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.

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.

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.

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.

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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Post-collisional extensional and thrust-nappe structures in northern part of Dabie Mountains

Thrust-nappe structures and extensional struc-tures simultaneously occur in the northern part of the Dabie Mountains. The systematic structural study reveals that extensional structures along the Mozitan-Xiaotian fault and thrust-nappe structures that take the Jinzhai-Shucheng fault as their frontal thrust share the same shear sense, and display a transitional relationship from the ductile exten- sional structure of deep level in the south to the ductile-brit- tle and brittle thrust-nappe structure of shallow level in the north. The extensional and thrust-nappe structures in the region are explained to result from post-collisional processes by the continuous subduction of the Yangtze continental block and the extension induced by the uplifting of the core part of the Dabie Mountains, which are components of the extensional structures produced in the exhumation process of the ultrahigh pressure metamorphic rocks in the Dabie Mountains. Because of the frontal blocking in the process of the north-westward spreading, the extension and detachment of the low-grade metamorphic rocks along the Mozi-tan-Xiaotian fault was transformed into the northwestward thrusting, resulting in the thrust-nappe structures. They de-veloped in the period of 200 170 Ma, maybe last till the late Jurassic.

Indosinian Foreland Fold-and-Thrust Belt Bordering Yunnan and Guangxi, China

Recent discoveries of ophiolites indicate that there must be a Palaeotethyan geosuture zone bordering China and Vietnam, which separates the Vietbac block from the South China subcontinent. The Indosinian foreland fold-and-thrust belt bordering Yunnan and Guangxi provided further evidence for the palaeotethysides. The oceanic crust was subducted southwestwards while the magmatic arc migrated northeastwards, and the continent-arc collision occurred in the Late Triassic with the thrusting being extended towards the north or northeast. The features of thrust-nappe structure are discussed, which proved the continental margin of the Palaeotethyan ocean there to be a complicated one. A face-to-face collision occurred first along the NW-striking segment and then along the ENE-striking segment accompanied by transpression or oblique thrusting occurring along the NW-striking one.

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。

准噶尔盆地南缘西部山前褶皱—冲断带构造分带特征及形成演化

准噶尔盆地南缘西部构造呈新的构造叠置特征和复杂的复合叠加构造样式,叠加构造在空间分布上具有明显的分带特征。根据野外地质调查和地震解释资料,采用平衡剖面恢复、楔型构造理论和构造地质学分析方法,研究复杂叠加构造变形差异及分带特征。结果表明:准噶尔盆地南缘西部发育受基底卷入与顺层滑脱联合与差异控制下的空间断褶体系,褶皱发育受断层控制,褶皱与断层相互叠加形成构造楔、双重构造、突发构造等复合构造样式,表现为多期活动特征。研究区按构造变形性质及变形差异可划分为山前逆冲推覆构造带、基底卷入型褶皱—冲断带、盖层滑脱型褶皱—冲断带3个构造带;其中,基底卷入型褶皱—冲断带与第一排断褶带重合,受控于基底卷入型断裂体系,发育基底卷入式大型构造楔、背形堆垛式双重构造与前倾双重构造,背斜轴线与断层线平面重合度高;盖层滑脱型褶皱—冲断带包括第二和第三排断褶带,受控于顺层滑脱型断裂体系,发育断展褶皱,背斜轴线与断层线平面重合度低,构造垂向上具有分层差异,构造变形程度自南向北表现为由强至弱。挤压应力作用的时期和强度、滑脱断层的向北滑脱、构造楔的楔入长度及推挤距离、滑脱层的厚度和上覆地层厚度,以及沉积时代、沉积速率和岩性差异等因素是引起研究区构造垂向分层、南北分带的原因。该结果对明确研究区构造发育及下一步油气地质勘探具有指导意义。

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。

超深层逆冲推覆构造致密砂岩储层地应力场扰动特征——以塔里木盆地博孜-大北地区白垩系储层为例

塔里木盆地库车坳陷博孜—大北地区白垩系致密砂岩储层在由北向南的逆冲推覆下,发育了一系列大规模的北倾断层和叠瓦状堆叠的褶皱构造。复杂的构造形貌致使该区地应力复杂多变,储层改造效果差异明显。因此,亟需厘清研究区内复杂构造对地应力的扰动特征。结合多种方法对单井现今地应力的精确解释,分别分析断裂、褶皱和断褶复合构造对地应力的扰动效果,明确了相关扰动机理,并绘制了研究区地应力扰动特征分区图。基于扰动特征,绘制了不同构造的地应力扰动特征模式图,并提出井位、井轨迹建议。断裂对地应力有卸载作用,断裂附近水平主应力梯度出现不同程度的降低,其中最大水平主应力梯度降低约0.3 MPa/hm;近EW走向的断裂使得近SN向的区域应力方向发生顺时针偏转,偏转角度最大达60°;不同规模断裂的扰动范围为断距的60%。当地层曲率超过0.4 km^(-1)时,褶皱对地应力存在扰动,褶皱地层上部张性扰动区地应力较区域应力减小,下部挤压扰动区地应力增加;张性扰动区最大水平主应力梯度最大约降低0.3 MPa/hm,地应力方向逆时针偏转,偏转角度最大达70°;褶皱变形曲率越大,张性扰动区厚度越大,扰动越明显。断褶复合构造下,断裂扰动区和褶皱张性扰动区叠加会使得地应力进一步减小,地应力方向在两者扰动效果抵消后较区域应力偏转较小或不偏转。综合考虑储层改造难易程度和致密气富集特征,应优先于断褶复合构造带断裂和褶皱张性扰动叠合区部署钻井,建议钻深不超过褶皱中性面,水平井轨迹沿EW向设计。

逆冲-走滑作用叠加的复合构造变形机制砂箱模拟研究:以张家口-蓬莱断裂带渤海段为例

逆冲构造体受走滑作用影响形成新的复合构造体系在自然界中较为常见。新生代以来张家口-蓬莱断裂带渤海段的左旋走滑运动,改造了渤海湾盆地内燕山期挤压运动形成的逆冲构造。北西向的张家口-蓬莱断裂带渤海段受新生代以来太平洋板块俯冲驱动,与共轭的北东向郯庐断裂带共同控制了渤海湾盆地现今的构造样式,同时又是地震多发区和油气聚集区。本文通过砂箱模拟实验,研究不同走滑速率不同基底强度条件下,逆冲推覆构造受走滑作用改造的复合构造演化机制。实验结果显示,在挤压背景下,实验模型中先产生一系列的逆冲断层,形成逆冲推覆构造和冲起构造;叠加走滑作用后,走滑断层切割先存逆冲断层,具有明显的负花状构造特征。剖面上看,走滑速率越大,则断层数量越多,断层断距更大,花状构造更为复杂。在局部塑性基底模型中,无叠加的走滑构造区可形成断陷。结合研究区构造演化过程,模拟结果与张家口-蓬莱断裂带渤海段构造演化过程具有一定相似性,尤其沙北断裂、沙东断裂内部花状构造发育最为典型。走滑断裂对构造圈闭具有一定的控制作用,本模型可对逆冲叠加走滑复合区域的构造演变及动力机制分析提供参考和借鉴。

Study of thrust and nappe tectonics in the eastern Jiaodong Peninsula, China

Thrust and nappe tectonics have affected the eastern Jiaodong Peninsula, the easternmost terminal of the Sulu Ultra-high Pressure Metamorphic Belt. Four nappes have been mapped, named respectively the Shidao, Rongcheng, Mishan and Mouping nappes. The methods used included multi-scale struc- tural analysis and structural chronology analysis. These nappes define four deep level slip-thrust shear zones that were mainly active in the Mesozoic. The amount of ductile deformation decreases from the Shidao to Rongcheng to Mouping to Mishan shear zones, and shows an inverse relationship with temperature. 40Ar/39Ar chronological analysis and the chronological results of former workers reveal four movement steps defined by the development of thrusts and nappes in the late Triassic (210-180 Ma), extensional movement from the Jurassic to early Cretaceous (180-130 Ma), slip-thrust movement in the Early Cretaceous (130-120 Ma), and extensional movement since the Late Cretaceous (120 Ma). The order of boundary shear zone motion in the period of slip-thrust movement during the Early Cre- taceous (130-120 Ma) was along the Shidao, Rongcheng, Mouping and finally the Mishan shear zone. This resulted in clockwise rotation of the nappes relative to block west to the Tan-Lu Faults. Because of the similar evolutionary history of the Tan-Lu Faults and the thrust and nappe structure in the eastern Jiaodong Peninsula, slip dislocation along the Tan-Lu Faults might have been absorbed by thrust and nappe tectonics in the Jiaodong area in the Mesozoic era, resulting in much less dislocation on the Tan-Lu faults in North Eastern China than that in south along the Jiaodong Peninsula.

秦岭南缘大巴山褶皱-冲断推覆构造的特征

秦岭造山带南缘的大巴山巨型逆冲推覆构造主要是在秦岭造山带板块俯冲碰撞造山与中、新生代以来陆内造山过程中长期复合作用形成的。详细的室内外构造研究表明,巴山逆冲推覆构造可以巴山弧形断裂带为界划分为北大巴山逆冲推覆构造和南大巴山逆冲推覆构造。北大巴山自北而南依次由安康-武当推覆体、紫阳-平利推覆体、高桥-镇坪推覆体和高滩推覆体逆冲叠置而成。南大巴山则以镇巴-阳日断裂为界,分为北部的前陆冲断褶皱带和南部的前陆褶皱带。北大巴山主要是印支期碰撞造山作用和燕山期陆内逆冲推覆作用叠加改造的结果,南大巴山则主要是燕山期递进变形过程中的产物。构造变形北强南弱,北以冲断褶皱变形为特征,南以皱褶作用为主;北部褶皱紧闭复杂,向南渐变为宽缓的薄皮构造。逆冲作用在时序上具有由北向南扩展传递的特点。

下扬子地区前陆变形构造格局及其动力学机制

华北板块与扬子板块于印支—早燕山期发生陆—陆碰撞时，使造山带南部的下扬子地区成为前陆变形带。下扬子前陆变形带上，大致以长江为界，北部的逆冲推覆构造系统为向南运动，南部的逆冲推覆构造系统为向北运动，总体呈两套对冲的逆冲推覆构造系统。长江以北前陆变形的动力来自华北与扬子板块沿大别—胶南造山带的碰撞，长江以南前陆变形的动力来自沿江南隆起带的板内造山。

鄂尔多斯西缘北段大型陆缘逆冲推覆体系

鄂尔多斯西缘北段是一个自中生代末以来形成的、结晶基底和早古生代大陆边缘沉积盖层同时卷入的巨型陆缘逆冲推覆构造体系。根据区域地层发育、变形岩石属性、冲断层几何学以及它们与联冲断层的关系,大体上可以分为不同形成阶段的3个冲断层构造组合,包括9个次级构造单元（B1-B7,BN,BS）。受冲断层运动自西向东的一致推进,整体呈现一个局部被近东西走向联冲断层切错、向东凸出的弧形：前端为陆缘褶皱冲断带;中部表现为一系列“原地”或“异地”推覆体和冲断席,发育低角度滑脱层和双冲构造;后部又被最晚期的冲断体叠置。侏罗-白垩纪为逆冲推覆构造的主要发展阶段,经历了3期主要的冲断层作用。第Ⅰ期发生在侏罗纪末,沿阿拉善-华北两类不同性质结晶基底之间的主滑脱面发生大规模冲断层作用,形成桌子山-岗德尔山褶皱冲断带。第Ⅱ期冲断层作用的持续位移,形成了具有上、下两个构造层的石嘴山-尖山大型异地推覆体,主滑脱面为石炭纪煤系地层,其中发育典型的双冲构造。新生代（距今65Ma）以来,印度-欧亚板块挤压碰撞和青藏高原早期向北推挤,加剧了鄂尔多斯西缘逆冲推覆构造的进一步发育,第Ⅲ期冲断层作用在东部陆缘褶皱冲断带形成了苏海图反冲构造的同时,在西部将异地推覆体下部的奥陶系再次推至地表。第Ⅰ期和第Ⅱ期冲断层作用累计位移幅度可能达到60~80km,第Ⅲ期冲断层作用的位移幅度为8km。相邻冲断席之间位移矢量的差异,通过近东西走向的联冲断层得到了调整。

柴达木盆地北缘走滑-冲断构造特征及其油气勘探思路

处于阿尔金左行走滑构造带东缘的柴北缘,过去一致认为是个前陆逆冲带,并对其逆冲构造特征作了大量的研究。通过本次的野外地质勘察和深部地震测线研究,证实柴达木盆地北缘的主要变形样式为走滑-挤压构造,具有挤压推覆特征的同时伴生有走滑构造,并且主要断层系统沿走向滑动的距离远大于沿倾向冲断推覆的距离,从而建立了柴北缘走滑-逆冲构造的地质模型;这对其地震解释有指导作用。从柴达木盆地的构造变形时间序列和演变特征从西向东依次扩展、构造活动从老变新,认为柴北缘的走滑-逆冲构造受阿尔金山大型走滑构造和祁连山剧烈的逆冲挤压构造共同控制。最后研究了柴北缘的走滑-逆冲构造特征对油气勘探的意义,加强勘探评价冷湖—南八仙走滑逆冲构造带的翼部断块圈闭和赛什腾山南缘逆冲推覆体下伏地层。

柯坪断隆古生代的构造属性及其演化特征

柯坪断隆与巴楚隆起古生代无论在地层系统、岩石组合、古生物及沉积相特征等方面均存在可比性 ,表明柯坪断隆和巴楚隆起前中生代是连为一体的 ,同属塔里木盆地的组成部分。中生代柯坪巴楚隆起形成雏形 ,柯坪地区缺失中生代沉积。新生代由于受欧亚板块南缘地体增生 ,板块碰撞远距离效应和西南天山地区复活造山影响 ,在上新世末—更新世初 ,柯坪断隆沿柯坪塔格沙井子断裂发生强烈挤压形成柯坪逆冲推覆构造带。柯坪断隆构成推覆构造带的上部掩冲构造层 ,巴楚隆起向西北延伸的部分构成推覆构造带的下伏构造层。地面油气显示不能证明地下已无油气藏存在 ,不能排除在该区找到大型逆冲断层遮挡圈闭型及牵引背斜圈闭型油气藏的可能。