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1.
米仓山、南大巴山前缘构造特征及其形成机制   总被引：6，自引：0，他引：6  
在对四川盆地东北部盆山结合部地表地质和石油地球物理资料综合分析的基础上,阐述了米仓山前缘构造、南大巴山前缘构造的几何学、运动学特征;发现了二者的共性和不同,二者均以双重构造为主,通过古生代构造层的叠置,而迅速抬升出露地表,米仓山前缘以被动顶板双重构造为主,即典型的"三角带"构造,南大巴山前缘以主动顶板双重构造为其显著特征;初步分析了原因,区域滑脱层,特别是嘉陵江组-雷口坡组膏盐岩滑脱层及古生界泥页岩滑脱层,构成了顶板和底板逆冲断层,其间的台地相碳酸盐岩构成了断夹块,受米仓山早期基底隆升和侧向挤压,形成了被动顶板双重构造,南大巴山递进挤压变形,形成了主动顶板双重构造。  相似文献   

2.
Triangle zones,generally found in foreland fold-and-thrust belts,serve as favorable objects of petroleum exploration.Taking the Dabashan foreland belt as an example,we studied the formation and development of triangle zones,and investigated the effect of decollements and the mechanical contrast of lithology by employing the method of physical modeling.Four experimental models were conducted in the work.The results showed that ’sand wedges’ grew episodically,recorded by deformational length,height and slope angle.The height versus shortening rate presented an S-shape curve,and uplifting occurred successively in the direction of the foreland belt.During the formation of the triangle zone,layer-parallel shortening took place at the outset;deformation decoupling then occurred between the upper and lower brittle layers,divided by a middle-embedded silicone polymers layer.The upper brittle layers deformed mainly by folding,while the lower sand layers by thrusting. As shortening continued,the geometry of a triangle zone was altered.We consider that the triangle zone in the Dabashan foreland belt was modified from an early one based on available seismic profiles and the experimental results.In addition,decollements and mechanical contrast impose significant influence on structural development,which can directly give rise to structural discrepancies.More decollements and obvious mechanical contrast between brittle layers can promote the coupling between the upper and lower brittle layers.Basal decollement controls the whole deformation and decreases the slope angle of the wedge,while roof decollement determines whether a triangle zone can be formed.  相似文献   

3.
We used two-dimensional finite element models to explore different configurations of weak layers in undeformed sedimentary sequences to investigate the occurrence of three characteristic types of thrust configurations: ramp-flat; imbricate; and duplex. In our models, we embedded two low-friction weak layers with a finite spatial extent in a sequence of stronger rock. These two weak layers were initially horizontal, were separated vertically by 1 km, and were arranged in three different relative positions to each other. When the models were deformed and these weak layers developed into décollements, they interacted to produce one of the three types of thrust faults as a function of their initial configurations. When the tips of weak layers were separated by a large gap (>10 km), only the lower-level décollement became active, producing imbricate thrusts. When the two weak layers overlapped for a large distance (>10 km), they simultaneously became active décollements, producing duplexes in the overlapped zone. When the gap or overlap was small (<5 km), the two weak layers also simultaneously became active décollements but their tips linked up to form a ramp-flat geometry. These results suggest that thrust geometry is highly sensitive to the initial arrangement of décollements.  相似文献   

4.
Two Hercynian duplexes are developed in Viséan limestones in the Basse Normandie quarry. The lower duplex is completely exposed in a subvertical quarry wall; the partially exposed upper duplex lies immediately above the lower duplex. The duplexes are both located in the footwall of the Hydrequent thrust which emplaced Devonian clastic sediments above the Viséan limestones. The lower duplex exposes all the internal thrusts, a reference bed of chalky limestone, the roof and floor thrusts, and the duplex tip. The duplex has been graphically restored to its pre-deformation geometry by line-length and area balancing and its resultant geometry is close to the model of Boyer & Elliott. The lower duplex shortened by two different mechanisms, an initial phase of layer-parallel shortening which produced no cleavage, followed by thrust imbrication. The average contraction of the front portion of the duplex was ?49% (natural strain) of which ?27% is layer-parallel shortening and ?22% is thrust imbrication. However, locally the bulk shortening increases from zero at the duplex tip to over ?120% in a down-dip direction. The area balancing provides the most accurate estimates of bulk shortening; line-length balance calculations give minimum estimates only. An area balance on the whole of the lower duplex gives a bulk shortening of ?84%. An area balance of the upper duplex yields an average contraction of ?75% and the total contraction produced by both duplexes is ?92%.  相似文献   

5.
A 100 km long balanced structural transect is presented for the Patagonian Andes at 50° S Latitude. The area studied is characterized by a fold belt in the eastern Andean foothills and basement-involved thrusts in a western-basement thrust zone. The basement thrust zone exposes pre-Jurassic, polydeformed sedimentary and layered metamorphic rocks emplaced over Lower Cretaceous rocks above an E-vergent thrust located at the western end of the fold belt.

The fold belt is developed in a 3 km thick deformed Cretaceous–Paleogene sedimentary cover with few basement outcrops and scarce calc-alkaline magmatism. Cover structures related to shallow décollements have a N-S to NW-SE strike, with fold wavelengths from 1100 to 370 m in the east to 20 to 40 m in the west. However, long-wavelength basement-involved structures related to deeper décollements have a dominant N-S to NE-SW trend along the eastern and western parts of the fold belt. Field evidence showing different degrees of inversion of N-S–trending normal faults suggests that the orientation of the Cenozoic compressive basement structures was inherited partially from the original geometry of Mesozoic normal faults.

The deformation propagated toward the foreland in at least two events of deformation. The effects of Paleogene (Eocene?) compressive episode are observed in the western fold belt and a Neogene (Late Miocene) compressive episode is present in the eastern fold belt. Basement-involved structures typically refold older cover structures, producing a mixed thick and thin-skinned structural style. By retrodeforming a regional balanced cross section in the fold belt, a minimum late Miocene shortening of 35 km (26%) was calculated.  相似文献   

6.
We investigate the factors that control the shortening distribution and its evolution through time in orogenic belts using numerical models. We present self‐consistent high‐resolution numerical models that simulate the inversion of a rift to generate an upper crustal antiformal stack, a wide outer pro‐wedge fold‐and‐thrust belt, characterised by a two‐phase evolution with early symmetric inversion followed by formation of an asymmetric doubly‐vergent orogen. We show that a weak viscous salt décollement promotes gravitational collapse of the cover. When combined with efficient erosion of the orogenic core and sedimentation in adjacent forelands, it ensures the thick‐skinned pro‐wedge taper remains subcritical, promoting formation of an upper crustal antiformal stack. Rift inheritance promotes a two‐phase shortening distribution evolution regardless of the shallow structure and other factors. Comparison to the Pyrenees strongly suggests that this combination of factors led to a very similar evolution and structural style.  相似文献   

7.
Jonas B. Ruh 《地学学报》2017,29(3):202-210
Numerical experiments on evolving accretionary wedges usually implement predefined weak basal décollements and constant strength parameters for overlying compressed sequences, although fluid pressure ratio, and therefore brittle strength, can vary strongly in sedimentary basins. A two‐dimensional finite difference model with a visco‐elasto‐plastic rheology is used to investigate the influence of different simplified fluid pressure ratio distributions on the structural evolution of accretionary wedge systems. Results show that a linear increase in fluid pressure ratio towards the base leads to toeward‐verging thrust sheets and underplating of strata, while simulations with a predefined décollement form conjugate shear zones supporting box‐fold‐type frontal accretion. Surface tapers are in agreement with the critical wedge theory, which here is modified for cases of varying fluid pressure ratio. Furthermore, the numerical results resemble findings from natural examples of accretionary wedges.  相似文献   

8.
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   

9.
This study investigated the evolution of frontal structures of fold and thrust belts with 2D numerical simulations using the discrete element method (DEM). Of specific interest is the occurrence of triangle zones, and how mechanical stratigraphy affects the formation of the triangle zones. In our simulations, we varied the strength of a two unit stratigraphy, as well as the décollement horizons, to determine the controlling parameters of different types of frontal structures. For models with homogenous stratigraphy, deformation was concentrated along forethrusts, which involved both the upper and lower units. With the addition of a mechanically weak upper unit, deformation along forethrusts and popup structures largely occurred in the upper unit with relatively little deformation of the lower unit. With thicker décollement surfaces and strong upper and lower units, decoupling was enhanced and allowed for the formation of triangle zones in front of the deforming wedge. The triangle zones were uplifted along lower forethrusts, until a new frontal triangle zone formed. Results compared favorably with triangle zones found in the Canadian Cordillera in southern Alberta.  相似文献   

10.
Changes in deformation style and amounts of shortening in the Osen-Røa thrust sheet of the Oslo Region occur vertically and laterally approaching the thrust front in the south. Deformation in the CambroMiddle Ordovician sequence passes laterally from closely spaced imbricates in the north (50–60% shortening), through triangle, pop-up and imbricate zones toward the south (20–37% shortening) to widely spaced zones of deformation (up to 20% shortening) approaching the thrust front. Changes in deformation style are attributed to changing boundary conditions across the Klekken thrust, declining end-of-orogenic forces and an increase in thickness of competent units in the Ordovician rocks to the south. Vertical changes in deformation style are attributed to the increasing percentage of competent units upward in the Cambro-Silurian sedimentary rocks. In the north, the accompanying decrease in shortening upwards requires a structurally necessary upper detachment horizon to separate folded late Middle Ordovician-Silurian sediments from imbricated early Cambro-Middle Ordovician sediments below; while southward in the Oslo area the upper detachment needs to be placed between Silurian and Cambro-Ordovician units. Finally, in Eiker, with less than 20% shortening, the whole CambroSilurian sequence appears to have deformed as a single unit. In the northern Oslo Region, the upper detachment probably has a backthrust sense of motion above an imbricate stack (passive roof duplex). Further south the upper detachment is probably directed toward the foreland.  相似文献   

11.
乌鲁木齐山前坳陷逆断裂-褶皱带及其形成机制   总被引：66，自引：9，他引：57  
乌鲁木齐山前坳陷位于天山新生代再生造山带北侧,南以准噶尔南缘断裂与天山相隔,内部发育了几排逆断裂 背斜带,每一排构造带又由多个逆断裂 背斜组成。最南的齐古逆断裂 背斜带形成于中生代末,其北的玛纳斯逆断裂背斜带包含霍尔果斯、玛纳斯和吐谷鲁逆断裂背斜,形成于上新世末、早更新世初,受上、下２ 个滑脱面和断坡的控制,形成上、下２ 个背斜。再向北的独山子逆断裂背斜带由独山子、哈拉安德和安集海逆断裂背斜组成,形成于早、中更新世之间,主逆断裂向下在８ ～９ ｋｍ 深处的侏罗系中变为近水平滑脱面。此外,在独山子和吐谷鲁背斜的西北和东北还分别发育有正在形成之中的西湖和呼图壁隆起。研究了这些逆断裂 背斜带的地表和深部的构造特征、二维和三维几何学及运动学后指出,它们是在天山向准噶尔盆地扩展过程中发育于近水平滑脱面和不同断坡上的断展褶皱,独山子和安集海逆断裂 背斜的水平缩短量分别为２ ９００ ,１ ３５０ ｍ ,缩短速率分别为３９７ ,１８７ ｍ ｍ／ ａ。霍尔果斯、玛纳斯、吐谷鲁逆断裂 背斜的水平缩短量分别为５ ９００ ,６ ５００ ,６ ０００ ｍ ,相应的缩短速率分别为２０２,２２３ ,２０６ ｍ ｍ／ａ,准噶尔南缘断裂和乌鲁木齐山前坳陷第四纪?  相似文献   

12.
This paper focuses on the behavior of a roof sequence in the Appalachian Plateau of West Virginia, U.S.A., and emplacement of the Wills Mountain duplex with 17.5 km of displacement. Unlike the Plateau along strike in Pennsylvania and New York where forethrusting was previously documented, this roof sequence lacks an underlying salt-dominated roof décollement. Kinematic analyses reveal that the roof sequence in the West Virginian Plateau accommodated about two-thirds of the 17.5 km of shortening by the adjacent Wills Mountain duplex, as a forethrusting kinematic response. The remaining shortening imbalance of about 5 km between the duplexes and younger roof sequence rocks is accommodated by additional forethrusting further into the foreland and local compensation. This kinematic response matches that along strike in the central Appalachians despite the loss of the salt décollement. We interpret that an Ordovician shale-dominated formation was sufficiently weak to substitute for the salt horizon. Thus, a weak mechanical unit rather than specifically a salt décollement is a necessary prerequisite for forethrusting. A contributing factor to forethrusting may be the subvertical front of the Wills Mountain duplex, which inhibited other responses by the roof sequence. Mesoscale and smaller processes, including grain-to-grain pressure solution, twinning and cleavage formation account for over 75% of the shortening in the roof sequence, and, if ignored, would result in an erroneous interpretation of backthrusting or local compensation. This result suggests that failure to consider all deformation scales could lead to incorrect kinematic conclusions in other tectonic systems.  相似文献   

13.
Detailed (1:60 scale) mapping of the Fort Foster Brittle Zone in the mylonitic Rye Formation of southernmost Maine has revealed the intricate internal duplex structure of a system of probable Paleozoic-age dextral strike-slip faults that have produced abundant pseudotachylyte and minor breccia. The internal configuration of this brittle zone consists of a mosaic of individual pseudotachylyte generation zones as slab-duplex structures. Individual duplex zones are up to 100 m in length and 1 m or less in width and are defined by pairs of layer-parallel slip surfaces along which frictional melts were produced. These slab-duplex structures are interpreted as zones of displacement transfer between long, overlapping, layer-parallel en échelon strike-slip fault surfaces. Contractional duplexes develop layer-parallel compressional structures that tend to shorten and thicken the fault-bounded slabs by the formation of lateral ramps and conjugate faults, kinks and asymmetric folds. Extensional duplexes develop layer-parallel stretching and thinning by the formation of oblique dextral shears, high-angle conjugate pairs and localized fault breccias. The production of pseudotachylyte by friction melting along layer-parallel fault surfaces in these exposures is attributed to rapid slip during paleoseismic events. The rupture structures developed during these events may be characteristic of fault structure and mechanics at near-focal depths in a strike-slip seismogenic zone.  相似文献   

14.
Folds and thrust faults formed by layer-parallel shortening coaxial with extensional structures such as normal dip-slip faults and ductile necking structures with orthorhombic fabric symmetry are usual, but little-recognised structures formed within normal dip-slip shear zones bounding rifts. They are generated because of the shear distribution in a zone of progressive deformation and may be later extended and disrupted depending on which part of the strain ellipsoid they may be located. We here describe folds and thrust faults from the southern margin of the Ala?ehir Rift in western Turkey as an opportunity to discuss the properties of pure extension–related structures formed by layer-parallel shortening. Such structures are more commonly generated during the early stages of rifting, when deformation rates are slow and the shear zones broader than those forming later in the life of a rift when strain rates are usually higher. Such structures have commonly been mistaken for witnesses documenting regional episodes of shortening rather than as integral parts of the extensional structures forming rifts. Not all layer-parallel shortening-related structures therefore indicate regional shortening. We plead that hasty statements concerning the meaning of geological structures at all scales be avoided before a thorough understanding of bulk strains that have affected a region are properly understood.  相似文献   

15.
南安集海背斜和南玛纳斯背斜属于准噶尔南缘山前中西段第一排构造带,构造变形异常强烈,呈典型的堆跺式双重构造.通过应用断层相关褶皱的构造几何分析方法,用计算机对南安集海-南玛纳斯背斜带内的基干地震剖面进行了构造解析,南玛纳斯背斜是在霍-玛-吐断裂上叠加一堆跺式双重构造组成,向西南玛纳斯背斜上的堆跺式双重构造逐渐消失,同时霍-玛-吐断裂位移量逐渐转换成反向逆冲断层,形成南安集海背斜的复合型构造三角楔.通过构造解析,弄清了它们在三维空间中的过渡转换关系,对后继的南缘山前构造带的勘探开发具有参考意义.  相似文献   

16.
The Lesser Himalayan duplex (LHD) is a prominent structure through much of the Lesser Himalayan fold–thrust belt. In the Darjeeling - Sikkim Himalaya a component of the LHD is exposed in the Rangit window as the Rangit duplex (RD). The RD consists of ten horses of the upper Lesser Himalayan Sequence (Gondwana, Buxa, Upper Daling). The duplex varies from hinterland-dipping in the north, through an antiformal stack in the middle to foreland-dipping in the south. The Ramgarh thrust (RT) is the roof thrust and, based on a balanced cross-section, the Main Himalayan Sole thrust is the floor thrust at a depth of ~ 10 km and with a dip of ~ 3.5° N.Retrodeformation suggests that the RD initiated as a foreland-dipping duplex with the Early Ramgarh thrust as the roof thrust and the RT as the floor thrust. The RT became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent RT reactivation. This kinematic history best explains the large translation of the overlying MCT sheets. The restoration suggests that RD shortening is ~ 125 km, and the original Gondwana basin extended ~ 142 km northward of its present northernmost exposures within the window.  相似文献   

17.
Abstract

The Cenozoic westward motion of the Betic-Rif internal zone (“Alboran block”) between Iberia and Africa is constrained by paleogeographic considerations and by wrench faulting which affects both sides of the external zones. However, in the Alboran domain itself there was so far no evidence of significant internal deformation related to this westward displacement which was consequently consider as an en bloc” motion. Our work, in Eastern Andalucia, demonstrates that the main tectonic units building up the Betic zone should be regarded as large-scale tectonic sheets with a typical duplex style. The direction of the tectonic transport is to the West. At meso-scale, the major structures exhibit a combination of hindward and foreward dipping imbricates on the respective east and west sides of antiformal stacks or “rigid cores”. On a broader scale, the same geometric framework appears on both east and west sides of the Sierra Nevada window which we interpret as a tectonic culmination on the hangingwall of a Subbetic décollement zone. The development of this tectonics, in retrogressive metamorphic conditions, postdates the ductile deformation of the internal complexes. The morpho-tectonic relationships between the culmination of the metamorphic cores and the Neogene basins give a way to date the westward motion of the “Alboran System of Nappes” of the middle and upper Miocene.  相似文献   

18.
《Gondwana Research》2010,17(3-4):697-715
The Lesser Himalayan duplex (LHD) is a prominent structure through much of the Lesser Himalayan fold–thrust belt. In the Darjeeling - Sikkim Himalaya a component of the LHD is exposed in the Rangit window as the Rangit duplex (RD). The RD consists of ten horses of the upper Lesser Himalayan Sequence (Gondwana, Buxa, Upper Daling). The duplex varies from hinterland-dipping in the north, through an antiformal stack in the middle to foreland-dipping in the south. The Ramgarh thrust (RT) is the roof thrust and, based on a balanced cross-section, the Main Himalayan Sole thrust is the floor thrust at a depth of ~ 10 km and with a dip of ~ 3.5° N.Retrodeformation suggests that the RD initiated as a foreland-dipping duplex with the Early Ramgarh thrust as the roof thrust and the RT as the floor thrust. The RT became the roof thrust during continued duplexing by a combination of footwall imbrication and concurrent RT reactivation. This kinematic history best explains the large translation of the overlying MCT sheets. The restoration suggests that RD shortening is ~ 125 km, and the original Gondwana basin extended ~ 142 km northward of its present northernmost exposures within the window.  相似文献   

19.
In orogenic belts, a basal décollement zone often develops at depth to accommodate the shortening due to folding and thrusting of the sedimentary cover. In the Early Mesozoic intracontinental Xuefengshan Belt of South China, such a décollement zone is exposed in the core of anticlines formed by the emplacement of the late-orogenic granitic plutons. Our detailed, multi-scale structural analysis documents a synmetamorphic ductile deformation. In the basal décollement, the Neoproterozoic pelite and sandstone, and the intruding Early Paleozoic granites were deformed and metamorphosed into mylonites and orthogneiss, respectively. The metamorphic foliation contains a NW–SE stretching lineation associated with top-to-the-NW kinematic indicators. The ductile shearing of these high-strained rocks can be correlated with NW-verging folds and thrusts recognized in the Neoproterozoic to Early Triassic sedimentary cover. Monazite U–Th–Pbtot chemical dating, and zircon SIMS U–Pb dating provide age constraints of the ductile shearing between 243 and 226?Ma, and late-orogenic granite emplacement around 235–215?Ma. In agreement with recent geochronological data, these new results show that the Xuefengshan Belt is an Early Mesozoic orogen dominated by the NW-directed shearing and thrusting. At the southeastern boundary of the Xuefengshan Belt, the Chenzhou-Linwu fault separates the Early Mesozoic domain to the NW from the Early Paleozoic domain to the SE. The tectonic architecture of this belt was possibly originated from the continental underthrusting to the SE of the South China block in response to northwest-directed subduction of the Paleo-Pacific plate.  相似文献   

20.
Late Palaeozoic deformation in the southern Appalachians is believed to be related to the collisional events that formed Pangaea. The Appalachian foreland fold and thrust belt in Alabama is a region of thin-skinned deformed Palaeozoic sedimentary rocks ranging in age from Early Cambrian to Late Carboniferous, bounded to the northwest by relatively undeformed rocks of the Appalachian Plateau and to the southeast by crystalline thrust sheets containing metasedimentary and metaigneous rocks ranging in age from late Precambrian to Early Devonian. A late Palaeozoic kinematic sequence derived for a part of this region indicates complex spatial and temporal relationships between folding, thrusting, and tectonic level of décollement. Earliest recognized (Carboniferous(?) or younger) compressional deformation in the foreland, observable within the southernmost thrust sheets in the foreland, is a set of large-scale, tight to isoclinal upright folds which preceded thrafing, and may represent the initial wave of compression in the foreland. Stage 2 involved emplacement of low-angle far-traveled thrust sheets which cut Lower Carboniferous rocks and cut progressively to lower tectonic levels to the southwest, terminating with arrival onto the foreland rocks of a low-grade crystalline nappe. Stage 3 involved redeformation of the stage 2 nappe pile by large-scale upright folds oriented approximately parallel to the former thrusts and believed to be related to ramping or imbrication from a deeper décollement in the foreland rocks below. Stage 4 involved renewed low-angle thrusting within the Piedmont rocks, emplacement of a high-grade metamorphic thrust sheet, and decapitation of stage 3 folds. Stage 5 is represented by large-scale cross-folding at a high angle to previous thrust boundaries and fold phases, and may be related to ramping or imbrication on deep décollements within the now mostly buried Ouachita orogen thrust belt to the southwest. Superposed upon these folds are stage 6 high-angle thrust faults with Appalachian trends representing the youngest (Late Carboniferous or younger, structures in the kinematic sequence.  相似文献   

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