首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Detailed mapping and structural analysis of three large-scale culminations (Sumeini and Asjudi half-windows and Haybi-Hawasina window) in the Oman Mountains shows a considerably more complex history of deformation than a simple foreland (or downward) sequence of thrust development. Early thrusting processes tended to create a regular stacking order of imbricate slices and major thrust sheets, complying with the “rules’ of thrust propagation, assembled progressively downwards and forwards in the direction of translation. ‘Out-of-sequence’ thrusts can also be demonstrated in places by truncation of footwall structures (folds, imbricate slices, etc.), gross strain differences between thrust sheets, downward-facing structures in footwall units and elimination of thrust sheets beneath. Late stage thrusts frequently cut up-section through the previously assembled stack putting previously younger, lower thrust sheets over previously older, higher ones. Many of the culminations in the northern and central Oman Mountains were formed by ramping associated with this late-stage leap-frog rethrusting event.  相似文献   

2.
The inter-relationships between the exact footwall geometry and the rheology of thrust sheets are investigated. Deviations in the thrust fault surface from an ideal plane will induce a local heterogeneous deformation. The resulting deformation processes depend upon the rate of thrust sheet displacement, the geometry of the feature causing heterogeneous flow, the deformation conditions and the lithologies involved. Two classes of features are particularly important in causing heterogeneous deformation in thrust sheets. The first features are small perturbations on bedding planes which may be inherited sedimentary structures or produced during layer-parallel shortening; the second class of features are ramps, where the thrust sheet climbs up the stratigraphic section. Displacement over these features causes repeated, cyclic straining in the hanging-wall during movement. The strain rates associated with deformation at perturbations, ramps of different geometries and different displacement rates are estimated and used to discuss the influence of footwall geometry on the structural evolution of a thrust sheet. Particular attention is given to the range of fault rocks and deformation microstructures preserved after movement over a footwall with a complex geometry. Perturbations are suggested to be important in the localization of ramps, either because they create ‘sticking points’ near the fault tip during propagation or because they induce eventual failure in the hanging-wall after the movement over a number of these features raises the accumulated damage to a critical level. Analysis of the influence of the exact geometry of ramps on deformation processes during displacement leads to two important conclusions. Firstly, the exact geometry of ramps (i.e. the maximum dip angle and the straining distance from a flat to this maximum angle) may be used to estimate a maximum displacement rate of the thrust sheet. Secondly, the listric geometry of ramps may be an equilibrium shape adjusted to the displacement rate and the rheology of the hanging-wall. Adjustments towards the final geometry may involve the generation of shortcuts on either hanging- or footwall which reduce the imposed deformation rate in the hanging-wall during displacement.  相似文献   

3.
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   

4.
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   

5.
We demonstrate that increasing erosion during the kinematic evolution of a thrust wedge will lead to out‐of‐sequence thrusting as a result of backwards critical taper movement. In‐sequence thrusting in the Subalpine German Molasse Basin built a critical‐tapered foreland Coulomb thrust wedge. Later, out‐of‐sequence thrusts dissected all but the frontal duplex stacks. The footwall/hangingwall relation visible on seismic data proves the out‐of‐sequence nature of the latest thrusting stage. Establishing a stable drainage system leads to increased erosion in elevated areas of the thrust wedge, resulting in flattening of the critical wedge. In order to keep its predefined angle, the critical wedge repositions and the tip of the taper moves towards the hinterland. Thus, thrusting will also reposition and move towards the hinterland.  相似文献   

6.
The Lewis thrust sheet of the southern Canadian Rocky Mountains contains many spectacular examples of small-scale duplex structures. This paper presents the results of a detailed analysis of such structures found in the Mississippian carbonates of the Banff Formation at Crowsnest Pass, southwestern Alberta.Foreland dipping, hinterland dipping and antiformal stacked duplexes are found in the hangingwall of the Lewis thrust. Out-of-sequence thrusts, back thrusts and folds that push out of the plane of the cross-section, termed lateral lobes, give rise to complex internal geometries. Dominant slip vectors are towards 080–090° but the complex fault geometries have generated significant variations in slip away from this direction. The duplex structures occur as discrete thrust fault-bounded packages with each package having different slip vectors. The panels above and below the duplex structures show consistent slip vectors towards 080–090° whereas the duplexes exhibit a wide scatter of slip vectors from 350–160°. The stacking of duplexes with many horses can be likened to the stacking of many inverted soup bowls, herein termed turtle back structures, and will involve a wide scatter of slip directions, particularly if the horses are of limited lateral extent. Such a stacking mechanism involving out-of-section movement invalidates the assumption of two-dimensional plane strain in the plane of the cross-section that contains the regional tectonic transport direction. Correctly balanced cross-sections cannot be constructed through such stacked duplex structures as described in this paper.  相似文献   

7.
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   

8.
Field work in the South-Central Pyrenees suggests that omission contacts (i.e. younger over older rocks) occur at the base of the Cadí unit (Cadí thrust), and pass laterally into thrusts. This change occurs across tear faults which are present in the hangingwall of the Cadí thrust sheet and which controlled the deposition of Upper Cretaceous sediments (Adraén formation). Detailed mapping in the contact area between the Nogueres and Cadí units has shown that the actual thrust geometry in the study area is controlled by preexisting normal and transfer faults which developed in an already compressional context. Lateral ramps or tear faults develop depending on the angle between the pre-existing extensional transfer fault and the thrust transport direction.  相似文献   

9.
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   

10.
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   

11.
The structure of the Chilean Frontal Cordillera, located over the Central Andes flat-slab subduction segment (27°–28.5°S), is characterized by a thick-skinned deformation, affecting both the pre-rift basement and the Mesozoic and Cenozoic infill of the NNE-SSW Lautaro and Lagunillas Basins, which were developed during the Pangea-Gondwana break-up. The compressive deformation show a complex interaction between Mesozoic rift structures and thrust systems, affecting a suite of Permo-Triassic (258–245 Ma) granitic blocks. We used a combination of geological mapping, new structural data, balanced and restored cross sections and geochronological data to investigate the geometry and kinematics of the Andean thick-skinned thrust systems of the region. The thrust systems include double-vergent thick-skinned thrust faults, basement-cored anticlines and minor thin-skinned thrusts and folds. The presence of Triassic and Jurassic syn-rift successions along the hanging wall and footwall of the basement thrust faults are keys to suggest that the current structural framework of the region should be associated with the shortening of previous Mesozoic half grabens. Based on this interpretation, we propose a deformation mechanism characterized by the tectonic inversion of rift-related faults and the propagation of basement ramps that fold and cut both, the early normal faults and the basement highs. New U–Pb ages obtained from synorogenic deposits (Quebrada Seca and Doña Ana formations) indicate at least three important compressive pulses. A first pulse at ∼80 Ma (Late Cretaceous), a second pulse related to the K-T phase of Andean deformation and, finally, a third pulse that occurred during the lower Miocene.  相似文献   

12.

From the early Late Permian onwards, the northeastern part of the Sydney Basin, New South Wales, (encompassing the Hunter Coalfield) developed as a foreland basin to the rising New England Orogen lying to the east and northeast. Structurally, Permian rocks in the Hunter Coalfield lie in the frontal part of a foreland fold‐thrust belt that propagated westwards from the adjacent New England Orogen. Thrust faults and folds are common in the inner part of the Sydney Basin. Small‐scale thrusts are restricted to individual stratigraphic units (with a major ‘upper decollement horizon’ occurring in the mechanically weak Mulbring Siltstone), but major thrusts are inferred to sole into a floor thrust at a poorly constrained depth of approximately 3 km. Folds appear to have formed mainly as hangingwall anticlines above these splaying thrust faults. Other folds formed as flat‐topped anticlines developed above ramps in that floor thrust, as intervening synclines ahead of such ramp anticlines, or as decollement folds. These contractional structures were overprinted by extensional faults developed during compressional deformation or afterwards during post‐thrusting relaxation and/or subsequent extension. The southern part of the Hunter Coalfield (and the Newcastle Coalfield to the east) occupies a structural recess in the western margin of the New England Orogen and its offshore continuation, the Currarong Orogen. Rocks in this recess underwent a two‐stage deformation history. West‐northwest‐trending stage one structures such as the southern part of the Hunter Thrust and the Hunter River Transverse Zone (a reactivated syndepositional transfer fault) developed in response to maximum regional compression from the east‐northeast. These were followed by stage two folds and thrusts oriented north‐south and developed from maximum compression oriented east‐west. The Hunter Thrust itself was folded by these later folds, and the Hunter River Transverse Zone underwent strike‐slip reactivation.  相似文献   

13.
丘里塔格背斜带是库车再生前陆褶皱逆冲带的前锋构造带。依据各段不同的构造特点,沿走向自东向西可分为东丘里塔格段、库车塔吾段、南、北丘里塔格段和亚克里克—阿瓦特段。其中东丘里塔格段和库车塔吾段以浅部膝折褶皱或断层传播褶皱与深部的断层转折褶皱相叠置为特点。而南、北丘里塔格段和亚克里克—阿瓦特段则以发育膝折褶皱、断层传播褶皱、断层转折褶皱以及相伴生的纵向走滑逆冲断层为特点。该构造带有良好的油气前景,寻找深部完整的断层转折褶皱背斜圈闭以及纵向走滑逆冲断层下盘的圈闭是重要的勘探方向。  相似文献   

14.
The Mesozoic and Cenozoic rocks exposed in the Arve valley region of the External French Alps are used to assess the role of early intrabasinal faults on later thrust fault evolution. The early intrabasinal faults produced at some time from latest Upper Cretaceous to Tertiary strike parallel or subparallel to later Neo-Alpine thrusts. Where early faults dip away from the thrusts they are generally cut through and occasionally are overturned during this process. In one example extreme overturning has allowed partial reactivation. Early faults dipping in the same direction as thrusts may: a) be reactivated b) initiate ramping of the thrust ahead of the preexisting fault c) be cut through by the thrust d) cause pinning of the thrust at the footwall of the fault and folding against the fault as displacement continues (buttressing). From this work it is evident that intrabasinal faults exerted a major influence on the distribution of mechanical heterogeneities. These heterogeneities include variations of stratigraphic thickness and type across faults, fault-related unconformities and the presence of the fault itself. During the period of contraction such features strongly controlled the development of the stress field produced ahead of an advancing thrust and hence influenced the position of thrust fault propagation within the stratigraphy.  相似文献   

15.
The Umbria-Marche-Sabina foreland fold and thrust belt (Northern Apennines, Italy) provides excellent test-cases for the hypothesis of ancient syndepositional structural features controlling thrust ramp development. The sedimentary cover, Late Triassic to Miocene in age, is made of platform and pelagic carbonates, whose deposition was controlled by significant synsedimentary extension. Normal faulting, mainly during the Jurassic and the Late Cretaceous-Palaeogene, determined sensible lateral thickness variations within the relative sequences. By late Miocene the sedimentary cover was detached from its basement along a mainly evaporitic horizon, and was deformed by means of eastward-verging folds and thrusts.
In order to locate the points where thrust ramps branch-off the basal detachment, both line-length and equal-area techniques were used in the construction of a balanced cross-section through three major fault-related folds in southeastern Umbria. The nucleation of thrust ramps was controlled by the occurrence of Jurassic and Cretaceous-Palaeogene synsedimentary normal faults. These interrupted the lateral continuity of the evaporitic unit (the Late Triassic Anidriti di Burano Fm.) at the base of the sedimentary cover, and acted as obstacles to the eastward propagation of the thrust system, giving rise to major folds which originated from tip-line folding processes.
Therefore, the inferred relationships between ancient normal faults and late thrusts indicate that synsedimentary tectonic structures and the related lateral stratigraphic variations can be envisaged as mechanically important perturbations, which effectively control the nucleation and development of thrust ramps.  相似文献   

16.
In the internal part of the Umbro-Marchean-Romagnan Apennines, the foredeep clastic wedge constituting the Neogene part of the sedimentary cover is completely detached from the underlying Mesozoic–Palaeogene succession. The resulting (Umbro-Romagnan) parautochthon consists of tectonostratigraphic units with a general geometry of broad synclinal blocks separated by narrow faulted anticlines.
Thrust-related structures observed in the field require thrust ramp propagation to have occurred within already folded rocks; therefore, they cannot be restored using simple fault-bend fold or fault-propagation folding models. Evidence for a passive fold origin in the studied rocks suggests that an early detachment folding episode preceded ramp propagation. The latter was facilitated by the enhanced thickness of incompetent material in the cores of detachment anticlines, which became the preferential sites where thrust ramps cut up-section. Depending on the trajectory of such thrust ramps, different types of fault-related structures could develop. Hanging-wall anticlines which give way to monoclinal structures higher up in the section are associated with listric thrust ramps, whereas hanging wall monoclines approximately parallel to the underlying fault surface are associated with straight-trajectory ramps.
This kinematic evolution, which occurred partly during syn-depositional compression, also accounts for the observed lithofacies distribution. The latter reflects an early differentiation of the foredeep trough into sub-basins that are progressively younger towards the foreland. The detachment anticlines that originally bounded such sub-basins were the site of later thrust propagation, leading to a tectonic juxtaposition of different tectonostratigraphic units consisting of broad NW-SE elongate synclinal blocks.  相似文献   

17.
An extensive dataset of vitrinite reflectance, FTIR parameters on organic matter, illite content in mixed layers illite‐smectite, apatite fission tracks and U‐Th/He dating has been used to reconstruct the stepwise propagation of the Eastern Sicily fold‐and‐thrust belt during Late Palaeogene and Neogene times. The results indicate that the fold‐and‐thrust belt is divisible into two levels of thermal maturity. These levels consist of a less evolved level of thermal maturity that records limited sedimentary burial and minor heating, and a more evolved level of thermal maturity that indicates tectonic burial and exhumation at different times. Deformation and exhumation of shallowly buried units are linked to wedge forward propagation by low‐angle thrusts, whereas the evolution of deeply buried units is associated with tectonic imbrications by duplex formation and steep thrusts. The two tectonic styles alternate during evolution of the fold‐and‐thrust belt under low erosion rates.  相似文献   

18.
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   

19.
Recent works suggest Proterozoic plate convergence along the southeastern margin of India which led to amalgamation of the high grade Eastern Ghats belt (EGB) and adjoining fold-and-thrust belts to the East Dhrawar craton. Two major thrusts namely the Vellikonda thrust at the western margin of the Nellore Schist belt (NSB) and the Maidukuru thrust at the western margin of the Nallamalai fold belt (NFB) accommodate significant upper crustal shortening, which is indicated by juxtaposition of geological terranes with distinct tectonostratigraphy, varying deformation intensity, structural styles and metamorphic grade. Kinematic analysis of structures and fabric of the fault zone rocks in these intracontinental thrust zones and the hanging wall and footwall rocks suggest spatially heterogeneous partitioning of strain into various combinations of E-W shortening, top-to-west shear on stratum parallel subhorizontal detachments or on easterly dipping thrusts, and a strike slip component. Although relatively less prominent than the other two components of the strain triangle, non-orthogonal slickenfibres associated with flexural slip folds and mylonitic foliation-stretching lineation orientation geometry within the arcuate NSB and NFB indicate left lateral strike slip subparallel to the overall N-S trend. On the whole an inclined transpression is inferred to have controlled the spatially heterogeneous development of thrust related fabric in the terrane between the Eastern Ghats belt south of the Godavari graben and the East Dharwar craton.  相似文献   

20.
 An important detachment is described in the allochthonous Ordenes Complex, in the NW Iberian Massif, and its meaning is related to the kinematics of contemporaneous convergent structures. The Corredoiras Detachment (CD) separates a hangingwall unit, characterised by a medium-pressure metamorphic gradient, from a footwall high-pressure and high-temperature unit and an underlying ophiolitic unit. An associated ductile shear zone, nearly 2000 m thick, developed in the lower part of the hangingwall unit, where the Corredoiras Orthogneiss, a Lower Ordovician metagranite, was progressively transformed into augengneisses, mylonitic and ultramylonitic gneisses. The attitude of the stretching and mineral lineation in the mylonites varies due to late refolding at map scale, but the sense of movement can be estimated, being roughly top to the SE. According to crosscutting relationships, the CD developed subsequent to the thrusting of the high-pressure/high-temperature unit onto the ophiolitic unit, and prior to younger extensional detachments, upright folding and strike-slip tectonics. The geometric relationships of the CD with the previous structures in the footwall unit, the subtractive character of the metamorphic gap between its hangingwall and footwall, and the available isotopic data suggest that the CD is an early Variscan, ductile extensional detachment, the movement of which was roughly simultaneous with the onset of thrusting of the allochthonous complexes over their relative autochthon. Received: 17 November 1998 / Accepted: 4 April 1999  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号