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1.
The terminology of structures in thrust belts   总被引：1，自引：0，他引：1  
A review of structures and geometric relationships recognized in thrust belts is presented. A thrust is defined as any contractional fault, a corollary being that thrusts must cut up-section in their transport direction. ‘Flats’ are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ‘ramps’ are those portions of thrusts which cut across datum surfaces. Ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust. Lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike-slip movement.An array of thrusts which diverge in their transport direction may form by either of two propagation models. These are termed ‘piggy-back’ propagation, which is foreland-directed, and ‘overstep’ propagation which is opposed to the thrust transport direction. An array of thrust surfaces is termed an ‘imbricate stack’ and should these surfaces anastamose upwards a ‘duplex’ will result; the fault-bounded blocks are termed ‘horses’. A duplex is bounded by a higher, ‘roof’ thrust and a lower, ‘floor’ thrust. The intersection of any two thrust planes is termed a ‘branch line’.Thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut. A further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one.The movement of thrust sheets over corrugated surfaces, or the local development of thrust structures beneath, will fold higher thrust sheets. These folds are termed ‘culminations’ and their limbs are termed ‘culmination walls’. Accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust. These accommodation surfaces are termed ‘hangingwall detachments’ and they need not root down into the active thrust. This category of detachment includes dip-slip ‘hangingwall drop faults’ which are developed by differential uplift of duplex roofs, and ‘out-of-the-syncline’ thrusts which develop from overtightened fold hinges. Back thrusts, as well as forming as hangingwall detachments, may also form due to layer-parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp.  相似文献   

2.
The Gran Sasso chain in Central Italy is made up of an imbricate stack of eight thrust sheets, which were emplaced over the Upper Miocene—Lower Pliocene Laga Flysch. The thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack, and their basal thrusts are numbered from T1 to T8, accordingly. On the basis of their different deformation features, the major thrust faults fall into three groups: (1) thrust faults marked by thick belts of incoherent gouges and breccia zones (T1, T2, T3); (2) thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks (T5, T6); and (3) thrust faults truncating folds developed in both the hangingwall and footwall units, and bordered by foliated fault rocks (T7). The deformation features observed for the different faults seem to vary because of two combined factors: (1) lithologic changes in the footwall and hangingwall units separated by the thrust faults; and (2) increasing amounts of deformation in the deepest portions of the imbricate stack. The upper thrust sheets (from 1 to 6) are characterized by massive calcareous and dolomitic rocks, they maintain a homoclinal setting and are truncated up-section by the cataclastic thrust faults. The lowermost thrust sheets (7 and 8) are characterized by a multilayer with competence contrasts, which undergoes shear-induced folding prior to the final emplacement of the thrust sheets. Bedding and axial planes of folds rotate progressively towards the T5, T6, T7 and T8 thrust boundaries, and are subsequently truncated by propagation of the brittle thrust faults. The maximum deformation is observed along the T7 thrust fault, consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack. The axial planes of the folds developed in the hangingwall and footwall units are parallel to the T7 thrust fault, and foliated fault rocks have developed. Field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis, cataclastic flow and pressure-solution slip, associated with pervasive shearing along subtly distributed slip zones parallel to the T7 thrust fault. The development of such fabrics at upper crustal levels creates easy-slip conditions in progressively thinner domains, which are regions of localized flow during the thrust sheet emplacement.  相似文献   

3.
The northern part of the Moine Thrust Zone as exposed around the valley of Srath Beag, Sutherland was developed by thrusts propagating in the tectonic transport direction. Deformation on any particular thrust surface evolved from dominantly ductile to dominantly brittle with time.The foreland has been progressively accreted onto the overriding Moine thrust sheet by duplex formation, a process which has continuously folded the roof thrust and the rocks above its hanging-wall. Fold culminations and depression can be related to lateral ramps which may give the rocks above the hanging-wall a complex history of extensional and compressional strains normal to the transport direction.Folds within the thrust zone are laterally independent because they are controlled by short lived variations in deformation style on an evolving thrust footwall topography. Therefore there may be no correlation between structures across or along the thrust zone. This variation limits the construction of balanced cross sections as structure cannot be projected onto particular section lines.  相似文献   

4.
An examination of thrust structures in the eastern part of the Dauphinois Zone of the external French Alps (referred to in the literature as the Ultradauphinois Zone) shows that major basement thrusts climb up section to produce cover-basement synclines. These thrusts also climb laterally and are continuous with thrust in the cover rocks. The external basement massifs are recognized as thrust sheets with variably deformed and thrust cover sequences. The distinction made in the previous literature between the Dauphinois and Ultradauphinois Zones is no longer tenable. Cover thrusting proceeded by both smooth slip and rough slip, the latter producing a duplex of cover thrust slices. Restoration of this duplex indicates that a shortening of 70 km in the cover occured during its formation. Possible errors in this estimate include uncertainties in the original stratigraphic thickness and in the overall shape of the duplex. Another duplex is thought to have formed at a basement ramp created by the presence of an early basement normal fault. Partial footwall collapse of this basement ramp gave rise to a basement horse at the bottom of the duplex. The overall relation between cover and basement thrusting is indicated using a hanging wall sequence diagram. Recent geophysical studies suggest that the basement thrusts developed from a mid-crustal décollement which passes down dip to offset the Moho. Model studies of thin-skinned tectonics may not be appropriate to such thrust geometries.  相似文献   

5.
河北兴隆复式叠瓦扇构造   总被引：4，自引：0，他引：4       下载免费PDF全文
姜波  刘洪章 《地质科学》1997,32(2):165-172
河北省北部兴隍-平泉复向斜的西端发育了一种特殊类型的推覆构造,该推覆构造具有三重结构的特点,即由上叠瓦扇、下叠瓦扇和下伏系统组成。上叠瓦扇可以分为被分支断裂分割的太古字、长城系、蓟县系、青白口系和寒武-奥陶系5个逆冲岩席;各分支断裂上陡下缓,向下逐渐归并于F1主逆冲断裂上。F1断层下的石炭-二叠系也发育了一组叠瓦状逆冲断层,形成了与上叠瓦扇具有不同变形特征的下叠瓦扇。由于这一构造特殊的两套叠瓦扇结构,故笔者称其为复式叠瓦扇构造,这是一种新的推覆构造类型。  相似文献   

6.
Abstract

The structure of the southern Pyrenees, east of the Albanyà fault (Empordà area), consists of several Alpine thrust sheets. From bottom upwards three main structural units can be distinguished : the Roc de Frausa, the Biure-Bac Grillera and the Figueres units. The former involves basement and Paleogene cover rocks. This unit is deformed by E-W trending kilometric-scale folds, its north dipping floor thrust represents the sole thrust in this area. The middle unit is formed by an incomplete Mesozoic succession overlain by Garumnian and Eocene sediments. Mesozoic rocks internal structure consists of an imbricate stack. The floor thrust dips to the south and climbs up section southwards. The upper unit exibits the most complete Mesozoic sequence. Its floor thrust is subhorizontal. The lower and middle units thrust in a piggy-back sequence. The upper unit was emplaced out of sequence.

Lower Eocene sedimentation in the Biure-Bac Grillera unit was controlled by emergent imbricate thrusts and synchronic extensional faults. One of these faults (La Salut fault) represents the boundary between a platform domain in the footwall and a subsident trough in the hangingwall. Southward thrust propagation produces the inversion of these faults and the development of cleavage-related folds in their hangingwalls (buttressing effect). This inversion is also recorded by syntectonic deposits, which have been grouped in four depositional sequences. The lower sequences represent the filling on the hangingwall trough and the upper sequences the spreading of clastics to the south once the extensional movement ends.  相似文献   

7.
In a cross-section through the southern arm of the Cantabrian Zone, several duplexes have been identified below the Esla Nappe, which is the uppermost and main thrust sheet of the area. The folds deforming the Esla Nappe are culmination walls linked to frontal and lateral ramps belonging to the lower thrust sheets. The thrust sequence can be established on the basis of quantitative analysis of displacement transfer and out of sequence thrusting. The primitive footwall ramps of the Esla Nappe Region were often subsequently broken by décollements developed in successively lower stratigraphic levels of these footwalls. The kinematics of the lowest duplex are more complicated than those of typical duplexes described elsewhere: some thrusts transfer only part of their displacement to the roof thrust, while the remaining part is accommodated along the higher thrusts of previously emplaced duplexes, cutting out of sequence one or more floor or roof thrusts. Cumulative displacement of the thrusts in this region is about 90 km, giving a present thickness 3 times that of the original pre-orogenic sequence, together with a translation of at least 60 km, for the synorogenic basin.  相似文献   

8.
Balanced and restored cross-sections through the central and eastern Pyrenees, constructed using both surface and borehole data, demonstrate the presence of c.18km of shortening above a flat lying N-directed Alpine décollement surface. Hangingwall diagrams show how the North Pyrenean satellite massifs are culminations within this thrust system. Pre-thrusting structures such as subhorizontal stretching lineations in the North Pyrenean Fault zone became rotated above these culminations as the North Pyrenean Fault was cut by Alpine thrusts. Stratigraphic evidence demonstrates that N-directed thrust movements occurred between mid Eocene and Oligocene time, and this is similar to the age of major S-directed thrust movements on the south side of the Axial Zone. The N-directed thrust system probably originated as a series of backthrusts to the dominant S-directed structures.  相似文献   

9.
Recent mapping and seismic survey reveal that intensive compression during the Early Cenozoic in the Qiangtang block of the central Tibetan Plateau formed an extensive complex of thrust sheets that moved relatively southward along several generally north-dipping great thrust systems. Those at the borders of the ~450 km wide block show it overrides the Lhasa block to the south and is overridden by the Hohxil-Bayanhar block to the north. The systems are mostly thin-skinned imbricate thrusts with associated folding. The thrust sheets are chiefly floored by Jurassic limestone that apparently slid over Triassic sandstone and shale, which is locally included, and ramped upward and over Paleocene-Eocene red-beds. Some central thrusts scooped deeper and carried up Paleozoic metamorphic rock, Permian carbonate and granite to form a central uplift that divides the Qiangtang block into two parts. These systems and their associated structures are unconformably overlain by little deformed Late Eocene-Oligocene volcanic rock or capped by Miocene lake beds. A thrust system in the northern part of the block, as well as one in the northern part of the adjacent Lhasa block, dip to the south and appear to be due to secondary adjustments within the thrust sheets. The relative southward displacement across this Early Cenozoic mega thrust system is in excess of 150 km in the Qiangtang block, and the average southward slip-rate of the southern Qiangtang thrusts ranged from 5.6 mm to 7.4 mm/a during the Late Eocene-Oligocene. This Early Cenozoic thrusting ended before the Early Miocene and was followed by Late Cenozoic crustal extension and strike-slip faulting within the Qiangtang block. The revelation and understanding of these thrust systems are very important for the evaluation of the petroleum resources of the region.  相似文献   

10.
云南临沧花岗岩的冲断叠瓦构造与推覆构造   总被引：8，自引：1，他引：8       下载免费PDF全文
 云南省西部沿澜沧江分布的临沧花岗岩,呈SN向延伸,长达500km,但平均宽度只有25km,系逆冲与推覆叠置变形缩短的结果。岩片冲断和推覆的方向普遍为自西向东,临沧花岗岩带向东推覆的距离为30-80km,最大距离120km,冲断叠瓦构造和推覆构造形成的时代主要为中、新生代。糜棱岩的同位素年龄为15.43Ma、25.55Ma和179Ma.新生代沿冲断层发生了近SN向水平走滑运动和沿NE、NW向断层的剪切运动。  相似文献   

11.
云南临沧花岗岩的冲断叠瓦构造与推覆构造   总被引：2，自引：0，他引：2       下载免费PDF全文
杨振德 《地质科学》1996,31(2):130-139
云南省西部沿澜沧江分布的临沧花岗岩,呈SN向延伸,长达500km,但平均宽度只有25km,系逆冲与推覆叠置变形缩短的结果。岩片冲断和推覆的方向普遍为自西向东,临沧花岗岩带向东推覆的距离为30-80km,最大距离120km,冲断叠瓦构造和推覆构造形成的时代主要为中、新生代。糜棱岩的同位素年龄为15.43Ma、25.55Ma和179Ma.新生代沿冲断层发生了近SN向水平走滑运动和沿NE、NW向断层的剪切运动。  相似文献   

12.
Analysis of the Gachsar structural sub-zone has been carried out to constrain structural evolution of the central Alborz range situated in the central Alpine Himalayan orogenic system. The sub-zone bounded by the northward-dipping Kandovan Fault to the north and the southward-dipping Taleghan Fault to the south is transversely cut by several sinistral faults. The Kandovan Fault that controls development of the Eocene rocks in its footwall from the Paleozoic–Mesozoic units in the fault hanging wall is interpreted as an inverted basin-bounding fault. Structural evidences include the presence of a thin-skinned imbricate thrust system propagated from a detachment zone that acts as a footwall shortcut thrust, development of large synclines in the fault footwall as well as back thrusts and pop-up structures on the fault hanging wall. Kinematics of the inverted Kandovan Fault and its accompanying structures constrain the N–S shortening direction proposed for the Alborz range until Late Miocene. The transverse sinistral faults that are in acute angle of 15° to a major magnetic lineament, which represents a basement fault, are interpreted to develop as synthetic Riedel shears on the cover sequences during reactivation of the basement fault. This overprinting of the transverse faults on the earlier inverted extensional fault occurs since the Late Miocene when the south Caspian basin block attained a SSW movement relative to the central Iran. Therefore, recent deformation in the range is a result of the basement transverse-fault reactivation.  相似文献   

13.
依据帕米尔—西昆仑北麓新生代前陆褶皱冲断带 3条构造剖面的详细分析,发现帕米尔—西昆仑北麓除山根地带发育高角度断层外,基本上以低角度逆掩断层为主,形成与逆冲推覆构造相关的褶皱变形。乌泊尔地区表现为由山脉向塔里木盆地滑移的隐伏冲断层和上覆褶皱;苏盖特—齐姆根—甫沙地区表现为山前的三角带和向盆地扩展的两排背斜带。帕米尔—西昆仑北麓前陆褶皱冲断带的主要构造变形时间始于上新世早期(距今约 4.6Ma),断层、褶皱的变形时代由山前向盆地逐步变新,变形强度由山脉向塔里木盆地逐步减弱。帕米尔—西昆仑北麓前陆褶皱冲断带的构造缩短量为 20～70km,缩短率为 35%～50%。  相似文献   

14.
汪新 《高校地质学报》2005,11(4):568-576
南天山山前发育叠瓦状断层和叠加褶皱,这类褶皱构造形态复杂,研究难度大。应用断层相关褶皱理论,依据地表倾角产状、二维地震剖面和钻测井数据,建立了南天山山前库车秋里塔克背斜和柯坪八盘水磨背斜的构造模型。该研究思路和手段对中国西部山前带复杂褶皱的研究有借鉴作用。  相似文献   

15.
In northwest Spain thrust sheets occur in an arcuate fold belt. The fault style consists of an array of thrusts, merging downdip into a single décollement surface. Most of the thrust sheets were initiated as thrusts cutting across flat lying beds. Folds above the hanging-wall ramps and some minor structures indicate that the body of the nappes has been subjected to an inhomogeneous simple shear parallel to bedding (y = 1.15), with slip concentrated along bedding planes. This allows the rocks forming the nappe to remain unstrained. At the base of the nappes a thin zone of deformed rock exists. The thrust sheets die out laterally against an anticline-syncline couple, oblique to the thrust direction. A geometrical analysis shows that if anticline and syncline axes are oblique, the thrust sheet was emplaced with a rotational movement, which can be evaluated. As deformation progressed two sets of folds were formed: a circumferential set, following the arc, and a radial set. An arcuate trace of the thrust structures remains after unfolding the radial folds. With a rotational emplacement, the displacement vector for successive points has a progressively greater length, and forms a progressively lower angle with the thrust. The main thrust units are broken into several slices with rotational movements, so that each unit was curved as it was being emplaced, producing a first tightening of the arc. Later folding increased the arc curvature to its present shape. The palaeomagnetic data available support the above conclusions.  相似文献   

16.
The Gavarnie nappe is a feature of the Tertiary Pyrenean orogen and is shown to consist of at least two thrust sheets of Palaeozoic rocks which are overlain by a southward-dipping sequence of Cretaceous and Eocene sediments, showing folded thrust structures. The Gavarnie nappe covers a basement and Mesozoic cover-rock sequence which is exposed in the tectonic windows of La Larri and the Troumouse Cirque. Here, previously unrecognized thrusts involving basement were responsible for folding the overlying Gavarnie nappe. These basement-involved thrusts climb up section westwards giving a westward lowering of the Gavarnie thrust along strike. The structural evolution of the Gavarnie nappe in a region extending from Heas in France to the Valle de Pineta in Spain can be explained in terms of a piggy-back thrusting sequence. On a regional scale, thrust-tectonic models may be used to explain the double vergence of the Pyrenean chain where early southward-directed thrusting was responsible for structures in the South Pyrenean zone. A later northward-directed back thrusting event, or rotation of southward-directed thrust sheets by the stacking of lower thrust horses, can explain the steepness of structures in the axial zone and the northward-verging North Pyrenean thrust zone. Both models suggest that prior to the Pyrenean orogeny, some of the Hercynian structures in the axial zone were flatter lying, and have been rotated to their present steepness during the Pyrenean orogeny.  相似文献   

17.
Interpretation and 2‐D forward modelling of aeromagnetic datasets from the Olary Domain to the north of the outcropping Kalabity Inlier, South Australia, is consistent with a buried structural architecture characterised by isolated anticlines (also referred to as growth anticlines) bounded by steeply dipping reverse faults. The isolated anticlines are interpreted to have formed by half‐graben inversion during crustal shortening associated with the ca 1600–1580 Ma Olarian Orogeny. We interpret the bounding reverse faults as reactivated high‐angle normal faults, originating from a listric extensional fault architecture. As shortening increased, ‘break‐back bypass’ and ‘short‐cut‘ thrusts developed because of buttressing of the hangingwall successions against the footwall. The resulting architecture resembles a combination of a thrust‐related imbricate fan and an accumulation of inverted basins. Using this structural architecture, synrift sediments proximal to interpreted normal faults were identified as prospective for sediment‐hosted massive sulfide Pb–Zn–Ag mineralisation.  相似文献   

18.
Strongly deformed volcaniclastic metasediments and ophiolitic slices hosting the Sukari gold mineralization display evidence of a complex structural evolution involving three main ductile deformational events (D1–D3). D1 produced ENE-trending folds associated with NNW-propagating thrust slices and intrusion of the Sukari granite (689 ± 3 Ma). D2 formed a moderately to steeply dipping, NNW-trending S2 foliation curved to NE and developed arcuate structure constituting the Kurdeman shear zone (≤ 595 Ma) and East Sukari imbricate thrust belt. Major NE-trending F2 folds, NW-dipping high-angle thrusts, shallow and steeply plunging mineral lineation and shear indicators recorded both subhorizontal and subvertical transport direction during D2. D3 (560–540 Ma) formed NNE-trending S3 crenulation cleavage, tight F3 folds, Sukari Thrust and West Sukari imbricate thrust. The system of NW-trending sinistral Kurdeman shear zone (lateral ramps and tear faults) and imbricate thrusts (frontal ramps) forming the actuate structure developed during SE-directed thrusting, whereas the prevailing pattern of NNE-trending dextral Sukari shear zone and imbricate thrusts forming Sukari thrust duplex developed during NE-directed tectonic shearing. Sukari granite intruded in different pluses between 689 and 540 Ma and associated with at least four phases of quartz veins with different geometry and orientation. Structural analysis of the shear fabrics indicates that the geometry of the mineralized quartz veins and alteration patterns are controlled by the regional NNW- and NE-trending conjugate zones of transpression. Gold-bearing quartz veins are located within NNW-oriented sinistral shear zones in Kurdeman gold mine area, within steeply dipping NW- and SE dipping thrusts and NE- and NS-oriented dextral and sinistral shear zones around Sukari mine area, and along E-dipping backthrusts and NW-SE and N-S fractures in Sukari granite. The high grade of gold mineralization in Sukari is mainly controlled by SE-dipping back-thrusts branched from the major NW-dipping Sukari Thrust. The gold mineralization in Sukari gold mine and neighboring areas in the Central Eastern Desert of Egypt is mainly controlled by the conjugate shear zones of the Najd Fault System and related to E-W directed shortening associated with oblique convergence between East and West Gondwana.  相似文献   

19.
The Mont Blanc massif is one of a chain of basement culminations which crop out along the external French Alps. Its southwestern margin is interpreted as being a major thrust belt which propagated in a piggy-back sequence towards the foreland. These imbricates have developed in the footwall of the high-level Valais thrust. The depth to the floor thrust and shortening within imbricates above this thrust are estimated by a series of partially balanced cross-sections drawn between the ‘synclinal median’ and the Valais thrust. These sections restore to a pre-thrust length of at least 50 km, probably exceeding 100 km, above a floor thrust never deeper than 1 km below the sub-Triassic unconformity. All this thrust displacement is transferred via a series of lateral branch lines onto the Mont Blanc thrust in the Chamonix area. A corollary of this is that the Aiguilles Rouges and the main part of the Mont Blanc massif were separated by probably as much as 100 km prior to Alpine thrusting. Such large shortening estimates imply a hitherto unsuspected Dauphinois stratigraphic consistency in both thickness and lithology.To achieve a balance a restored crustal cross-section must show an equal length of both lower and upper crust. Thus a high-level basal detachment which floors large thrust displacements must overlie a long, undeformed lower crustal wedge. A restored section 100 km long requires such a lower crustal wedge to exist beneath the entire Alpine internal zones. Perrier & Vialon's crustal velocity profile through the western Alps is reinterpreted in these terms. The Ivrea body is considered to be a portion of an external lower crustal wedge which has been uplifted by thrusts after most of the displacement on the external thrust belt.  相似文献   

20.
姬广义汪洋  夏希凡 《城市地质》2005,17(4):1-32,F0003
在燕山中段南麓的蓟县北部山区有着中国国家地质公园，中国北方中-新元古代正层型剖面标志碑就耸立在那里。对这一地区基本地质事实和地质体真实位态的研究，不仅关系着对华北地区晚前寒武纪标准剖面可靠性的评价，也关系着燕山运动命名地的基本地壳结构的合理解析和我国北方中生代以来构造一岩浆活动序列的正确建立。本文展示的基础地质调查成果可揭示：蓟县北部常州沟-杨庄一带的地质结构构造远不是我国大多数地学学者们对此描述的那样简单。调查区约200km。面积可代表燕山中段南麓的大面积中-新元古界分布区的基本地质结构构造特征。已识别出的18条断层和由其限制的21个以上构造岩片的现实位态表明，该地区地壳上部是由多个复杂地块堆叠构成的，主体构造形成于燕山晚期，在形成方式上以大规模多次不同方向运移的薄皮构造岩片叠覆为主要特征。  相似文献   

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