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1.
The Mt Isa Rift Event is a Palaeoproterozoic intracontinental extension event that defines the beginning of sedimentation into the Isa Superbasin in the Western Fold Belt, Mt Isa terrane. In the mildly deformed Fiery Creek Dome region, on the northwest flanks of the Mt Isa Rift, elements of the Mt Isa Rift Event rift architecture are preserved without being intensely overprinted by later deformation. In this region two discrete generations of northwest‐dipping normal faults have been identified. Early generation normal faults were active during the deposition of fluvial and immature conglomerate and sandstone of the Bigie Formation. Renewed rifting and the development of late‐generation normal faults occurred during deposition of shallow‐marine sandstone and siltstone of the lower Gunpowder Creek Formation. Differential uplift between tilt blocks formed an array of spatially and temporally discontinuous synrift unconformities on the crests of uplifted tilt blocks. Applying the domino model yields ～28% crustal extension for the entire Mt Isa Rift Event. Northwest‐striking transverse faults facilitated differential displacement along normal faults and formed boundaries to normal fault segments, creating smaller depositional compartments along half‐graben axes. Three large domes were formed during laccolith emplacement. These domes produced palaeogeographical highs that divided the region into sub‐basins and were a source for the coarse fluvial synrift sequences deposited during the early Mt Isa Rift Event. The basin architecture in the Fiery Creek Dome region is consistent with northwest‐southeast‐directed extension.  相似文献   

2.
In this paper we assess two competing tectonic models for the development of the Isa Superbasin (ca 1725–1590 Ma) in the Western Fold Belt of the Mt Isa terrane. In the ‘episodic rift‐sag’ tectonic model the basin architecture is envisaged as similar to that of a Basin and Range province characterised by widespread half‐graben development. According to this model, the Isa Superbasin evolved during three stages of the Mt Isa Rift Event. Stage I involved intracontinental extension, half‐graben development, the emergence of fault scarps and tilt‐blocks, and bimodal volcanism. Stage II involved episodic rifting and sag during intervening periods of tectonic quiescence. Stage III was dominated by thermal relaxation of the lithosphere with transient episodes of extension. Sedimentation was controlled by the development of arrays of half‐grabens bounded by intrabasinal transverse or transfer faults. The competing ‘strike‐slip’ model was developed for the Gun Supersequence stratigraphic interval of the Isa Superbasin (during stage II and the beginning of stage III). According to this model, sinistral movements along north‐northeast‐orientated strike‐slip faults took place, with oblique movements along northwest‐orientated faults. This resulted in the deposition of southeast‐thickening ramp sequences with local sub‐basin depocentres forming to the west and north of north‐northeast‐ and northwest‐trending faults, respectively. It is proposed that dilation zones focused magmatism (e.g. Sybella Granite) and transfer of strike‐slip movement resulted in transient uplift along the western margin of the Mt Gordon Arch. Our analysis supports the ‘episodic rift‐sag’ model. We find that the inferred architecture for the strike‐slip model correlates poorly with the observed structural elements. Interpretation is made difficult because there has been significant modification and reorientation of fault geometry during the Isan Orogeny and these effects need to be removed before any assertion as to the basin structure is made. Strike‐slip faulting does not explain the regional‐scale pattern of basin subsidence. The ‘episodic rift‐sag’ model explains the macroscopic geometry of the Isa Superbasin and is consistent with the detailed sedimentological analysis of basin facies architecture, and the structural history and geometry.  相似文献   

3.
The Mellish Park Syncline is located in the northern part of the Mt Isa terrane. It has an axial trace that transects the remnants of the unconformity‐bounded Palaeoproterozoic Leichhardt and Isa Superbasins. The syncline is separated into a lower and upper component based upon variation in fold geometry across the basin‐bounding unconformity. The lower syncline, in the Leichhardt Superbasin, is tight and has an inclined west‐dipping axial plane. The upper syncline, in the Isa Superbasin, is open and upright. The geometry of the lower syncline is a consequence of a period of shortening and basin inversion which post‐dated the Leichhardt Rift Event (ca 1780–1740 Ma) and pre‐dated the Mt Isa Rift Event (ca 1710–1655 Ma), forming an open and upright north‐oriented syncline. Subsequent southeast tilting and half‐graben development during the Mt Isa Rift Event resulted in the lower syncline being tilted into its inclined geometry. Sequences of the Isa Superbasin were then deposited onto the eroded syncline. The geometry of the upper syncline reflects regional east‐west shortening during the Isan Orogeny (ca 1590–1500 Ma). The position of the upper syncline was largely controlled by the pre‐existing lower syncline. At this time the lower syncline was reactivated and tightened by flexural slip folding.  相似文献   

4.
The geometry and architecture of a well exposed syn-rift normal fault array in the Suez rift is examined. At pre-rift level, the Nukhul fault consists of a single zone of intense deformation up to 10 m wide, with a significant monocline in the hanging wall and much more limited folding in the footwall. At syn-rift level, the fault zone is characterised by a single discrete fault zone less than 2 m wide, with damage zone faults up to approximately 200 m into the hanging wall, and with no significant monocline developed. The evolution of the fault from a buried structure with associated fault-propagation folding, to a surface-breaking structure with associated surface faulting, has led to enhanced bedding-parallel slip at lower levels that is absent at higher levels. Strain is enhanced at breached relay ramps and bends inherited from pre-existing structures that were reactivated during rifting. Damage zone faults observed within the pre-rift show ramp-flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear. Damage zone faults within the syn-rift are commonly very straight, and may be discrete fault planes with no visible fault rock at the scale of observation, or contain relatively thin and simple zones of scaly shale or gouge. The geometric and architectural evolution of the fault array is interpreted to be the result of (i) the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface; (ii) differences in deformation response between lithified pre-rift units that display high competence contrasts during deformation, and unlithified syn-rift units that display low competence contrasts during deformation, and; (iii) the history of segmentation, growth and linkage of the faults that make up the fault array. This has important implications for fluid flow in fault zones.  相似文献   

5.
There is ongoing debate with respect to the genetic models for shale‐hosted massive sulfide Pb–Zn–Ag deposits contained in the Palaeoproterozoic to Mesoproterozoic intracontinental Isa Superbasin in the Western Fold Belt, Mt Isa terrane. Favourable sites of mineralisation can be predicted based on understanding the tectonic setting of the Isa Superbasin, the structural controls of mineralisation and the chemically favourable environments for ore deposition. Shale‐hosted massive sulfide Pb–Zn–Ag deposits are hosted in successions deposited during the dominant sag‐phase of the Isa Superbasin. These deposits are localised at the intersections of major basin‐scale extensional faults and are hosted in both shallow‐marine and deeper water carbonaceous shales that are characteristically anoxic and located near or at maximum flooding surfaces. All major shale‐hosted massive sulfide Pb–Zn–Ag deposits are located to the west of the Mt Isa Rift (ca 1710–1670 Ma). This spatial association is explained by an asymmetrical lithosphere extension model for the evolution of the Isa Superbasin. Elevated geothermal gradients at the location of maximum subcrustal lithospheric thinning to the west of the Mt Isa Rift may have driven the migration of basinal brines. Increased subsidence at this location produced favourable anoxic sedimentary horizons for metal precipitation during orebody formation.  相似文献   

6.
Deep seismic reflection profiling confirms that the Paleo- to Mesoproterozoic Mount Isa mineral province comprises three vertically stacked and partially inverted sedimentary basins preserving a record of intracontinental rifting followed by passive margin formation. Passive margin conditions were established no later than 1655 Ma before being interrupted by plate convergence, crustal shortening and basin-wide inversion at 1640 Ma in both the 1730–1640 Ma Calvert and 1790–1740 Ma Leichhardt superbasins. Crustal extension and thinning resumed after 1640 Ma with formation of the 1635–1575 Ma Isa Superbasin and continued up to ca. 1615 Ma when extensional faulting ceased and a further episode of basin inversion commenced. The 1575 Ma Century Pb–Zn ore-body is hosted by syn-inversion sediments deposited during the initial stages of the Isan Orogeny with basin inversion accommodated on east- or northeast-dipping reactivated intrabasinal extensional faults and footwall shortcut thrusts. These structures extend to considerable depths and served as fluid conduits during basin inversion, tapping thick syn-rift sequences of immature siliciclastic sediments floored by bimodal volcanic sequences from which the bulk of metals and mineralising fluids are thought to have been sourced. Basin inversion and fluid expulsion at this stage were entirely submarine consistent with a syn-sedimentary to early diagenetic origin for Pb–Zn mineralisation at, or close to, the seafloor. Farther east, a change from platform carbonates to deeper water continental slope deposits (Kuridala and Soldiers Cap groups) marks the position of the original shelf break along which the north–south-striking Selwyn-Mount Dore structural corridor developed. This corridor served as a locus for strain partitioning, fluid flow and iron oxide–copper–gold mineralisation during and subsequent to the onset of basin inversion and peak metamorphism in the Isan Orogeny at 1585 Ma. An episode of post-orogenic strike-slip faulting and hydrothermal alteration associated with the subvertical Cloncurry Fault Zone overprints west- to southwest-dipping shear zones that extend beneath the Cannington Pb–Zn deposit and are antithetic to inverted extensional faults farther west in the same sub-basin. Successive episodes of basin inversion and mineralisation were driven by changes in the external stress field and related plate tectonic environment as evidenced by a corresponding match to bends in the polar wander path for northern Australia. An analogous passive margin setting has been described for Pb–Zn mineralisation in the Paleozoic Selwyn Basin of western Canada.  相似文献   

7.
A quantitative analysis is presented of the scaling properties of faults within the exceptionally well-exposed Kino Sogo Fault Belt (KSFB) from the eastern part of the 200-km-wide Turkana rift, Northern Kenya. The KSFB comprises a series of horsts and grabens within an arcuate 40-km-wide zone that dissects Miocene–Pliocene lavas overlying an earlier asymmetric fault block. The fault belt is 150 km long and is bounded to the north and south by transverse (N50°E and N140°E) fault zones. An unusual feature of the fault system is that it accommodates very low strains (<1%) and since it is no older than 3 Ma, it could be characterised by extension rates and strain rates that are as low as 0.1 mm/yr and 10−16 s−1, respectively. Despite its immaturity, the fault system comprises segmented fault arrays with lengths of up to 40 km, with individual fault segments ranging up to 9 km in length. Fault length distributions subscribe to a negative exponential scaling law, as opposed to the power law scaling typical of other fault systems. The relatively long faults and segments are, however, characterised by maximum throws of no more than 100 m, providing displacement/length ratios that are significantly below those of other fault systems. The under-displaced nature of the fault system is attributed to early stage rapid fault propagation possibly arising from reactivation of earlier underlying basement fabrics/faults or magmatic-related fractures. Combined with the structural control exercised by pre-existing transverse structures, the KSFB demonstrates the strong influence of older structures on rift fault system growth and the relatively rapid development of under-displaced fault geometries at low strains.  相似文献   

8.
The Mount Woods Domain in the Gawler Craton, South Australia records a complex tectonic evolution spanning the Palaeoproterozoic and Mesoproterozoic. The regional structural architecture is interpreted to represent a partially preserved metamorphic core complex that developed during the ~1600–1580 Ma Hiltaba Event, making this one of the oldest known core complexes on Earth. The lower plate is preserved in the central Mount Woods Domain, which comprises the Mount Woods Metamorphics. These rocks yield a detrital zircon maximum depositional age of ~1860 Ma and were polydeformed and metamorphosed to upper amphibolite to granulite facies during the ~1740–1690 Ma Kimban Orogeny. The upper plate comprises a younger succession (the Skylark Metasediments) deposited at ~1750 Ma. Within the upper plate, sedimentary and volcanic successions of the Gawler Range Volcanics were deposited into half graben that evolved during brittle normal faulting. The Skylark Shear Zone represents the basal detachment fault separating the upper and lower plate of the core complex. The geometry of normal faults in the upper plate is consistent with NE-SW extension.Both the upper and lower plates are intruded by ~1795–1575 Ma Hiltaba Suite granitic and mafic plutons. The core complex was extensively modified during the ~1570–1540 Ma Kararan Orogeny. Exhumation of the western and eastern Mount Woods Domain is indicated by new 40Ar/39Ar biotite cooling ages that show that rock packages in the central Mount Woods Domain cooled past ~300 °C ± 50 °C at ~1560 Ma, which was ~20 million years before equivalent cooling in the western and eastern Mount Woods Domain. Exhumation was associated with activity along major syn-Kararan Orogeny faults.  相似文献   

9.
Experimental (clay) models of inversion structures   总被引：3，自引：0，他引：3  
Experimental modeling is used to study the geometry and evolution of inversion structures. Two main types of inversion structures are analyzed:

1. (1) structures formed by fault-propagation folding; and

2. (2) structures formed by fault-bend folding on listric faults.

Fault-propagation inversion structures initially develop as broad drape folds with possible fault breakthrough during an early extensional phase. Syn-extensional strata deposited in the hanging wall typically thicken away from the fault. Compressional reactivation results in reversal of slip on the master and secondary faults, their rotation to shallower dips, and the development of a compressional fault-propagation fold. Key features of the fault-propagation fold are basinward thickening of syn-extensional units and resulting steep dips of the front limb of the structure. Fault-bend inversion structures initiate as rollover folds within extensional half-graben. Deformation is primarily localized along a system of antithetic faults. Syn-extensional strata typically thicken across the fault but also thin basinward away from the fault. During compression, the extensional rollover folds are folded into compressional fault-bend folds. Key features of this structure are thinning of syn-extensional units into the basin. Inversion of more symmetric graben results in a doubly-convex geometry of syn-extensional units. These observations of bed geometry and thickness provide predictive models for interpreting the geometries of inversion structures in areas of poor data quality.  相似文献   


10.
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   


11.
The Vidigueira–Moura fault (VMF) is a 65 km long, E–W trending, N dipping reverse left-lateral late Variscan structure located in SE Portugal (W Iberia), which has been reactivated during the Cenozoic with reverse right-lateral slip. It is intersected by, and interferes with the NE–SW trending Alentejo–Plasencia fault. East of this intersection, for a length of 40 km the VMF borders an intracratonic tectonic basin on its northern side, thrusting Paleozoic schists, meta-volcanics and granites, on the north, over Cenozoic continental sediments preserved in the basin, on the south. West of the faults intersection, evidence of Cenozoic reactivation is scarce. In the eastern sector, Plio-Quaternary VMF reactivation is indicated by geomorphologic, stratigraphic, and structural data, showing reverse movement with a right-lateral strike-slip component, in response to a NW–SE trending compressive stress. An average vertical displacement rate of 0.06 to 0.08 mm/yr since late Pliocene (roughly the last 2.5 Ma) is estimated. The Alqueva fault (AF) is a subparallel, northward dipping, 7.5 km long anastomosing fault zone that affects Palaeozoic basement rocks, and is located 2.5 km north and on the hanging block of the VMF. The AF is also a reverse left-lateral late Variscan structure, which has been reactivated during the Tertiary with reverse right-lateral slip; however, Plio-Quaternary reactivation was normal left-lateral, as shown by abundant kinematical criteria (slickensides) and geomorphic evidence. It shows an average displacement rate of 0.02 mm/yr for the vertical component of movement in the approximately last 2.5 Ma. It is proposed that the normal displacements on the AF result from tangential longitudinal strain on the upthrown block of the VMF above a convex ramp of this main reverse structure. According to this model of faults interaction, the AF is interpreted to work as a bending-moment fault sited above the VMF thrust ramp. Consequently, it is expected that the displacements on the AF increase towards the topographic surface with the increase in the imposed extension, declining downwards until they vanish above or at the VMF ramp. In order to constrain the proposed scheme, numerical modeling was performed, aiming at the reproduction of the present topography across the faults using different geodynamic models and fault geometries and displacements.  相似文献   

12.
The Buchan Rift, in northeastern Victoria, is a north–south-trending basin, which formed in response to east–west crustal extension in the Early Devonian. The rift is filled mostly with Lower Devonian volcanic and volcaniclastic rock of the Snowy River Volcanics. Although the structure and geometry of the Buchan Rift and its major bounding faults are well mapped at the surface, a discrepancy exists between the surface distribution of the thickest rift fill and its expected potential field response. To investigate this variation, two new detailed land-based gravity surveys, which span the rift and surrounding basement rocks in an east–west orientation, have been acquired and integrated with pre-existing government data. Qualitative interpretation of the observed magnetic data suggests the highly magnetic rocks of the Snowy River Volcanics have a wider extent at depth than can be mapped at the surface. Forward modelling of both land-based gravity data and aeromagnetic data supports this interpretation. With the Snowy River Volcanics largely confined within the Buchan Rift, resolved geometries also allow for the interpretation of rift boundaries that are wider at depth. These geometries are unusual. Unlike typical basin inversions that involve reactivation of rift-dipping faults, the bounding faults of the Buchan Rift dip away from the rift axis and thus appear unrelated to the preceding rifting episode. Limited inversion of previous extensional rift faults to deform the rift-fill sequences (e.g. Buchan Synclinorium) appears to have been followed by the initiation of new reverse faults in outboard positions, possibly because the relatively strong igneous rift fill began to act as a rigid basement ramp during continued E–W crustal shortening in the Middle Devonian Tabberabberan Orogeny. Overthrusting of the rift margins by older sediments and granite intrusions of the adjacent Tabberabbera and Kuark zones narrowed the exposed rift width at surface. This scenario may help explain the steep-sided geometries and geophysical expressions of other rift basins in the Tasmanides and elsewhere, particularly where relatively mechanically strong basin fill is known or suspected.  相似文献   

13.
Abstract

Positive structural inversion involves the uplift of rocks on the hanging-walls of faults, by dip slip or oblique slip movements. Controlling factors include the strike and dip of the earlier normal faults, the type of normal faults — whether they were listric or rotated blocks, the time lapsed since extension and the amount of contraction relative to extension. Steeply dipping faults are difficult to invert by dip slip movements; they form buttresses to displacement on both cover detachments and on deeper level but gently inclined basement faults. The decrease in displacement on the hanging-walls of such steep buttresses leads to the generation of layer parallel shortening, gentle to tight folds — depending on the amount of contractional displacement, back-folds and back-thrust systems, and short-cut thrust geometries — where the contractional fault slices across the footwall of the earlier normal fault to enclose a “floating horse”. However, early steeply dipping normal faults readily form oblique to strike slip inversion structures and often tramline the subsequent shortening into particular directions.

Examples are given from the strongly inverted structures of the western Alps and the weakly inverted structures of the Alpine foreland. Extensional faulting developed during the Triassic to Jurassic, during the initial opening of the central Atlantic, while the main phases of inversion date from the end Cretaceous when spreading began in the north Atlantic and there was a change of relative motion between Europe and Africa. During the mid-Tertiary well over 100 km of Alpine shortening took place; Alpine thrusts, often detached along, or close to, the basement-cover interface, stacking the late Jurassic to Cretaceous sediments of the post-extensional subsidence phase. These high level detachments were joined and breached by lower level faults in the basement which, in the external zones of the western Alps, generally reactivated and rotated the earlier east dipping half-graben bounding faults. The external massifs are essentially uplifted half-graben blocks. There was more reactivation and stacking of basement sheets in the eastern part of this external zone, where the faults had been rotated into more gentle dips above a shallower extensional detachment than on the steeper faults to the west.

There is no direct relationship between the weaker inversion of the Alpine foreland and the major orogenic contraction of the western Alps; the inversion structures of southern Britain and the Channel were separated from the Alps by a zone of rifting from late Eocene to Miocene which affected the Rhone, Bresse and Rhine regions. Though they relate to the same plate movements which formed the Alps, the weaker inversion structures must have been generated by within plate stresses, or from those emanating from the Atlantic rather than the Tethyan margin.  相似文献   

14.
We present hornblende, white mica, biotite and alkali feldspar 40Ar/39Ar data from Paleo-Mesoproterozoic rocks of the Mt. Isa Inlier, Australia, which reveal a previously unrecognised post-orogenic, non-linear cooling history of part of the Northern Australian Craton. Plateau and total fusion 40Ar/39Ar ages range between 1500 and 767 Ma and record increases in regional cooling rates of up to 4 °C/Ma during 1440–1390 and 1260–1000 Ma. Forward modelling of the alkali feldspar 40Ar/39Ar Arrhenius parameters reveals subsequent increases in cooling rates during 600–400 Ma. The cooling episodes were driven by both erosional exhumation at average rates of 0.25 km/Ma and thermal relaxation following crustal heating and magmatic events. Early Mesoproterozoic cooling is synchronous with exhumation and shearing in the Arunta Block and Gawler Craton. Late Mesoproterozoic cooling could have either been driven by increased rates of exhumation, or a result of thermal relaxation following a heat pulse that was synchronous with dyke emplacement in the Arunta, Musgrave and Mt. Isa province, as well as Grenville-aged orogenesis in the Albany–Fraser Belt. Latest Neoproterozoic–Cambrian cooling and exhumation was probably driven by the convergence of part of the East Antarctic Shield with the Musgrave Block and Western Australia (Petermann Ranges Orogeny), as well as collisional tectonics that produced the Delamerian–Ross Orogen. Major changes in the stress field and geothermal gradients of the Australian plate that are synchronous with the assembly and break-up of parts of Rodinia and Gondwana resulted in shearing and repeated brittle reactivation of the Mt. Isa Inlier, probably via the displacement of long-lived basement faults within the Northern Australian Craton.  相似文献   

15.
Stresses in a block around a dipping fracture simulating a damage zone of a fault are reconstructed by finite-element modeling. A fracture corresponding to a fault of different lengths, with its plane dipping at different angles, is assumed to follow a lithological interface and to experience either compression or shear. The stress associated with the destruction shows an asymmetrical pattern with different distances from the highest stress sites to the fault plane in the hanging and foot walls. As the dip angle decreases,the high-stress zone becomes wider in the hanging wall but its width changes negligibly in the foot wall.The length of the simulated fault and the deformation type affect only the magnitude of maximum stress,which remains asymmetrical relative to the fault plane. The Lh/Lfratio, where Lhand Lfare the widths of high-stress zones in the hanging and foot walls of the fault, respectively, is inversely proportional to the fault plane dip. The arithmetic mean of this ratio over different fault lengths in fractures subject to compression changes from 0.29 at a dip of 80°to 1.67 at 30°. In the case of shift displacement, ratios are increasing to 1.2 and 2.94, respectively.Usually they consider vertical fault planes and symmetry in a damage zone of faults. Following that assumption may cause errors in reconstructions of stress and fault patterns in areas of complex structural setting. According geological data, we know the structures are different and asymmetric in hanging and foot walls of fault. Thus, it is important to quantify zones of that asymmetry. The modeling results have to be taken into account in studies of natural faults, especially for practical applications in seismic risk mapping, engineering geology, hydrogeology, and tectonics.  相似文献   

16.
吐哈盆地中央构造带正反转演化特征   总被引：5，自引：3，他引：5  
吐哈盆地中央构造带由火焰山构造和七克台构造组成。中央构造带形成于三叠纪晚期至侏罗纪早期,表现为伸展构造特征,生长断层上盘地层厚度明显大于下盘,并于断层上盘所在的台北凹陷形成沉降中心。晚侏罗世,由于拉萨陆块与欧亚大陆的碰撞作用导致吐哈盆地由伸展盆地转变为挤压盆地,中央构造带也于此时发生构造反转,由早期的伸展正断层转变为挤压逆断层。发生于55Ma的喜山构造事件对天山地区产生了深刻的影响,但影响时间略有滞后,大致发生在晚渐新世至早中新世,中央构造带即在此次构造事件中强烈变形,逆冲出露于地表。  相似文献   

17.
The western Liaodong (辽东) Bay subbasin displays examples of segment,linkage of extensional fault,and fault-related folds.The Liaoxi (辽西) extensional fault system consists of a series of NNE- and NE-trending segments that were linked through relay ramps.The fault hanging walls are characterized by a series of en echelon synclines with axial traces sub-parallel to the faults.The synclines are doubly plunging located on the hanging wall of normal faults,with the strata dip sub-parallel to the fault.These folds result from along-strike displacement variations of the individual fault segments,as well as from extensional fault-related folding.In the study area,the synclines are separated by transverse intra-basin highs and relay ramps that formed where segment linkage occurred.These hanging wall synclines and their relation to fault displacement variations indicate that they are formed by extensional fault-related fold.  相似文献   

18.
李理  钟大赉  陈霞飞  陈衍 《地质学报》2018,92(3):413-436
不同于华北克拉通东部普遍存在的NE走向断层,鲁西地块广泛发育一组特征明显的NW走向断层,包括非控盆断层和控盆断层两类。前者位于鲁西地块最南部,倾角相对较陡,错开了古生界及以下地层,下盘太古宇中发育韧性剪切带,断层碎裂岩指示断层存在多期活动;后者位于非控盆断层以北,除蒙山断层外韧性剪切带不发育,倾角相对较缓,控制了中生代以来的沉积。磷灰石/锆石裂变径迹证据分析得出NW走向断层的活动存在差异。断层上、下盘样品磷灰石裂变径迹表观年龄在在67±5~35±2Ma之间,径迹直方图表明样品在冷却过程中没有受到热扰动。通过平均径迹长度-年龄(或香蕉图)图、单颗粒峰值年龄、径迹年龄谱模式以及热史反演模拟综合分析来约束断层的活动时间,结果表明非控盆断层可能在早侏罗世约184Ma开始活动,之后在晚白垩世80~75Ma以及新生代~61Ma和51~43Ma活动,43Ma之后不再活动。控盆断层活动时间稍晚,于早白垩世约141Ma、晚白垩世80~75Ma活动,新生代活动时间为约61Ma、49~42Ma以及36~32Ma。总体上,NW走向断层由早到晚由南向北发育,非控盆断层活动时间早、结束早;控盆断层活动晚、结束晚,并控制了凹陷的向北发育。中生代以来区域构造应力场的变化和郯庐断裂带的走滑作用是导致两类NW走向断层差异演化的根本原因,在深部则受控于晚三叠世以来华北、扬子板块陆陆碰撞和古太平洋板块俯冲方向和速度的改变。印支期后挤压到伸展的转变,加上郯庐断裂带的左行走滑,使靠近华北克拉通南缘的前端NW走向断层首先发育,因倾角较大故不控制盆地发育;向北的后端相对伸展,成为控盆断层,后经早白垩世约141Ma期间的伸展、晚白垩世末80~75Ma和新生代的发育断层最终成型。NW走向断层的这种大致向北迁移的规律,隐示华北克拉通破坏可能始于早侏罗世或晚侏罗世,且由南向北逐渐拆沉。  相似文献   

19.
《Gondwana Research》2014,25(3-4):886-901
The Late Mesoproterozoic (1085–1040 Ma) Ngaanyatjarra Rift, previously referred to as the Giles Event, is the dominant component of the Warakurna Large Igneous Province (LIP) that affected much of central and western Australia. This rift is well preserved and provides excellent examples of rift structure at a variety of crustal levels and times in the rift's evolution. Geological knowledge is integrated with geophysical interpretations and models to understand the crustal structure and evolution of this rift. Two phases are identified: an early rift stage (1085–1074 Ma) that is characterised by voluminous magmatism within the upper crust and relatively little tectonic deformation; and a late rift stage that is characterised by tectonic deformation, synchronous with the deposition of a thick pile of volcanic and sedimentary rocks (1074–1040 Ma). Compared to modern rift examples, this rift is unusual in that the crust was thickened by ~ 15 km and overall extension was very limited. However, its structure and evolution are very similar to the near-contemporaneous Midcontinent Rift, which shows the addition of a similar quantity of magmatic material as well as crustal thickening and limited extension. For these Mesoproterozoic rifts, we suggest that magmatism was the dominant process, and that the extension observed was a response to magmatism-induced crustal thickening and the gravitational collapse of the crustal column. Other Proterozoic rifts show similar characteristics (e.g. Transvaal Rift), whereas most Phanerozoic rifts are dissimilar, showing instead a dominance of extension, with magmatism largely a result of this extension. This change in the style of rifting from the Precambrian to the Phanerozoic may relate to the influence of a typically cooler and stronger lithosphere, which has caused stronger strain localisation and a greater role for extension as the controlling factor in rift evolution.  相似文献   

20.
Oblique displacement on the Alpine Fault, which forms the principal structure along the Australian–Pacific plate boundary in South Island, New Zealand, has resulted in exhumation of a kilometre-wide mylonite zone in the hanging wall adjacent to the current brittle fault trace. The mylonites formed under amphibolite facies conditions at depths of ca. 25 km and have been uplifted during the past 5 Ma. A suite of 65–70 Ma pegmatite veins in the hanging wall Alpine schists has been progressively deformed within the mylonite zone and sheared out over a strike length of ca. 100 km. Measurements of the thickness distribution of the pegmatite veins within the non-mylonitised schists and at three localities within the progressively strained mylonites have been used to estimate strain values within the mylonites. The thicknesses approximate a log-normal distribution, with a mean value that is progressively reduced through the protomylonites, mylonites and ultramylonites. By assuming that the thickness distribution currently observed in the schists was the same for the pegmatites within the mylonites before strain, a model of deformation incorporating simple shear and simultaneous pure shear is used to strain the undeformed veins until a fit is obtained with the strained distributions. Shear strains calculated range from 12 to 22 for the protomylonites, 120 to 200 for the mylonites and 180 to 300 for the ultramylonites, corresponding to pure shear values of 1–3 in each case. These values are compatible with the strains predicted if most of the surface displacement on the fault over the past 5 Ma were accommodated within a 1–2-km-wide mylonite zone through the middle and lower crusts. The results suggest that processes such as erosional focussing of deformation and thermal weakening may cause intense strain localisation within the lower crust, with plate boundary deformation restricted to narrow zones rather than becoming increasingly distributed over a widening shear zone with depth.  相似文献   

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