The southeastern margin of Qinghai-Tibet Plateau(SMQTP)is of a typical large landslide-prone area due to intense tectonic activity,deeply incised valleys,high geostress and frequent earthquakes.To gain insights into l...The southeastern margin of Qinghai-Tibet Plateau(SMQTP)is of a typical large landslide-prone area due to intense tectonic activity,deeply incised valleys,high geostress and frequent earthquakes.To gain insights into large landslides in southeastern margin of Qinghai-Tibet Plateau,an area covering 3.34×105 km2 that extends 80e150 km on both sides of the Sichuan-Tibet traffic corridors(G318)was used to examine the spatial distribution and corresponding characteristics of landslides.The results showed that the study area contains at least 629 large landslides that are mainly concentrated on 7 zones(zones IeVII).Zones IeVII are in the southern section of the Longmenshan fault zone(with no large river)and sections with Dadu River,Jinsha River,Lancang River,Nujiang River and Yarlung Zangbo River.There are more landslides in the Jinsha River section(totaling 186 landslides)than the other sections.According to the updated Varnes classification,408 large landslides(64.9%)were recognized and divided into 4 major types,i.e.flows(275 cases),slides(58 cases),topples(44 cases)and slope deformations(31 cases).Flows,which consist of rock avalanches and iceerock avalanches,are the most common landslide type.Large landslide triggers(178 events,28.3%)are also recognized,and earthquakes may be the most common trigger.Due to the limited data,these landslide type classifications and landslide triggers are perhaps immature,and further systematic analysis is needed.展开更多
A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type...A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shear- zone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new 40Ar/39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained 40Ar/39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonic- magmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in large- scale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.展开更多
The Middle Triassic Ladinian-Upper Triassic Norian series in the Mesozoic-Cenozoic Ruo’ergai basin of Songpan area is characterized of large thick shallow marine-deep marine fine grained clastic.The strata are region...The Middle Triassic Ladinian-Upper Triassic Norian series in the Mesozoic-Cenozoic Ruo’ergai basin of Songpan area is characterized of large thick shallow marine-deep marine fine grained clastic.The strata are regionally unconformable between each adjacent two of the Middle-Late Triassic fine grained clastic,the Jurassic coal-containing clastic,the Cretaceous-Paleogene variegated coarse clastic。展开更多
We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred duri...We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.展开更多
In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plat...In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plateau, adjacent to the Sichuan basin, is characterized by very steep relief with high mountain ranges. The crust beneath this region slows the velocities in the middle and lower crust. We have adopted a relatively dense network to inverse the detailed structure of the crust and upper mantle along the eastern margin of the Tibetan plateau and Sichuan basin, using teleseismic data via receiver function analysis. The results are in-line with the hypothesis that viscous crustal material is flowing beneath the eastern margin of the Tibetan plateau and that this process drives overlying crustal material around the strong and rigid Sichuan basin. When the viscous material hits this obstruction, flows are divided into two or more branches with different directions. The upper part of the upwelling viscous flow produces the pressure to intrude the upper crust, thereby driving uplift of mountain ranges and high peaks. In contrast, the lower part of the downwelling viscous flow produces the pressure to intrude the lower crust and upper mantle to deepen the Moho discontinuity, causing observed crustal thickening.展开更多
The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the E...The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.展开更多
The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background o...The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in China's Mainland and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block's interior. In this paper, the three-dimensional (3D) P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai-Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north-south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by low- velocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan-Dian and Songpan-Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan-Ganzi Block and the sub-block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80-120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background for the area's strong earthquake activity.展开更多
This study examines the relationship between high positive isostatic gravity anomalies (IGA), steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has revealed uplift a...This study examines the relationship between high positive isostatic gravity anomalies (IGA), steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains (the LMS). Firstly, The high positive IGA zone corresponds to the LMS orogenic belt. It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography, crustal thickness and rock density along the LMS. Secondly, on the basis of the Airy isostasy theory, simulations and inversions of the positive IGA were conducted using three-dimensional bodies. The results indicated that the LMS lacks a mountain root, and that the top surface of the lower crust has been elevated by 11 km, leading to positive IGA, tectonic load and density load. Thirdly, according to Watts's flexural isostasy model, elastic deflection occurs, suggesting that the limited (i.e. narrow) tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge. Finally, based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS, the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.展开更多
The characteristics of the permafrost along National Highway No. 214(G214) in Qinghai province(between kilometer markers K310 and K670),including the distribution patterns of permafrost and seasonally frozen ground(SF...The characteristics of the permafrost along National Highway No. 214(G214) in Qinghai province(between kilometer markers K310 and K670),including the distribution patterns of permafrost and seasonally frozen ground(SFG), ground ice content and mean annual ground temperature(MAGT), were analyzed using a large quantity of drilling and measured ground temperature data. Three topographic units can be distinguished along the highway: the northern mountains, including Ela Mountain and Longstone Mountain; the medial alluvial plain and the southern Bayan Har Mountains.The horizontal distribution patterns of permafrost can be divided into four sections, from north to south: the northern continuous permafrost zone(K310-K460),the island permafrost zone(K460-K560), the southern continuous permafrost zone(K560-K630),and the discontinuous permafrost zone(K630-K670).Vertically, the permafrost lower limits(PLLs) of the discontinuous zone were 4200/4325 m, 4230/4350 m,and 4350/4450 m on the north-facing/south-facing slopes of Ela Mountain, Longstone Mountain and Bayan Har Mountains, respectively. The permafrost was generally warm, with MAGTs between-1.0°C and0°C in the northern continuous permafrost zone,approximately-0.5°C in the island permafrost zone,between-1.5°C and 0°C in the southern continuous permafrost zone, and higher than-0.5°C in the discontinuous permafrost zone. In contrast, the spatial variations in ground ice content were mainly controlled by the local soil water content and lithology.The relationships between the mean annual air temperature(MAAT) and the PLLs indicated that the PLLs varied between-3.3°C and-4.1°C for the northern Ela and Longstone Mountains and between-4.1°C and-4.6°C in the southern Bayan Har Mountains.展开更多
We applied the material balance principle of the denudation volume and sedimentary flux to study the denudation-accumulation system between the Longmen Mountains (Mts.) and the foreland basin. The amount of sediment...We applied the material balance principle of the denudation volume and sedimentary flux to study the denudation-accumulation system between the Longmen Mountains (Mts.) and the foreland basin. The amount of sediment in each sedimentation stage of the basin was estimated to obtain the denudation volume, erosion thickness and deposit thickness since the Late Triassic Epoch, to enable us to recover the paleoelevation of the provenance and the sedimentary area. The results show the following: (1) Since the Late Triassic Epoch, the elevation of the surface of the Longmen Mts. has uplifted from 0 m to 2751 m, and the crust of the Longmen Mts. has uplifted by 9.8 km. Approximately 72% of the materials introduced have been denuded from the mountains. (2) It is difficult to recover the paleoelevation of each stage of the Longmen Mts. foreland basin quantitatively by the present-day techniques and data. (3) The formation of the Longmen Mts. foreland basin consisted of three stages of thrust belt tectonic load and three stages of thrust belt erosional unload. During tectonic loading stages (Late Triassic Epoch, Late Jurassic-Early Cretaceous, Late Cretaceous-Miocene), the average elevation of Longmen Mts. was lower (approximately 700-1700 m). During erosional unloading stages (Early and Middle Jurassic, Middle Cretaceous and Jiaguan, Late Cenozoic), the average elevation of Longmen Mts. was high at approximately 2000-2800m.展开更多
The magnetotelluric (MT) survey along the Zhada (札达)-Quanshui (泉水) Lake profile on the western margin of the Qinghai (青海)-Tibet plateau shows that the study area is divided into three tectonic provinces ...The magnetotelluric (MT) survey along the Zhada (札达)-Quanshui (泉水) Lake profile on the western margin of the Qinghai (青海)-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong (班公)-Nujiang (怒江) sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang (羌塘) terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture, Bangong.Nujiang suture, and the major faults of Longmucuo (龙木错) and Geerzangbu are inferred.展开更多
The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau (TP) are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP i...The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau (TP) are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP is mainly controlled by the Indian summer monsoon, and detailed studies on the loess-paleosol sequences in this region can provide valuable terrestrial evidence of past changes in the Indian summer monsoon. Secondly, the river terraces in the eastern margin of the TP are considered to be a sensitive recorder of neotectonism to reflect the timing and amplitude of the TP uplift.展开更多
Project INDEPTH (InterNational DEep Profiling of Tibet and the Himalaya) is an interdisciplinary program designed to develop a better understanding of deep structures and mechanics of the Tibetan Plateau. As a compo...Project INDEPTH (InterNational DEep Profiling of Tibet and the Himalaya) is an interdisciplinary program designed to develop a better understanding of deep structures and mechanics of the Tibetan Plateau. As a component of magnetoteUuric (MT) work in the 4th phase of the project, MT data were collected along a profile that crosses the eastern segment of the Altyn Tagh fault on the northern margin of the plateau. Time series data processing used robust algorithms to give high quality responses. Dimensionality analysis showed that 2D approach is only valid for the northern section of the profile. Consequently, 2D inversions were only conducted for the northern section, and 3D inversions were conducted on MT data from the whole profile. From the 2D inversion model, the eastern segment of the Altyn Tagh fault only appears as a crustal structure, which suggests accommodation of strike slip motion along the Altyn Tagh fault by thrusting within the Qilian block. A large-scale off-proffie conductor within the mid-lower crust of the Qilian block was revealed from the 3D inversion model, which is probably correlated with the North Qaidam thrust belt. Furthermore, the unconnected conductors from the 3D inversion model indicate that deformations in the study area are generally localized.展开更多
Due to a series of linear projects built along National Highway 214,the second"Permafrost Engineering Corridor"on the Qinghai-Tibet Plateau has formed.In this paper,by overcoming the problems of data decentr...Due to a series of linear projects built along National Highway 214,the second"Permafrost Engineering Corridor"on the Qinghai-Tibet Plateau has formed.In this paper,by overcoming the problems of data decentralization and standard inconsistency,permafrost characteristics and changes along the engineering corridor are systematically summarized based on the survey and monitoring data.The results show that:1)Being controlled by elevation,the permafrost is distributed in flake discontinuity with mountains as the center along the line.The total length of the road section in permafrost regions is 365 km,of which the total length of the permafrost section of National Highway 214 is 216.7 km,and the total length of the permafrost section of Gong-Yu Expressway is 197.3 km.The mean annual ground temperature(MAGT)is higher than−1.5℃,and permafrost with MAGT lower than−1.5℃ is only distributed in the sections at Bayan Har Mountain and E'la Mountain.There are obvious differences in the distribution of ground ice in the different sections along the engineering corridor.The sections with high ice content are mainly located in Zuimatan,Duogerong Plain and the top of north and south slope of Bayan Har Mountain.The permafrost thickness is controlled by the ground temperature,and permafrost thickness increases with the decrease of the ground temperature,with the change rate of about 37 m/℃.2)Local factors(topography,landform,vegetation and lithology)affect the degradation process of permafrost,and then affect the distribution,ground temperature,thickness and ice content of permafrost.Asphalt pavement has greatly changed the heat exchange balance of the original ground,resulting in serious degradation of the permafrost.Due to the influence of roadbed direction trend,the phenomenon of shady-sunny slope is very significant in most sections along the line.The warming range of permafrost under the roadbed is gradually smaller with the increase of depth,so the thawing settlement of the shallow section with high ice-content permafrost is more significant.展开更多
The topographic margin of the Tibetan Plateau adjacent to the Sichuan Basin is one of the World’s most impressive continental escarpments, rising from ~600 meters in the basin to peak elevations exceeding 6km across...The topographic margin of the Tibetan Plateau adjacent to the Sichuan Basin is one of the World’s most impressive continental escarpments, rising from ~600 meters in the basin to peak elevations exceeding 6km across a horizontal distance of only 50~60km. Despite this relief, recent geodetic results (King et al., 1997; Chen et al., 1999) indicate that active shortening across this margin of the plateau is <3mm/a, and is within uncertainty of zero. Recent geodynamic models for active deformation in eastern Tibet (Royden et al., 1997) explain this discrepancy as a consequence of flow of lower crust from beneath the central plateau. These models predict relatively high rates of rock uplift in the near absence of horizontal shortening. Rivers along this margin of the plateau are actively incising into bedrock and afford the opportunity to better resolve the distribution of rock uplift along the margin.展开更多
Four consecutive days of rainstorm happened in the eastern part of the Qinghai-Tibet Plateau from 08:00 on July 24 to 08:00 on July 27,2017,and the high-altitude circulation situation,sounding data,ground station data...Four consecutive days of rainstorm happened in the eastern part of the Qinghai-Tibet Plateau from 08:00 on July 24 to 08:00 on July 27,2017,and the high-altitude circulation situation,sounding data,ground station data,physical quantity field,and satellite cloud picture were analyzed.It is concluded that the triggering environment of this rainstorm weather was formed under the common effect of the stable restriction of the confrontational weather scale of the Western Pacific subtropical high and the Middle East continental high,and the continuous forced disturbance of the wide low-value area over Eurasia;the indicators of water vapor,unstable energy,and upward movement in Qinghai Province had certain indications on whether heavy precipitation will be triggered;meanwhile,the special topography of the Hehuang valley in the east played an important role in the triggering of local heavy precipitation.展开更多
基金This study was supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(Grant No.2021QZKK0202)the China Postdoctoral Science Foundation(Grant No.2021T140650)the National Natural Science Foundation of China(Grant No.42007273).The authors express their gratitude for this financial assistance.
文摘The southeastern margin of Qinghai-Tibet Plateau(SMQTP)is of a typical large landslide-prone area due to intense tectonic activity,deeply incised valleys,high geostress and frequent earthquakes.To gain insights into large landslides in southeastern margin of Qinghai-Tibet Plateau,an area covering 3.34×105 km2 that extends 80e150 km on both sides of the Sichuan-Tibet traffic corridors(G318)was used to examine the spatial distribution and corresponding characteristics of landslides.The results showed that the study area contains at least 629 large landslides that are mainly concentrated on 7 zones(zones IeVII).Zones IeVII are in the southern section of the Longmenshan fault zone(with no large river)and sections with Dadu River,Jinsha River,Lancang River,Nujiang River and Yarlung Zangbo River.There are more landslides in the Jinsha River section(totaling 186 landslides)than the other sections.According to the updated Varnes classification,408 large landslides(64.9%)were recognized and divided into 4 major types,i.e.flows(275 cases),slides(58 cases),topples(44 cases)and slope deformations(31 cases).Flows,which consist of rock avalanches and iceerock avalanches,are the most common landslide type.Large landslide triggers(178 events,28.3%)are also recognized,and earthquakes may be the most common trigger.Due to the limited data,these landslide type classifications and landslide triggers are perhaps immature,and further systematic analysis is needed.
基金the Major State BasicResearch Program of China(G19992043203)underthe State Science and Technology Commission,the National Natural Science Foundation of China(No.40202012)+1 种基金the State Planning Commission(Special Program 98-1) the Ministry of Land and Resources(K1.4-3-4).
文摘A lot of new gold deposits have been found on the eastern margin of the Qinghai-Tibet Plateau during the past two decades. Among them, three main types of gold deposits have been recognized, including quartz-vein-type, shear- zone-type and porphyry-type. The former two types of gold deposits are mainly hosted within metamorphic rocks, while the latter is related to Cenozoic magmatism. Although all of these gold deposits are believed to have been formed during the uplift process of the Qinghai-Tibet Plateau in the Cenozoic era (Wang et al., 2002b), precise isotopic age constraints have still been lacking until quite recently. This paper presents new 40Ar/39Ar data of some gold deposits on the eastern margin of the Qinghai-Tibet Plateau, which indicate that gold mineralization in the region occurred in response to the episodic stages of the orogenies. Recently obtained 40Ar/39Ar data on quartz and feldspars from several gold deposits, such as the Sandiao deposit, the Baijintaizi deposit, the Pusagang deposits, provide new constraints on gold mineralization on the eastern margin of the Qinghai-Tibet Plateau. Geochronological studies of gold deposits along the Daduhe River indicate that there are three stages of gold mineralization. The early two stages occurred as early as 65.1 Ma in the Shuibaiyang deposit and 58.95 Ma in the Ruoji deposit, while the latter stage occurred as late as 25.35 Ma in Baijintaizi and 24.70 Ma in Sandiao. Isotopic dating of three plagioclases from the Beiya deposit, Zhifanggou deposit and Luobodi deposit and a K-feldspar from the Jinchangqing deposit in Yunnan Province indicates that these deposits were formed at two stages. The Zhifanggou and Jinchangqing deposits have early stage records as old as 58.82 Ma in Zhifanggou and 55.49 Ma in Jinchangqing, but all of the above four deposits in Yunnan have late stage records of 23.18 Ma in Jinchangqing, 24.54 Ma in Zhifanggou, 24.60 Ma in Luobodi and 24.56 Ma in Hongnitang. The above results suggest that the gold deposits on the eastern margin of the Qinghai-Tibet Plateau were formed concentratedly at two main episodes, i.e. the end of the Paleocene (about 58 Ma) and the boundary between the Paleogene and the Neogene (about 25 Ma). The later episode appears to be looks like more important and was coupled with the Sichuan movement, which was extensively activated at that period. The beginning of the Cenozoic Era (about 65 Ma) might be another episode of gold mineralization, but only one deposit (Shuibaiyang) in this study has been proved to have been be formed at this stage and might be earlier than the initial collision between the Indian Plate and the Eurasia Plate. In view of geology, the above three episodes of gold mineralization are associated with three events of tectonic- magmatism and/or fluid events. Even though the gold deposits (for example, the Shuibaiyang deposit, Ruoji deposit and Pusagang deposit) were formed at different episodes, all of them are genetically related to tectonic movements in large- scale shear zones. It looks like theat tectonic events (including large-scale strike-slip) between Paleogene and Neogene had a wide influence upon gold mineralization, with new deposits formed and old deposits enriched or superimposed to be a higher grade by new stage of mineralization. The above data suggest that gold deposits were not only concentrated in some areas, but also formed mainly at different boundaries of geological times, indicating that there existed some peak stages of gold mineralization (metallogenic episodes), and that the gold deposits were formed mainly by episodic mineralization.
文摘The Middle Triassic Ladinian-Upper Triassic Norian series in the Mesozoic-Cenozoic Ruo’ergai basin of Songpan area is characterized of large thick shallow marine-deep marine fine grained clastic.The strata are regionally unconformable between each adjacent two of the Middle-Late Triassic fine grained clastic,the Jurassic coal-containing clastic,the Cretaceous-Paleogene variegated coarse clastic。
基金supported jointly by the China Geological Survey project(grant number:1212011120167,12120114002201)China National Natural Science Foundation(grant number 41472178)
文摘We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.
基金supported by National Natural Science Foundation of China under grant Nos. 40839909,41074062, and 40674040
文摘In large continental orogens, an important research topic is the behavior of deep crustal and upper mantle deformation, and the flow styles of ductile material. The morphology of the eastern margin of the Tibetan plateau, adjacent to the Sichuan basin, is characterized by very steep relief with high mountain ranges. The crust beneath this region slows the velocities in the middle and lower crust. We have adopted a relatively dense network to inverse the detailed structure of the crust and upper mantle along the eastern margin of the Tibetan plateau and Sichuan basin, using teleseismic data via receiver function analysis. The results are in-line with the hypothesis that viscous crustal material is flowing beneath the eastern margin of the Tibetan plateau and that this process drives overlying crustal material around the strong and rigid Sichuan basin. When the viscous material hits this obstruction, flows are divided into two or more branches with different directions. The upper part of the upwelling viscous flow produces the pressure to intrude the upper crust, thereby driving uplift of mountain ranges and high peaks. In contrast, the lower part of the downwelling viscous flow produces the pressure to intrude the lower crust and upper mantle to deepen the Moho discontinuity, causing observed crustal thickening.
基金supported by a geological survey project of the China Geological Survey (No.1212011140013, No.12120113009800)
文摘The Wenchuan earthquake has altered the crustal motion characteristics in the eastern margin of the Tibetan Plateau and adjacent regions.Using discontinuous GPS survey data for 2008–2012, the velocity field for the Eurasia reference framework has been obtained, and the general trend of contemporary crustal motion after the occurrence of the Wenchuan earthquake has been studied.In addition, using the velocity field, the block movement velocity has been estimated by least-squares fitting.Furthermore, the properties and displacement rates of main faults have been obtained from the differences in velocity vectors of the blocks on both sides of the faults.The results reveal that there are no obvious changes in the general characteristics of crustal motion in this area after the Wenchuan earthquake.The earthquake mainly changed the rate of the movement of the Chuan-Qing block and caused variation in the movement direction of the South China block.The effect of the earthquake on faults is mainly reflected in variations in fault displacement velocity; there is no fundamental change in the properties of fault activity.The displacement rates of the Xianshuihe fault decreased by 3–4 mm/a, the Longmenshan fault increased by 9–10 mm/a, and the northern segment of the Anninghe fault increased by approximately 9 mm/a.Furthermore, the displacement rates of the Minjiang, Xueshan, Huya, Longquanshan, and Xinjin faults increased by 2–3 mm/a.This implies that the effects of the Wenchuan earthquake on crustal movement can mainly be observed in the Chuan-Qing, South China, and N-Chuan-Dian blocks and their internal faults, as well as the Xianshuihe and Longmenshan faults and the northern section of the Anninghe fault.The reason for this is that the Wenchuan earthquake disturbed the kinematic and dynamic balance in the region.
基金supported by China earthquake scientific array exploration Southern section of North South seismic belt(201008001)Northern section of North South seismic belt(20130811)+1 种基金National Natural Science Foundation of China(41474057)Science for Earthquake Resllience of China Earthquake Administration(XH15040Y)
文摘The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in China's Mainland and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block's interior. In this paper, the three-dimensional (3D) P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai-Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north-south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by low- velocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan-Dian and Songpan-Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan-Ganzi Block and the sub-block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80-120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background for the area's strong earthquake activity.
基金funded by the National Natural Science Foundation of China(Grant Nos.41372114,41502116,41340005,41172162,40972083,40841010)a research project of the National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation(Grant No.SK-0801)
文摘This study examines the relationship between high positive isostatic gravity anomalies (IGA), steep topography and lower crustal extrusion at the eastern margin of the Tibetan Plateau. IGA data has revealed uplift and extrusion of lower crustal flow in the Longmen Shan Mountains (the LMS). Firstly, The high positive IGA zone corresponds to the LMS orogenic belt. It is shown that abrupt changes in IGA correspond to zones of abrupt change of topography, crustal thickness and rock density along the LMS. Secondly, on the basis of the Airy isostasy theory, simulations and inversions of the positive IGA were conducted using three-dimensional bodies. The results indicated that the LMS lacks a mountain root, and that the top surface of the lower crust has been elevated by 11 km, leading to positive IGA, tectonic load and density load. Thirdly, according to Watts's flexural isostasy model, elastic deflection occurs, suggesting that the limited (i.e. narrow) tectonic and density load driven by lower crustal flow in the LMS have led to asymmetric flexural subsidence in the foreland basin and lifting of the forebulge. Finally, based on the correspondence between zones of extremely high positive IGA and the presence of the Precambrian Pengguan-Baoxing complexes in the LMS, the first appearance of erosion gravels from the complexes in the Dayi Conglomerate layer of the Chengdu Basin suggest that positive IGA and lower crustal flow in the LMS took place at 3.6 Ma or slightly earlier.
基金supported financially by the Chinese Academy of Sciences (CAS) Key Research Program (Grant No. KZZD-EW-13)the Major State Basic Research Development Program of China (Grant No. 2013CBA01803)+2 种基金the National Natural Science Foundation of China (Grant No. 41271084)the Research Program of State Key Laboratory of Frozen Soil Engineering of Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences (Grant No. SKLFSE-ZT-10)the Natural Science Foundation of Gansu Province (Grant No. 145RJY304)
文摘The characteristics of the permafrost along National Highway No. 214(G214) in Qinghai province(between kilometer markers K310 and K670),including the distribution patterns of permafrost and seasonally frozen ground(SFG), ground ice content and mean annual ground temperature(MAGT), were analyzed using a large quantity of drilling and measured ground temperature data. Three topographic units can be distinguished along the highway: the northern mountains, including Ela Mountain and Longstone Mountain; the medial alluvial plain and the southern Bayan Har Mountains.The horizontal distribution patterns of permafrost can be divided into four sections, from north to south: the northern continuous permafrost zone(K310-K460),the island permafrost zone(K460-K560), the southern continuous permafrost zone(K560-K630),and the discontinuous permafrost zone(K630-K670).Vertically, the permafrost lower limits(PLLs) of the discontinuous zone were 4200/4325 m, 4230/4350 m,and 4350/4450 m on the north-facing/south-facing slopes of Ela Mountain, Longstone Mountain and Bayan Har Mountains, respectively. The permafrost was generally warm, with MAGTs between-1.0°C and0°C in the northern continuous permafrost zone,approximately-0.5°C in the island permafrost zone,between-1.5°C and 0°C in the southern continuous permafrost zone, and higher than-0.5°C in the discontinuous permafrost zone. In contrast, the spatial variations in ground ice content were mainly controlled by the local soil water content and lithology.The relationships between the mean annual air temperature(MAAT) and the PLLs indicated that the PLLs varied between-3.3°C and-4.1°C for the northern Ela and Longstone Mountains and between-4.1°C and-4.6°C in the southern Bayan Har Mountains.
基金the Project of the National Natural Science Foudation of China (Grant No.41372114,41340005,41172162,40972083)
文摘We applied the material balance principle of the denudation volume and sedimentary flux to study the denudation-accumulation system between the Longmen Mountains (Mts.) and the foreland basin. The amount of sediment in each sedimentation stage of the basin was estimated to obtain the denudation volume, erosion thickness and deposit thickness since the Late Triassic Epoch, to enable us to recover the paleoelevation of the provenance and the sedimentary area. The results show the following: (1) Since the Late Triassic Epoch, the elevation of the surface of the Longmen Mts. has uplifted from 0 m to 2751 m, and the crust of the Longmen Mts. has uplifted by 9.8 km. Approximately 72% of the materials introduced have been denuded from the mountains. (2) It is difficult to recover the paleoelevation of each stage of the Longmen Mts. foreland basin quantitatively by the present-day techniques and data. (3) The formation of the Longmen Mts. foreland basin consisted of three stages of thrust belt tectonic load and three stages of thrust belt erosional unload. During tectonic loading stages (Late Triassic Epoch, Late Jurassic-Early Cretaceous, Late Cretaceous-Miocene), the average elevation of Longmen Mts. was lower (approximately 700-1700 m). During erosional unloading stages (Early and Middle Jurassic, Middle Cretaceous and Jiaguan, Late Cenozoic), the average elevation of Longmen Mts. was high at approximately 2000-2800m.
基金This paper is supported by the National Natural Science Foundation of China (No. 40404006)the Focused Subject Program of Beijing (No. XK104910598).
文摘The magnetotelluric (MT) survey along the Zhada (札达)-Quanshui (泉水) Lake profile on the western margin of the Qinghai (青海)-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong (班公)-Nujiang (怒江) sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang (羌塘) terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture, Bangong.Nujiang suture, and the major faults of Longmucuo (龙木错) and Geerzangbu are inferred.
基金supported by the National Department Public Benefit Research Foundation of China(grant No.201211077)National Natural Science Foundation of China(Grant No.40802033)
文摘The eolian deposits distributed in the river valleys in the eastern margin of the Tibetan Plateau (TP) are very useful in neotectonic and paleoclimatic studies. Firstly, the climate in the eastern margin of the TP is mainly controlled by the Indian summer monsoon, and detailed studies on the loess-paleosol sequences in this region can provide valuable terrestrial evidence of past changes in the Indian summer monsoon. Secondly, the river terraces in the eastern margin of the TP are considered to be a sensitive recorder of neotectonism to reflect the timing and amplitude of the TP uplift.
基金supported by grants from the National Natural Science Foundation of China(General Program No.40974058)National Science Fund for Distinguished Young Scholars(No.40904025 and 41404060)+4 种基金Fundamental Research Funds for the Central Universities(2652014016)National Natural Science Foundation of ChinaUnited States National Science FoundationScience Foundation of Ireland(award 08/RFP/GEO1693 to AGJ)Natural Science and Engineering Research Council(Canada)for financial support
文摘Project INDEPTH (InterNational DEep Profiling of Tibet and the Himalaya) is an interdisciplinary program designed to develop a better understanding of deep structures and mechanics of the Tibetan Plateau. As a component of magnetoteUuric (MT) work in the 4th phase of the project, MT data were collected along a profile that crosses the eastern segment of the Altyn Tagh fault on the northern margin of the plateau. Time series data processing used robust algorithms to give high quality responses. Dimensionality analysis showed that 2D approach is only valid for the northern section of the profile. Consequently, 2D inversions were only conducted for the northern section, and 3D inversions were conducted on MT data from the whole profile. From the 2D inversion model, the eastern segment of the Altyn Tagh fault only appears as a crustal structure, which suggests accommodation of strike slip motion along the Altyn Tagh fault by thrusting within the Qilian block. A large-scale off-proffie conductor within the mid-lower crust of the Qilian block was revealed from the 3D inversion model, which is probably correlated with the North Qaidam thrust belt. Furthermore, the unconnected conductors from the 3D inversion model indicate that deformations in the study area are generally localized.
基金This research was supported by the National Natural Science Foundation of China(Grant No.41971093).
文摘Due to a series of linear projects built along National Highway 214,the second"Permafrost Engineering Corridor"on the Qinghai-Tibet Plateau has formed.In this paper,by overcoming the problems of data decentralization and standard inconsistency,permafrost characteristics and changes along the engineering corridor are systematically summarized based on the survey and monitoring data.The results show that:1)Being controlled by elevation,the permafrost is distributed in flake discontinuity with mountains as the center along the line.The total length of the road section in permafrost regions is 365 km,of which the total length of the permafrost section of National Highway 214 is 216.7 km,and the total length of the permafrost section of Gong-Yu Expressway is 197.3 km.The mean annual ground temperature(MAGT)is higher than−1.5℃,and permafrost with MAGT lower than−1.5℃ is only distributed in the sections at Bayan Har Mountain and E'la Mountain.There are obvious differences in the distribution of ground ice in the different sections along the engineering corridor.The sections with high ice content are mainly located in Zuimatan,Duogerong Plain and the top of north and south slope of Bayan Har Mountain.The permafrost thickness is controlled by the ground temperature,and permafrost thickness increases with the decrease of the ground temperature,with the change rate of about 37 m/℃.2)Local factors(topography,landform,vegetation and lithology)affect the degradation process of permafrost,and then affect the distribution,ground temperature,thickness and ice content of permafrost.Asphalt pavement has greatly changed the heat exchange balance of the original ground,resulting in serious degradation of the permafrost.Due to the influence of roadbed direction trend,the phenomenon of shady-sunny slope is very significant in most sections along the line.The warming range of permafrost under the roadbed is gradually smaller with the increase of depth,so the thawing settlement of the shallow section with high ice-content permafrost is more significant.
文摘The topographic margin of the Tibetan Plateau adjacent to the Sichuan Basin is one of the World’s most impressive continental escarpments, rising from ~600 meters in the basin to peak elevations exceeding 6km across a horizontal distance of only 50~60km. Despite this relief, recent geodetic results (King et al., 1997; Chen et al., 1999) indicate that active shortening across this margin of the plateau is <3mm/a, and is within uncertainty of zero. Recent geodynamic models for active deformation in eastern Tibet (Royden et al., 1997) explain this discrepancy as a consequence of flow of lower crust from beneath the central plateau. These models predict relatively high rates of rock uplift in the near absence of horizontal shortening. Rivers along this margin of the plateau are actively incising into bedrock and afford the opportunity to better resolve the distribution of rock uplift along the margin.
文摘Four consecutive days of rainstorm happened in the eastern part of the Qinghai-Tibet Plateau from 08:00 on July 24 to 08:00 on July 27,2017,and the high-altitude circulation situation,sounding data,ground station data,physical quantity field,and satellite cloud picture were analyzed.It is concluded that the triggering environment of this rainstorm weather was formed under the common effect of the stable restriction of the confrontational weather scale of the Western Pacific subtropical high and the Middle East continental high,and the continuous forced disturbance of the wide low-value area over Eurasia;the indicators of water vapor,unstable energy,and upward movement in Qinghai Province had certain indications on whether heavy precipitation will be triggered;meanwhile,the special topography of the Hehuang valley in the east played an important role in the triggering of local heavy precipitation.