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Zhang Y.,Nanjing University | Zhang Y.,Chinese Academy of Geological Sciences | Li H.,Key Laboratory of Neotectonic Movement and Geohazard | Li J.,Key Laboratory of Neotectonic Movement and Geohazard
Acta Geologica Sinica

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. © 2016 Geological Society of China. Source

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

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. Source

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

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. Source

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.

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. Source

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

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. Source

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