Geodetic constraints on contemporary three-dimensional crustal deformation in the Laji Shan—Jishi Shan tectonic belt

The Laji Shan—Jishi Shan tectonic belt(LJTB),located in the southern part of the northeastern Tibetan Plateau(NETP),is a tectonic window to reveal regional tectonic deformation in the NETP.However,its kinematics in the Holocene remains controversial.We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations.Combined with fault kinematics from geologic observations,we analyze the crustal deformation characteristics along the LJTB.The results show that:(1)The Laji Shan fault(LJF)is inactive,and the northwest-oriented Jishi Shan fault(JSF)exhibits a significant dextral and thrust slip.(2)The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault.(3)With the continuous pushing of the Indian plate,internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

Petrogenesis of Indosinian Granitoids in Middle-Segment of South Qinling Tectonic Belt:Constraints from Sr-Nd Isotopic Systematics

South Qinling Tectonic Belt（SQTB）is located between the Shangzhou-Danfeng and Mianxian-Lueyang sutures.There are a lot of early Mesozoic granitoid plutons in its middle segment, comprising the Dongjiangkou-Zhashui granitoid plutons at the northeast,Huayang-Wulong-Laocheng granitoid plutons at the central part,Xiba granitoid pluton at the northwest and Guangtoushan-Liuba granitoid plutons at the southwest.These Indonisian granitoids contain a mass of various scale mafic enclaves,which show sometimes clear boundaries and sometimes transitional boundaries with their host granitoids.These granitoids also exhibit metaluminous to peraluminous series,commonly higher Mg# and a wide range of petrochemistry from low-K tholeiite series,through mid-K and high-K calc-alkaline series to shoshonite series and predominated samples are attributed to mid-K and high-K calc-alkaline series.Detailed analyses in Sr-Nd isotopic systematics and petrochemistry reveal that there may be regionally initial granitoid magma of the Indonisian granitoid plutons,comprising Dongjiangkou-Zhashui,Huayang-Wulong-Laocheng,Xiba,and Guangtoushan-Liuba granitoid plutons,which were produced by hybrids of magmas in various degrees,and the initial magmas were derived from both the mantle and the lower continental crust（LCC）sources in the SQTB.The initial granitoid magma further did the magma hybrid with the magmas from the LCC,crystallization fractionation,and assimilation with upper crustal materials during their emplacement to produce these granitoid plutons in the SQTB.These magmatism processes are most likely to occur under continent marginal arc and syn-collision to post-collision tectonic backgrounds.

Geochemistry of Permian Mafic Igneous Rocks from the Napo-Qinzhou Tectonic Belt in Southwest Guangxi, Southwest China: Implications for Arc-Back Arc Basin Magmatic Evolution

The Napo-Qinzhou Tectonic Belt （NQTB） lies at the junction of the Yangtze, Cathaysia and Indochina （North Vietnam） Blocks, which is composed of five major lithotectonic subunits： the Qinzhou-Fangcheng Suture Zone （QFSZ）, the Shiwandashan Basin （SB）, the Pingxiang-Nanning Suture Zone （PNSZ）, the Damingshan Block （DB） and the Babu-Lingma Suture Zone （BLSZ）. On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups： （1） mafic igneous rocks （Group 1） from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; （2） mafic igneous rocks （Group 2） from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and （3） mafic igneous rocks （Group 3） from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206 Pb/ 238 U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd （t） values （-2.61 to ＋1.10） and high initial 87 Sr/ 86 Sr isotopic ratios （0.705309-0.707434）, indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province （SW China） and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian （or Yunkai） Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time.

The Deep Geophysical Structure of the Middle Section of the Longmen Mountains Tectonic Belt and its Relation to the Wenchuan Earthquake

Investigation of the deep geophysical structure of the Longmen Mountains tectonic belt and its relation to the Wenchuan Earthquake is important for the study of earthquakes.By using magnetotelluric sounding profiles of the Luqu-Zhongjiang and Anxian-Suining; seismic sounding profiles of the Sichuan Maowen-Chongqing Gongtan,the Qinghai Huashi Gorge-Sichuan Jianyang,and the Batang-Zizhong; and magnetogravimetric data of the Longmen Mountains region,the deep geophysical structure of the Songpan-Ganzi block,the western Sichuan foreland basin,and the Longmen Mountains tectonic belt and their relation was discussed.The eastward extrusion of the Qinghai-Tibet Plateau thrusts the Songpan-Ganzi block upon the Yangtze block,which obstructs the eastward movement of the Qinghai-Tibet Plateau.The Maoxian-Wenchuan,Beichuan-Yingxiu,and Anxian-Guanxian faults of the Longmen Mountains fault belt dip to northwest with different dip angles and gradually converge in the deeper parts.Geophysical structure suggests that an intracrustal low-velocity,low-resistivity,and high-conductivity layer is common between the middle and upper crust west of the Longmen Mountains tectonic belt but not in the upper Yangtze block.The Sichuan Basin has a thick low-resistance sedimentary layer on a stable high-resistance basement; moreover,there are secondary paleohighs and depression structures at the lower part of the western Sichuan foreland basin with characteristic of high magnetic anomalies,whereas the Songpan-Ganzi block has a high resisitivity cover of upper crust and continues to a low-resistance layer.Considering the Longmen Mountains tectonic belt as the boundary,there are Bouguer gravity anomalies of ＂one belt between two zones.＂ Thus,we infer that there is a corresponding relation between the inferred crystalline basement of the Songpan block and the underlying basin basement of the Longmen Mountains fault belt.Furthermore,there may be an extensive ancient Yangtze block,which is west of the Ruoergai block.In addition,the crust-mantle ductile shear zone under the Longmen Mountains tectonic belt is the main fault,whereas the Beichuan-Yingxiu and Anxian-Guanxian faults at the surface are earthquake faults.The Wenchuan Ms 8.0 earthquake might be attributed to the collision of the Yangtze block and the Qinghai-Tibet Plateau.The eastward obduction of the eastern edge of the Qinghai-Tibet Plateau and eastward subduction of its deeper part under the influence of the collision of the Indian,Pacific,and Philippine Plates with the Eurasia Plate might have caused the Longmen Mountains tectonic belt to cut the Moho and extend to the middle and upper crust; thus,creating high stress concentration and rapid energy release zone.

The Identification of Large-Giant Bedrock Landslides Triggered by Earthquake in the Longmenshan Tectonic Belt

The identification of large-giant bedrock landslides triggered by earthquake aims to the landslide prevention and control. Previous studies have described the basic characteristics, distribution, and the formation mechanism of seismic landslides （Bijan Khazai et al., 2003; Chong Xu et al., 2013; Lewis a. Owen et al., 2008; Randall W. Jibson et al., 2006）. However, few researches have focused on the early identification indicators of large-giant bedrock landslides triggered by earthquake （David k. Keefer., 1984; Janusz Wasowski et al., 2011; Alexander L.Strom., 2009; Patrick Meunier et al., 2008; Shahriar Vahdani et al., 2002; Bijan Khazai et al., 2003）. This paper presents the identification indicators of large-giant bedrock landslides triggered by earthquake in the Longmenshan tectonic belt on the basic of their characteristics, distribution and the relationship between seismic landslides and the peak ground motion acceleration.

Evolution of hydrocarbon generation of Jurassic source rock of the Lenke-1 well in Lenghu tectonic belt of Qaidam basin,China

The Lenghu tectonic belt is located at or near the northern margin in the Qaidam Basin,which is an intracontinental composite basin evolved during the Mesozoic and Cenozoic epochs.The Lower Jurassic is considered a good source rock with a wide distribution.Since the deposit of the Lower Jurassic hydrocarbon source rock,the basin has undergone many tectonic events of subsidence and uplift.The source rocks in the Lengke-1 well,have experienced a complicated tectonic-burial history during which different hydrocarbon generation(HG) evolutions have taken place.We have investigated the history of burying,heating and hydrocarbon generation of the Lower Jurassic source rocks,not just on the basis of tectonic disturbance and deep burial,but also from new studies in fluid inclusion measurements and the application of numerical simulation with EASY%Ro.Our study reveals the evolution process,tectonic episodes and the strength of the HG of the Jurassic source rock.We conclude that twice HG processes have taken place since the Lower Jurassic formation and infer from that the important conclusion that more HG of the Lower Jurassic source rock took place during the Eocene-Miocene epochs.Finally,we discuss the oil and gas tarp formation and destruction in the Lenghu tectonic belt and point out that more attention should be paid to the thrust faults,which formed during the late Himalayan epoch.

ON SOUTHERN STRETCH OP THE S-N TECTONIC BELT, CHINA

It can be inferred from the geophysical data, linear structures, tectonic evolu-tion history and metallogeny that the S-N tectonic Belt stretches further south in a different di-rection and manner after intercepted by the Red River Fault, The stretching segment is the im-portant tectonic boundary in Indo-Asia and assiminlates the S-N tectonic belt with some differ-ences.

ON GOLD-BEARING CHARACTERISTICS OF GEOSYNCLINAL TECTONIC LAYER IN XUEFENG MOUNTAIN TECTONIC BELT,HUNAN,CHINA

1. Material composition of the geosynclinal tectonic LayerThe geosynclinal tectonic layer is mainly composed of the following two parts: sandyslate rocks of Precambrin and volcanic rocks inbeded within the sand-slate rocks.The sandy-slate rocks embrace the chemical compositional characteristics of light metamorphic rocks: SiO2=54.5681.63（Wt%）, with average of 63.96（wt%）（n=58, the same as following）; Al2O3=9.4717.75（wt%）, with average of 15.36（wt%）, and Al2O3】K2O+Na2O+CaO; the content of （FeO+Fe2O3） varies greatly with FeO】Fe2O3; （CaO+MgO）=0.789.22 （wt%）with average of 23 （wt%）, and MgO】CaO; the ratios of K2O/Na2O rang from 2 to 4（】1）. By comparing all this chemical data with that of the other kind rocks, We can know that the sand y-slate rocks were the eunic and /or bathyal sediments which formed under the strongly active eugeosynclinal tectonic setting.

Permian-Triassic Magmatism in the Qin-Fang Tectonic Belt,SW China:New Insights into Tectonic Evolution of the Eastern Paleo-Tethys

The granites of ambiguous geodynamic mechanism in the Qin-Fang tectonic belt(SW China)were studied in detail based on petrological,element geochemical,zircon U-Pb geochronological,and Hf isotopic data.LA-ICPMS U-Pb analyses on zircon yield ages of 248-245 Ma for the granites from the Qin-Fang tectonic belt.The geochemical data show that they are high-K,calc-alkaline,and peraluminous series.Their ε_(Hf)(t)values are from -14.01 to -7.75 with two-stage model ages of 1.74-1.43 Ga.These data,integrated with low Al_(2)O_(3)/TiO_(2),Rb/Sr,Rb/Ba,and(Na_(2)O+K_(2)O)/(FeO^(T)+MgO+TiO_(2))ratios,and high CaO/Na_(2)O ratios for the granite,suggest an origin from psammite source which was contaminated by mantle-derived components.These observations,in combination with the age data and stratigraphic records in the Jinshajiang,Ailaoshan,and Hainan Island areas suggest that the granites were formed in a post-collision tectonic setting.The Qin-Fang tectonic belt was likely a branched ocean basin of the eastern Paleo-Tethys.

Anisotropic zoning in the upper crust of the Tianshan Tectonic Belt

The Tianshan Tectonic Belt is an intracontinental orogenic belt formed by continental convergence that has undergone long-term tectonic evolution. The reactivation that began during the Cenozoic Period has led to complex structural changes. The goals of this study are to review the seismic observational data obtained during 2009–2019 in the Xinjiang regional seismic network and analyze the anisotropy of the upper crust in the Tianshan area. Therefore, a shear-wave splitting system was adopted to collect and analyze shear-wave splitting parameters of 33 stations in the study area. The anisotropy of the upper crust of the Tianshan is spatially diverse, and the dominant polarization directions of fast shear-wave reflect the spatial variations of regional tectonic stress. In addition, the time delays of slow waves are proportional to the intensities of anisotropy in the upper crustal medium. The dominant polarization direction of the fast waves in the western segment of the North Tianshan Mountain,northwestern corner of the Tarim Basin, and northeastern edge of Pamir is consistent with the tectonic stress fields in the area. In the northern part of the Keping Block, the dominant polarization directions of the fast waves are consistent with the fault trends;however, they are at a high angle to the dominant directions of the regional tectonic stress field indicating that the anisotropy is affected by the faults in the area. The anisotropy of the eastern segment of the South Tianshan Mountains and the surrounding area of Urumqi are affected by the local stress field and fault structure. The polarization directions at some of the stations are subparallel to the directions of the regional principal stress. However, for other stations, the polarization directions are aligned with the neighboring faults. The polarization directions of the fast waves in most of the study area are consistent with the local tectonic stress fields. Thus, stress compression phenomena such as the Tarim Basin being thrusted and subducted between the Tianshan crust and the upper mantle due to the far field effects of the convergence between the Indian and Siberian plates are evident.Furthermore, the zoning of the time delays is distinct, and the time delays share an increasing trend from east to west in the North Tianshan and South Tianshan Mountain ranges. These results are consistent with the north-south convergence deformations across the Tianshan Mountains, where the deformation rate increased from east to west. The average values of time delays in northeastern Pamir are significantly higher than that in the other areas due to the occurrence of the most intensive tectonic movements suggesting that the anisotropy of the zone is significantly stronger than that of the other zones in the Tianshan Tectonic Belt. We successfully deciphered the seismic anisotropy in the upper crust and provided a comprehensive and systematic understanding of the dynamic mechanisms of the Tianshan Tectonic Belt.

Mineralization-related geochemical anomalies derived from stream sediment geochemical data using multifractal analysis in Pangxidong area of Qinzhou-Hangzhou tectonic joint belt, Guangdong Province, China

Distinguishing geochemical anomalies from background is a basic task in exploratory geochemistry. The derivation of geochemical anomalies from stream sediment geochemical data and the decomposition of these anomalies into their component patterns were described. A set of stream sediment geochemical data was obtained for 1 880 km 2 of the Pangxidong area, which is in the southern part of the recently recognized Qinzhou-Hangzhou joint tectonic belt. This belt crosses southern China and tends to the northwest (NE) direction. The total number of collected samples was 7 236, and the concentrations of Ag, Au, Cu, As, Pb and Zn were measured for each sample. The spatial combination distribution law of geochemical elements and principal component analysis (PCA) were used to construct combination models for the identification of combinations of geochemical anomalies. Spectrum-area (S-A) fractal modeling was used to strengthen weak anomalies and separate them from the background. Composite anomaly modeling was combined with fractal filtering techniques to process and analyze the geochemical data. The raster maps of Au, Ag, Cu, As, Pb and Zn were obtained by the multifractal inverse distance weighted (MIDW) method. PCA was used to combine the Au, Ag, Cu, As, Pb, and Zn concentration values. The S-A fractal method was used to decompose the first component pattern achieved by the PCA. The results show that combination anomalies from a combination of variables coincide with the known mineralization of the study area. Although the combination anomalies cannot reflect local anomalies closely enough, high-anomaly areas indicate good sites for further exploration for unknown deposits. On this basis, anomaly and background separation from combination anomalies using fractal filtering techniques can provide guidance for later work.

Dextral strike-slip of Sanguankou-Niushoushan fault zone and extension of arc tectonic belt in the northeastern margin of the Tibet Plateau

The kinematic characteristics of the Sanguankou-Niushoushan fault（SGK-NSSF） are of great significance to the understanding of the extension of the arc tectonic belt in the northeastern margin of the Tibet Plateau. Using field surveys and various data collection methods, including large-scale geological mapping, measurement of typical topographies, and dating of sedimentary strata, it was determined that the SGK-NSSF exhibits obvious dextral strike-slip characteristics and thus is not a sinistral strike-slip fault, as believed by previous researchers. The results of this study show that the geological boundaries for the Paleozoic, Mesozoic, and Cenozoic eras were all dextrally dislocated by the fault, with the faulted displacements being similar. The maximum strike-slip displacement of the fault, after elimination of topographic effects, was found to be 961±6 m. The Sanguankou fault at the northern section exhibits obvious characteristics of more recent activities, with a series of small gullies having undergone synchronized dextral writhing after traversing the fault. The average horizontal slip rate of the fault since the late Quaternary was determined to be approximately 0.35 mm/a. The pre-existing fold structures formed during the late Pliocene were dislocated by the fault and became ex situ, indicating that dextral strike-slip of the fault could not have occurred prior to the late Pliocene. The maximum displacements and average slip rates were used to estimate the onset time of the dextral strike-slip activities of the fault as being after 2.7 Ma. In this study, the understanding of previous researchers concerning the extension in the northeastern margin of the Tibet Plateau was combined with analyses of the successive relationships between fold deformations and fault activities. This led to the finding that the extension in the northeastern margin of the Tibet Plateau reached the vicinity of the SGK-NSSF during the late Pliocene（~2.7 Ma）, causing regional uplift and fold deformations of the strata there. During the early Quaternary, the northeastern compression of the Tibet Plateau and the counterclockwise rotation of the Ordos block collectively resulted in the dextral strike-slip activities of the SGK-NSSF. This then formed the foremost margin of the arc tectonic belt extension in the northeastern margin of the Tibet Plateau.

Early Mesozoic structural deformation in the Chuandian N-S Tectonic Belt,China

The Helan-Chuandian N-S Tectonic Belt is a mantle transitional belt in China. The southem part, forming the Chuandian N-S Tectonic Belt, comprises several tectonic systems, each displaying different characteristics. The Chuandian N-S Tectonic Belt along the western margin of yangtze Block is a strike-slip tectonic belt with a series of echelon left-lateral slip faults. The strike-slip fault systems experienced two stages of structural deformation： early NW-SE striking thrust faults formed under a NE-SW compression stress field, and later sinistral strike-slip structures formed along thrust faults under a NW-SE compression stress field. Mesozoic basins developed between the left-lateral slip faults. Sedimentary facies and paleocurrent directions indicate that basin development was controlled by the strike-slip faults. The oldest strata in the Chuandian N-S Tectonic Belt constrain its formation to early Mesozoic. In fact, The slip tectonic belt formed by clockwise rotation and north-directed subduction-collision of the Yangtze Block in Late Triassic-Jurassic. The strike-slip faults that developed within the belt also formed at this time.

Deep Duplex Thrust in the Sangzhi-Shimen Tectonic Belt,in the West Hunan and Hubei Areas

Recent studies indicate that there is a large buried body developing in the Sangzhi-Shimen tectonic belt,which is between the Xuefeng intracontinental deformation system and the Xiangexi tectonic belt.In order to explore the tectonic evolution and main deformation-controlling factors of the buried body,we carried out a series of studies and built two new models based on the latest seismic data and fault-related fold theory.These new models show that the deformation of the buried body in the north segment of the study area is different from that in the middle-south segment.After further study,we found the main factors leading to these differences were:(1)the magnitude of the principal stress,(2)the range of tectonic movements,and(3)the morphology and depth of the basement detachment.Subsequently,with the physical simulation experiments,a 3D evolution model of the study area was built.

Evolution of Mesozoic Volcanic Basins and Red Basins in the Gan-Hang Tectonic-Volcanic Metallogenic Belt

This paper mainly proposes six major regional geological events in the active continental-margin mantle uplift zone and discusses the oscillation nature of the evolution of Mesozoic volcanic basins and red basins, origin of erosion in the late stage of red basins and mechanism of volcanism.

Geochronology, Geochemistry and Tectonic Setting of the Bairiqiete Granodiorite Intrusion(Rock Mass) from the Buqingshan Tectonic Mélange Belt in the Southern Margin of East Kunlun

This study focuses on the zircon U-Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion （rock mass） from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun.The results show that the zircons are characterized by internal oscillatory zoning and high Th/U （0.14-0.80）,indicative of an igneous origin.LA-ICP-MS U-Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma （MSWD =0.34）,implying that the Bairiqiete granodiorite formed in the early Silurian.Geochemical analyses show that the rocks are medium-K calc-alkaline,relatively high in Al2O3 （14.57-18.34 wt％） and metaluminous to weakly peraluminous.Rare-earth elements have low concentrations （45.49-168.31 ppm） and incline rightward with weak negative to weak positive Eu anomalies （δEu =0.64-1.34）.Trace-element geochemistry is characterized by negative anomalies of Nb,Ta,Zr,Hf and Ti and positive anomalies of Rb,Th and Ba.Moreover,the rocks have similar geochemical features with adakites.The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting.The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.

Tectonic Nature of the Northern Segment of the Jiao-Liao-Ji Belt:A Rift or Continental Collision Belt?

Objective The tectonic characteristics and evolution of the Paleoproterozoic Jiao-Liao-Ji belt have been extensively studied in recent decades （Fig. 1 a）. Two main models have been proposed for the formation of this belt： a continental-or arc-continent collisional belt, and the opening and closure of an intra-continental rift. The main reasons for these ongoing debates are own to the complex composition, including metamorphosed volcano-sedimentary rocks, multiple pulses of granitic magmatism, meta-mafic intrusions, and tectono- metamorphic history. In addition, earlier work focused on the geochronology and metamorphic evolution, whereas the source properties, petrogenesis, and tectonic setting of the metamorphosed volcano-sedimentary sequence and meta- mafic intrusions are poorly understood.

Hydrodynamic Evolution and Hydrocarbon Accumulation in the Dabashan Foreland Thrust Belt,China

There are two plays in the Dabashan foreland tectonic belt： the upper and the lower plays. The lower play experienced one sedimentary hydrodynamic stage, two burial hydrodynamic stages, two tectonic hydrodynamic stages and two infiltration hydrodynamic stages from the Sinian to the Cenozoic, while the upper play had one sedimentary hydrodynamic stage, one burial hydrodynamic stage, two tectonic hydrodynamic stages and one infiltration hydrodynamic stage from the Permian to the Cenozoic. Extensive flows of both sedimentary water, including hydrocarbons, and deep mantle fluid occurred in the Chengkou faults during collision orogeny in the Middle-Late Triassic Indosinian orogeny, and fluid flow was complicated during intracontinental orogeny in the Middle-Late Jurassic. In addition to these movements, infiltration and movement of meteoric water took place in the Chengkou faults, whereas in the covering-strata decollement tectonic belt, extensive sedimentary water flow （including hydrocarbons） occurred mainly in the Zhenba and Pingba faults. During the stage of rapid uplift and exhumation from the Cretaceous to the Cenozoic, the fluid flow was characterized mainly by infiltration of meteoric water and gravity-induced flow caused by altitude difference, whereas sedimentary water flow caused by tectonic processes was relatively less significant. Sedimentary water flow was more significant to the lower play in hydrocarbon migration and accumulation during collision orogeny in the Middle-Late Triassic Indosinian orogeny, but its influence is relatively slight on the upper play. On one hand, hydrodynamics during intracontinental orogeny in the Middle-Late Jurassic adjusted, reformed or oven destroyed oil reservoirs in the lower play; on the other hand, it drove large amounts of hydrocarbons to migrate laterally and vertically and is favorable for hydrocarbon accumulation. Infiltration hydrodynamics mainly adjusted and destroyed oil reservoirs from the Cretaceous to the Cenozoic.

Earthquake-induced Soft-sediment Deformation Structures in the Dengfeng Area,Henan Province,China:Constraints on Qinling Tectonic Evolution during the Early Cambrian

Soft-sediment deformation structures are abundant in the Cambrian Zhushadong and Mantou formations of the Dengfeng area, Henan Province, China. Soft-sediment deformation structures of the Zhushadong Formation consist of fluidized deformation, synsedimentary faults, seismo-folds and plastic deformation; the Mantou Formation is dominated by small-scale horst faults, intruded dikes, fluidized veins, and seismo-cracks. These structures are demonstrated to be earthquake-related by analysis of trigger mechanisms, and may indicate the activity of the Qinling tectonic belt during the early Cambrian. Furthermore, the assemblages of soft-sediment deformation structures altered with time： large-scale, intense deformation in the Zhushadong Formation alters to small-scale, weak deformation in the Mantou Formation. This striking feature may have been caused by changes in hypocentral depth from deep-focus to shallow-focus earthquakes, indicating that the Qinling tectonic belt developed from the subduction of the Shangdan Ocean to the extension of the Erlangping back-arc basin. This study suggests that soft-sediment deformation structures can be used to reveal the activity of a tectonic belt, and, more importantly, changes in deformation assemblages can track the evolution of a tectonic belt.

Insights into the long-term stability of landslide dams on the eastern margin of the Tibetan Plateau, China——A case study of the Diexi area

Landslide dams,especially long-term stable landslide dams,have been recognized as important contributors to regional geomorphological evolution.Here,the Diexi area,a long-term stable dam-prone area located in upstream of the Minjiang River on the eastern Tibetan Plateau,was adopted to reveal reasons that landslide dams are concentrated in this area and maintain long-term stability via detailed field investigations,landslide dam sampling,unmanned aerial vehicle(UAV)images,and digital surface models(DSM).The results show the controlling factors that the slopes are prone to sliding and rock mass structure deterioration including lithological combination mode,slope structure,topographic conditions,a series of NNE-trending radial fissures and hydrological conditions.Fault activities,which have caused many earthquakes,are the main inducing factor.Landslide dams are prone to occurrence in the Diexi area owing to the combined effect of the narrow channels,the large landslide dam volume and the rock fragments.The river flow,and the landslide dam volume,material,structure,and parameters control the stability of landslide dams.The landslide dam consists of various sizes of boulders and all landslide dams exhibit an obvious inverse grading sequence,and this size combination could consume most of the flow energy,and consequently protect the dam from incision.Additionally,a total of seven knickpoints were formed by landslide dams,and the longitudinal gradient upstream of every landslide dam was found to decrease by the action of knickpoint.In the eastern margin of the Tibetan Plateau,there are numerous landslide dams existed for hundreds or thousands of years.Studies on the long-term stable landslide dams in the Diexi area could provide experience for studying similar kinds of landslide dams in this region.