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Jianjun D.U.,Chinese Academy of Geological Sciences | Jianjun D.U.,Key Laboratory of Neotectonic Movement and Geohazard | Dunpeng L.I.,Fuzhou University | Yinsheng M.A.,Chinese Academy of Geological Sciences | Yinsheng M.A.,Key Laboratory of Neotectonic Movement and Geohazard
Acta Geologica Sinica | Year: 2017

The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well–known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high–angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high–angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip–slip was 1.67–2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid–Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging–wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall. © 2017 Geological Society of China

Qiao Y.,Chinese Academy of Geological Sciences | Qiao Y.,Key Laboratory of Neotectonic Movement and Geohazard | Hao Q.,CAS Institute of Geology and Geophysics | Peng S.,Chinese Academy of Geological Sciences | And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

The loess-paleosol sequences in the middle-lower reaches of the Yantgze River are valuable geological records of Quaternary environments that bear information about climate change for the subtropical zone of southern China. Type sections containing eolian deposits in this region mostly include the upper loess-soil sequence referred to as Xiashu Loess Formation, the middle Vermiculated Red Soil (VRS) and the underlying fluvial deposits or bedrock. In this study, Xiashu loess, paleosol formed in the Xiashu loess, and the VRS samples from Xuancheng (XC) and Jiujiang (JJ) sections were analyzed for their elemental (major and trace elements) and isotopic (Sm-Nd) geochemistry and compared with Pleistocene loess and paleosol samples from the Chinese Loess Plateau (CLP) in northern China. The results show an overall similarity in geochemical characteristics between the southern China loess and the average UCC, indicating that the dust materials were derived from well-mixed sedimentary protoliths which had undergone numerous upper crustal recycling processes. In comparison with the loess of northern China, the eolian deposits in southern China have higher TiO2, Zr, Hf and lower Ba concentrations, higher TiO2/Al2O3, U/Pb, Th/Pb and lower Ba/Rb, Zr/Hf, Eu/Eu-, Ce/Yb, Eu/Yb ratios, and lower -Nd(0) values with relatively greater range. These features coincide with the complicated source rock compositions in the middle-lower Yangtze River, which suggests local sources for the eolian deposits in this region. The eolian deposits in southern China have experienced the intermediate K removal weathering stage, Ca, Sr, Na, Mg and K are the main mobile elements in the weathering process. In comparison with the Xiashu Loess Formation, the VRS has greater depletion of Na, Mg, K and Mn, indicating a stronger weathering intensity or perhaps a longer period of weathering. © 2011 Elsevier B.V.

Chen X.,Key Laboratory of Neotectonic Movement and Geohazard | Chen X.,Chinese Academy of Geological Sciences | Gehrels G.,University of Arizona | Yin A.,University of California at Los Angeles | And 4 more authors.
Acta Geologica Sinica | Year: 2012

The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian (493.1±4.9 Ma), the Silurian (422.9±8.0 Ma-420.4±4.6 Ma) and the Late Permian-Middle Triassic (257.8±4.0 Ma-228.8±1.5 Ma), respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma (main), 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic (P-T) granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism (293.6-270 Ma) occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation (triggered at the middle and lower crust), whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover (the upper crust).

Hao Q.,CAS Institute of Geology and Geophysics | Guo Z.,CAS Institute of Geology and Geophysics | Qiao Y.,Chinese Academy of Geological Sciences | Qiao Y.,Key Laboratory of Neotectonic Movement and Geohazard | And 2 more authors.
Quaternary Science Reviews | Year: 2010

The provenance of middle Pleistocene loess in the middle and lower reaches of the Yangtze River, the most intensively investigated loess deposits outside the Loess Plateau region in China, remains controversial. Identification of the provenance will provide crucial insight into the environmental implications of this valuable sedimentary archive, and into the potential role of the East Asian winter monsoon in transporting the dust from deserts in the Asian interior. In this study, geochemistry was used to compare the provenance of loess in the lower reaches of the Yangtze River in southern China with that inferred for loess deposits on the Loess Plateau in northern China. Compared with samples from the Loess Plateau, the <20 μm fraction in the loess deposits of southern China has higher TiO2/Al2O3, Zr/Nb, Zr/Al, Zr/Ti, Zr/Hf, Y/Al and LaN/SmN ratios, and lower Eu/Eu*, Th/Nb, Y/Nb and Al/Nb ratios. The clear distinction in immobile element ratios between samples from the two regions indicates that the loess deposits in the two regions have different provenances. The inferred difference in source area is also supported by variations in the major element composition of bulk samples obtained in this study and collected from published data. These lines of evidence indicate that the deserts in the Asian interior are not the primary provenance for the southern loess. It is suggested that the adjacent floodplains to the north of Yangtze River are the dominant dust sources, and the occurrence of sustained loess deposits in the lower reaches of the Yangtze River, currently an area of northern subtropical climate, is an indication of local aridification and strengthened winter monsoon activity during glacial periods as a regional response to the Middle Pleistocene climate transition around 0.8 Ma. The role of the East Asian winter monsoon in transporting the dust from northern deserts to southern China has been overestimated in previous studies. © 2010 Elsevier Ltd.

Li H.,Chinese Academy of Geological Sciences | Li H.,China University of Geosciences | Li H.,Key Laboratory of Neotectonic Movement and Geohazard | Zhang Y.,Chinese Academy of Geological Sciences | Zhang Y.,Key Laboratory of Neotectonic Movement and Geohazard
Tectonophysics | Year: 2013

The Konggar massif, about 120. km long and 13 - 18. km wide, developed along the eastern segment of the Xianshuihe fault zone in East Tibet. It consists of two rock units: the Konggar granitic pluton and an elongate migmatite zone about 70. km long and 1 - 3. km wide. A metamorphic event was well recorded by the growth rims of zircons in the migmatite, their SHRIMP U-Pb dating of two rock samples taken from leucosome and melanosome yields respectively the ages of ca. 31.75. Ma and ca. 26.9. Ma. The SHRIMP U-Pb dating of zircons from two rock samples of the granitic pluton yields respectively the crystalline ages of 17.35. Ma and 14.4. Ma. These new data, together with the previously zircon U-Pb ages, the mica Ar-Ar dating ages and whole rock Rb-Sr age of the granitoid, allows to constraining the tectono-thermal evolution history of the Xianshuihe fault zone. It is inferred that this fault zone suffered along its eastern segment from high temperature metamorphism and migmatization during the Oligocene (in 32 - 27. Ma), which was followed by magma intrusion during the Miocene (in 18 - 12. Ma); sinistral shearing began to occur at about 10. Ma and continues to present-day. © 2013 Elsevier B.V.

Sun P.,Key Laboratory of Neotectonic Movement and Geohazard | Sun P.,Chinese Academy of Geological Sciences | Yin Y.,China Institute of Geo Environment Monitoring | Wu S.,Key Laboratory of Neotectonic Movement and Geohazard | And 2 more authors.
Environmental Earth Sciences | Year: 2012

The Wenchuan earthquake triggered 15,000 rock avalanches, rockfalls and debris flows, causing a large number of causalities and widespread damage. Similar to many rock avalanches, field investigations showed that tensile failure often occurred at the back edge. Some soil and rock masses were moved so violently that material became airborne. The investigation indicates that this phenomenon was due to the effect of a large vertical seismic motion that occurred in the meizoseismal area during the earthquake. This paper analyses the effect of vertical earthquake force on the failure mechanism of a large rock avalanche using the Donghekou rock avalanche as an example. This deadly avalanche, which killed 780 people, initiated at an altitude of 1,300 m and had a total run-out distance of 2,400 m. The slide mass is mainly composed of Sinian limestone and dolomite limestone, together with Cambrian slate and phyllite. Static and dynamic stability analysis on the Donghekou rock avalanche has been performed using FLAC finite difference method software, under the actual seismic wave conditions as recorded on May 12, 2008. The results show that the combined horizontal and vertical peak acceleration caused a higher reduction in slope stability factor than horizontal peak acceleration alone. In addition, a larger area of tensile failure at the back edge of the avalanche was generated when horizontal and vertical peak acceleration were combined than when only horizontal acceleration was considered. The force of the large vertical component of acceleration was the main reason rock and soil masses became airborne during the earthquake. © 2011 Springer-Verlag.

Yin Y.,China Geological Survey | Zheng W.,Chengdu Center | Li X.,China Geological Survey | Sun P.,Key Laboratory of Neotectonic Movement and Geohazard | Li B.,Key Laboratory of Neotectonic Movement and Geohazard
Bulletin of Engineering Geology and the Environment | Year: 2011

Numerous earthquake-induced landslides occurred in the Longmenshan tectonic belt associated with the 12th May 2008 Wenchuan earthquake where the vertical acceleration was greater than the horizontal ground motion. Many of these landslides originated in the steep mountain terrain which amplified the effect of the ground shaking. Three typical landslides are discussed: the Niujuangou sturzstrom, the Chengxi rock slide and the 1,100 million m3 Daguangbao rock slide. Having discussed the individual slides and some previously published models, a mechanism to explain both the very fast velocity of the slides and their long run-out distance is proposed, taking into account aerodynamic principles. The model postulates that air trapped in the steep-sided valley by the collapsing rock mass forms a "cushion-effect" on which the debris moves. © 2010 Springer-Verlag.

Yin Y.,China Geological Survey | Sun P.,Key Laboratory of Neotectonic Movement and Geohazard | Sun P.,Chinese Academy of Geological Sciences | Zhang M.,Key Laboratory of Neotectonic Movement and Geohazard | And 3 more authors.
Landslides | Year: 2011

Because of the existence of a front stable rockmass barrier, the failure pattern of an oblique inclined bedding slope is conventionally recognized as a lateral rockfall/topple, and then a transformation into a rockfall accumulation secondary landslide. However, the Jiweishan rockslide, Wulong, Chongqing, which occurred on June 5, 2009, illustrates a new failure pattern of massive rock slope that rockmass rapidly slides along apparent dip, and then transforms into a long runout rock avalanche (fragment flow). This paper analyzes the mechanism of the new failure pattern which is most likely triggered by gravity, karstification, and the processes associated with mining activities. A simulation of the failure processes is shown, using the modeling software, FLAC3D. The results show that there are five principal conditions for an apparent dip slide associated with an oblique inclined bedding slope are necessary: (1) a block-fracture bedding structure. The rockmass is split into obvious smaller, distinct blocks with several groups of joints, (2) an inclined rockmass barrier. The sliding rockmass (i.e., the rockslide structure before movement) exists along a dip angle and is barricaded by an inclined stable bedrock area, and the subsequent sliding direction is deflected from a true dip angle to an apparent dip angle; (3) apparent dip exiting. The valley and cliff provide a free space for the apparent dip exiting. (4) Driving block sliding, which means the block has a push type of effect on the motion of the rockslide. The "toy bricks" rockmass is characterized by a long-term creeping that induces the shear strength reduction from peak to residual value along the bottom soft layer, and the sliding force is therefore increased. (5) The key block resistance and brittle failure. The pressure on the key block is increased by the driving rockmass and its strength decreases due to karstification, rainfall, and mining. The brittle failure of the karst zone between the key block and the lateral stable bedrock occurs instantaneously and is largely responsible for generating the catastrophic rockslide-rock avalanche. If there was not a pre-existing key block, the failure pattern of such the inclined bedding rockmass could be piecemeal disintegration or small-scale successive rockfall or topple. The recognition of catastrophic failure potential in such inclined bedding slopes requires careful search for not only structures dipping in the direction of movement, but also key block toe-constrained condition. © 2010 Springer-Verlag.

Zhang Y.,Key Laboratory of Neotectonic Movement and Geohazard | Zhang Y.,Chinese Academy of Geological Sciences | Shi W.,Key Laboratory of Neotectonic Movement and Geohazard | Shi W.,Chinese Academy of Geological Sciences | Dong S.,Chinese Academy of Geological Sciences
Acta Geologica Sinica | Year: 2011

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was estabIished from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozok tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates (the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west) towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.

Zhang Y.-Q.,Key Laboratory of Neotectonic Movement and Geohazard | Zhang Y.-Q.,Chinese Academy of Geological Sciences | Dong S.-W.,Chinese Academy of Geological Sciences | Li J.-H.,Chinese Academy of Geological Sciences | And 2 more authors.
Geology in China | Year: 2011

The Sichuan basin located far away from the active plate boundaries is well known for its surrounding fold zones whose genesis and tectonic settings have long been one of the key issues in the geotectonic study of South China. Based on a compilation of regional structural geology and an analysis of superimposed folding structures, this paper presents a synthetic discussion on the Mesozoic compressional tectonics in such aspects as its deformation features and structural styles, main tectonic events and their timing. Strudies show that the Sichuan basin and its surrounding zones experienced three major tectonic events during Mesozoic, each one creating fold zones that were compounded spatially and resulted in the formation and reformation of the Sichuan basin. The Triassic collisional orogeny along the northern and western margins of the Yangtze cratonic block resulted in the formation of the proto basin, i.e., the Chuan-Yu-Dian -Qian sedimentary basin whose extending size is larger than the present -day Sichuan basin. Folds created by this tectonic event mainly trend in W -E direction. Tectonic regime changed profoundly during the Middle -Late Jurassic, dominated by multi -directional plate convergences in Asia, which caused rejuvenation of old orogenic belts and formation of new tectonic systems. In particular, the rejuvenation of the Qinling orogenic belt resulted in the development of the Micangsahn - Dabashan foreland fold and fault zone along the northern margin of the Sichuan basin; the westward subduction of the Paleo -Pacific plate activated the Xuefengshan tectonic zone and created the oroclinal folds in east and south Sichuan; the eastward extrusion of the Songpan -Ganze orogenic belt reactivated the Longmenshan - Jinpingshan thrust zone in west Sichuan. This multi-directional compressional event greatly reformed the proto Sichuan basin, and shaped the basic structural pattern surrounding the Sichuan basin. The third major event occurred in latest Cretaceous and was characterized by NW-SE compression, and it strengthened the NE-SW trending structures. It is concluded that the main fold zones in and around the Sichuan basin was characterized by pervasively distributed thin -skinned structures mainly formed in Middle -Late Jurassic, and in consequence of multi-directional intracontinental orogeny, they constituted in turn part of the convergent tectonic system in east Asia.

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