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1.
The late Eocene to Neogene tectonic evolution of the Dinarides is characterised by shortening and orogen-parallel wrenching superposed on the late Cretaceous and Eocene double-vergent orogenic system. The Central Dinarides exposes NW-trending tectonic units, which were transported towards the Adria/Apulian microcontinent during late Cretaceous–Palaeogene times. These units were also affected by subsequent processes of late Palaeogene to Neogene shortening, Neogene extension and subsidence of intramontane sedimentary basins and Pliocene–Quaternary surface uplift and denudation. The intramontane basins likely relate to formation of the Pannonian basin. Major dextral SE-trending strike-slip faults are mostly parallel to boundaries of major tectonic units and suggest dextral orogen-parallel wrenching of the whole Central Dinarides during the Neogene indentation of the Apulian microplate into the Alps and back-arc type extension in the Pannonian basin. These fault systems have been evaluated with the standard palaeostress techniques. We report four palaeostress tensor groups, which are tentatively ordered in a succession from oldest to youngest: (1) Palaeostress tensor group 1 (D1) of likely late Eocene age indicates E–W shortening accommodated by reverse and strike-slip faults. (2) Palaeostress tensor group 2 (D2) comprises N/NW-trending dextral and W/WSW-trending sinistral strike-slip faults, as well as WNW-striking reverse faults. These indicate NE–SW contraction and subordinate NW–SE extension related to Oligocene to early Miocene shortening of the Dinaric orogenic wedge. (3) Palaeostress tensor group 3a (D3a) comprises mainly NW-trending normal faults, which indicate early/middle Miocene NE–SW extension related to syn-rift extension in the Pannonian basin. The subsequent palaeostress tensor group 3b (D3b) includes NE-trending, SE-dipping normal faults indicating NW–SE extension, which is likely related to further extension in the Pannonian basin. (4) Palaeostress tensor group 4 (D4) is characterised by mainly NW-trending dextral and NE-trending sinistral strike-slip faults. Together, with some E-trending reverse faults, they indicate roughly N–S shortening and dextral wrenching during late Miocene to Quaternary. This is partly consistent with the present-day kinematics, with motion of the Adriatic microplate constrained by GPS data and earthquake focal mechanisms. The north–north-westward motion and counterclockwise rotation of the Adriatic microplate significantly contribute the shortening and present-day wrenching in the Central Dinarides.  相似文献   

2.
Quaternary and directly underlying Late Miocene (Pannonian) outcrops were analysed by structural, tectono-morphologic and sedimentologic methods to describe the main fault directions, to separate mass movements from faulting and folding and to separate earthquake-induced sediment deformations from other (e.g. periglacial) effects in the Somogy Hills. This is a gentle hilly area elevated at 200–300 m above sea level, located immediately south of Lake Balaton, Hungary.

Quaternary outcrops showed several consistent directions of faulting, and co-depositional seismic activity. Three different Mohr-sets of faults/joints could be differentiated in Quaternary sediments. The three sets are considered Late Quaternary since all cut young loess sections and have morphological expressions.

On the basis of the microtectonic measurements and morphotectonic investigations, the following sequence of Quaternary events can be proposed:

1. A (W)NW–(E)SE compression and perpendicular extension would create E–W to WNW–ESE oriented right lateral, NNW–SSE to N–S oriented left lateral shear zones, and NW–SE striking normal faults. Some of these can be evidenced in morphology and among the individual fault measurements. Some reactivated faults might suggest that this field is a relatively older one, but fresh topographic elements suggest that this stress field might be operational sub-recently.

2. A second stress field with NNW–SSE extensional and ENE–WSW oriented compressional directions could be separated. This stress field could create NNE–SSW and NW–SE oriented shear fractures and ENE–WSW oriented conjugate normal faults. Flat thrusts giving ENE directed shear may also be active under this field.

3. A third stress field might be proposed with N–S compression and perpendicular extension directions. This would create NE–SW and NW–SE oriented shear fractures, which are observed in the measured fault data. It is remarkable that the NE–SW faults are all steep, subvertical, and give a very well defined fault set. Based on the fresh topographic expression, this stress field is also sub-recent.

The different sub-recent stress fields and related fault patterns might succeed each other or might alternate through time. The first and third deformations have fresh topographic expressions and cannot play synchronously. The observed features suggest a compressionally active neotectonics of the study area.  相似文献   


3.
《Geodinamica Acta》1999,12(2):113-132
The Aguilón Subbasin (NE Spain) was originated daring the Late Jurassic-Early Cretaceous rifting due to the action of large normal faults, probably inherited from Late Variscan fracturing. WNW-ESE normal faults limit two major troughs filled by continental deposits (Valanginian to Early Barremian). NE-SW faults control the location of subsidiary depocenters within these troughs. These basins were weakly inverted during the Tertiary with folds and thrusts striking E-W to WNW-ESE involving the Mesozoic-Tertiary cover with a maximum estimated shortening of about 12 %. Tertiary compression did not produce the total inversion of the Mesozoic basin but extensional structures are responsible for the location of major Tertiary folds. Shortening of the cover during the Tertiary involved both reactivation of some normal faults and development of folds and thrusts nucleated on basement extensional steps. The inversion style depends mainly on the occurrence and geometry of normal faults limiting the basin. Steep normal faults were not reactivated but acted as buttresses to the cover translation. Around these faults, affecting both basement and cover, folds and thrusts were nucleated due to the stress rise in front of major faults. Within the cover, the buttressing against normal faults consists of folding and faulting implying little shortening without development of ceavage or other evidence of internal deformation.  相似文献   

4.
《Geodinamica Acta》2003,16(2-6):131-147
Combining fieldwork and surface data, we have reconstructed the Cenozoic structural and tectonic evolution of the Northern Bresse. Analysis of drainage network geometry allowed to detect three major fault zones trending NE–SW, E–W and NW–SE, and smooth folds with NNE trending axes, all corroborated with shallow well data in the graben and fieldwork on edges. Cenozoic paleostress succession was determined through fault slip and calcite twin inversions, taking into account data of relative chronology. A N–S major compression, attributed to the Pyrenean orogenesis, has activated strike-slip faults trending NNE along the western edge and NE–SW in the graben. After a transitional minor E–W trending extension, the Oligocene WNW extension has structured the graben by a collapse along NNE to NE–SW normal faults. A local NNW extension closes this phase. The Alpine collision has led to an ENE compression at Early Miocene. The following WNW trending major compression has generated shallow deformation in Bresse, but no deformation along the western edge. The calculation of potential reactivation of pre-existing faults enables to propose a structural sketch map for this event, with a NE–SW trending transfer fault zone, inactivity of the NNE edge faults, and possibly large wavelength folding, which could explain the deposit agency and repartition of Miocene to Quaternary deformation.  相似文献   

5.
The “Nares Strait problem” represents a debate about the existence and magnitude of left-lateral movements along the proposed Wegener Fault within this seaway. Study of Palaeogene Eurekan tectonics at its shorelines could shed light on the kinematics of this fault. Palaeogene (Late Paleocene to Early Eocene) sediments are exposed at the northeastern coast of Ellesmere Island in the Judge Daly Promontory. They are preserved as elongate SW–NE striking fault-bounded basins cutting folded Early Paleozoic strata. The structures of the Palaeogene exposures are characterized by broad open synclines cut and displaced by steeply dipping strike-slip faults. Their fold axes strike NE–SW at an acute angle to the border faults indicating left-lateral transpression. Weak deformation in the interior of the outliers contrasts with intense shearing and fracturing adjacent to border faults. The degree of deformation of the Palaeogene strata varies markedly between the northwestern and southeastern border faults with the first being more intense. Structural geometry, orientation of subordinate folds and faults, the kinematics of faults, and fault-slip data suggest a multiple stage structural evolution during the Palaeogene Eurekan deformation: (1) The fault pattern on Judge Daly Promontory is result of left-lateral strike-slip faulting starting in Mid to Late Paleocene times. The Palaeogene Judge Daly basin formed in transtensional segments by pull-apart mechanism. Transpression during progressive strike-slip shearing gave rise to open folding of the Palaeogene deposits. (2) The faults were reactivated during SE-directed thrust tectonics in Mid Eocene times (chron 21). A strike-slip component during thrusting on the reactivated faults depends on the steepness of the fault segments and on their obliquity to the regional stress axes.Strike-slip displacement was partitioned to a number of sub-parallel faults on-shore and off-shore. Hence, large-scale lateral movements in the sum of 80–100 km or more could have been accommodated by a set of faults, each with displacements in the order of 10–30 km. The Wegener Fault as discrete plate boundary in Nares Strait is replaced by a bundle of faults located mainly onshore on the Judge Daly Promontory.  相似文献   

6.
We present the results of a thrust fault reactivation study that has been carried out using analogue (sandbox) and numerical modelling techniques. The basement of the Pannonian basin is built up of Cretaceous nappe piles. Reactivation of these compressional structures and connected weakness zones is one of the prime agents governing Miocene formation and Quaternary deformation of the basin system. However, reactivation on thrust fault planes (average dip of ca. 30°) in normal or transtensional stress regimes is a problematic process in terms of rock mechanics. The aim of the investigation was to analyse how the different stress regimes (extension or strike-slip), and the geometrical as well as the mechanical parameters (dip and strike of the faults, frictional coefficients) effect the reactivation potential of pre-existing faults.

Results of analogue modelling predict that thrust fault reactivation under pure extension is possible for fault dip angle larger than 45° with normal friction value (sand on sand) of the fault plane. By making the fault plane weaker, reactivation is possible down to 35° dip angle. These values are confirmed by the results of numerical modelling. Reactivation in transtensional manner can occur in a broad range of fault dip angle (from 35° to 20°) and strike angle (from 30° to 5° with respect to the direction of compression) when keeping the maximum horizontal stress magnitude approximately three times bigger than the vertical or the minimum horizontal stress values.

Our research focussed on two selected study areas in the Pannonian basin system: the Danube basin and the Derecske trough in its western and eastern part, respectively. Their Miocene tectonic evolution and their fault reactivation pattern show considerable differences. The dominance of pure extension in the Danube basin vs. strike-slip faulting (transtension) in the Derecske trough is interpreted as a consequence of their different geodynamic position in the evolving Pannonian basin system. In addition, orientation of the pre-existing thrust fault systems with respect to the Early to Middle Miocene paleostress fields had a major influence on reactivation kinematics.

As part of the collapsing east Alpine orogen, the area of the Danube basin was characterised by elevated topography and increased crustal thickness during the onset of rifting in the Pannonian basin. Consequently, an excess of gravitational potential energy resulted in extension (σv > σH) during Early Miocene basin formation. By the time topography and related crustal thickness variation relaxed (Middle Miocene), the stress field had rotated and the minimum horizontal stress axes (σh) became perpendicular to the main strike of the thrusts. The high topography and the rotation of σh could induce nearly pure extension (dip-slip faulting) along the pre-existing low-angle thrusts. On the contrary, the Derecske trough was situated near the Carpathian subduction belt, with lower crustal thickness and no pronounced topography. This resulted in much lower σv value than in the Danube basin. Moreover, the proximity of the retreating subduction slab provided low values of σh and the oblique orientation of the paleostress fields with respect to the master faults of the trough. This led to the dominance of strike-slip faulting in combination with extension and basin subsidence (transtension).  相似文献   


7.
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   

8.
Several models of basin inversion described in the literature are tested in a study of Triassic and Early Jurassic strata exposed along the southern margin of the Bristol Channel Basin in Somerset, England that has been exhumed by <3 km. Two key features of the superbly exposed normal faults are that they formed at several times during basin evolution—not during Triassic to Early Jurassic growth, but during Late Jurassic rifting, and during and after inversion; and that >95% of them are still in net extension, despite widespread kinematic evidence for reverse reactivation. When coupled with the general absence of thin-skinned thrusts and the widespread occurrence of regional contractional folds, it appears that none of three main inversion models—the fault-reactivation model, the thin-skinned model and the buttress model—are by themselves applicable. We erect a new model of basin inversion, the distributed deformation model, which consists of three stages of basin inversion. Stage one involved early partial reactivation of large-displacement steep normal faults. Stage two was dominated by folding, wherein fault blocks underwent oblique (non-coaxial) shortening by map scale folding, accompanied by formation of outer arc normal faults, minor cleavage and neoformed thrusts. Stage three involved reverse reactivation of outer arc normal faults and activation of oblique and strike-slip faults that partitioned deformation into compartments.  相似文献   

9.
Processing of gravity and magnetic maps shows that the basement of the Upper Rhine Graben area is characterized by a series of NE–SW trending discontinuities and elongated structures, identified in outcrops in the Vosges, Black Forest, and the Odenwald Mountains. They form a 40 km wide, N30–40° striking, sinistral wrench-zone that, in the Visean, shifted the Variscan and pre-Variscan structures by at least 43 km to the NE. Wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340–325 Ma. The sub-vertical, NE–SW trending discontinuities in the basement acted as zones of weakness, susceptible to reactivation by subsequent tectonism. The first reactivation, marked by mineralizations and palaeomagnetic overprinting along NE–SW faults of the Vosges Mountains, results from the Liassic NW–SE extension contemporaneous with the break-up of Pangea. The major reactivation occurred during the Late Eocene N–S compression and the Early-Middle Oligocene E–W extension. The NE–SW striking basement discontinuities were successively reactivated as sinistral strike-slip faults, and as oblique normal faults. Elongated depocenters appear to form in association with reactivated Variscan wrench faults. Some of the recent earthquakes are located on NE–SW striking Variscan fault zones, and show sinistral strike-slip focal mechanisms with the same direction, suggesting also present reactivation.  相似文献   

10.
The study provides a regional seismic interpretation and mapping of the Mesozoic and Cenozoic succession of the Lusitanian Basin and the shelf and slope area off Portugal. The seismic study is compared with previous studies of the Lusitanian Basin. From the Late Triassic to the Cretaceous the study area experienced four rift phases and intermittent periods of tectonic quiescence. The Triassic rifting was concentrated in the central part of the Lusitanian Basin and in the southernmost part of the study area, both as symmetrical grabens and half-grabens. The evolution of half-grabens was particularly prominent in the south. The Triassic fault-controlled subsidence ceased during the latest Late Triassic and was succeeded by regional subsidence during the early Early Jurassic (Hettangian) when deposition of evaporites took place. A second rift phase was initiated in the Early Jurassic, most likely during the Sinemurian–Pliensbachian. This resulted in minor salt movements along the most prominent faults. The second phase was concentrated to the area south of the Nazare Fault Zone and resulted here in the accumulation of a thick Sinemurian–Callovian succession. Following a major hiatus, probably as a result of the opening of the Central Atlantic, resumed deposition occurred during the Late Jurassic. Evidence for Late Jurassic fault-controlled subsidence is widespread over the whole basin. The pattern of Late Jurassic subsidence appears to change across the Nazare Fault Zone. North of the Nazare Fault, fault-controlled subsidence occurred mainly along NNW–SSE-trending faults and to the south of this fault zone a NNE–SSW fault pattern seems to dominate. The Oxfordian rift phase is testified in onlapping of the Oxfordian succession on salt pillows which formed in association with fault activity. The fourth and final rift phase was in the latest Late Jurassic or earliest Early Cretaceous. The Jurassic extensional tectonism resulted in triggering of salt movement and the development of salt structures along fault zones. However, only salt pillow development can be demonstrated. The extensional tectonics ceased during the Early Cretaceous. During most of the Cretaceous, regional subsidence occurred, resulting in the deposition of a uniform Lower and Upper Cretaceous succession. Marked inversion of former normal faults, particularly along NE–SW-trending faults, and development of salt diapirs occurred during the Middle Miocene, probably followed by tectonic pulses during the Late Miocene to present. The inversion was most prominent in the central and southern parts of the study area. In between these two areas affected by structural inversion, fault-controlled subsidence resulted in the formation of the Cenozoic Lower Tagus Basin. Northwest of the Nazare Fault Zone the effect of the compressional tectonic regime quickly dies out and extensional tectonic environment seems to have prevailed. The Miocene compressional stress was mainly oriented NW–SE shifting to more N–S in the southern part.  相似文献   

11.
Late Cenozoic transtensional fault belt was discovered on Shajingzi fault belt, NW boundary of the Awati Sag in the northwestern Tarim Basin. And numerous Quaternary normal faults were discovered on Aqia and Tumuxiuke fault belts, SW boundary of Awati. This discovery reveals Quaternary normal fault activity in the Tarim Basin for the first time. It is also a new discovery in the southern flank of Tianshan Mountains. Shajingzi transtensional fault belt is made up of numerous, small normal faults. Horizontally, the normal faults are arranged in right-step, en echelon patterns along the preexisting Shajingzi basement fault, forming a sinistral transtensional normal fault belt. In profile, they cut through the Paleozoic to the mid-Quaternary and combine to form negative flower structures. The Late Cenozoic normal faults on the SW boundary of Awati Sag were distributed mainly in the uplift side of the preexisting Aqia and Tumuxiuke basement-involved faults, and combined to form small horst and graben structures in profile. Based on the intensive seismic interpretation, careful fault mapping, and growth index analysis, we conclude that the normal fault activity of Shajingzi transtensional fault belt began from Late Pliocene and ceased in Late Pleistocene (mid-Quaternary). And the normal faulting on the SW boundary of Awati Sag began from the very beginning of Quaternary and ceased in Pleistocene. The normal faulting on Awati’s SW boundary began a little later than those on the NW boundary. The origin of Shajingzi transtensional normal fault belt was due to the left-lateral strike-slip occurred in the southern flank of Tianshan, and then, due to the eastward escape of the Awati block, a tensional stress developed the normal faults on its SW boundary.  相似文献   

12.
We constructed a geological map, a 3D model and cross-sections, carried out a structural analysis, determined the stress fields and tectonic transport vectors, restored a cross section and performed a subsidence analysis to unravel the kinematic evolution of the NE emerged portion of the Asturian Basin (NW Iberian Peninsula), where Jurassic rocks crop out. The major folds run NW-SE, normal faults exhibit three dominant orientations: NW-SE, NE-SW and E-W, and thrusts display E-W strikes. After Upper Triassic-Lower Jurassic thermal subsidence, Middle Jurassic doming occurred, accompanied by normal faulting, high heat flow and basin uplift, followed by Upper Jurassic high-rate basin subsidence. Another extensional event, possibly during Late Jurassic-Early Cretaceous, caused an increment in the normal faults displacement. A contractional event, probably of Cenozoic age, led to selective and irregularly distributed buttressing and fault reactivation as reverse or strike-slip faults, and folding and/or offset of some previous faults by new generation folds and thrusts. The Middle Jurassic event could be a precursor of the Bay of Biscay and North Atlantic opening that occurred from Late Jurassic to Early Cretaceous, whereas the Cenozoic event would be responsible for the Pyrenean and Cantabrian ranges and the partial closure of the Bay of Biscay.  相似文献   

13.
Northwest Iran is dominated by two main sets of active strike slip faults that accommodate oblique convergence between the Arabian and Iranian Plates. The best known are the right-lateral North-Tabriz, Qoshadagh, Maragheh and Zagros (Main Recent) strike slip Faults. This work reports that these dominant NW–SE to E–W striking faults are conjugate to smaller, NNE–SSW striking, left-lateral faults with minor dip slip component. All of these active faults displace Precambrian rock units, which suggests that they root in the crystalline basement of the NW Iranian microcontinent. Coulomb stress variance during co-seismic rupture along one of these faults may cause reactivation of the other faults. The minor set of left-lateral fault is therefore important to introduce in seismic risk assessment.  相似文献   

14.
Analysis of Neogene-Quaternary structures from seismic lines, surface measurements and geological-mapping is presented from the border zone between the Alps, Dinarides and Pannonian Basin. First, Early Miocene extension was possibly characterised by ENE directed extension. It was partly synchronous with NW-SE shortening. Second, Middle Miocene extension was possibly characterised by NW-SE to WNW-ESE directed extension. Again, this event was followed by a new generation of thrusts related to end-Sarmatian shortening. The last, Late Miocene E-W to WNW-ESE directed extension was followed by a final shortening that created major, map-scale folds, basement pop-ups and inverted former basins. Geometry, onlap and thickness patterns of the youngest syn-tectonic basin fill indicate that this last, N-S to NW-SE directed shortening started in Late Pontian and continued up to the present time. When taking into account the wider surrounding area, it seems that the structures related to this latest shortening are arranged in often perpendicular directions, centred at the eastern end of the Periadriatic lineament. To explain this fan-like pattern of synchronous shortenings a kinematic model is proposed combining counter-clockwise rotation with north- or northwestward shift of the Dinaridic block with respect to the more stable Alpine buttress.  相似文献   

15.
Three-dimensional modelling tools are used with structural and palaeomagnetic analysis to constrain the tectonic history of part of the Dauphiné zone (external Western Alps). Four compressive events are identified, three of them being older than the latest Oligocene. Deformation D1 consists of W–SW directed folds in the Mesozoic cover of the study area. This event, better recorded in the central and southern Pelvoux massif, could be of Eocene age or older. Deformation D2 induced N-NW-oriented basement thrusting and affected the whole southern Dauphiné basement massifs south of the study area. The main compressional event in the study area (D3) was WNW oriented and occurred before 24 Ma under a thick tectonic load probably of Penninic nappes. The D2-D3 shift corresponds to a rapid transition from northward propagation of the Alpine collision directly driven by Africa-Europe convergence, to the onset of westward escape into the Western Alpine arc. This Oligocene change in the collisional regime is recorded in the whole Alpine realm, and led to the activation of the Insubric line. The last event (D4) is late Miocene in age and coeval with the final uplift of the Grandes Rousses and Belledonne external massifs. It produced strike-slip faulting and local rotations that significantly deformed earlier Alpine folds and thrusts, Tethyan fault blocks and Hercynian structures. 3D modelling of an initially horizontal surface, the interface between basement and Mesozoic cover, highlights large-scale basement involved asymmetric folding that is also detected using structural analysis. Both, Jurassic block faulting and basement fold-and-thrust shortening were strongly dependent on the orientation of Tethyan extension and Alpine shortening relative to the late Hercynian fabric. The latter’s reactivation in response to oblique Jurassic extension produced an en-échelon syn-rift fault pattern, best developed in the western, strongly foliated basement units. Its Alpine reactivation occurred with maximum efficiency during the early stages of lateral escape, with tectonic transport in the overlying units being sub-perpendicular to it.  相似文献   

16.
The interplay between the emplacement of crustal blocks (e.g. “ALCAPA”, “Tisza”, “Dacia”) and subduction retreat is a key issue for understanding the Miocene tectonic history of the Carpathians. Coeval thrusting and basin formation is linked by transfer zones, such as the Mid-Hungarian fault zone, which seperates ALCAPA from Tisza-Dacia. The presented study provides new kinematic data from this transfer zone. Early Burdigalian (20.5 to ∼18.5 Ma) SE-directed thrusting of the easternmost tip of ALCAPA (Pienides), over Tisza-Dacia is linked to movements along the Mid-Hungarian fault zone and the Periadriatic line, accommodating the lateral extrusion of ALCAPA. Minor Late Burdigalian (∼18.5 to 16 Ma) NE-SW extension is interpreted as related to back-arc extension. Post Burdigalian (post-16 Ma) NE–SW shortening and NW–SE extension correlate with “soft collision” of Tisza-Dacia with the European foreland coupled with southward migration of active subduction. During this stage the Bogdan-Voda and Dragos-Voda faults were kinematically linked to the Mid-Hungarian fault zone. Sinistral transpression (16 to 12 Ma) at the Bogdan-Voda fault was followed by sinistral transtension (12–10 Ma) along the coupled Bogdan-Dragos-Voda fault system. During the transtensional stage left-lateral offset was reduced eastwards by SW trending normal faults, the fault system finally terminating in an extensional horse-tail splay.  相似文献   

17.
The east margin of the Siberian craton is a typical passive margin with a thick succession of sedimentary rocks ranging in age from Mesoproterozoic to Tertiary. Several zones with distinct structural styles are recognized and reflect an eastward-migrating depocenter. Mesozoic orogeny was preceded by several Mesoproterozoic to Paleozoic tectonic events. In the South Verkhoyansk, the most intense pre-Mesozoic event, 1000–950 Ma rifting, affected the margin of the Siberian craton and formed half-graben basins, bounded by listric normal faults. Neoproterozoic compressional structures occurred locally, whereas extensional structures, related to latest Neoproterozoic–early Paleozoic rifting events, have yet to be identified. Devonian rifting is recognized throughout the eastern margin of the Siberian craton and is represented by numerous normal faults and local half-graben basins.Estimated shortening associated with Mesozoic compression shows that the inner parts of ancient rifts are now hidden beneath late Paleozoic–Mesozoic siliciclastics of the Verkhoyansk Complex and that only the outer parts are exposed in frontal ranges of the Verkhoyansk thrust-and-fold belt. Mesoproterozoic to Paleozoic structures had various impacts on the Mesozoic compressional structures. Rifting at 1000–950 Ma formed extensional detachment and normal faults that were reactivated as thrusts characteristic of the Verkhoyansk foreland. Younger Neoproterozoic compressional structures do not display any evidence for Mesozoic reactivation. Several initially east-dipping Late Devonian normal faults were passively rotated during Mesozoic orogenesis and are now recognized as west-dipping thrusts, but without significant reactivation displacement along fault surfaces.  相似文献   

18.
The Abitibi belt is one of the largest and most extensively studied Late Archean greenstone belts. The structural geology of the Abitibi belt consists of one generation of upright to slightly overturned, doubly plunging first-order folds with half-wavelengths of 20–60 km, and E–W-striking, steeply dipping fault zones that are parallel to the fold limbs. Two of the main fault zones are continuous for hundreds of kilometers. Previous tectonic models for the Abitibi belt interpret the fault zones to have formed as extensional growth faults bounding a volcanic-sedimentary basin, which were reactivated as thrusts during subsequent crustal shortening. Other models propose that the fault zones represent tectonic sutures, implying that the Abitibi belt is a collage of exotic terranes. However, distinct geological terranes have not been geologically demonstrated. We propose a new detachment fold model for the deformational history of the southern Abitibi belt, in Ontario, that explains the formation of the fault zones during the single, well-documented folding event that deformed the entire region. The internal structure of the fault zones, documented here with emphasis on the Porcupine–Destor fault zone, consists of isoclinally folded, strongly schistose, highly metamorphosed rock, cross-cut by numerous fault segments. We interpret that the upper crust (greenstones) was folded above a proposed detachment in the lower part of the volcanic stratigraphy. The fault zones would be, in essence, highly evolved detachment anticlines. Ultramafic metavolcanic rock that crops out within the fault zones would represent material from the detachment horizon that was emplaced in the cores of the detachment anticlines. The numerous segments that make up the mapped fault zones would be linked faults that formed within the isoclinal detachment anticlines to accommodate folding of the rheologically complex greenstones. The detachment fold model is compared to the results of analogue experiments designed to investigate crustal-scale folding, using viscous and frictional materials. Detachment folds are produced in the brittle upper crustal analogue on the limbs of folds formed in the ductile middle and lower crust analogues. The experimentally produced structures scale to the structures in the study area and indicate the detachment fold model for the southern Abitibi is mechanically viable.  相似文献   

19.
During Eocene to Early Quaternary period, three compressive tectonic phases are recognized in Northeast Tunisia: a NW–SE to north–south phase during the Late Eocene, a N120-to-N140 phase in the Late Miocene, and a NW–SE to north–south phase in the Plio-Early Quaternary. The first Eocene phase has built NE–SW folds and remobilised east–west-to-N120 and NE–SW faults with a reverse component. The second Miocene phase is characterized by east–west-to-N120 faults with a normal component and NE–SW folds. The third phase occurred during the Plio-Early Quaternary has edified NE–SW folds associated with east–west-to-N120 dextral reverse strike-slip faults and NE–SW faults with a reverse component. To cite this article: H. Mzali, H. Zouari, C. R. Geoscience 338 (2006).  相似文献   

20.
Dextral-slip in the Nyainqentangiha region of Tibet resulted in oblique underthrusting and granite generation in the Early to Middle Miocene, but by the end of the epoch uplift and extensional faulting dominated. The east-west dextral-slip Gangdise fault system merges eastward into the northeast-trending, southeast-dipping Nyainqentangiha thrust system that swings eastward farther north into the dextral-slip North Damxung shear zone and Jiali faults. These faults were took shape by the Early Miocene, and the large Nyainqentangiha granitic batholith formed along the thrust system in 18.3-11.0 Ma as the western block drove under the eastern one. The dextral-slip movement ended at -11 Ma and the batholith rose, as marked by gravitational shearing at 8.6-8.3 Ma, and a new fault system developed. Northwest-trending dextral-slip faults formed to the northwest of the raisen batholith, whereas the northeast-trending South Damxung thrust faults with some sinistral-slip formed to the southeast. The latter are replaced farther to the east by the west-northwest-trending Lhunzhub thrust faults with dextral-slip. This relatively local uplift that left adjacent Eocene and Miocene deposits preserved was followed by a regional uplift and the initiation of a system of generally north-south grabens in the Late Miocene at -6.5 Ma. The regional uplift of the southern Tibetan Plateau thus appears to have occurred between 8.3 Ma and 6.5 Ma. The Gulu, Damxung-Yangbajain and Angan graben systems that pass east of the Nyainqentangiha Mountains are locally controlled by the earlier northeast-trending faults. These grabens dominate the subsequent tectonic movement and are still very active as northwest-trending dextral-slip faults northwest of the mountains. The Miocene is a time of great tectonic change that ushered in the modern tectonic regime.  相似文献   

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