Lower Continental Crusts Involved in the Alpine Orogeny:New Insight from the Santa Lucia Nappe Metasediments(Corsica,France)

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.

A Large-scale Tertiary Salt Nappe Complex in the Leading Edge of the Kuqa Foreland Fold-Thrust Belt, the Tarim Basin, Northwest China

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.

Triassic Nappe in the Central Part of the Southern Central Asian Orogenic Belt(Ejinaq,NW China):Evidence from Structural Analysis and Geothermochronology

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.

The Origin of the 2008 Wenchuan Earthquake Determined by the Analysis on the Active Longmenshan Nappe in Terms of Rockmass Mechanics

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.

Mechanical genesis of Henan(China) Yima thrust nappe structure

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.

THE THRUST AND NAPPE TECTONIC ZONE ALONG THE SOUTHERN MARGIN OF THE COAL-FORMING REGION OF NORTH CHINA

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.

Early Cretaceous Thrust and Nappe Tectonics in North Qilian Shan,Northern Tibetan Plateau:Evidence from Field Mapping,Geochronology,and Deep Structural Analysis

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.

The Arcuate Nappe Structure on the Northern Margin of the Wuliang Moutnains in Western Yunnan

The arcuate nappe structure on the north edge of the Wuliang Mountains in westernYunnan Province is a complex nappe structural system with multiple superimposed structures.The autochthonous system is a WNW-trending arcuate fold belt consisting of the Jurassic andCretaceous and the allochthonous system is mainly composed of Upper Triassic rocks. Generally,the nappe structure moved from south to north, with the hanging wall thrusting in a WNW direc-tion for a distance of over 10km. The deep nappe structural system was formed at depths ofabout 5-10km in an environment not exceeding the greenschist facies. It occurred in theOligocene (about 40-20 Ma).

Characteristics of Nappes and Segmentation of the Longmen Mountains Thrust Belt, Western Sichuan Basin, China

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.

TRANSPRESSIVE DEFORMATION OF THE LONGXINGGOU NAPPE AND ITS SIGNIFICANCE,SOUTH OF TONGBAI MOUNTAINS, CENTRAL CHINA

The Longxinggou Nappe which is located in Guangshui county, north of Hubei province, has been first identified by our detail mapping. It is composed of lowgrade metamorphosed rocks of middle Proterozoic Shuixian group, late Proterozoic Yaolinghe group, Sinian Liantuo,Doushantuo and Dengying formations. It is quite different from the lower beds, middle.Proterozoic Hong’an epidote-amphibole facies metamorphose metapelite and metagranite. They are different not only in composition, metamorphic degree, but also in deformation forms. The Longxinggou nappe has characteristics both of ductile thrusting and ductile dextral strike-sliping, illustrating a transpressive deformation regime of middle crustal in the orogenic belt due to the oblique collision, between the Shuiying terrain and the Tongbai terrain during Caledonian period.

Zircon age depth-profiling sheds light on the early Caledonian evolution of the Seve Nappe Complex in west-central J?mtland

The Scandinavian Caledonides comprise nappe stacks of far-travelled allochthons that record closure of the Iapetus Ocean and subsequent continental collision of Baltica and Laurentia.The Seve Nappe Complex(SNC)of the Scandinavian Caledonides includes relics of the outermost Baltoscandian passive margin that were subducted to mantle depths.The earliest of the deep subduction events has been dated to ca.500-480 Ma.Evidence of this event has been reported from the northern exposures of the SNC.Farther south in the central and southern segments of the SNC,(ultra)high-pressure rocks have yielded younger ages in the range of ca.470-440 Ma.This study provides the first record of the early Caledonian event in the southern SNC.The evidence has been obtained by depth profiling of zircon grains that were extracted from the Tv?r?klumparna microdiamond-bearing gneiss.These zircon grains preserve eclogite facies overgrowths that crystallized at 482.6±3.8 Ma.A second,chemically-distinct zircon overgrowth records granulite facies metamorphism at 439.3±3.6 Ma,which corroborates previous geochronological evidence for granulite facies metamorphism at this time.Based on these results,we propose that the entire outer margin of Baltica was subducted in the late Cambrian to early Ordovician,but the record of this event may be almost entirely eradicated in the vast majority of lithologies by pervasive late Ordovician to early Silurian metamorphism.

Experimental Investigation of Discharge Capacity of Labyrinth Weirs with and without Nappe Breakers

Labyrinth weirs provide higher discharge capacity than conventional weirs, with the ability to pass large flows at comparatively low heads. Labyrinth weirs are primarily used as spillways for dams where the spillway width is restricted. In recent years, many research investigations have considered the hydraulic performance of labyrinth weirs, particularly as dependent on the geometric features. The previous work has improved the design basis for such weirs. However, their design still requires experimentally derived and generalized performance curves. It is especially important to observe the behavior of the weir nappe to ensure the design provides hydraulic optimization and to account for pressure fluctuations, possible vibrations, resonance effect, noise and flow surging. In the present study, discharge coefficients were experimentally determined for both circular labyrinth weirs and sharp crested trapezoidal labyrinth weirs of varying side wall angle (α). Additional studies were completed with nappe breakers included to reduce the impact of vibration on the labyrinth weirs. In general, the test data indicated that nappe breakers placed on the trapezoidal labyrinth weirs and circular labyrinth weirs reduced the discharge coefficient by up to 4% of the un-amended weir.

THRUST NAPPE STRUTRUE IN THE JINGGANG MOUNTAIN: CHARACTERISTICS AND SIGNIFICANCE FOR PROSPECTION OF ORE DEPOSITS

Nappe structure, as was first discovered by the authors during the regional geological survey at the scale of 1:50,000 in The Jinggang Mountain, is mainly comprised of a series of NNE-NE-striking thrust fault zones and thrust sheets among them. Sinian, Cambrian, Ordovician, Devonian, Carboniferous,Triassic, Jurassic and Cretaceous strata are involved in the thrust nappe system. The nappe structure is of the type of duplex structures formed as a result of the earlier stage migration from SE to NW and late stage migration from E to W of sedimentary cover or basement strata. Formation of the nappe structure in the studied area involves two main epochs: Early Yanshanian and Late Yanshanian to Early Himalayan. The mineral deposits and the buried coalfields in the area, especially the latter, are extensively controlled by the nappe structure.

Analysis of Nappes and Glided Nappes in China

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NAPP体外抗乙型肝炎病毒作用的实验研究

[目的]应用HepG2.2.15细胞株作为体外抗乙型肝炎病毒的实验模型,研究NAPP对乙肝病毒的抑制作用。[方法]以NAPP梯度浓度与HepG2.2.15细胞混合培养,通过MTT法检测药物的细胞毒性,9 d后取细胞培养上清液,用ELISA法测定HBsAg、HBeAg含量,荧光定量PCR检测上清液中病毒载量。[结果]NAPP浓度在1 mg/ml时,对细胞无明显毒性;NAPP在所稀释的各浓度下,对HBsAg、HBeAg均有抑制作用,对HBsAg、HBeAg的治疗指数分别大于188.7和64.5;NAPP可抑制HBV-DNA的复制。[结论]NAPP体外对HBV有显著的抑制作用。

安徽宣城矿集区控矿构造特征及其深部找矿指示意义

宣城矿集区因近年发现了茶亭斑岩型铜金矿、长山热液型铅锌矿等大-中型矿产地而成为长江中下游成矿带较热门矿集区之一。通过详细的野外调查和系统分析,本文厘定了研究区北东向构造格架为一条深大断裂带、两个坳陷盆地、三条逆冲推覆构造带,其中推覆构造带由多个自南东向北西运动的倒转复式褶皱和叠瓦状逆冲岩席组成。根据典型矿床控矿构造解析,明确了江南深大断裂和深部主推覆构造是区内一级控岩控矿构造,北东向断裂带及其次级构造、推覆体上盘倒转褶皱转折端和翼部、层间破碎带、五通组与黄龙-船山组的“硅钙面”、燕山晚期中酸性侵入岩与碳酸盐岩的接触带等为区内重要的控矿、容矿构造,并据此提出了该区下一步深部找矿方向。

2024年1月23日M_(W)7.0乌什地震InSAR同震形变场和断层滑动分布

2024年1月23日,新疆维吾尔自治区乌什县发生了M_(W)7.0地震,本次地震是南天山断裂带近一个世纪以来的最大地震事件.为确定乌什地震的发震断层位置及其产状,本研究基于Sentinel-1A数据和差分干涉测量、像素偏移技术获得乌什地震升降轨同震形变场,并通过贝叶斯非线性反演方法估计了发震断层的几何参数,获得乌什地震同震滑动分布.研究结果显示,升轨最大视线向抬升形变达80 cm,最大视线向沉降约16 cm.视线向同震形变与像素偏移量结果表明乌什地震显著的垂向运动特征,而升降轨像素偏移方位向观测的反向运动特征表明乌什地震发震断层明显的左旋走滑运动分量.反演结果显示乌什地震发震断层为东北东—西南西走向,北西倾的断裂产状,最优断层倾角约67°,平均滑动角约60°,表明乌什地震同震滑动以逆冲运动为主,兼具少量左旋走滑分量.本文获取的乌什地震变形方式和断层参数与天山南缘盆—山边界的迈丹—沙依拉姆断裂的运动学和几何学相符.乌什地震的高倾角断层走滑-逆冲活动表明南天山与塔里木盆地之间的斜向汇聚作用,天山地区的地壳缩短由山前新生的逆冲推覆带和造山区的高角度逆断层共同吸收.

新疆若羌县砂梁西逆冲推覆构造特征及勘查找矿意义

青藏高原北缘阿尔金成矿带新发现了多处古生代的伟晶岩型锂铍矿床,其中以吐格曼、阿亚格、瓦石峡南锂铍矿床为代表,显示该成矿带具有良好的稀有金属找矿前景。近年来,在若羌县砂梁西铁矿区中也发现了伟晶岩型锂-铌钽矿化,含矿伟晶岩赋存于长城系巴什库尔干岩群和古生代花岗质岩体中,钻探显示其北带部分伟晶岩型矿体深部具有“无根”的特征。本文基于野外地质调查资料,在矿区发现一条第四纪低角度逆冲推覆构造,严格控制着含矿伟晶岩的深部空间展布特征。针对逆冲推覆断层中发育的擦痕,利用Faultkin软件进行了古应力方向的反演分析,确定逆冲推覆的最大主应力作用方向为NNW-SSE。综合分析区域资料,认为阿尔金造山带北缘第四纪逆冲推覆构造形成于青藏高原自南向北扩展期间,伴随着阿尔金走滑断裂的左旋走滑作用,在阿尔金北缘断裂附近出现了大规模的逆冲推覆。逆冲推覆构造的发现及其推覆方向的准确判定,下一步对该区分析含矿伟晶岩矿体的空间展布特征及其找矿工程部署提供了参考资料。

萍乐凹陷东段逆冲推覆构造特征及油气资源效应

萍乐凹陷东段二叠系乐平组官山段致密油藏作为了解凹陷内石油地质条件的良好窗口,经过长期对致密油藏的解剖,通过详细的地表构造填图、二维地震和油田及煤田钻孔综合揭示了盆地存在大量的逆冲推覆构造。致密油藏主要分布在九岭自北向南逆冲推覆片体上构造天窗内出露的二叠系中,主要表现为新元古界浅变质岩地层推覆至元古宇之上,致密油藏含油层位是古生界二叠系乐平组官山段致密砂岩。

蚌埠—淮北地区电性结构及地质意义

通过安徽蚌埠—淮北地区开展大地电磁剖面探测,结合重磁异常,获得了该区深部电性结构及主要地层展布和断裂性质的信息,尤其是徐宿弧形构造形态和深部含煤系地层发育情况。结果表明:①上古生界主要分布在徐宿弧形构造地表高阻推覆体之下,具有低阻、低密度的物性特征,连续性较好,认为推覆构造下煤矿勘查潜力大。②剖面上断层早期以逆断层为主,使得局部下古生界及元古宇覆于上古生界之上,后期以正断层为主,控制新生界沉积。③徐宿弧形构造海拔-4 km以浅表现为“高、低”双层电性结构,主冲断层面由F 5、F 6断裂组成;其地表高阻推覆体前缘西北至萧县,南至固镇县北,在闸河地区被广泛剥蚀。上述成果为该区基础地质研究和找矿勘查提供了重要地球物理信息。