In order to reveal the nature of the segmentation of Longmen Mountains Thrust Belt caused by the three nappes (Jiaoziding, Jiudingshan, and Baoxing Nappe), several methods are applied in this paper, including field in...In order to reveal the nature of the segmentation of Longmen Mountains Thrust Belt caused by the three nappes (Jiaoziding, Jiudingshan, and Baoxing Nappe), several methods are applied in this paper, including field investigation, seismic explanation and balanced crossed section, etc. Results of research reveal that nappes in Longmen Mountains vary in geometry, kinematics, and dynamics. Jiaoziding Nappe has generally behaved in a ductile manner, whereas Jiudingshan Nappe has been rigid, and the rheology of Baoxing Nappe has been intermediate between that of the other two nappes. The development of nappes has resulted in tectonic segmentation of Longmen Mountains: the main structural style of the northern segment is thrust faulting, with Jiaoziding Nappe representing a giant syncline. Given its ductility, it absorbed lots of stress, with the least amount of tectonic shortening in the SE part of the nappe. In the middle segment, the deformation is controlled by the rigid Jiudingshan Nappe, whose frontal area records lots of tectonic shortening. Deformation in the southern segment is intermediate in character between that of the other two segments, characterized by horizontal zonation, as demonstrated by fault development, and vertical stratification, which indicates that fault development was controlled by lithology.展开更多
Controlled by the squeezing collision between the Yangtze block and the North China block and the left movement of the Tanlu fault, the Xu-Su region developed into an arc-shaped nappe structure, and many destructive e...Controlled by the squeezing collision between the Yangtze block and the North China block and the left movement of the Tanlu fault, the Xu-Su region developed into an arc-shaped nappe structure, and many destructive earthquakes occurred in its periphery. The geological structure of this area is complex, and there is the possibility of moderate and strong earthquakes. To further explore the crust density structure and identify the main faults and deep structural features in the Xu-Su region, based on the observed seismic data and gravity/GNSS co-site observation data, combined with the EGM2008 global gravity field model, we obtained the density of three-dimensional structure using cross gradient method joint inversion. Based on this, a geological model of the Xu-Su region was established. The results show that the crustal density anomaly amplitude within 0-25 km of the Xu-Su region ranges from-280 to 490 kg/m3, showing a zonal distribution in east-west direction and a segmented north-south direction. There are several density anomalies in the shallow(0-4 km) region at Tongshan, Huaibei, Xiayi, Woyang, etc. The density anomalies are significantly correlated with the distribution of regional faults. The density structure is divided into two large regions by Subei fault, which can be further divided along the eastwest Kouziji-Nanzhao fault and Guzhen-Huaiyuan fault. The earthquakes are obviously related to the regional fault activity and the spatial distribution of abnormal bodies. The earthquake-prone areas(5-15 km) correspond to the abnormal density mutation zone, upper uplift zone, and transformation zone near Xiaoxian, Tongshan, and Xushuanglou faults. The comprehensive results show three weak seismic activity areas in the whole region, which are located near the Huaibei, Xiaoxian, and Wohe faults. The results provide theoretical support for seismic risk analysis in this area, and these three areas should be emphasized in future seismic hazard analysis.展开更多
The Beyşehir-Hoyran Nappes,one of the tectonostratigraphic units of the Taurides,are thought to be originated from the Izmir-Ankara Ocean(northern branch of Neotethys).In this study,Late Paleozoic rock units from the ...The Beyşehir-Hoyran Nappes,one of the tectonostratigraphic units of the Taurides,are thought to be originated from the Izmir-Ankara Ocean(northern branch of Neotethys).In this study,Late Paleozoic rock units from the blocks of Beyşehir-Hoyran Nappes were studied in detail using foraminiferal assemblages in two different locations from the southwest of Karaman City(southern Turkey).In both places,blocks/slices and pebbles of various origins are embedded within a highly sheared matrix of Late Cretaceous Age,and the whole unit can be regarded as a sedimentary mélange.The ages of the blocks from the southwest of Karaman City range from the Late Serpukhovian(Late Mississippian)to Late Capitanian(Middle Permian)with some depositional breaks(e.g.,Bashkirian,Kasimovian).Combined with the previous data from the Mersin Mélange,which also include the remnants of the Beyşehir-Hoyran Nappes,our new findings suggest that a shallowing-upward sequence,characterized by a shallow water environment with foraminifera-bearing limestones,was deposited over the Tournaisian pelagic sequence in the Beyşehir-Hoyran Nappes till the Early Moscovian(Early Middle Pennsylvanian).This shallowing-upward sequence in the Beyşehir-Hoyran Nappes could be related to the Late Paleozoic Glaciation on the Gondwana supercontinent(Glacial Ⅱ),which resulted in a sea-level drop and deposition of platform carbonates during the Viséan–Early Moscovian(Middle Mississippian to Early Middle Pennsylvanian)time interval.The absence of the main part of the Middle-Upper Pennsylvanian deposits(continental phase during the Middle Moscovian–Middle Gzhelian)in the Beyşehir-Hoyran Nappes can be mainly attributed to the occurrence of a mantle plume and partially to the effect of Late Paleozoic Gondwanan Glaciation(Glacial Ⅲ).Progressive uplifting by the buoyant mantle plume material has resulted in rifting at the center of the basin where the Beyşehir-Hoyran Nappes have deposited.The rifting process led to tectonic destabilization of the platform in the basin,causing accumulation of the Upper Gzhelian(uppermost Pennsylvanian)detrital limestone with broken and abraded foraminiferal shells.Following this,deep basinal conditions prevailed during the Late Asselian–Kungurian(Early Permian),as revealed in the Mersin Mélange,where radiolarian cherts are associated with continental within-plate lavas of extreme incompatible trace element enrichment.Similar processes were responsible for the continual deposition of detrital limestones in the same basin until the end of Late Capitanian(Middle Permian).Based on all these,the uplifting process followed by rift-related volcanic rocks and detrital limestones can be interpreted as the opening of the Izmir-Ankara Ocean(northern Neotethys).展开更多
In the Alpine Corsica(France),the Santa Lucia Nappe represents a peculiar unit preserving the unique relicts of Paleozoic lower to medium continental crust.It consists of composite basement affected by Permian granuli...In the Alpine Corsica(France),the Santa Lucia Nappe represents a peculiar unit preserving the unique relicts of Paleozoic lower to medium continental crust.It consists of composite basement affected by Permian granulite facies metamorphic conditions unconformably covered by a Late Cretaceous clastic sequence(Tomboni Conglomerate and Tralonca Flysch)affected by polyphase deformation and low-grade-metamorphism.In this work,we present a new reconstruction of the deformation events registered by the Tralonca Flysch during the Alpine orogeny.The D1 phase was testified by rare isoclinal folds.The D2 phase produced a continuous foliation and a map-scale sheath-fold with a top-to-W sense of shear.The D3 phase produced E-verging non-cylindrical folds and S3 crenulation cleavage that is not associated to metamorphic blastesis.We present the first temperature-pressure-deformation(P-T-d)path for the Tralonca Flysch,demonstrating that the Santa Lucia Nappe underwent accretion and then first stage exhumation in the Alpine wedge during the D1 phase with pressure and temperature peaks both occurred under blueschist metamorphic conditions.The D2 phase occurred at lower pressure-temperature conditions during a second stage exhumation.This pressure-temperaturedeformation path is comparable with those of the Lower Units(i.e.,the subducted continental units of Alpine Corsica)suggesting a common geodynamic history.展开更多
By analyzing and interpreting the newly acquired seismic profile supported by the national 973 Program and synthesizing the data with other geologic ＆ geographic information, we draw conclusions as follows, a） Two s...By analyzing and interpreting the newly acquired seismic profile supported by the national 973 Program and synthesizing the data with other geologic ＆ geographic information, we draw conclusions as follows, a） Two seismic reflections located at the northeast South China Sea （SCS） slope and the Hengchun ridge are the Bottom Simulated Reflections （BSRs）. Yet, the genesis and process of the gas hydrate in these two areas are different because of different regional tectonics and geological environments; b） The genesis of gas hydrate located at the northeast SCS slope area is related to the broadly existing fracture zones, slumping tectosomes, and the distinctive shielding environment of pressure masking field formed by them. But the genesis of the gas hydrate at the Hengchun ridge is associated with the thrust nappe structures and accretionary wedges formed along the Manila subduction zone and the related sub-floor fluid channel system built by them; c） Since the analogous geologic bodies are broadly distributed at slope areas around SCS and the temperature-press environment is very suitable to the formation and conservation of the gas hydrate, we suggest that much more of this resource should be stored in these areas.展开更多
通过介绍数字农业系统整体方案和接入协议的设计,系统以Linux为开发环境,用JSP和Java为开发工具,开发出基于移动技术的数字农业平台.整个系统主要有短信交互平台、WEB管理平台、USSD服务平台和WAP服务平台4个子系统组成,采用数字农业点...通过介绍数字农业系统整体方案和接入协议的设计,系统以Linux为开发环境,用JSP和Java为开发工具,开发出基于移动技术的数字农业平台.整个系统主要有短信交互平台、WEB管理平台、USSD服务平台和WAP服务平台4个子系统组成,采用数字农业点对点协议(Numeral Agriculture Peer to Peer,NAPP)接入协议,可为用户提供多种接入方式,用户能使用手机等移动设备获取大量的数字农业信息.展开更多
The Dabashan nappe structural belt links the Hannan block to the west with the Huangling block to the east between Yangxian and Xiangfan. The Dabashan arc-shaped fold belt formed during late Jurassic and was superpose...The Dabashan nappe structural belt links the Hannan block to the west with the Huangling block to the east between Yangxian and Xiangfan. The Dabashan arc-shaped fold belt formed during late Jurassic and was superposed on earlier Triassic folds. To achieve an improved understanding of the deep tectonics of the Dabashan nappe structural belt, we processed and interpreted the gravity and magnetic data for this area using new deep reflection seismic and other geophysical data as constraints. The results show that the Sichuan basin and Daba Mountains lie between the Longmenshan and Wulingshan gravity gradient belts. The positive magnetic anomalies around Nanchong-Tongjiang-Wanyuan-Langao and around Shizhu result from the crystalline basement. Modeling of the gravity and magnetic anomalies in the Daba Mountains and the Sichuan basin shows that the crystalline basement around Nanchong-Tongjiang-Wanyuan-Langao extends to the northeast underneath the Wafangdian fault near Ziyang. The magnetic field boundary in the Zhenba-Wanyuan-Chengkou-Zhenping area is the major boundary of the Dabashan nappe thrusting above the Sichuan Basin. This boundary might be the demarcation between the south Dabashan and the north Dabashan structural elements. The low gravity anomaly between Tongjiang and Chengkou might be partly caused by thickened lower crust. The local low gravity anomaly to the south of Chengkou-Wanyuan might result from Mesozoic strata of low density in the Dabashan foreland depression area.展开更多
The thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt(CAOB).However,the timing,structural style and kinematic processes of the thrust nappe ...The thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt(CAOB).However,the timing,structural style and kinematic processes of the thrust nappe remain controversial,particularly the detail of the thrust nappe in the Guaizihu region(110 km east of Ejinaq).In this study,we investigate new field mapping,seismic sections,geochronology and low-temperature thermochronometric dating to provide constraints on the history of this thrust nappe in the Chaheilingashun area(northwestern Guaizihu region).The field mapping,seismic sections and structural analysis reveal that the autochthonous system had developed a series of strong fold structures in the upper Permian strata.The allochthonous system mainly contains Devonian monzogranite(U-Pb age,ranges from 386.7 to 389.0 Ma)and Meso–Neoproterozoic schists(the maximum depositional age,~880 Ma),which were thrust upon the upper Permian strata during Middle to Late Triassic.Based on similar rocks,geochronological dating and the Yagan thrust,we suggest that the postulated root zone of this allochthon might have originated from the Huhetaoergai area(40–60 km northwest of the study area).The geochronological results reveal that the lower age limit of this thrust nappe is constrained by the Lower–Middle Triassic syntectonic sediments(tuffaceous sandstone,~247 Ma),which is the sedimentary response of the fold structure.,The timing of the termination of this thrust nappe is defined by the cooling age(^(40)Ar/^(39)Ar data,217–211 Ma)of the Devonian monzogranite and Meso–Neoproterozoic schists.Thus,we consider this thrust event in the study area to potentially have occurred in the period from 247 Ma to 211 Ma,which may represent the tectonic response to the closure of the Paleo-Asian Ocean.展开更多
The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Ol...The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Oligocene-Quaternary supra-salt sequence. The salt sequence is composed mainly of light grey halite, gypsum, marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold belt, in which the most fascinating structures are salt nappe complex. Based on field observation, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east-west for over 200 km and occurs along the west Qiulitag Mountains. Its thrusting displacement is over 30 km. The salt nappe complex appears as an arcuate zone projecting southwestwards along the leading edge of the Kuqa foreland fold belt. The major thrust fault is developed along the Paleocene-Eocene salt beds. The allochthonous nappes comprise large north-dipping faulting monoclines which are made up of Paleocene-Pliocene sediments. Geological analysis and cross-section restoration revealed that the salt nappes were mainly formed at the late Himalayan stage (c.a. 1.64 Ma BP) and have been active until the present day. Because of inhomogeneous thrusting, a great difference may exist in thrust displacement, thrust occurrence, superimposition of allochthonous and autochthonous sequences and the development of the salt-related structures, which indicates the segmentation along the salt nappes. Regional compression, gravitational gliding and spreading controlled the formation and evolution of the salt nappe complex in the Kuqa foreland fold belt.展开更多
Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are...Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma （（87Sr/86Sr）0=0.708807） for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma （（87Sr/86Sr）o=0.708514） for sphalerite residues and 31.8±0.3 Ma （（143Nd/144Nd）o=0.512362） for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.展开更多
The North Qilian Shan fold and thrust belt,located at the northern Tibetan Plateau and southern margin of the Hexi Corridor,is a key tectonic unit to decode the formation and expansion of the plateau.Previous studies ...The North Qilian Shan fold and thrust belt,located at the northern Tibetan Plateau and southern margin of the Hexi Corridor,is a key tectonic unit to decode the formation and expansion of the plateau.Previous studies emphasize the Cenozoic deformation due to the far-field response to the Indo-Asian collision,but the Mesozoic deformations are poorly constrained in this area.We conducted detailed field mapping,structural analysis,geochronology,and structural interpretation of deep seismic reflectional profiling and magnetotelluric(MT)sounding,to address the superposed results of the Mesozoic and Cenozoic deformation.The results recognized the North Qilian thrust and nappe system(NQTS),the root and the frontal belt are the North Qilian thrust(NQT),and the Yumu Shan klippe(YK),respectively.The middle belt is located between the NQT and the YK.Monzonitic granite zircon U-Pb dating from the middle belt yields an age of ca.415 Ma,which is similar to south NQT.The thrusting displacement is estimated at ca.48 km by structural interpretation of deep profiles.The timing is constrained in the early stage of the Early Cretaceous by the formation of simultaneous growth strata.We suggest that the NQTS has resulted from the far-field effect of the Lhasa-Qiangtang collision,and the Yumu Shan is uplifted by the superposed Cenozoic deformation.展开更多
Multi-stage Mesozoic thrust-nappe and extensional structures are distributed in the east segment of the Southeast Yangtze Block situated in the junction region of Zhejiang-Jiangxi-Anhui provinces. The features and gen...Multi-stage Mesozoic thrust-nappe and extensional structures are distributed in the east segment of the Southeast Yangtze Block situated in the junction region of Zhejiang-Jiangxi-Anhui provinces. The features and genetic mechanism of the deformations were analyzed after a detailed field observation of their distribution, geometry, and kinematics. In addition, the time sequences of the thrust and extensional structures were determined by combining the results of the comparative analysis with the chronological evidence of strata and magmatic rocks cut by a fault or formed after a fault according to field facts. This study identified three stages of the nappe structures and at least two stages of the extensional structures during the Mesozoic. The geotectonic setting of the nappe and extensional structures was considered to be related to the different geodynamics in the study area including the Early Mesozoic geological event, i.e., N-S compression, forming Lantian fault, etc.;the Late Mesozoic flat-slab subduction, forming Xiaoxi thrust fault and tectonic window;and the roll-back of the paleoPacific Plate, forming extensional structures like basin marginal fault;the last compression, forming Wucheng-Shenxian fault. These findings provide additional evidence for remodeling the tectonic and geodynamic evolution of Southeast China.展开更多
On 12 May 2008, the magnitude 8.0 Wenchuan Earthquake occurred along the Longmen Shan nappe, Sichuan, China. This devastating earthquake led to a heavy death toll of greater than 80,000. The seismic origin of this ear...On 12 May 2008, the magnitude 8.0 Wenchuan Earthquake occurred along the Longmen Shan nappe, Sichuan, China. This devastating earthquake led to a heavy death toll of greater than 80,000. The seismic origin of this earthquake is currently hotly debated. We suppose that it is a special type of intraplate earthquake called an active-nappe-type earthquake. Using a holistic methodology, incorporating rockmass structure cybernetics and Byerlee's law, we present a comprehensive study on the geological origin of macroseisms in the Longmen Shan area and the seismic origin of the 2008 Wenchuan earthquake. Previous studies of neotectonic activity indicate that the Longmen Shan nappe moves at a rate of 1~3 mm/yr, due to horizontal compressive stress from the Tibetan Plateau. The difference between movement rates in the Bayankala block, Longmen Shan nappe and Sichuan Basin cause slow shear stress and strain accumulation in the Longmen Shan nappe. It is exhibited a relatively simple linear relations for the shear strength and the buried depth of the structural planes, and the detachment layer of the nappe has a higher shearing-sliding strength compared to the overlying fault planes and the underlying ductile shear belts, thus making it more prone to stick-slip deformation. Therefore, the detachment layer was the main section responsible for the Wenchuan earthquake. The initial rupture burst in the detachment layer under the Yingxiu-Beichuan fault, the rupture area nearly 1.4454 × 104 km2,encompassed the cross point of the Yingxiu and the Anxian-Guanxian faults with the detachment layer, then caused the Yingxiu-Beichuan and Anxian-Guanxian faults took an active part in this earthquake, so this earthquake might consist of three chain-like earthquake stages, totally increasing the duration of this earthquake an unusually large amount, to 120 s. The focal depth spanned range of 10-20km,consistent with the observed result of this focal depth by several agencies.展开更多
Considering the serious coal and rock dynamic disasters around the main slip plane called F16 in the coal mining area) of Henan Yima(China) thrust nappe structure,the mechanical genesis of the Yima thrust nappe struct...Considering the serious coal and rock dynamic disasters around the main slip plane called F16 in the coal mining area) of Henan Yima(China) thrust nappe structure,the mechanical genesis of the Yima thrust nappe structure was studied comprehensively using geomechanics,fault mechanics,elastic mechanics,and Coulomb's law of friction.First,using the centrifugal inertia force of Earth's rotation as a source,a mechanical model of N-S compression superimposed with W-E reverse torsion was established to explain the formation of the early Yima coal basin and Jurassic Yima Group coal measures.Second,an equation for the ultimate stress in the forming stage of F16 was derived using the plastic slip-line field theory and the parabolic Mohr failure criterion.Moreover,the distribution of ultimate stress and the geometric characteristics of the fault profile were obtained using the field model parameters.Finally,the stress field of F16 and the mechanical genesis of the large-scale reverse thrust sheet were discussed based on elastic mechanics theory and Coulomb's law of friction.The results show that the tectonic framework of the early Yima coal basin and the formation pattern of Jurassic Yima Group coal measures given by the model are consistent with the in-situ explorations.The geometric characteristics of the fault profile obtained by numerical calculation can better reflect the shape of F16 in its forming stage,and the mechanical genesis of the large-scale reverse thrust sheet also concurred with the field situations.Thus,this work can provide a foundation for further studies on the genesis of the thrust nappe structure,the mechanism of rock bursts induced by F16,and the characteristics of the residual stress field in the Yima mining area.展开更多
A thrust and nappe tectonic zone with imbricate branch thrusts is developed along the southern margin of the coal-forming region of North China. This tectonic zone is tightly related to the Qinling-Dabie collision oro...A thrust and nappe tectonic zone with imbricate branch thrusts is developed along the southern margin of the coal-forming region of North China. This tectonic zone is tightly related to the Qinling-Dabie collision orogen in genesis and belongs to the frontal zone of a huge thrust system developed during Yanshanian episode at the northern foot of the orogen. It is pointed out that thrusting had distorted the original depositional margin of the coal-forming region and some new coal-bearing blocks would be found out in the frontal sheets and under the undulate sole thrust.展开更多
Whole rock elemental and Sr-Nd isotope geochemistry and in situ zircon Hf isotope geochemistry were used to identify the sources of the Neoproterozoic granites from the Socorro batholith,Socorro-GuaxupéNappe(SGN)...Whole rock elemental and Sr-Nd isotope geochemistry and in situ zircon Hf isotope geochemistry were used to identify the sources of the Neoproterozoic granites from the Socorro batholith,Socorro-GuaxupéNappe(SGN),South Brasilia Orogen,Brazil.Zircon trace elements and Hf isotope geochemistry provided information about sources and crystallization(T,f_(O2))conditions.Three main types of granites built the bulk of the batholiths,beginning with probably pre-collisional~640–630 Ma charnockites,and ending with~610 Ma voluminous post-collisional high-K calc-alkaline(HKCA)Ⅰ-type granites(Bragan?a Paulista-type).Several types of leucogranites were generated from 625 to 610 Ma,spanning the interval from collisional to post-collisional tectonics.Two charnockite bodies occur in the study area:the~640 Ma Socorro charnockite has remarkable chemical similarities with Braganca Paulista-type granites,but higherε_(Nd)(t)=-6.1 and average zirconε_(Hf)(t)=-9.1 and lower^(86)Sr/^(87)Sr_(t)(0.7093)values,indicative of more juvenile and water-poor source.The~633 Ma Atibaia charnockite has distinct geochemical signature(lower Mg^(#)and Sr content;higher Zr),more negativeε_(Nd)(t)=-14.1,similar average zirconε_(Hf)(t)=-8.9,and much higher^(86)Sr/^(87)Sr_(t)=0.7197,probably reflecting a larger component from old crust.The predominant~610 Ma Bragan?a Paulista-type granites were emplaced in a post-collisional setting,and correspond to porphyritic biotite-hornblende monzogranites of high-K calc-alkaline character with 61 wt.%–67 wt.%SiO_(2),high Mg^(#)(39–42),Sr/Y(19–40),La/Yb(12–69),highly negativeε_(Nd)(t)(-12.3 to-12.9)and zirconε_(Hf)(t)(-12 to-17)and^(87)Sr/^(86)Sr_(t)=0.7119–0.7131.These features are interpreted as indicative of magma generation in a thickened crust,where melts from enriched mantle sources emplaced in the lowermost crust,heated host old continental crust rocks(gneisses and granulites)and partially mixed with their melting products.Leucogranite plutons(SiO_(2)>72 wt.%)occurring in the southern portion of the batholith have a range of geochemical and isotope signatures,reflecting melting of crustal sources in space and time between~625 Ma(Bocaina Pluton)and~610 Ma(Bairro da Pedreira Pluton).Highly negativeε_(Nd)(t)(-16.2)and average zirconε_(Hf)(t)=-16,and high^(87)Sr/^(86)Sr_(t)(0.7156–0.7171)are consistent with relatively old orthoand paragneiss sources similar to those which generated regionally abundant migmatites and anatectic granites in the collisional to post-collisional setting.展开更多
The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distingu...The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at > 776°C temperature and >6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.展开更多
We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of ear...We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings, seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated, and have revealed the primary features of the thrust-fold- nappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are inter- preted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, con- sisting of the lower （root） thrust fault, middle detachment, and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east, which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases, this section of the nappe structure near the city has an earthquake risk of M6.5-7, An earthquake Ms6.6, 60 km east to Urumqi city occurred along the structure in 1965.展开更多
文摘In order to reveal the nature of the segmentation of Longmen Mountains Thrust Belt caused by the three nappes (Jiaoziding, Jiudingshan, and Baoxing Nappe), several methods are applied in this paper, including field investigation, seismic explanation and balanced crossed section, etc. Results of research reveal that nappes in Longmen Mountains vary in geometry, kinematics, and dynamics. Jiaoziding Nappe has generally behaved in a ductile manner, whereas Jiudingshan Nappe has been rigid, and the rheology of Baoxing Nappe has been intermediate between that of the other two nappes. The development of nappes has resulted in tectonic segmentation of Longmen Mountains: the main structural style of the northern segment is thrust faulting, with Jiaoziding Nappe representing a giant syncline. Given its ductility, it absorbed lots of stress, with the least amount of tectonic shortening in the SE part of the nappe. In the middle segment, the deformation is controlled by the rigid Jiudingshan Nappe, whose frontal area records lots of tectonic shortening. Deformation in the southern segment is intermediate in character between that of the other two segments, characterized by horizontal zonation, as demonstrated by fault development, and vertical stratification, which indicates that fault development was controlled by lithology.
基金funded by the National Natural Science Foundation of China(No.42174104,No.42204089)the Hubei Provincial Natural Science Foundation of China(2022CFB350)+1 种基金the Basic Research Fund of Institute of Seismology,China Earthquake Administration(IS202326341)Open Fund ofWuhan,Gravitation and Solid Earth Tides,National Observation and Research Station(WHYWZ202108,WHYWZ202301)。
文摘Controlled by the squeezing collision between the Yangtze block and the North China block and the left movement of the Tanlu fault, the Xu-Su region developed into an arc-shaped nappe structure, and many destructive earthquakes occurred in its periphery. The geological structure of this area is complex, and there is the possibility of moderate and strong earthquakes. To further explore the crust density structure and identify the main faults and deep structural features in the Xu-Su region, based on the observed seismic data and gravity/GNSS co-site observation data, combined with the EGM2008 global gravity field model, we obtained the density of three-dimensional structure using cross gradient method joint inversion. Based on this, a geological model of the Xu-Su region was established. The results show that the crustal density anomaly amplitude within 0-25 km of the Xu-Su region ranges from-280 to 490 kg/m3, showing a zonal distribution in east-west direction and a segmented north-south direction. There are several density anomalies in the shallow(0-4 km) region at Tongshan, Huaibei, Xiayi, Woyang, etc. The density anomalies are significantly correlated with the distribution of regional faults. The density structure is divided into two large regions by Subei fault, which can be further divided along the eastwest Kouziji-Nanzhao fault and Guzhen-Huaiyuan fault. The earthquakes are obviously related to the regional fault activity and the spatial distribution of abnormal bodies. The earthquake-prone areas(5-15 km) correspond to the abnormal density mutation zone, upper uplift zone, and transformation zone near Xiaoxian, Tongshan, and Xushuanglou faults. The comprehensive results show three weak seismic activity areas in the whole region, which are located near the Huaibei, Xiaoxian, and Wohe faults. The results provide theoretical support for seismic risk analysis in this area, and these three areas should be emphasized in future seismic hazard analysis.
基金grateful to Hacettepe University,Scientific Research Project Department(No.FBA-2018-16915)for providing financial support to this research.
文摘The Beyşehir-Hoyran Nappes,one of the tectonostratigraphic units of the Taurides,are thought to be originated from the Izmir-Ankara Ocean(northern branch of Neotethys).In this study,Late Paleozoic rock units from the blocks of Beyşehir-Hoyran Nappes were studied in detail using foraminiferal assemblages in two different locations from the southwest of Karaman City(southern Turkey).In both places,blocks/slices and pebbles of various origins are embedded within a highly sheared matrix of Late Cretaceous Age,and the whole unit can be regarded as a sedimentary mélange.The ages of the blocks from the southwest of Karaman City range from the Late Serpukhovian(Late Mississippian)to Late Capitanian(Middle Permian)with some depositional breaks(e.g.,Bashkirian,Kasimovian).Combined with the previous data from the Mersin Mélange,which also include the remnants of the Beyşehir-Hoyran Nappes,our new findings suggest that a shallowing-upward sequence,characterized by a shallow water environment with foraminifera-bearing limestones,was deposited over the Tournaisian pelagic sequence in the Beyşehir-Hoyran Nappes till the Early Moscovian(Early Middle Pennsylvanian).This shallowing-upward sequence in the Beyşehir-Hoyran Nappes could be related to the Late Paleozoic Glaciation on the Gondwana supercontinent(Glacial Ⅱ),which resulted in a sea-level drop and deposition of platform carbonates during the Viséan–Early Moscovian(Middle Mississippian to Early Middle Pennsylvanian)time interval.The absence of the main part of the Middle-Upper Pennsylvanian deposits(continental phase during the Middle Moscovian–Middle Gzhelian)in the Beyşehir-Hoyran Nappes can be mainly attributed to the occurrence of a mantle plume and partially to the effect of Late Paleozoic Gondwanan Glaciation(Glacial Ⅲ).Progressive uplifting by the buoyant mantle plume material has resulted in rifting at the center of the basin where the Beyşehir-Hoyran Nappes have deposited.The rifting process led to tectonic destabilization of the platform in the basin,causing accumulation of the Upper Gzhelian(uppermost Pennsylvanian)detrital limestone with broken and abraded foraminiferal shells.Following this,deep basinal conditions prevailed during the Late Asselian–Kungurian(Early Permian),as revealed in the Mersin Mélange,where radiolarian cherts are associated with continental within-plate lavas of extreme incompatible trace element enrichment.Similar processes were responsible for the continual deposition of detrital limestones in the same basin until the end of Late Capitanian(Middle Permian).Based on all these,the uplifting process followed by rift-related volcanic rocks and detrital limestones can be interpreted as the opening of the Izmir-Ankara Ocean(northern Neotethys).
基金supported by the PRIN 2020(P.I.M.Marroni)Fondi Ateneo Grant by The University of Pisa。
文摘In the Alpine Corsica(France),the Santa Lucia Nappe represents a peculiar unit preserving the unique relicts of Paleozoic lower to medium continental crust.It consists of composite basement affected by Permian granulite facies metamorphic conditions unconformably covered by a Late Cretaceous clastic sequence(Tomboni Conglomerate and Tralonca Flysch)affected by polyphase deformation and low-grade-metamorphism.In this work,we present a new reconstruction of the deformation events registered by the Tralonca Flysch during the Alpine orogeny.The D1 phase was testified by rare isoclinal folds.The D2 phase produced a continuous foliation and a map-scale sheath-fold with a top-to-W sense of shear.The D3 phase produced E-verging non-cylindrical folds and S3 crenulation cleavage that is not associated to metamorphic blastesis.We present the first temperature-pressure-deformation(P-T-d)path for the Tralonca Flysch,demonstrating that the Santa Lucia Nappe underwent accretion and then first stage exhumation in the Alpine wedge during the D1 phase with pressure and temperature peaks both occurred under blueschist metamorphic conditions.The D2 phase occurred at lower pressure-temperature conditions during a second stage exhumation.This pressure-temperaturedeformation path is comparable with those of the Lower Units(i.e.,the subducted continental units of Alpine Corsica)suggesting a common geodynamic history.
文摘By analyzing and interpreting the newly acquired seismic profile supported by the national 973 Program and synthesizing the data with other geologic ＆ geographic information, we draw conclusions as follows, a） Two seismic reflections located at the northeast South China Sea （SCS） slope and the Hengchun ridge are the Bottom Simulated Reflections （BSRs）. Yet, the genesis and process of the gas hydrate in these two areas are different because of different regional tectonics and geological environments; b） The genesis of gas hydrate located at the northeast SCS slope area is related to the broadly existing fracture zones, slumping tectosomes, and the distinctive shielding environment of pressure masking field formed by them. But the genesis of the gas hydrate at the Hengchun ridge is associated with the thrust nappe structures and accretionary wedges formed along the Manila subduction zone and the related sub-floor fluid channel system built by them; c） Since the analogous geologic bodies are broadly distributed at slope areas around SCS and the temperature-press environment is very suitable to the formation and conservation of the gas hydrate, we suggest that much more of this resource should be stored in these areas.
文摘通过介绍数字农业系统整体方案和接入协议的设计,系统以Linux为开发环境,用JSP和Java为开发工具,开发出基于移动技术的数字农业平台.整个系统主要有短信交互平台、WEB管理平台、USSD服务平台和WAP服务平台4个子系统组成,采用数字农业点对点协议(Numeral Agriculture Peer to Peer,NAPP)接入协议,可为用户提供多种接入方式,用户能使用手机等移动设备获取大量的数字农业信息.
基金supported by Crust Probe Project of China(SINOPROBE-02-01,SINOPROBE-02-03,SINOPROBE-02-06,SINOPROBE-08-02)the Natural Science Foundation of China(Nos.40830316,40874045)+1 种基金China Geological Survey(Nos.1212010611809,1212010711813,1212010811033)scientific research project for public welfare from the Ministry of Land and Resources of China(Nos.200811021,201011042)
文摘The Dabashan nappe structural belt links the Hannan block to the west with the Huangling block to the east between Yangxian and Xiangfan. The Dabashan arc-shaped fold belt formed during late Jurassic and was superposed on earlier Triassic folds. To achieve an improved understanding of the deep tectonics of the Dabashan nappe structural belt, we processed and interpreted the gravity and magnetic data for this area using new deep reflection seismic and other geophysical data as constraints. The results show that the Sichuan basin and Daba Mountains lie between the Longmenshan and Wulingshan gravity gradient belts. The positive magnetic anomalies around Nanchong-Tongjiang-Wanyuan-Langao and around Shizhu result from the crystalline basement. Modeling of the gravity and magnetic anomalies in the Daba Mountains and the Sichuan basin shows that the crystalline basement around Nanchong-Tongjiang-Wanyuan-Langao extends to the northeast underneath the Wafangdian fault near Ziyang. The magnetic field boundary in the Zhenba-Wanyuan-Chengkou-Zhenping area is the major boundary of the Dabashan nappe thrusting above the Sichuan Basin. This boundary might be the demarcation between the south Dabashan and the north Dabashan structural elements. The low gravity anomaly between Tongjiang and Chengkou might be partly caused by thickened lower crust. The local low gravity anomaly to the south of Chengkou-Wanyuan might result from Mesozoic strata of low density in the Dabashan foreland depression area.
基金support from the China Geological Survey(Grant No.DD20190018)。
文摘The thrust nappe played an important role in the Mesozoic tectonic evolution of the middle part of the Central Asian Orogenic Belt(CAOB).However,the timing,structural style and kinematic processes of the thrust nappe remain controversial,particularly the detail of the thrust nappe in the Guaizihu region(110 km east of Ejinaq).In this study,we investigate new field mapping,seismic sections,geochronology and low-temperature thermochronometric dating to provide constraints on the history of this thrust nappe in the Chaheilingashun area(northwestern Guaizihu region).The field mapping,seismic sections and structural analysis reveal that the autochthonous system had developed a series of strong fold structures in the upper Permian strata.The allochthonous system mainly contains Devonian monzogranite(U-Pb age,ranges from 386.7 to 389.0 Ma)and Meso–Neoproterozoic schists(the maximum depositional age,~880 Ma),which were thrust upon the upper Permian strata during Middle to Late Triassic.Based on similar rocks,geochronological dating and the Yagan thrust,we suggest that the postulated root zone of this allochthon might have originated from the Huhetaoergai area(40–60 km northwest of the study area).The geochronological results reveal that the lower age limit of this thrust nappe is constrained by the Lower–Middle Triassic syntectonic sediments(tuffaceous sandstone,~247 Ma),which is the sedimentary response of the fold structure.,The timing of the termination of this thrust nappe is defined by the cooling age(^(40)Ar/^(39)Ar data,217–211 Ma)of the Devonian monzogranite and Meso–Neoproterozoic schists.Thus,we consider this thrust event in the study area to potentially have occurred in the period from 247 Ma to 211 Ma,which may represent the tectonic response to the closure of the Paleo-Asian Ocean.
基金This research received financial supports from the National Natural Science Foundation of China(grant 40172076)the National Major Fundamental Research and Development Project(grant G1999043305)the National Key Project of the Ninth Five—Year Plan(grant 99—1111)
文摘The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Oligocene-Quaternary supra-salt sequence. The salt sequence is composed mainly of light grey halite, gypsum, marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold belt, in which the most fascinating structures are salt nappe complex. Based on field observation, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east-west for over 200 km and occurs along the west Qiulitag Mountains. Its thrusting displacement is over 30 km. The salt nappe complex appears as an arcuate zone projecting southwestwards along the leading edge of the Kuqa foreland fold belt. The major thrust fault is developed along the Paleocene-Eocene salt beds. The allochthonous nappes comprise large north-dipping faulting monoclines which are made up of Paleocene-Pliocene sediments. Geological analysis and cross-section restoration revealed that the salt nappes were mainly formed at the late Himalayan stage (c.a. 1.64 Ma BP) and have been active until the present day. Because of inhomogeneous thrusting, a great difference may exist in thrust displacement, thrust occurrence, superimposition of allochthonous and autochthonous sequences and the development of the salt-related structures, which indicates the segmentation along the salt nappes. Regional compression, gravitational gliding and spreading controlled the formation and evolution of the salt nappe complex in the Kuqa foreland fold belt.
文摘Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma （（87Sr/86Sr）0=0.708807） for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma （（87Sr/86Sr）o=0.708514） for sphalerite residues and 31.8±0.3 Ma （（143Nd/144Nd）o=0.512362） for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.
基金financially supported by the China Geological Survey(Grant Nos.DD20230229,DD20160083,DD20190011,DD20221643-5)the National Key Research and Development Program of China(the DREAM—Deep Resource Exploration and Advanced Mining+1 种基金Grant No.2018YFC0603701)the Cooperative Project between the Chinese Academy of Geological Sciences and the Sinopec Shengli Oilfield Company(Grant No.P22065)。
文摘The North Qilian Shan fold and thrust belt,located at the northern Tibetan Plateau and southern margin of the Hexi Corridor,is a key tectonic unit to decode the formation and expansion of the plateau.Previous studies emphasize the Cenozoic deformation due to the far-field response to the Indo-Asian collision,but the Mesozoic deformations are poorly constrained in this area.We conducted detailed field mapping,structural analysis,geochronology,and structural interpretation of deep seismic reflectional profiling and magnetotelluric(MT)sounding,to address the superposed results of the Mesozoic and Cenozoic deformation.The results recognized the North Qilian thrust and nappe system(NQTS),the root and the frontal belt are the North Qilian thrust(NQT),and the Yumu Shan klippe(YK),respectively.The middle belt is located between the NQT and the YK.Monzonitic granite zircon U-Pb dating from the middle belt yields an age of ca.415 Ma,which is similar to south NQT.The thrusting displacement is estimated at ca.48 km by structural interpretation of deep profiles.The timing is constrained in the early stage of the Early Cretaceous by the formation of simultaneous growth strata.We suggest that the NQTS has resulted from the far-field effect of the Lhasa-Qiangtang collision,and the Yumu Shan is uplifted by the superposed Cenozoic deformation.
文摘Multi-stage Mesozoic thrust-nappe and extensional structures are distributed in the east segment of the Southeast Yangtze Block situated in the junction region of Zhejiang-Jiangxi-Anhui provinces. The features and genetic mechanism of the deformations were analyzed after a detailed field observation of their distribution, geometry, and kinematics. In addition, the time sequences of the thrust and extensional structures were determined by combining the results of the comparative analysis with the chronological evidence of strata and magmatic rocks cut by a fault or formed after a fault according to field facts. This study identified three stages of the nappe structures and at least two stages of the extensional structures during the Mesozoic. The geotectonic setting of the nappe and extensional structures was considered to be related to the different geodynamics in the study area including the Early Mesozoic geological event, i.e., N-S compression, forming Lantian fault, etc.;the Late Mesozoic flat-slab subduction, forming Xiaoxi thrust fault and tectonic window;and the roll-back of the paleoPacific Plate, forming extensional structures like basin marginal fault;the last compression, forming Wucheng-Shenxian fault. These findings provide additional evidence for remodeling the tectonic and geodynamic evolution of Southeast China.
文摘On 12 May 2008, the magnitude 8.0 Wenchuan Earthquake occurred along the Longmen Shan nappe, Sichuan, China. This devastating earthquake led to a heavy death toll of greater than 80,000. The seismic origin of this earthquake is currently hotly debated. We suppose that it is a special type of intraplate earthquake called an active-nappe-type earthquake. Using a holistic methodology, incorporating rockmass structure cybernetics and Byerlee's law, we present a comprehensive study on the geological origin of macroseisms in the Longmen Shan area and the seismic origin of the 2008 Wenchuan earthquake. Previous studies of neotectonic activity indicate that the Longmen Shan nappe moves at a rate of 1~3 mm/yr, due to horizontal compressive stress from the Tibetan Plateau. The difference between movement rates in the Bayankala block, Longmen Shan nappe and Sichuan Basin cause slow shear stress and strain accumulation in the Longmen Shan nappe. It is exhibited a relatively simple linear relations for the shear strength and the buried depth of the structural planes, and the detachment layer of the nappe has a higher shearing-sliding strength compared to the overlying fault planes and the underlying ductile shear belts, thus making it more prone to stick-slip deformation. Therefore, the detachment layer was the main section responsible for the Wenchuan earthquake. The initial rupture burst in the detachment layer under the Yingxiu-Beichuan fault, the rupture area nearly 1.4454 × 104 km2,encompassed the cross point of the Yingxiu and the Anxian-Guanxian faults with the detachment layer, then caused the Yingxiu-Beichuan and Anxian-Guanxian faults took an active part in this earthquake, so this earthquake might consist of three chain-like earthquake stages, totally increasing the duration of this earthquake an unusually large amount, to 120 s. The focal depth spanned range of 10-20km,consistent with the observed result of this focal depth by several agencies.
基金Project(2010CB226805) supported by the National Basic Research Program of ChinaProject(CXLX13-949) supported by the Research and Innovation Project for College Graduates of Jiangsu Province,China+1 种基金Project(51174285) supported by the National Natural Science Foundation of ChinaProject(SZBF2011-6-B35) supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Considering the serious coal and rock dynamic disasters around the main slip plane called F16 in the coal mining area) of Henan Yima(China) thrust nappe structure,the mechanical genesis of the Yima thrust nappe structure was studied comprehensively using geomechanics,fault mechanics,elastic mechanics,and Coulomb's law of friction.First,using the centrifugal inertia force of Earth's rotation as a source,a mechanical model of N-S compression superimposed with W-E reverse torsion was established to explain the formation of the early Yima coal basin and Jurassic Yima Group coal measures.Second,an equation for the ultimate stress in the forming stage of F16 was derived using the plastic slip-line field theory and the parabolic Mohr failure criterion.Moreover,the distribution of ultimate stress and the geometric characteristics of the fault profile were obtained using the field model parameters.Finally,the stress field of F16 and the mechanical genesis of the large-scale reverse thrust sheet were discussed based on elastic mechanics theory and Coulomb's law of friction.The results show that the tectonic framework of the early Yima coal basin and the formation pattern of Jurassic Yima Group coal measures given by the model are consistent with the in-situ explorations.The geometric characteristics of the fault profile obtained by numerical calculation can better reflect the shape of F16 in its forming stage,and the mechanical genesis of the large-scale reverse thrust sheet also concurred with the field situations.Thus,this work can provide a foundation for further studies on the genesis of the thrust nappe structure,the mechanism of rock bursts induced by F16,and the characteristics of the residual stress field in the Yima mining area.
基金This project was supported by the Coal Science Foundation of China
文摘A thrust and nappe tectonic zone with imbricate branch thrusts is developed along the southern margin of the coal-forming region of North China. This tectonic zone is tightly related to the Qinling-Dabie collision orogen in genesis and belongs to the frontal zone of a huge thrust system developed during Yanshanian episode at the northern foot of the orogen. It is pointed out that thrusting had distorted the original depositional margin of the coal-forming region and some new coal-bearing blocks would be found out in the frontal sheets and under the undulate sole thrust.
基金supported by the FAPESP(Nos.2015/01817-6 and 2019/17550-0)to Valdecir de Assis Janasia CNPq Productivity Research(No.306102/2019-6)。
文摘Whole rock elemental and Sr-Nd isotope geochemistry and in situ zircon Hf isotope geochemistry were used to identify the sources of the Neoproterozoic granites from the Socorro batholith,Socorro-GuaxupéNappe(SGN),South Brasilia Orogen,Brazil.Zircon trace elements and Hf isotope geochemistry provided information about sources and crystallization(T,f_(O2))conditions.Three main types of granites built the bulk of the batholiths,beginning with probably pre-collisional~640–630 Ma charnockites,and ending with~610 Ma voluminous post-collisional high-K calc-alkaline(HKCA)Ⅰ-type granites(Bragan?a Paulista-type).Several types of leucogranites were generated from 625 to 610 Ma,spanning the interval from collisional to post-collisional tectonics.Two charnockite bodies occur in the study area:the~640 Ma Socorro charnockite has remarkable chemical similarities with Braganca Paulista-type granites,but higherε_(Nd)(t)=-6.1 and average zirconε_(Hf)(t)=-9.1 and lower^(86)Sr/^(87)Sr_(t)(0.7093)values,indicative of more juvenile and water-poor source.The~633 Ma Atibaia charnockite has distinct geochemical signature(lower Mg^(#)and Sr content;higher Zr),more negativeε_(Nd)(t)=-14.1,similar average zirconε_(Hf)(t)=-8.9,and much higher^(86)Sr/^(87)Sr_(t)=0.7197,probably reflecting a larger component from old crust.The predominant~610 Ma Bragan?a Paulista-type granites were emplaced in a post-collisional setting,and correspond to porphyritic biotite-hornblende monzogranites of high-K calc-alkaline character with 61 wt.%–67 wt.%SiO_(2),high Mg^(#)(39–42),Sr/Y(19–40),La/Yb(12–69),highly negativeε_(Nd)(t)(-12.3 to-12.9)and zirconε_(Hf)(t)(-12 to-17)and^(87)Sr/^(86)Sr_(t)=0.7119–0.7131.These features are interpreted as indicative of magma generation in a thickened crust,where melts from enriched mantle sources emplaced in the lowermost crust,heated host old continental crust rocks(gneisses and granulites)and partially mixed with their melting products.Leucogranite plutons(SiO_(2)>72 wt.%)occurring in the southern portion of the batholith have a range of geochemical and isotope signatures,reflecting melting of crustal sources in space and time between~625 Ma(Bocaina Pluton)and~610 Ma(Bairro da Pedreira Pluton).Highly negativeε_(Nd)(t)(-16.2)and average zirconε_(Hf)(t)=-16,and high^(87)Sr/^(86)Sr_(t)(0.7156–0.7171)are consistent with relatively old orthoand paragneiss sources similar to those which generated regionally abundant migmatites and anatectic granites in the collisional to post-collisional setting.
基金the financial support from the UGC CAS-I & II grantDSTs New Delhi for financial assistance to MJ. BPD
文摘The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at > 776°C temperature and >6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ?0.54 and Nb ?10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late-and post-COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover o f the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.
基金supported by Teachers Fund of China Earthquake Administration under Grant No. 20120101National Natural Science Foundation of China under Grant No. 41372216+1 种基金the State Special Project for International Cooperation on Science and Technology 2012DFR20440K02the Fundamental Research Funds for the Central Universities under Grant No. ZY20120102
文摘We have studied the characteristics of the active faults and seismicity in the vicinity of Urumqi city, the capital of Xinjiang Autonomous Region, China, and have proposed a seismogenic model for the assessment of earthquake hazard in this area. Our work is based on an integrated analysis of data from investigations of active faults at the surface, deep seismic reflection soundings, seismic profiles from petroleum exploration, observations of temporal seismic stations, and the precise location of small earthquakes. We have made a comparative study of typical seismogenic structures in the frontal area of the North Tianshan Mountains, where Urumqi city is situated, and have revealed the primary features of the thrust-fold- nappe structure there. We suggest that Urumqi city is comprised two zones of seismotectonics which are inter- preted as thrust-nappe structures. The first is the thrust nappe of the North Tianshan Mountains in the west, con- sisting of the lower （root） thrust fault, middle detachment, and upper fold-uplift at the front. Faults active in the Pleistocene are present in the lower and upper parts of this structure, and the detachment in the middle spreads toward the north. In the future, M7 earthquakes may occur at the root thrust fault, while the seismic risk of frontal fold-uplift at the front will not exceed M6.5. The second structure is the western flank of the arc-like Bogda nappe in the east, which is also comprised a root thrust fault, middle detachment, and upper fold-uplift at the front, of which the nappe stretches toward the north; several active faults are also developed in it. The fault active in the Holocene is called the South Fukang fault. It is not in the urban area of Urumqi city. The other three faults are located in the urban area and were active in the late Pleistocene. In these cases, this section of the nappe structure near the city has an earthquake risk of M6.5-7, An earthquake Ms6.6, 60 km east to Urumqi city occurred along the structure in 1965.
