qilian Shan. Our detrital AFT ages indicate that a Cenozoic initial rapid exhumation event occurred in the Qilian Shan in the late Paleocene-early Eocene (~60–54 Ma), followed by another rapid exhumation event during the middle-late Eocene (~42–38 Ma) and some exhumation during the Oligocene-middle Miocene (~33–14 Ma). Distinct changes in detrital AFT ages at depositional ages of ~12 Ma and ~2.1 Ma suggest that further tectonic deformation affected the Qilian Shan at these times. Our results, along with those of previous studies, suggest that tectonic deformation propagated into the northeastern edge of the Tibetan Plateau almost simultaneously with the India-Asia collision. The spatial evolution of Cenozoic deformation in the Qilian Shan is likely based on the distribution of weak structures in the upper crust. Graphical abstract Unlabelled Image Highlights • Detrital AFT ages from Cenozoic sediments in the northeastern Qaidam Basin • The initial Cenozoic deformation in the Qilian Shan occurred at ~60–54 Ma • Subsequent tectonic deformation events occurred at ~42–38 Ma, ~12 Ma, and ~2.1 Ma • Deformation propagated into the NE TP simultaneously with the India-Asia collision [ABSTRACT FROM AUTHOR]

Abstract Xianshuihe Fault Zone (XFZ), with a maximum sinistral offset of ∼60 km since 13–5 Ma, is one of the major active fault zones on the eastern Tibetan Plateau. In this study, we investigated the tectonic landforms and slip rate along the central segment of the left-lateral strike-slip XFZ. Field investigations and topographic features show that horizontal offset has been accumulated on the topographical markers of different scales formed since the Late Pleistocene. The central segment of the XFZ is composed of three major faults: Yalahe, Selaha, and Zheduotang faults arranged in a right-stepping echelon pattern, which is mainly characterized by systematical offset of drainages, alluvial fans and terrace risers with typical scissoring structures, indicating a feature of strike-slip fault. We have estimated that the Selaha and Zheduotang Faults participate a slip rate of 5.6 ± 0.8 mm/yr and 3.4 ± 0.4 mm/yr respectively of the total ∼10 mm/yr slip rate across the central XFZ, based on the offset glacial morphology and radiocarbon dates. The present results suggest that the left-lateral slip of the XFZ partitions the deformation of eastward extrusion and northeastward shortening of the central Tibetan Plateau to accommodate the continuing penetration of the Indian plate into the Eurasian plate. [ABSTRACT FROM AUTHOR]

Abstract Cretaceous granites are widely exposed in the Tengchong Terrane that is the southern extension of the Tibetan Plateau, resulting from the evolution of the Tethys. They, therefore, play a critical role in deciphering the Tethys evolution and the growth of the Tibetan Plateau. In this paper, we present new zircon U Pb dating and Hf isotopic results, along with whole-rock elemental and Sr Nd isotopic data of the granitoids from the Lushui-Pianma (LP) batholith and its mafic enclaves and the strongly deformed granites from the Gaoligong shear zone in the northern Tengchong Terrane. The dating results show that both the LP granitic batholith and the strongly deformed granites in the Gaoligong shear zone formed in the Early Cretaceous of 122–110 Ma. They are composed of granodiorite, quartz monzodiorite and monzogranite with minor gabbroic enclaves. Mineralogically and geochemically, the granitoids in the LP batholith, particularly for the less evolved ones, display a metaluminous nature and an affinity to I-type granite. All the granitoids are characterized by similar rare and trace patterns and whole-rock Nd and zircon Hf isotopic compositions, indicating a common origin. The sodium-rich feature for the less evolved dioritic rocks and the predominantly negative zircon ε Hf (t) and whole-rock ε Nd (t) values for all the granitoids demonstrate that they were derived mainly from the partial melting of the Mesoproterozoic metabasic rocks (likely the basement rocks of the Gaoligong Group) in the lower crust of the Tengchong Terrane. In the case of the mafic enclaves, they share similar mineralogical assemblages and Nd Hf isotopic compositions to its host granodiorite, indicating a cognate origin with the latter. In combination with previous data for the granitoids in the Tengchong Terrane, our study further illustrates that the Early Cretaceous granitic rocks are dominated by metaluminous I-type granites with minor highly fractionated peraluminous I-type granites, rather than the dominant S-type granites as assumed before. The new identification of the Myitkyina Meso-Tethys ophiolitic suite in eastern Myanmar, together with regional Early Cretaceous magmatic and sedimentation patterns, indicate that these Early Cretaceous magmatic rocks were the products of the evolution of the Myitkyina Tethys Ocean, which was related to post-collisional slab breakoff. Highlights • Early Cretaceous granitoids and its mafic enclaves in the Northern Tengchong Terrane. • Cognate origin is an important mechanism for some mafic enclaves in granitoids. • Different batholiths originated from the heterogeneous basic crustal sources. • Slab breakoff of the Myitkyina ocean resulted in the Early Cretaceous magmatism. [ABSTRACT FROM AUTHOR]

Complex topographic features on the surfaces of rock avalanche deposits have been regarded as important indicators for understanding avalanche kinematics and dynamics. Based on a combination of remote sensing data and in-situ observations of surface landforms, including toreva blocks, transverse and longitudinal ridges, ridges separated by conjugate troughs, and hummocks, a giant Holocene rock avalanche on the Tibetan Plateau is recognized. This work aims to understand the kinematics of this event. In planview, the tongue-shaped rock avalanche exhibits a clear sequential distribution of various landforms. The translation zone (II) is characterised by toreva blocks originating from extension. In subzone III-1 of the accumulation zone (III), compression-related transverse ridges are well developed. Longitudinal ridges resulting from lateral velocity differences due to radial spreading are present in the front part of subzone III-1. Farther down, ridges separated by conjugate troughs (generated by a combination of compression and radial spreading) are common in subzone III-2. Subzone III-3 is characterised by abundant scattered hummocks with circular to oval shapes. Based on the distributions of these landforms, this rock avalanche is proposed to have mainly experienced a motion featuring laminar flow with radial spreading in its distal and marginal parts. During transport, three distinct processes appear to have occurred in the avalanche mass from the proximal to the distal zones: extension-dominated sliding in zone II, compression-dominated sliding in subzones III-1 and III-2, and rapid radial spreading in subzone III-3. [ABSTRACT FROM AUTHOR]

Climate change is receiving mounting attentions from various fields and phenology is a commonly used indicator signaling vegetation responses to climate change. Previous phenology studies have mostly focused on vegetation greening-up and its climatic driving factors, while autumn phenology has been barely touched upon. In this study, vegetation phenological metrics were extracted from MODIS NDVI data and their temporal and spatial patterns were explored on the Tibetan Plateau (TP). The results showed that the start of season (SOS) has significantly earlier trend in the first decade, while the end of season (EOS) has slightly (not significant) earlier trend. In the spatial dimension, similar patterns were also identified. The SOS plays a more significant role in regulating vegetation growing season length than EOS does. The EOS and driving effects from each factor exhibited spatially heterogeneous patterns. Biological factor is the dominant factor regulating the spatial pattern of EOS, while climate factors control its inter-annual variation. [ABSTRACT FROM AUTHOR]

As the largest Cenozoic terrestrial intermountain basin in the Tibetan Plateau, the Qaidam Basin is an ideal basin to understand the coupling controls of tectonics and climate on plateau lake evolution. More than 10,000 data of chloride content from the Paleogene sediments of the endorheic Qaidam Basin have been collected to monitor changes in lake paleosalinity. Results show that there were two prominent salinity increase events in the Paleogene paleolake, one in the late Eocene (~ 40 Ma) and the other in the transition from the Eocene to Oligocene (EOT, ~ 35.5 Ma). The first salinity increase event was evidenced by the expansion of saline water, the connection of two previous separated saline centers and the deposition of thick-bedded halite in a local sag, which correlated with the late Eocene’s frequently fluctuated climate. The other salinity increase event at the EOT was characterized by the expansion of mesosaline water range, which corresponded well to the drier condition of the Oligocene icehouse climate. The synchronous migration of the saline centers and depocenters demonstrates that the Qaidam Basin was a tectonically active saline basin, where the activity of main faults controlled the occurrence and disappearance of supersaline center under the overall brackish background. The deposition of over 200-m thick-bedded halite during the late Eocene in a local sag was the result of coupled effects by active tectonics and fluctuated climate. [ABSTRACT FROM AUTHOR]

Pre-existing weakness due to repeated tectonic, metamorphic, and magmatic events is a fundamental feature of the continental lithosphere on Earth. Because of this, continental deformation results from a combined effect of boundary conditions imposed by plate tectonic processes and heterogeneous and anisotropic mechanical strength inherited from protracted continental evolution. In this study, we assess how this interaction may have controlled the Cenozoic evolution of the eastern Tibetan plateau during the India–Asia collision. Specifically, we use analogue models to evaluate how the pre-Cenozoic structures may have controlled the location, orientation, and kinematics of the northwest-striking Xianshuihe and northeast-striking Longmen Shan fault zones, the two most dominant Cenozoic structures in eastern Tibet. Our best model indicates that the correct location, trend, and kinematics of the two fault systems can only be generated and maintained if the following conditions are met: (1) the northern part of the Songpan–Ganzi terrane in eastern Tibet has a strong basement whereas its southern part has a weak basement, (2) the northern strong basement consists of two pieces bounded by a crustal-scale weak zone that is expressed by the Triassic development of a northwest-trending antiform exposing middle and lower crustal rocks, and (3) the region was under persistent northeast–southwest compression since ∼35 Ma. Our model makes correct prediction on the sequence of deformation in eastern Tibet; the Longmen Shan right-slip transpressional zone was initiated first as an instantaneous response to the northeast–southwest compression, which is followed by the formation of the Xianshuihe fault about a half way after the exertion of northeast–southwest shortening in the model. The success of our model highlights the importance of pre-existing weakness, a key factor that has been largely neglected in the current geodynamic models of continental deformation. [ABSTRACT FROM AUTHOR]

Determining density structure of the Tibetan Plateau is helpful in better understanding of tectonic structure and development. Seismic method, as traditional approach obtaining a large number of achievements of density structure in the Tibetan Plateau except in the centre and west, is primarily inhibited by the poor seismic station coverage. As the implementation of satellite gravity missions, gravity method is more competitive because of global homogeneous gravity coverage. In this paper, a novel wavelet-based gravity method with high computation efficiency and excellent local identification capability is developed to determine multilayer densities beneath the Tibetan Plateau. The inverted six-layer densities from 0 to 150 km depth can reveal rich tectonic structure and development of study area: (1) The densities present a clockwise pattern, nearly east-west high-low alternating pattern in the west and nearly south-north high-low alternating pattern in the east, which is almost perpendicular to surface movement direction relative to the stable Eurasia from the Global Positioning System velocity field; (2) Apparent fold structure approximately from 10 to 110 km depth can be inferred from the multilayer densities, the deformational direction of which is nearly south-north in the west and east-west in the east; (3) Possible channel flows approximately from 30 to 110 km depth can also be observed clearly during the multilayer densities. Moreover, the inverted multilayer densities are in agreement with previous studies, which verify the correctness and effectiveness of our method. [ABSTRACT FROM AUTHOR]

How the eastward motion of crust in the central Tibetan Plateau is accommodated in the remote regions of the eastern Himalayan syntaxis remains uncertain. Although the Yarlung Zangbo suture (YZS) forms a striking lineament in the topography of the region, evidence for recent faulting along this zone has been equivocal. To understand whether faults along the YZS are active, we performed a geological investigation along the eastern segments of the YZS. Geomorphic observations suggest the presence of active faulting along several segments of the YZS, which we collectively refer to as the “Milin fault”. Paleoseismologic data from trenches reveal evidence for one faulting event, which is constrained to occur between 5620 and 1945 a BP. The latest faulting event displaced alluvial surface T2 by ~ 7 m. The offset on this earthquake place the minimum value on the vertical slip rate of ~ 0.3 mm/yr. Empirical relationships between surface rupture length, displacement and magnitude, suggest that magnitude of the latest event could have been Mw ~ 7.3–7.7. On the basis of this slip rate and the elapsed time since the last event, it is estimated that a seismic moment equivalent to Mw ~ 7.0 has been accumulated on the Milin fault. It is pose a threat to the surrounding region. Our results suggest that shortening occurs in the vicinity of the eastern Himalayan syntaxis, and part of eastward motion of crust from the central Tibetan Plateau is absorbed by uplift of the eastern Himalayan syntaxis. [ABSTRACT FROM AUTHOR]

Delineating glacier change during the Little Ice Age (LIA) is of great importance when attempting to understand regional climatic changes and can also help to improve the understanding of any predictions of future glacial changes. However, such knowledge is still lacking for some critical regions of the Tibetan Plateau (TP). In this study, we mapped 4188 contemporary glaciers and reconstructed 1216 LIA areas of glacial coverage in the Gangdise Mountains to the north of the Himalaya using Google Earth satellite imagery. We estimated their paleoglacial areas and equilibrium line altitudes (ELAs) based on the toe-to-headwall altitude ratio (THAR) method. Results show that most glaciers are small (<1 km 2 ), with slope/hanging glaciers the most common (2844 out of 4188 glaciers), while valley glaciers have the greatest coverage (1009.0 km 2 out of a total area of 1723.7 km 2 ). Contemporary glaciers have retreated significantly since the LIA, with reductions in length of between 5.5% and 94.7% (mean glacier length 696 m; mean reduction in length 41.7%) and reductions in glacier area of between 4.1% and 94.9% (mean glacier area 0.42 km 2 ; mean reduction in area 44.8%). These reductions have occurred under different local climatic and topographic conditions. The contemporary ELA ranges from 5516 to 6337 m asl; the LIA ELA ranged from 5476 to 6329 m asl. Contemporary and LIA ELA values rise from southeast to northwest. As a general rule, the rise in the ELA value decreases from the eastern to the central Gangdise Mountains and then increases westward, with a mean ELA rise of 45 m. Multiple regression models suggest that 46.8% of the glacier area loss can be explained by glacier elevation, area, and slope. However, only 15.5% of the rise in ELA values can be explained by glacial geometric, topographic, or locational parameters. The spatial pattern of modern ELA values in this region appears inversely related to precipitation, which decreases from southeast to northwest, implying that precipitation is one of the key controls of ELAs. This is also consistent with results from elsewhere in High Asia. In contrast to the Gangdise Mountains' eastern and western sectors, glaciers in the central sector have undergone less change, i.e., in terms of reductions in length, area loss, and rises in ELA. Topography can of course also influence glacial change by creating shielding and/or rainshadow effects and by affecting local temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The East Asian geological setting has a long duration related to the superconvergence of the Paleo‐Asian, Tethyan and Paleo‐Pacific tectonic domains. The Triassic Indosinian Movement contributed to an unified passive continental margin in East Asia. The later ophiolites and I‐type granites associated with subduction of the Paleo‐Pacific Plate in the Late Triassic, suggest a transition from passive to active continental margins. With the presence of the ongoing westward migration of the Paleo‐Pacific Subduction Zone, the sinistral transpressional stress field could play an important role in the intraplate deformation in East Asia during the Late Triassic to Middle Jurassic, being characterized by the transition from the E‐W‐trending structural system controlled by the Tethys and Paleo‐Asian oceans to the NE‐trending structural system caused by the Paleo‐Pacific Ocean subduction. The continuously westward migration of the subduction zones resulted in the transpressional stress field in East Asia marked by the emergence of the Eastern North China Plateau and the formation of the Andean‐type active continental margin from late Late Jurassic to Early Cretaceous (160‐135 Ma), accompanied by the development of a small amount of adakites. In the Late Cretaceous (135‐90 Ma), due to the eastward retreat of the Paleo‐Pacific Subduction Zone, the regional stress field was replaced from sinistral transpression to transtension. Since a large amount of late‐stage adakites and metamorphic core complexes developed, the Andean‐type active continental margin was destroyed and the Eastern North China Plateau started to collapse. In the Late Cretaceous, the extension in East Asia gradually decreased the eastward retreat of the Paleo‐Pacific subduction zones. Futhermore, a significant topographic inversion had taken place during the Cenozoic that resulted from a rapid uplift of the Tibet Plateau resulting from the India‐Eurasian collision and the formation of the Bohai Bay Basin and other basins in the East Asian continental margin. The inversion caused a remarkable eastward migration of deformation, basin formation and magmatism. Meanwhile, the basins that mainly developed in the Paleogene resulted in a three‐step topography which typically appears to drop eastward in altitude. In the Neogene, the basins underwent a rapid subsidence in some depressions after basin‐controlled faulting, as well as the intracontinental extensional events in East Asia, and are likely to be a contribution to the uplift of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Early Cenozoic plate collision of India and Eurasia was a significant geological event, which resulted in Tibetan Plateau (TP) uplift and altered regional and global atmospheric circulations. However, the timing of initial collision is debated. It also remains unclear whether the TP was deformed either progressively northward, or synchronously as a whole. As the largest basin in the hinterland of the TP, evolution of the Hoh Xil Basin (HXB) and its structural relationship with development of the Tanggula Thrust System (TTS) have important implications for unraveling the formation mechanism and deformation history of the TP. In this study, we present results from a long sedimentary sequence from the HXB that dates the Fenghuoshan Group to ∼72–51 Ma based on magnetostratigraphy and radiometric ages of a volcanic tuff layer within the group. Three depositional phases reflect different stages of tectonic movement on the TTS, which was initialized at 71.9 Ma prior to the India–Eurasia collision. An abrupt sediment accumulation rate increase from 53.9 Ma is a likely response to tectonic deformation in the plateau hinterland, and indicates that initial India–Eurasia collision occurred at no later than that time. This remote HXB tectonosedimentary response implies that compressional deformation caused by India–Eurasia collision likely propagated to the central TP shortly after the collision, which supports the synchronous deformation model for TP. [ABSTRACT FROM AUTHOR]

The Tuolai Group dominates the Central Qilian Terrane, and there are different opinions on the age and tectonic attribute of the Tuolai Group. Based on large-scale geologic mapping and zircon dating, the Tuolai Group is divided into four parts: metamorphic supracrustal rocks, Neoproterozoic acid intrusive rocks, early–middle Ordovician acid intrusive rocks and middle Ordovician basic intrusive rocks. The metamorphic supracrustal rocks are the redefined Tuolai complex-group and include gneiss and schist assemblage by faulting contact. Zircon U–Pb LA-MC-ICP-MS dating was conducted on these samples of gneiss and migmatite from the gneiss assemblage, quartzite, two-mica schist and slate from the schist assemblage. The five detrital samples possess similar age spectra; have detrital zircon U–Pb main peak ages of 1.7 Ga with youngest U–Pb ages of ~1150 Ma. They are intruded by Neoproterozoic acid intrusive rocks. Therefore, the Tuolai Group belonging to late Mesoproterozoic and early Neoproterozoic. With this caveat in mind, we believe that U–Pb detrital zircon dating, together with the geologic constraints obtained from this study and early work in the neighboring regions. We suggest that the formation age of the entire crystalline basement rocks of metasedimentary sequence from the Central Qilian Terrane should be constrained between the Late Mesoproterozoic and the Late Neoproterozoic, but not the previous Paleoproterozoic. The basement of the Central Qilian Terrane contains the typical Grenville ages, which indicates the Centre Qilian Terrane have been experienced the Grenville orogeny event. [ABSTRACT FROM AUTHOR]

Abstract: The Xichang Basin in southeastern Tibet provides crucial information about formation and tectonic processes affecting the eastern Tibetan Plateau. To determine when and how the uplift developed, we conducted detailed studies of structures and obtained thermochronology data from the Xichang Basin and its periphery. The Xichang Basin is characterized by gentle deformation of the strata, segmented by an E‐vergent boundary thrust fault. Two stages of deformation, strike‐slip followed by an E‐W oriented shortening resulted in oblique shortening between the southeastern Tibetan Plateau and the Sichuan Basin. New apatite fission‐track data interpreted together with (U‐Th)/He data confirm a simple burial/heating and exhumation/cooling history across the Xichang Basin and its periphery. Subsidence and burial of the Xichang Basin peaked between 80–30 Ma, followed by mountain building with a protracted cooling starting at around 40–20 Ma, with rates of ca. 2.0–8.0 °C Myr−1 (i.e. 0.1–0.3 mm year−1). Our data indicate that the Xichang Basin has experienced ca. 2.5–5 km of exhumation, much more intensive than the ca. 1–2 km of exhumation inferred for the southwestern Sichuan Basin. Restored balanced cross‐sections of post‐Late‐Triassic strata along a ca. 250 km traverse indicate ca. 10–20% east‐west shortening strain (i.e. ca. 20–30 km) at the southeastern Tibetan Plateau during Cenozoic time. Study of crustal thickening and erosion supports a tectonic shortening mechanism to account for the uplift of the Xichang Basin on the southeastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

When and how the Bangong-Nujiang Tethyan Ocean closed is a highly controversial subject. In this paper, we present a detailed study and review of the Cretaceous ophiolites, ocean islands, and flysch deposits in the middle and western segments of the Bangong-Nujiang suture zone (BNSZ), and the Cretaceous volcanic rocks, late Mesozoic sediments, and unconformities within the BNSZ and surrounding areas. Our aim was to reconstruct the spatial-temporal patterns of the closing of the middle and western segments of the Bangong-Nujiang Tethyan Ocean. Our conclusion is that the closure of the ocean started during the Late Jurassic and was mainly complete by the end of the Early Cretaceous. The closure of the ocean involved both 'longitudinal diachronous closure' from north to south and 'transverse diachronous closure' from east to west. The spatial-temporal patterns of the closure process can be summarized as follows: the development of the Bangong-Nujiang Tethyan oceanic lithosphere and its subduction started before the Late Jurassic; after the Late Jurassic, the ocean began to close because of the compressional regime surrounding the BNSZ; along the northern margin of the Bangong-Nujiang Tethyan Ocean, collisions involving the arcs, back-arc basins, and marginal basins of a multi-arc basin system first took place during the Late Jurassic-early Early Cretaceous, resulting in regional uplift and the regional unconformity along the northern margin of the ocean and in the Southern Qiangtang Terrane on the northern side of the ocean. However, the closure of the Bangong-Nujiang Tethyan Ocean cannot be attributed to these arc-arc and arc-continent collisions, because subduction and the development of the Bangong-Nujiang Tethyan oceanic lithosphere continued until the late Early Cretaceous. The gradual closure of the middle and western segments of Bangong-Nujiang Tethyan Ocean was diachronous from east to west, starting in the east in the middle Early Cretaceous, and being mainly complete by the end of the Early Cretaceous. The BNSZ and its surrounding areas underwent orogenic uplift during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

The Lower Cretaceous sedimentary strata in the Lhasa Terrane record the palaeogeographic and tectonic history of the Tibetan Plateau prior to the India-Asia collision. The Lower Cretaceous strata in the Coqen Basin of the northern Lhasa subterrane include the Duoni and Langshan Formations. The Duoni Formation is composed of conglomerates, sandstones, siltstones and mudstones in the south deposited in a fluvial environment and quartzose-lithic sandstones, siltstones and mudstones in the north deposited in a shelf-coastal environment. The overlying Langshan Formation is characterized by abundant Orbitolina - and rudist-bearing wackestones and packstones, which were deposited on a low-energy carbonate ramp. The Langshan Formation in the Coqen Basin was deposited between ~ 119–115 Ma and ~ 98 Ma based on its large benthic foraminiferal assemblages. Age constraints based on the interbedded tuff and conformably overlying Langshan Formation indicate that the Duoni Formation was deposited between ~ 123 and 115 Ma. Sandstone detrital modal compositions further indicate that the Duoni Formation was primarily derived from magmatic arc and recycled orogen sources. Detrital zircons from the Duoni Formation yield a primary age population of 160–110 Ma (peaking at ~ 130 Ma), with negative ε Hf ( t ) values (− 18.7 to − 2.7), and additional age ranges of 550–500, 1200–900, and 1600–1500 Ma, thereby indicating that the Zenong volcanic rocks and Palaeozoic sedimentary bedrocks in the northern Lhasa subterrane are the most likely sources. The palaeogeography of the northern Lhasa subterrane can be approximately described in two stages. During the Aptian (~ 123–115 Ma), with the eruption of the Zenong volcanic rocks, the Duoni Formation accumulated in fluvial and shelf-coastal environments and was sourced from the Zenong volcanic rocks and basement rocks from the southern region of the northern Lhasa subterrane. The enhanced magmatic activities in the northern Lhasa subterrane may have influenced the Duoni Formation deposition. During the Late Aptian-Early Cenomanian (~ 115–98 Ma), a north-south transgression occurred, causing the majority of the northern Lhasa region to be dominated by shallow-marine limestones of the Langshan Formation. [ABSTRACT FROM AUTHOR]

The lower crustal flow model is one of several competing models considered to interpret the growth and expansion of southeastern Tibet. However, the dynamic processes involved in the evolution and deformation of the Tibetan plateau remain poorly understood due to the absence of reliable geophysical observations. In this study, 159 earthquakes of magnitude Ms ≥ 6.2 were selected, which were recorded by 50 permanent broadband stations deployed in southwest China, and 1873 pairs of P-wave receiver functions with high signal-to-noise ratio were isolated. On the basis of a linearized inversion algorithm, a two-step inversion procedure was implemented that not only reduced the dependence of the inversion results on the initial models, but also provided a statistical estimation of the solution. Thus, we obtained an accurate 3D image of the S-wave velocity structure of the crust and uppermost mantle in the southeast margin of the Tibetan plateau. Our results reveal that an extensive intracrustal low-velocity zone spreads beneath southwest China, and further suggest that a lower crustal flow coming from eastern Tibet is blocked by the Jinshajiang-Red River fault to the west and the Xiaojiang fault to the east and extends largely by the Sichuan-Yunnan diamond-shaped block. This crustal flow along the southeastern margin of Tibet does not appear to be restricted to two narrow low-velocity channels as was advanced, but rather reflects the southeastward extrusion of crustal material as a way of tectonic escape. [ABSTRACT FROM AUTHOR]

The Denan Depression is a unique depression in the northeastern Qaidam basin, with a maximum Cenozoic sedimentary thickness of ~ 5 km. Detailed field work, interpretation of seismic profiles and analyzation of well data were conducted to define the Cenozoic tectonic evolution of the northeastern Qaidam basin. All geological evidences indicate that the Denan Depression is controlled by the northeast-directed Olongbulak Thrust at its southern boundary. The Denan Depression grew in concert with the development of the northeast-directed Olongbulak Thrust at least since it began to accept the Xiaganchaigou Formation, supporting the early Cenozoic growth of the northern Tibetan Plateau. Surface and subsurface data both point to enhanced tectonic activity since the Quaternary in the northeastern Qaidam basin, leading to a more individual Denan Depression relative to the main Qaidam basin. The northern boundary of the Denan Depression is a passive boundary, and no foreland developed at the northern slope of the Denan Depression. [ABSTRACT FROM AUTHOR]

The tectonically active eastern Tibetan Plateau (TP) impacts the populous Sichuan Basin in the form of dust and exhumed detrital materials. To better understand a detailed transport process of detrital material from the eastern TP to the Sichuan Basin, eight samples were collected from the upper reaches of the Min River in the eastern TP to the Sichuan Basin, for zircon U-Pb chronological and grain-size analysis. The results are compared with those of previously studies. Zircon grains are comparatively coarse in three bedrock samples, one fluvial sand sample and one dust sample, but are distinctly fine in three lacustrine samples. Intriguingly, the zircon grain-size parameters from the fluvial sand and dust samples are similar to each other. Consistent with previous studies of this area, the analysis of our U-Pb zircon ages indicates five major age populations at 180–350 Ma, 350–550 Ma, 700–1000 Ma, 1600–2000 Ma, and 2200–2600 Ma, which broadly correspond to five known granitoid magmatic events within the Yangtze Block. The Min River links lacustrine sediments from Lixian, fluvial sands from Wenchuan, Leshan, Yibin, and from the Dadu River and the Dayi conglomerate, implying the Dayi conglomerate was transported by fluvial rather than glacial processes. The denuded detrital material, mainly generated by seismic events in the eastern TP, was transported by water flow into the western Sichuan Basin, where two thick sedimentary depocenters developed, and the relatively fine grains were then transported by wind to the northern Sichuan Basin. Thus, the thick sediments in the western Sichuan Basin mainly transported by the Min River probably exerted a major influence on dust deposition in the northern Sichuan Basin. In contrast, the Jialing and Dadu rivers made a minor contribution. [ABSTRACT FROM AUTHOR]

In order to test the hypothesis that the stationary nature of the Yarlung Tsangpo Gorge is tectonically controlled, the rock uplift pattern in the southeast Tibetan Plateau and the critical condition to sustain a stable knickpoint must be derived. Via slope-area analysis and the integral approach, we first quantify the pattern of channel steepness in southeast Tibet and find that the steepness index shows higher values around the gorge but lower values toward the inner land and the mountain front. Such a pattern of channel steepness indicates that the active rock uplift is restricted in the zone just around the Yarlung Tsangpo Gorge. Then, we derive a general knickpoint migration model that accounts for spatially variant rock uplift rates. From the model, a critical condition for maintaining a stable knickpoint is concluded that the difference of incision rates in the downstream and upstream reaches of the knickpoint should match that of rock uplift. Employing a stream-power river incision model, we calculate the incision rate in the gorge and find a higher correspondence with differential rock uplift rates in the downstream and upstream reaches of the knickpoint. Therefore, we favor tectonic control as the primary mechanism to explain the stability of the knickpoint within the Yarlung Tsangpo Gorge. [ABSTRACT FROM AUTHOR]

Recently, we have processed the gravitational and geomagnetic data from a geophysical survey along a profile (Baicheng to Da Qaidam) which crosses the northern and eastern Tarim Basin, the Altyn Tagh Mountains, and the Qaidam Basin, respectively. Based on the P- and S-wave velocities (Zhao et al., 2006), both the density and magnetic intensity of the crust and uppermost mantle were determined by using a joint inversion of gravity versus geomagnetism. Our new results at the northern margin of the Tibetan Plateau reflect different crustal structures beneath Tarim basin and Qaidam basin, and these two basins may be produced by different terranes. In addition, strong deformation has occurred in the basement and interior of the Qaidam Basin during the tectonic evolution. [ABSTRACT FROM AUTHOR]

CHAMP and Swarm satellite magnetic data are combined to establish the lithospheric magnetic field over the Tibetan Plateau at satellite altitude by using zonal revised spherical cap harmonic analysis (R-SCHA). These data are integrated with geological structures data to analyze the relationship between magnetic anomaly signals and large-scale geological tectonic over the Tibetan Plateau and to explore the active tectonic region based on the angle of the magnetic anomaly. Results show that the model fitting error is small for a layer 250-500 km high, and the RMSE of the horizontal and radial geomagnetic components is better than 0.3 nT. The proposed model can accurately describe medium- to long-scale lithospheric magnetic anomalies. Analysis indicates that a negative magnetic anomaly in the Tibetan Plateau significantly differs with a positive magnetic anomaly in the surrounding area, and the boundary of the positive and negative regions is generally consistent with the geological tectonic boundary in the plateau region. Significant differences exist between the basement structures of the hinterland of the plateau and the surrounding area. The magnetic anomaly in the Central and Western Tibetan Plateau shows an east-west trend, which is identical to the direction of the geological structures. The magnetic anomaly in the eastern part is arc-shaped and extends along the northeast direction. Its direction is significantly different from the trend of the geological structures. The strongest negative anomaly is located in the Himalaya block, with a central strength of up to -9 nT at a height of 300 km. The presence of a strong negative anomaly implies that the Curie isotherm in this area is relatively shallow and deep geological tectonic activity may exist. [ABSTRACT FROM AUTHOR]

The extrusion model suggests that the India-Eurasia collision triggered lateral escape of the Tibetan Plateau via strike-slip faults from south to north. However, questions remain as to how the collision resulted in the different geological settings of northern Tibet. The area between the Haiyuan fault and the eastern Kunlun fault is ideal for investigating whether major strike-slip faults contributed to lateral extrusion of the plateau. This study uses a deep seismic profile spanning a 257 km transect, along with regional geologic, gravity, and magnetic data. Examining our results integrated with those of previous studies, we propose that the block between the Elashan and Riyueshan faults extruded southward under the background of a large-scale eastward extrusion of the Tibetan Plateau. According to regional tectonic events, the north-dipping intracrustal seismic reflectors that appear beneath the Western Qinling orogen are the remnants of the Indosinian Mianlue suture zone. The subduction of the Mianlue Ocean led to the underthrusting of South China beneath the Qinling orogen, similar to the process that occurred in the Western Kunlun Range and central Alps. As a result, the Moho was duplicated beneath the Western Qinling orogen. Southward extrusion resulted in the offset of the eastern Kunlun fault from the Diebu-Bailongjiang fault, which transferred part of the Western Qinling orogen to the Ruo'ergai basin and pulled the Ruo'ergai basin as well. Based on interpretations of structures and other evident features, we develop a kinematic model to specifically explain how the northern Tibetan Plateau between the Elashan and Riyueshan faults, located between the Haiyuan and Kunlun faults, accommodates southwesterly compression. [ABSTRACT FROM AUTHOR]

The eastern margin of the Qinghai-Tibet Plateau (QTP) is the focus of studies on eastward lateral extrusion of the latter's crustal material. This study aims to explore the structural response of the QTP's eastern crust-mantle to the extrusion, and the basis for the latter's geological structure. Data on the long-period magnetotelluric sounding of cross-tectonic units and Bouguer gravity were used to determine the physical structure of the crust-mantle at the plateau's eastern margin. The findings are as follows: (i) the apparent density structure indicates the large presence of a low-density material in the middle-lower crusts of the Songpan and Sichuan-Yunnan blocks at the QTP's eastern margin. On the other hand, the Yangtze cratonic block (Sichuan Basin) contains a material with a significantly higher density. To the west of the Longmenshan-Panxi tectonic zones, and along the lower crust at 40-50 km depth, is an obvious low-density zone aligned in a northeast-southwest orientation. (ii) The electrical structural model spanning Songpan block-Longmenshan tectonic zone-Yangtze block reveals three distinct electrical structural units along the cross-section bounded by the Longmenshan tectonic zone. The first is the Songpan block, which has high and low resistivity at the superficial layer and middle-lower crusts, respectively. Next is the Yangtze craton, which has a low and relatively higher resistivity at the superficial layer and middle-lower crusts, respectively. The third is the Longmenshan transitional tectonic zone, whose shallow layer and deep structure are characterized by an electrical structure with a thrust nappe towards the east, and a high-conductivity material extending to the lithospheric mantle, respectively. (iii) The apparent density and electrical structures indicate that the Panxi tectonic zone has a weakened structure in the lower crust; and (iv) physical properties of the QTP's deep structure show that its eastern margin may contain a middle-lower crustal fluid material with the attributes of high conductivity and low density. Its distribution is interrelated to the uplift mechanism and deep seismogenic activities at the QTP's eastern margin. [ABSTRACT FROM AUTHOR]

Using silicone slabs as a model analogue for lithospheric plates subducting into a box of glucose syrup, as an analogue of the mantle, we explore the subduction of continental lithosphere in a context of intercontinental collision. The continental indenter pushed by a piston, reproducing the collision, attached to a dense oceanic plate, subducts to two-thirds of the depth of the mantle box. We show that, surprisingly, the continental plate attached to the back wall of the box subducts, even if not attached to a dense oceanic slab. The engine of this subduction is not the weight of the slab, because the slab is lighter than the mantle, but the motion of the piston, which generates horizontal tectonic forces. These are transmitted to the back wall plate through the indenter and the upper plate at the surface, and by the advancing indenter slab through the mantle at shallow depth. We define this process as collisional subduction occurring in a compressional context. The collisional subduction absorbs between 14% and 20% of the convergence, and represents an unexplored component of collisional mass balance. The transmission of tectonic forces far from the collision front favors the formation of a wide plateau. Our experiments reproduce adequately the amount and geometry of the Asian lithosphere subduction episodes inferred during the collision, leading us to conclude that it reproduces adequately the physics of such process. [ABSTRACT FROM AUTHOR]

The eastern margin of the Tibetan Plateau is characterized by frequent earthquakes, which are closely associated with tectonic activity. To assess tectonic activity during the Late Pleistocene, we studied a well-exposed, 23-m-thick lacustrine sequence on the eastern margin of the plateau and found a variety of soft-sediment deformation (SSD) structures. Distributed in 24 stratigraphic levels, they comprise clastic dykes, ball-and-pillow structures, flame structures, clastic gravels, micro-faults, and slump folds. Most of the SSD structures indicate deformation mechanisms related to liquefaction and/or fluidization processes, most probably triggered by paleoseismic events. Given at least 4 historical earthquakes of M > 7 in the study area, most SSD structures in the Lixian lacustrine sequence indicate seismic events with M > 6 while simple flame structures point to some lower-magnitude earthquakes. OSL dating indicates that the sequence accumulated between 15.8 and 6.0 ka, giving a mean recurrence interval of 480 years for the 24 events, and demonstrating that lacustrine sediments in eastern Tibet have the potential to record a continuous seismic history on the centennial scale. [ABSTRACT FROM AUTHOR]

GPS measurements indicate rapid lateral extrusion of the NE Tibetan Plateau, which causes active NE-directed crustal shortening and has initiated oblique shearing along the margins of NE Tibet. However, the Tibetan highlands terminate around 103°E longitude and topographic relief disappears to the northeast. The exact reasons for this drop in elevation remain obscure due to widespread Tertiary sediments and Quaternary loess, which obscure details of the lithospheric structure. This study describes a new 310 km-long deep seismic reflection line striking NE-SW across the interior of NE Tibet. Integrating its data with a previously described 165 km-long deep seismic profile of the Tibet–Ordos transition zone together, these datasets provide a complete picture of the crustal architecture of the north-easternmost Tibetan Plateau. Gravity anomaly and previous geological evidence also help constrain complex deformation pattern in the region. Interpretations of these patterns indicate the importance of the large-scale sinistral Haiyuan fault zone and inherited vertical variation in mechanical properties of the lithosphere in the overall tectonic evolution of the NE Tibetan Plateau. The overall crustal architecture obtained in this study provides spatial context for the neotectonic evolution of NE Tibet and helps constrain the interplay of geologic and geodynamic processes affecting NE Tibet and adjacent regions. [ABSTRACT FROM AUTHOR]

The tectonic and topographic history of the Himalaya-Tibet orogenic system remains controversial, with several competing models that predict different exhumation histories. Here, we present new low-temperature thermochronological data from the Mount Everest region, which, combined with thermal-kinematic landscape evolution modeling, indicate asymmetric exhumation of Mount Everest consistent with a scenario in which the southern edge of the Tibetan Plateau was located >100 km farther south during the mid-Miocene. Northward plateau retreat was caused by erosional incision during the Pliocene. Our results suggest that the South Tibetan Detachment was a localized structure and that no coupling between precipitation and erosion is required for Miocene exhumation of Greater Himalayan Sequence rocks on Mount Everest. [ABSTRACT FROM AUTHOR]

The Litang fault system (LTFS) in the eastern Tibetan Plateau has generated several large (7.5 > M > 7) historical earthquakes and has exhumed granitic peaks rising > 1700 m above the mean elevation of the plateau, despite being located within a tectonic block surrounded by highly active faults. We study horizontally offset moraine crests from the Cuopu basin and a vertically offset alluvio-glacial fan from the eastern Maoya basin. We determine a left-lateral rate of 0.09 ± 0.02 mm/yr along a slowly slipping secondary fault at Cuopu, while the main active fault at present is the normal range-front N Cuopu fault, along which we determined a left-lateral rate of 2.3 ± 0.6 mm/yr since 173 ka. At Maoya fan, matching the vertical 12 ± 1 m cumulative offset with the 21.7 ± 4.2 ka fan age yields a vertical (normal) rate of 0.6 ± 0.1 mm/yr. This rate is very similar to that recently determined at the same location using low-temperature thermochronology (0.59 ± 0.03 mm/yr since 6.6 ± 0.5 Ma). Left-lateral rates along the main faults of the LTFS range between 0.9 and 2.3 mm/yr at all timescales from a few years to ~ 6 Ma. The facts that the LTFS is highly segmented and that at present, the Cuopu, Maoya and South Jawa segments are mostly normal (while the Litang and Dewu segments are left-lateral/normal), could prevent the occurrence of M > 7.5 destructive earthquakes along the LTFS, as is generally assumed. However, motion on the normal faults appears to be linked with motion on the strike–slip faults, potentially allowing for exceptional larger earthquakes, and implying that the area is not experiencing pure ~ NS extension but rather NW–SE left-lateral transtension. [ABSTRACT FROM AUTHOR]

A 3D Magnetotelluric (MT) inversion for a 2D broadband MT profile along 92°E in the eastern Lhasa terrane was applied to understand the crustal electrical structures and deep processes in the India–Tibet continental collision zone. The middle and lower (− 20 to − 50 km) crust is distributed with conductors that are primarily concentrated north of the Yarlung–Zangbo sutures (YZS). The results imply that the hypothesis of middle (and/or lower) crustal flow between the Tethyan Himalaya and Lhasa terrane are not supported by the MT data within the profile area. We suggest that given the possibility of the existence of channel flow in the middle (and/or lower) crust extruding southward from Tibet, the southernmost portion should be limited in the northern YZS. The electric model also indicates that the primarily conductive region in the middle to lower crust can be imaged from the YZS to ~ 30.8°N, while the crust of the northern Lhasa terrane north of ~ 30.8°N has a higher resistivity. From this result, it can be inferred that the northern Lhasa terrane might have a cold and strong middle to lower crust and that the front of the India crust might be halted in the northern Lhasa terrane (~ 30.8°N) along 92°E. [ABSTRACT FROM AUTHOR]

The eastern Tibetan plateau has been getting more and more attention because it combines active faults, uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus, a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative (THD) had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks, including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the Songpan-Garze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion, which is coincident with the flowing direction indicated from the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault. [ABSTRACT FROM AUTHOR]

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008-2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are (17.02±0.60) mm/a, (8.77±.51) mm/a, (13.85±.31) mm/a and (6.84 ± 0.74) mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are (7.30±1.25-8.30±1.26) mm/a, (10.07±0.97-11.79±0.89) mm/a, (0.96±0.74-2.98±1.73) mm/a, (2.03±0.49-3.20±0.73) mm/a, (3.45±0.40-6.02±0.50) mm/a and (6.23±0.56) mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show left-lateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strike-slip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism. [ABSTRACT FROM AUTHOR]

Following the 2008 Wenchuan earthquake (Sichuan, China), the dextral strike-slip Longriba fault system (LFS) has been recognized as a main intracontinental structural boundary within the eastern Tibetan Plateau. While numerous studies have focused on the Longmen Shan frontal range to constrain the dynamics of the eastern Tibetan margin, little is known on the LFS, particularly on its eventual influence on the geomorphological evolution of the latter. Here, we provide a new data set of denudation rates derived from beryllium-10 concentrations in river sediments from 33 medium-sized catchments. Our sampling area covers the frontier between the dissected margin and the low relief interior plateau. Our results reveal a sharp increase of denudation across the LFS, from < 0.1 mm/y in the Ruoergai basin to 0.3 mm/y toward the Longmen Shan range. Such denudation pattern indicates a major morphotectonic control of the fault system on the eastern Tibetan margin evolution. Additional topographic analysis confirms the role of the LFS as an important geomorphological boundary, restraining the westward propagation of river incision into the low-relief areas, thus partly preventing the dismantling of the eastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The Ganzi-Yushu-Xianshuihe Fault Zone (GYXFZ) is a typical active strike-slip fault that has triggered many large historic earthquakes, including the 2010 M w 6.9 Yushu earthquake in the central Tibetan Plateau. This fault zone extends for ca. 800 km from the central Tibetan Plateau to its southeastern margin and varies in trend from WNW-ESE in the northwestern segment of the fault zone to NNW-SSE in the southeastern segment, having the geometry of an arc projecting northeastwards. In this study, we present evidence for the systematical sinistral deflection and/or offset of the Yangtze River and its branch stream channels and valleys along the GYXFZ. Topographic analysis of three-dimensional (3D) perspective images constructed using digital elevation model (DEM) data, 0.5 m-resolution WorldView and GeoEye images, and 15 m-resolution Landsat-Enhanced Thematic Mapper (ETM+) images, together with analysis of geological structures, reveals the following: (i) the main river channels and valleys of the Yangtze River drainage system show systematic sinistral deflections and/or offsets along the GYXFZ; (ii) various amounts of sinistral offset have accumulated on the tributary stream channels, valleys, and gullies of the Yangtze River along the fault, with a linear relation, D = aL , between the upstream length L from the deflected point and the offset amount D with a certain coefficient a ; (iii) the maximum amount of sinistral offset is up to ca. 60 km, which was accumulated in the past 13–5 Ma; and (iv) the long-term average strike-slip rate is ca. 4.6–12 mm/year. Geological and geomorphic evidence, combined with geophysical data, demonstrates that the GYXFZ is currently active as one of the major seismogenic faults in the Tibetan Plateau, dominated by left-lateral strike-slip motion. Our findings supply important evidence for the tectonic evolution of strike-slip faults in the Tibetan Plateau since the Eurasia-India continental collision. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Lhasa terrane (southern Tibetan Plateau) played a fundamental role in the formation of the Tibetan Plateau. However, many uncertainties remain with regard to the tectonic and paleogeographic evolution of the Lhasa terrane prior to the India-Asia collision. To determine the early tectonic processes that controlled the topographic evolution of the Lhasa terrane, we analyze the Cretaceous strata exposed in the Coqen Basin (northern Lhasa subterrane), which comprises the Langshan and Daxiong Formations. The Langshan Formation unconformably overlies the volcanic rocks of the Lower Cretaceous Zelong Group and consists of ~80 m of Orbitolina-bearing limestones, which were deposited in a low-energy, shallow marine environment. Micropaleontological analysis indicates that the Langshan Formation in the Coqen Basin was deposited from late Aptian to early Cenomanian times (ca. 113-96 Ma). The overlying Daxiong Formation (~1700 m thick) consists of conglomerate, coarse sandstone, and siltstone with interbedded mud-stone, and represents deposits of alluvial fans and braided rivers. The Daxiong Formation was deposited after the early Cenomanian (ca. 96 Ma) and accumulated until at least ca. 91 Ma, indicating accumulation rates of greater than 0.3 km m.y.-1. By combining paleocurrent data, sandstone petrology, detrital zircon U-Pb ages, and Hf isotope analysis, we demonstrate that the Daxiong Formation was derived from Lower Cretaceous volcanic rocks and pre-Cretaceous strata in the northern Lhasa subterrane. During Late Cretaceous time, two thrust systems with opposite vergence were responsible for transforming the northern Lhasa subterrane into an elevated mountain range. This process resulted in the evolution from a shallow marine environment (Langshan Formation) into a terrestrial depositional environment (Daxiong Formation) on the southern margin of the northern Lhasa subterrane. Given the regional paleogeographic context, we conclude that the Daxiong Formation in the Coqen Basin records local crustal shortening and flexure resulting in foreland basin development on the southern margin of the northern Lhasa subterrane, which implies early topographic growth of the northern Lhasa subterrane in southern Tibet prior to the India-Asia collision. [ABSTRACT FROM AUTHOR]

The northeastward growth process of the Tibetan Plateau has been a key issue to be long-termly debated, which is well documented by the South Ningxia region at the northeasternmost periphery of the Tibetan Plateau due to its Cenozoic convex-to-the-northeast arcuate range-and-basin structures. Here new structural measurements and fault kinematic analysis, together with new geochronological results, delineate a two-stage Cenozoic tectonic evolution in the region, providing the new structural evidences to decipher the northeastward growth process of the Tibetan Plateau. The first stage is marked by widespread sedimentary basin formation during the Oligocene to Late Miocene (ca. 30–10.5 Ma) under NW-SE extensional regime, and subsequent basin inversion triggered by NW-SE compression in the Late Miocene (ca. 10.5–9.5 Ma); these events were probably associated mainly with the far-field effect of the northwestward subduction of the Pacific Plate, a little related to the plateau growth. The second stage largely presents an intensive mountain building process and following re-deformation since the Late Miocene (ca. 9.5 Ma), which was predominantly a result of the far-field responses to the northeastward growth of the Tibetan Plateau, and partially to the Pacific subduction. The second stage further comprises three alternating episodes of shortening and extension events. The earliest episode of NE-SW compression caused intensive crustal shortening in a long period from the Late Miocene to Early Pleistocene (ca. 9.5–1.8 Ma), leading to a significant mountain building process in this region. A gentle NE-SW extension subsequently dominated here in the Late Pleistocene (?–ca. 18 ka), as manifested by the widespread appearance of paleo-lakes along the NW-striking boundary faults. Since the end of the Late Pleistocene (ca. 18 ka), a youngest tectonic regime affected this region, characteristic of a tectonic transpression, causing evidently strike-slip activities on the primary faults and the development of small-scale pull-apart basins along the Haiyuan Fault. [ABSTRACT FROM AUTHOR]

Voluminous Early Paleozoic intrusive rocks occur in the Qilian orogenic belt, northeastern margin of the Tibetan Plateau. Their petrogenesis can provide insights into the tectonic evolution of Qilian and its adjacent areas. This paper carries out an integrated study of U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions for the Bamishan and Heishishan plutons in the eastern Qilian orogen. Both the Bamishan and Heishishan plutons consist of mafic, intermediate and felsic intrusive rocks. U–Pb zircon dating yielded the magma crystallization ages of 459–449 Ma for the Bamishan pluton and 447–438 Ma for the Heishishan pluton. Their geochemical and Sr–Nd–Hf isotopic data show that the parental magmas of the Bamishan monzogranites and quartz diorites were generated by slab (MORB and overlying sediments) melting. The Bamishan hornblende gabbros have extremely high Cr (1159–1163 ppm), Ni (220–353 ppm) and Mg# (73–74), indicating a cumulate origin. The Heishishan granodiorite–granite has adakitic geochemical signatures and they were produced by partial melting of the mafic lower crust. The Heishishan hornblende gabbro and quartz diorites were derived from the enriched lithospheric mantle metasomatized by subduction-related fluid/melt. In light of the available data, we propose that there was an Early Paleozoic ocean basin between the Central-South Qilian and Qaidam–West Qiling belts. The northward closure of this basin and subsequent continental collision and post-collisional processes resulted in the generation of the Early Paleozoic magmatism in the eastern Central Qilian. The Late Ordovician to Early Silurian (~ 460–440 Ma) intrusive rocks in the eastern Central Qilian formed in a post-collisional setting. A slab break-off model may account for the magma generation. [ABSTRACT FROM AUTHOR]

Models for how shortening is accommodated in the India–Asia collision vary between an end member in which largely rigid blocks are extruded eastwards between lithospheric-scale strike-slip faults and an end member in which a hot, weak mid-crustal layer aids distributed deformation. Here the mode of crustal deformation is evaluated by studying the intersection of two main conjugate strike-slip faults at the west end of the Tibetan plateau. Our field mapping suggests that these faults, the right-lateral Karakoram fault and the left-lateral Longmu–Gozha Co fault, an eastward continuation of the Altyn Tagh fault, may be connected by a large-scale, east-dipping listric normal fault, exposing a wedge of mid-crustal rocks in its footwall. Pseudosection modeling of matrix and porphyroclast rim compositions from footwall metamorphic rocks yield late-syntectonic pressures of 640 ± 100 MPa and temperatures around 600 ± 50 °C . Extensive networks of narrow granitic dikes give U–Pb zircon ages as young as 13.7 ± 0.2 Ma , suggesting that footwall rocks remained hot until the late Miocene and were not exhumed until after this time. We infer >40 km heave across the Angmong fault, and suggest that it absorbs effectively all of the slip across the Longmu–Gozha Co fault (which it appears to truncate), so the Longmu–Gozha Co fault is seemingly confined to the upper crust. Similar mechanical decoupling likely occurs throughout the plateau, with strike-slip faulting in western Tibet limited to the upper, brittle part of the crust. [ABSTRACT FROM AUTHOR]

A curved belt consisting of terranes or blocks and associated late Paleozoic to early Mesozoic sutures are features of the southeastern part of the Tibetan Plateau. The southeastern Tibetan Plateau Paleotethyan belt is divided into a northwestern segment (central Tibetan Plateau) and a southern segment (the Sanjiang orogenic belt). The Paleotethyan tectonic history of this belt remains a subject of considerable debate. A major controversy concerns whether or not it evolved as a single genetic element. This paper provides new geochronological, geochemical, and structural data to constrain the Paleotethyan tectonics of this belt. A detailed field study across three sections of the Sanjiang orogenic belt has identified two volcaniclastic successions separated by a regional angular unconformity in the northwestern segment, and one continuous volcaniclastic succession in the southern segment. New zircon U-Pb ages reveal that: (1) the lower succession of the northwestern segment was produced by three volcanic phases at ca. 272 Ma, 253-247 Ma, and 240-235 Ma; (2) the upper succession of the northwestern segment formed during a shorter period along the Yushu-Yidun arc from ca. 227 to 211 Ma; and (3) the single volcaniclastic succession of the southern segment was produced continuously from ca. 260 to 210 Ma. Whole-rock geochemical data including trace elements show that the late Paleozoic to early Mesozoic magmatic activity has a continental arc-like affinity. The spatial distribution and field relationships of the magmatic rocks define two continuous vol canic arcs in the southeastern Tibetan Plateau, which correspond to two phases of arclike magmatism. The Late Triassic Yushu-Yidun arc belt is exposed along the northern half of the northwestern segment to the south of the western Jinsha-Garzê-Litang suture. Southward subduction along the western Jinsha-Garzê-Litang suture is likely to have generated the Yushu-Yidun arc. The second arc (Jomda-Weixi-Yunxian) was diachronous and is continuous through the southeastern Tibetan Plateau. The northwestern part of the Jomda-Weixi-Yunxian arc belt is overlain by the Yushu-Yidun arc from the north. From northwest to southeast, the cessation of magmatism in the Jomda-Weixi-Yunxian arc varies from the Middle Triassic (ca. 235 Ma) to the Late Triassic (ca. 210 Ma), whereas the onset of magmatism appears to have been in the Early Permian throughout the arc. Zircon Lu-Hf isotopic data suggest that large degrees of melting of a depleted mantle source produced the earliest magmas in each segment of the Jomda-Weixi-Yunxian arc. The similarity in zircon ages of the ophiolitic units and their distribution imply that the Longmu Co-Shuanghu suture is a continuation of the Changning-Menglian suture. The spatial relationship between the Jomda-Weixi-Yunxian arc and the Longmu Co-Shuanghu-Changning-Menglian suture suggests that diachronous eastward subduction of part of the Paleotethys along the suture produced the Jomda-Weixi-Yunxian arc belt. Widespread folds of the continental arc-volcaniclastics with orogen-parallel hinges reflect compression perpendicular to the orogen, subsequent to arc magmatism. As such, the Paleotethyan tectonics of the southeastern Tibetan Plateau are characterized by two-phase subduction and subsequent two-phase continent-continent collision. [ABSTRACT FROM AUTHOR]