Study of overthrust nappe structure and its geodynamic mechanism along the southeastern margin of Nansha Trough

On the basis of interpretation of comprehensive geophysical data and foreign data analysis,there existed a lot of overburden detachment shear thrust faults along the southeastern margin of Nansha Trough,which composed imbricated overthrust nappe structure.Thrust-faulted nappe structure pattern is determined in this area,which consists of frontal fault zone,thrust fault-folded zone and root zone structures,and presents regularly zonation on plane.The detail description of the structural geometrical characteristics is given in shallow thrust fault zone,and the kinematical mechanism of thrust fault nappe structure is furtherly discussed.Overthrnst nappe structure in this area is resulted from island arc-continent collision and orogenic activities.

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.

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.

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.

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。

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。

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。

浙东南石平川钼矿区构造特征及控矿机制

浙东南石平川钼矿区经过近数十年的地质勘查,累计查明钼资源量已达大型规模。为了更好地理解石平川钼矿区的控矿机制,为在老矿山外围确定新的找矿靶区提供理论依据,通过实地观测和分析矿区的层内构造、节理裂隙发育特征、石英细脉及微细脉穿切关系,利用区域构造解析法、节理统计分析法等,系统研究了石平川钼矿区的构造特征和控矿机制。钼矿床整体受到石平川火山穹窿和断裂构造的共同控制,均产于石平川火山穹隆范围内的断裂或层内构造带内,并严格受层内构造的控制,层内构造为辉钼矿脉的形成提供了运移通道和储矿空间,区域构造应力场及岩体冷凝收缩作用共同形成了矿区的层内构造。研究成果可为石平川钼矿区外围找矿靶区的筛选提供参考。

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。

下扬子逆冲推覆构造后缘凹陷油气富集关键要素及有利勘探方向

通过开展系统的构造特征、沉积环境、油气富集规律分析,在钻探新发现的新资料基础上,对下扬子北缘逆冲推覆构造后缘凹陷油气富集规律和有利勘探方向进行了研究。研究结果表明:(1)下扬子北缘逆冲推覆构造后缘凹陷中油气显示表现为“三气两油”特征,即二叠系大隆组和孤峰组页岩气、龙潭组煤层气和致密砂岩气、大隆组页岩油和三叠系殷坑组灰岩裂隙油。(2)以宣城凹陷为代表的下扬子北缘逆冲推覆构造后缘凹陷带油气富集受3个关键要素控制,即后缘凹陷块体稳定,已形成的油气体系具有较好的保存环境;该地区二叠系大隆组(P3d)和孤峰组(P2g)沉积环境属深水陆棚环境,是有利的沉积相带,发育2套富有机质的烃源岩层系;顶、底板有效封存条件均较好,烃源岩上部有三叠系泥灰岩地层覆盖,下部有栖霞组生物碎屑灰岩为垫层,顶、底地层控制了纵向油气的散逸。(3)研究区下三叠统—上二叠统自上而下依次富集泥灰岩裂隙油、页岩油、页岩气、煤层气、致密砂岩气,整体呈“上油下气”多种非常规油气同生共存的特征,形成了特殊的油气富集模式。(4)宣城凹陷与南陵凹陷、句容凹陷和常州凹陷具有相似的地质条件,是下一步页岩油气勘探的首选有利区。

巨厚推覆体对深部回采巷道矿压分布规律研究

在巨厚推覆体下进行采掘活动,矿压分布规律复杂,围岩变形破坏控制难度大。为了获得巨厚推覆体下回采巷道矿压分布规律,以新集一矿360801工作面为工程背景,通过FLAC^(3D)数值模拟研究,得到了推覆体厚度、岩性以及推覆体位置对回采巷道的影响。研究结果表明:推覆体存在时的巷道变形量和集中应力均大于无推覆体的情况,回采巷道围岩变形量与推覆体厚度呈负相关,推覆体岩性和推覆体位置的改变对回采巷道的影响较小。

Reservoir differences and formation mechanisms in the Ke-Bai overthrust belt,northwestern margin of the Junggar Basin,China

There are some differences in reservoir quality of clastic rock between the hanging wall and the foot wall of the Ke-Bai overthrust belt, northwestern margin of the Junggar Basin, western China, which affect the efficient petroleum exploration in this highly mature exploration area. Based on a large number of thin-sections, cast thin-sections, and physical property analysis of cores, we systematically discuss the Permian-Jurassic reservoir differences between the hanging wall and the foot wall of the Ke- Bai overthrust fault from the aspects of structural evolution, time-space distribution of the depositional system, diagenesis characteristics, and reservoir quality and analyzed the reasons for the differences in reservoir properties. The overthrusting of the Ke-Bai fault directly results in different burial histories, diagenesis evolution, and porosity evolution between the hanging wall and the foot wall. The diflbrences of reservoir characteristics are mainly embodied in buried depth, grain size, sedimentary facies, diagenetic stage, and reservoir quality. The analysis results showed that burial history and depositional characteristics controlled by overthrusting are direct influencing factors of reservoir differences. Because of shallow burial depth of the hanging wall, the reservoir compaction is weak and primary pores are preserved well. The porosity of reservoir on the hanging wall is generally 10%-25%. The strata on the foot wall are deeply buried, and there are mainly mixed pores with the average porosity of 5%-20%. The favorable reservoir on the foot wall is generally developed near faults or in the channel sand bodies, which are usually dissolution development areas.

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.

某大底盘双塔部分框支剪力墙结构设计分析

某项目采用大底盘双塔部分框支剪力墙结构,存在多项不规则,属于超限高层建筑结构。本文介绍了项目的结构体系及超限情况,采用两种软件进行结构计算分析。针对工程的特点及难点,基于结构性能化要求,对结构采取了中震和大震静力推覆分析,并结合分析结果采取了相应的加强措施。分析表明,结构安全可靠,满足预设目标。

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).

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.

Oil source and accumulation in the overthrust belt in the Ke-Bai region,Junggar Basin,west China

The region around the Karamay-Baikouquan （Ke-Bai） overthrust belt is the richest in hydrocarbon accumulation in the Junggar Basin. Previous research has indicated that oil in the region came from the Fengcheng Formation in the Mahu Depression to the northeast of the region, but the oil distribution around the Mahu Depression is remarkably uneven. Large amounts of oil have been found in the Ke-Bai overthrust belt to the west of the depression and only some small oilfields have been discovered in the eastern margin of the depression. This uneven distribution revealed that the oil source of the Ke- Bai region might not be from the Mahu Depression. The oil type distribution and the oil migration pattern revealed in this paper showed that there may be another oil source under the Karamay overthrust. Based on geochemical data, the oil was classified into two types from the sterane and terpane characteristics. Type A oil was mainly distributed in the Huwan area and blocks V and VIII of the Karamay Oilfield in the southern part of the region, while type B oil was mainly distributed in the Baikouquan Oilfield in the northern part of the region. In addition, oil migration pathways and direction were determined by the values of diasterane / regular sterane and C30 moretane / C30 hopane ratios. It is shown that the oil of Huwan area on the hanging wall of the overthrust was mainly charged along the overthrust fault surfaces and then migrated to the west, whereas the oil in blocks V and VIII on the foot wall of the overthrust came from the Mahu Depression in the east. As a result, there may be at least two hydrocarbon source kitchens in the study area. The hydrocarbons in the blocks V and VIII on the footwall of the overthrust belt and in the Baikouquan Oilfield mainly came from the Fengcheng Formation in the Mahu Depression, and the hydrocarbons in the Huwan area on the hanging wall of the overthrust belt may come from another hydrocarbon source kitchen below the overthrust. This recognition indicates that there is substantial exploration potential in the deep Carboniferous strata on the hanging wall of the overthrust belt.

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

A thrust and nappe tectonlc.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.