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1.
—Prerif Ridges are located at the frontal part of the Rif Cordillera, which develops at the Eurasian-African plate boundary. The ridges are formed by recent tectonic structures that also deform foreland basins (Saïss and Gharb basins) and the foreland (Moroccan Meseta). The position of the ridges is the consequence of inversion tectonics undergone in the area. The ENE-WSW trend of the northern edge of the Neogene Saïss basin is determined by the location of Mesozoic basins. Although Prerif ridges probably started to develop since the Early Miocene, the most active deformation phase affecting Pliocene rocks consisted of N-S to NW-SE oriented compression. Striated pebbles show that this compression has prolate stress ellipsoids. The deformation produces southwards vergent folds and NNW-SSE striae on reverse faults at the base of the ridges. The flexure of the Paleozoic basement by the emplacement of the Ridges produced extensional deformation and the development of the Saïss foreland basin. The extension in this basin is oblate and features a well determined NNE-SSW trend near the Ridges, whereas it becomes prolate and pluridirectional near the foreland edge represented by the Rabat region. This part of the Moroccan Meseta, commonly considered to be stable, is deformed by sets of orthogonal joints and faults with short slip that affect up to Quaternary sediments. Southwestward, the Meseta rocks are also deformed by transcurrent faults, which indicate NW-SE and N-S trends of compression. The NW-SE approximation of Eurasia and Africa determines a regional stress field with the same trend of compression. Regional stresses are notably disturbed by the development of the active structures in the Rif, which exhibit alternating trends of compression and extension. The clearest evidence of the relationship between the local deformation and the general plate motion is found at the deformation front of the Cordillera, that is, the Prerif Ridges. 相似文献
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The superimposed basin must have undergone the changes of regional stress field. Study on the nature and switch of regional stress field of superimposed basin is very useful to understanding its stress state and tectonic events during its formation and evolution. As sensitive markers of small stress changes, joint and shear fracture, characterized by consistency of orientation over wide area, can be used to reconstruct paleostress state and its evolution. Detailed observations and analysis on the orientations, geometrical patterns, sequences of joints and shear fractures and their chronological relation to faults and folds show that, the NEE-SWW systematic joints and NNW-SSE systematic joints developed in the Mesozoic and Cenozoic strata are much more prominent than NW-SE systematic joints and shear fractures with different orientations. And the NWW-SEE and NW-SE systematic joints formed later than NEE-SWW systematic joints but earlier than shear fractures with different orientations. According to the relationships between joint and shear fractures and stress, the NEE-SWW systematic joints are inferred to result from lateral weak extension caused by the late Cretaceous regional uplift, while the NNW-SSE and NW-SE systematic joints are interpreted as syn-tectonic deformation relating to strong N-S compression in the Neogene. But some conjugate shear fractures occur probably due to sinistral strike-slip faulting in the Kuqa depression. At the beginning of the Neogene, the stress field changed and the maximal principal stress σ1 switched from vertical to horizontal. 相似文献
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The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera.The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region – considered up to date as stable – is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments.Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE–WSW to ESE–WNW compression; (2) NNW–SSE to NE–SW compression and (3) NNE–SSW compression. These stresses can be attributed mainly to the NW–SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable. 相似文献
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对华南地区有代表性的几条宽角地震剖面进行了研究,利用初动到时资料拟合剖面地带地壳上部详细的速度分布,结合其他地球物理资料与地质资料对地壳基底和沉积盖层的构造进行了综合解释. 结果表明,浙-闽-粤东部地区在地壳基底上分布一系列中生代火山岩断陷盆地,火山岩盖层厚度变化为1000-4000m. 浙西-皖南以及湘-赣地区地壳基底起伏较大,盖层主要为古生界,并发育许多受基底形态与边界断裂控制的小型中生代白垩纪盆地. 华南西部的楚雄盆地为一构造复杂的深坳陷,其中侏罗-白垩系的厚度超过10km,并被分割为东部斜坡和西部坳陷两个单元,而西部坳陷又被一中央隆起分割为东、西两个更次级的凹陷. 区内一些主要的断裂构造在速度等值线图上均有明显的反映,如东部的江绍断裂、莲花山断裂和吴川-四会断裂以及西部的程海断裂和绿汁江断裂都是重要的构造分界,此外众多的基底断裂多是盆地与隆起的边界. 相似文献
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通过研究库车地区的地震活动性 ,由地震分布的规律性推断可能的基底断裂 ,并分析了基底活动断裂与地表构造的对应关系、盖层变形和基底变形特征的差异及成因。结果表明 :1)地震震中分布揭示库车坳陷内对应东、西秋里塔格背斜带位置上 ,基底中发育东秋里塔格深断裂和南、北秋里塔格深断裂 ;另外 ,依奇克里克背斜和亚肯背斜位置上也存在对应的深断裂 ,这表明地表构造的形成受深部构造的控制。 2 )依奇克里克构造西端至东秋 5井连线位置上发育 1条NE向走滑断裂 ,在拜城西侧发 1条NW走向的活动断裂 ,这 2条切穿构造走向的活动断裂是库车坳陷构造分段的主因。 3)基底和盖层变形特征的差异主要源于二者之间介质特性的差异。盆地基底岩石圈强度非常高 ,决定了其变形以脆性破裂———地震活动为主 ;而盖层中沉积岩层强度较弱 ,且存在煤和膏盐等极软弱的薄层 ,在构造挤压作用下 ,可以产生黏性或塑性流动大变形及顺层无震滑脱 相似文献
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Aeromagnetic anomalies uncover the Precambrian basement in the Chhattisgarh basin area,Central India
This paper presents aeromagnetic images for the Chhattisgarh basin region, in Central India, to provide a new window on Precambrian
basement geology and structure. On the basis of aeromagnetic patterns, the Chhattisgarh basin is sub-divided into a northern
low (negative) anomaly zone and a southern high (positive) anomaly zone. The northern portion of the main Chhattisgarh basin
has been further divided into two subbasins, the Hirri sub-basin in the west, and Baradwar sub-basin in the east. A prominent
negative anomaly delineates a NW-SE trending greenstone belt separating these sub-basins. Positive magnetic anomalies delineate
the extent of the Dongargarh granite and equivalents, while the weak magnetic anomaly in the southeast of the Dongargarh granite
and equivalents reflect granulite gneisses of the Eastern Ghat Mobile Belt. By applying the reduced-to-the-equator filter
we enhanced the possible magnetic sources and structural lineaments within the Chhattisgarh basin.
A new sketch map of structural elements was then compiled from aeromagnetic interpretation over the Chhattisgarh basin area.
It includes possible faults, folds and an inferred lithological boundary. 相似文献
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Research on the dynamics of the South China Sea opening:Evidence from analogue modeling 总被引：15，自引：1，他引：15
SUN Zhen ZHOU Di ZHONG Zhihong XIA Bin QIU Xuelin ZENG Zuoxun JIANG Jianqun 《中国科学D辑(英文版)》2006,49(10):1053-1069
Independent of Indochina extrusion, the South China Sea experienced a process from passive continental rifting to marginal sea drifting. According to the fault patterns in the Beibu Gulf basin and the Pearl River Mouth basin, the continental rifting and early spreading stage from 32 to 26 Ma were controlled by extensional stress field, which shifted clockwise from southeastward to south southeastward. From 24 Ma on, the sea spread in NW-SE direction and ceased spreading at around 15.5 Ma. Integrated geological information with the assumption that the South China Sea developed along a pre-Cenozoic weakness zone, we did analogue experiments on the South China Sea evolu- tion. Experiments revealed that the pre-existing weakness zone goes roughly along the uplift zone between the present Zhu-1 and Zhu-2 depression. The pre-existing weakness zone is composed of three segments trending NNE, roughly EW and NEE, respectively. The early opening of the South China Sea is accompanied with roughly 15° clockwise rotation, while the SE sub-sea basin opened with SE extension. Tinjar fault was the western boundary of the Nansha block (Dangerous Ground), while Lupar fault was the eastern boundary of the Indochina, NW-trending rift belt known as Zengmu basin developed between above two faults due to block divergent of Indochina from Nansha. In the experiment, transtensional flower structures along NW-trending faults are seen, and slight inversion occurs along some NE-dipping faults. The existence of rigid massifs changed the orientations of some faults and rift belt, and also led to deformation concentrate around the massifs. The rifting and drifting of the South China Sea might be caused by slab pull from the proto South China Sea subducting toward Borneo and/or mantle flow caused by India-Asia collision. 相似文献
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Cenozoic structural deformation and expression of the “Tan-Lu Fault Zone” in the West Sag of Liaohe Depression, Bohaiwan basin province, China 总被引：1，自引：0，他引：1
Based on the interpretation of 3D seismic data and structural mapping we analyzed the geometry and kinematics of the fault system and validated the expression of the “Tan-Lu Fracture Zone” in the West Sag of Liaohe Depression, Bohaiwan basin province. The Cenozoic structural deformation within the West Sag of Liaohe Depression can be divided into extensional structure system and dextral structure system. The extensional system is constituted by numerous NNE-NE trending Paleogene normal faults, where the Taian-Dawa fault (F1) is the master boundary fault (MBF) dominating the deposition during Paleogene so that the sag shows a complex half-graben with “boundary fault in the east and overlap in the west”. The dextral system is constituted by 2–3 dextral basement faults in NNE-NE trending (F2, F3, F4) and associated structure, and the time of structural action started in Oligocene and continued to Quarternary so that some associated secondary faults of the dextral system cut off the Neogene and Quaternary. Under the influence of the position and attitude of NNE-NE trending basement strike-slip faults, the central north part and the south part of the West Sag show obviously different structural features. The former appears to be a complex “graben” structure limited by the reversed strike-slip fault in the west and bounded by the inverted normal fault in the east, the latter remains the complex half-graben structure with “boundary fault in the east and overlap in the west”, and the graben was mildly reconstructed by one or two normal strike-slip faults. The dextral system within the West Sag is the element of the west branch fault of the Tan-Lu Fracture Zone, which is a deep fracture zone extending along the east of the Liaodongwan Gulf. The deep fracture zone branches off into two separate faults within the Liaohe Depression. The east branch goes through from northern part of the Liaodongwan Gulf to the East Sag of Liaohe Depression and links with the Denghua-Mishan Fault near Shenyang, and the west branch passes from northern part of the Liaodongwan Gulf to the West Sag and Damintun Sag of Liaohe Depression and links with the Yilan-Yitong Fault. The principal displacement zone of the west branch of the Tan-Lu Fracture Zone cuts off the master extensional fault (F1) within the West Sag of Liaohe Depression and induces many cover faults in EW trending within the Neogene and Quaternary. 相似文献
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银川盆地是华北克拉通西部构造活动较为强烈的一个新生代断陷盆地.为了研究银川盆地的地壳浅部结构和活动断裂特征,我们利用2014年在银川盆地完成的深地震反射剖面数据,采用初至波层析成像方法得到了银川盆地高精度的基底P波速度结构和构造形态;考虑到仅根据速度结构剖面还难以确定断裂的准确位置、断层上断点埋深、断层的近地表构造组合样式等特征,研究中还采用浅层地震反射波勘探方法对银川盆地内的隐伏断裂和1739年平罗8.0级地震的地表破裂带浅部结构进行了高分辨率成像.研究结果表明:银川盆地与两侧地块的浅层P波速度结构和沉积盖层厚度差异较大,银川盆地总体呈现出明显的低速结构特征,盆地基底面起伏变化较大,基底最深处位于芦花台断裂和银川断裂之间的银川市下方,其深度约为7000~7200 m;贺兰山隆起区显示为明显的高速特征,地表出露中-古生代基岩地层,缺失新生代地层;鄂尔多斯地块西缘的浅层P波速度明显高于银川盆地,基底埋深相对较浅,推测其新生界地层厚度小于2500 m.浅层地震反射剖面揭示的地层反射界面形态和断裂的浅部构造特征非常清楚,黄河断裂、贺兰山东麓断裂、银川断裂和芦花台断裂不仅是错断盆地基底的断裂,而且还是第四纪以来的隐伏活动断裂,这些断裂的交替活动形成了"堑中堑"的盆地结构,并对银川盆地的形成、盆地内的新生代地层厚度和第四纪沉降中心具有重要的控制作用;在近地表这些断裂表现为由2~3条断层组成的"Y字形"断裂构造,且主断裂的最新活动可追踪至晚更新世末期或全新世,是构造继承性活动的结果.本文的研究结果不仅可为进一步分析银川盆地的基底结构、隐伏断裂特征和活动构造研究等提供新的地震学证据,而且还可为该区城市规划中避让活动断层提供科学依据. 相似文献
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滑动速率是研究断裂运动学特征、地震活动性和区域应变分配的重要参数和依据。前人关于甘孜-玉树断裂带滑动速率的研究结果存在较大差异,因此,其晚第四纪滑动速率有待进一步调查研究。本文基于卫星影像解译和野外实地考察,对甘孜-玉树断裂带西段（玉树断裂）上典型断错地貌点进行测量分析,得到玉树断裂晚第四纪走滑速率为6.6±0.1-7.4±1.2mm/a。通过与前人对甘孜-玉树断裂带东段（甘孜断裂）滑动速率的研究结果进行对比,发现甘孜-玉树断裂带东、西段滑动速率不一致,其原因是甘孜断裂的左旋滑移在向西传递的过程中,一部分应变被分配到了巴塘盆地南缘断裂上。巴塘盆地南缘断裂的存在很好地解释了玉树断裂的走滑速率比甘孜断裂偏低的原因。但是,从区域变形来看,巴塘盆地南缘断裂分配的滑动速率恰好说明了甘孜-玉树断裂带东、西段及鲜水河断裂带的水平构造变形是协调一致的。 相似文献
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滑脱面空间特征的研究可以反映次级浅断裂与区域深断裂之间的构造关系, 在西宁盆地中, 第三纪地层在NNE向区域挤压应力作用下, 沿近NW向发生弯曲褶皱变形。 利用平衡剖面方法, 通过对垂直构造走向的一条剖面进行反演, 得到西宁盆地的滑脱面深度在4~5 km, 并向南倾, 与物探资料得到的盆地沉积盖层的底界位置和形态基本相同。 因此得出盆地沉积盖层的变形方式以柔皱褶曲为主, 并沿沉积盖层底界进行滑脱。 同时根据区域地震背景分析, 认为在西宁盆地浅滑脱的结构面不具备强震的发震条件。 相似文献
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利用流动地震台阵记录的地震数据,通过地震层析技术反演了天山—帕米尔结合带的P波速度结构,揭示出地壳结构的非均匀特征及其与地震活动的对应关系. 分析结果表明,天山和西昆仑的双向挤压导致塔里木西部边缘地壳严重变形,在山前地区形成基底隆起带,地壳深部则被断裂分割成为若干块体,有的块体可能卷入造山带内部;喀什坳陷地壳深部结构相对完整,变形程度较弱;天山和西昆仑的地壳结构显示出缩短增厚的波速特性,在与塔里木接壤的局部地区,壳幔边界附近存在热物质的侵入迹象. 大部分地震都发生在塔里木西部边缘的壳内高速块体周围,推测块体之间的相互作用和应力调整是导致天山—帕米尔结合带频繁发生地震的主要原因,伽师地震则与构造变形由天山向塔里木内部扩展以及该地区的地壳非均匀结构有关. 相似文献
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First results are presented of a recent onshore seismic survey complementary to the Valsis-2 Cruise, which consisted of ESP, COP and CDP marine seismic profiles across the Valencia Trough (Western Mediterranean).The marine energy source used was an airgun array of 5800 cubic inch recorded at 2 land stations on the western flank of the Valencia Trough, at distances between 10–120 km.The experiment has resulted in an extended sampling of the deep crustal structure of the eastern Mediterranean flank of the Iberian peninsula, as well as the offshore-onshore transition.Three transverse NW-SE profiles have been interpreted. Local thinning of the sedimentary cover has been determined towards the centre of the basin which, together with the shallow high velocities observed on the southern profile, could be related to volcanic episodes.A seismic continental basement has been found at depths between 3 and 5 km. A thin lower crust (3–5 km) with velocities around 6.8 km/s has been identified in the northern part of the basin. Alternative crustal models considered for the 3 profiles have been tested, not only from arrival times but also from relative amplitude distributions. A first-order Moho discontinuity fits the data best. The welldefined Moho boundary results in energetic PMP reflections, and a clear updoming is observed towards the interior of the basin, from depths about 20–21 km inshore of Barcelona to 15–17 km depths 60 km offshore. An anomalous upper mantle with low Pn velocities of about 7.7 km/s is confirmed in most of the sampled areas. 相似文献
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前寒武纪变质基底的起伏变化特征和沉积盖层的厚度变化对研究地质构造、能源和资源勘探具有重要意义.而前寒武纪变质基底与沉积盖层之间通常存在一定的磁性差异,这就为利用航磁资料研究磁性基底深度提供了地球物理条件.本文集合了中国国土资源航空物探遥感中心30多年来编制的中国陆域30多个盆地和地区的磁性基底深度图以及补算的部分地区磁性基底深度,经过统一坐标系、统一比例尺之后编制了1/100万比例尺的中国陆域磁性基底深度图(成图比例尺为1/250万).研究结果表明,以E105°线为界,我国西部地区沉积坳陷区盖层厚度大,集中分布在塔里木盆地、准噶尔盆地、柴达木盆地和西藏地区;东部地区沉积坳陷区盖层厚度整体上相对较薄,主要分布在松辽盆地、二连盆地、鄂尔多斯盆地、华北南部盆地、四川盆地、南黄海—苏北盆地等,但最厚处在四川盆地的西南部和鄂尔多斯盆地西缘.这些研究成果展现了我国前寒武纪变质基底和具有一定规模的岩浆岩侵入岩体的深度变化特征,同时反映了沉积盖层的厚度和赋存现状,可直观了解各种类型的沉积盆地和沉积坳陷区的深度和范围,为寻找基底之上油气藏提供了直接依据. 相似文献
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秦岭-大别造山带横贯中国大陆中部,并将我国东部分为南北两部;即华北克拉通和扬子克拉通.在南、北相向运动力系驱动下构成了一个极为复杂的复合、叠加构造带、成矿带和地震活动带.同时导致了该地域异常变化的沉积建造和强烈起伏的结晶基底.然而对它们形成的地球物理边界场响应,岩相和结构的异常变化尚不清晰,特别对盆山之间的耦合响应更缺乏深层动力过程的理解.为此本文通过该区榆林-铜川-涪陵长1000 km剖面的地震探测和研究结果提出：（1）沉积建造厚度变化为4~10 km,结晶基底起伏强烈,幅度可达4~6 km;（2）一系列基底断裂将该区切割为南鄂尔多斯盆地和秦岭北缘前陆盆地、秦岭-大巴造山带和南缘前陆盆地与东北四川盆地,其中前陆盆地为秦岭北渭河盆地和秦岭南通江-万源盆地;（3）秦岭造山带是北部华北克拉通向南推挤、南部扬子克拉通向北推挤下隆升的陆内山体,并构筑了其南、北前陆盆地;（4）秦岭造山带的南、北边界并非是一条边界断层,而应是包括前陆盆地在内的组合界带;（5）秦岭与大巴弧形山系源于同一深部结晶基底,即同根生.这一系列的新认识对深化理解秦岭-大巴造山带形成的深层动力过程和演化机理及厘定扬子克拉通的真实北界具有极为重要的意义. 相似文献