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.
This article focuses on the reinterpretation of well, seismic reflection, magnetic, gravimetric, surface wave and geological surface data, together with the acquisition of seismic noise data to study the Lower Tagus Cenozoic Basin tectono‐sedimentary evolution. For the first time, the structure of the base of the basin in its distal and intermediate sectors is unravelled, which was previously only known in the areas covered by seismic reflection data (distal and small part of intermediate sectors). A complex geometry was found, with three subbasins delimited by NNE‐SSW faults and separated by WNW‐ESE to NW‐SE oriented horsts. In the area covered by seismic reflection data, four horizons were studied: top of the Upper Miocene, Lower to Middle Miocene top, the top of the Palaeogene and the base of Cenozoic. Seismic data show that the major filling of the basin occurred during Upper Miocene. The fault pattern affecting Neogene and Palaeogene units derived here points to that of a polyphasic basin. In the Palaeogene, the Vila Franca de Xira (VFX) and a NNE‐SSW trending previously unknown structure (ABC fault zone) probably acted as the major strike‐slip fault zones of the releasing bend of a pull‐apart basin, which produced a WNW‐ESE to NW‐SE fault system with transtensional kinematic. During the Neogene, as the stress regime rotated anticlockwise to the present NW‐SE to WNW‐ESE orientation, the VFX and Azambuja fault zones acted as the major transpressive fault zones and Mesozoic rocks overthrusted Miocene sediments. The reactivation of WNW‐ESE to NW‐SE fault systems with a dextral strike‐slip component generated a series of horsts and grabens and the partitioning of the basin into several subbasins. Therefore, we propose a polyphasic model for the area, with the formation of an early pull‐apart basin during the Palaeogene caused by an Iberia–Eurasia plates collision that later evolved into an incipient foreland basin along the Neogene due to a NW‐SE to WNE‐ESE oriented Iberia–Nubia convergence. This convergence is producing uplift in the area since the Quaternary except for the Tagus estuary subbasin around the VFX fault, where subsidence is observed. This may be due to the locking or the development of a larger component of strike‐slip movement of the NNE‐SSW to N‐S thrust fault system with the exception of the VFX fault, which is more favourably oriented to the maximum compressive stress.  相似文献   

2.
The Kunlun fault is one of the largest strike-slip faults in northern Tibet, China. In this paper, we focus upon the Kusai Lake–Kunlun Pass segment of the fault to understand the geomorphic development of offset streams caused by repeated large seismic events, based on tectono-geomorphic analysis of high-resolution satellite remote sensing images combined with field studies. The results indicate that systematic left-lateral stream offsets appear at various scales across the fault zone: Lateral offsets of small gullies caused by the 2001 Mw 7.8 Kunlun earthquake vary typically from 3 m to 6 m, meanwhile streams with cumulative offsets of 10 m, 25–30 m, 50–70 m, 250–300 m and 750–1400 m have resulted from repeated large seismic events during the late Quaternary. An average slip rate of 10 ± 1 mm/year has been estimated from the lateral stream offsets and 14C ages of alluvial fan surfaces incised by the streams. A three-dimensional model showing tectono-geomorphic features along a left-lateral strike-slip fault is also presented. The Kusai Lake–Kunlun Pass segment provides an opportunity to understand the relationship between geomorphic features produced by individual large seismic events and long-term geomorphic development caused by repeated large seismic events along a major strike-slip fault.  相似文献   

3.
Transtensional basins are sparsely described in the literature compared with other basin types. The oblique‐divergent plate boundary in the southern Gulf of California has many transtensional basins: we have studied those on San Jose island and two other transtensional basins in the region. One major type of transtensional basin common in the southern Gulf of California region is a fault‐termination basin formed where normal faults splay off of strike‐slip faults. These basins suggest a model for transtensional fault‐termination basins that includes traits that show a hybrid nature between classic rift and strike‐slip (pull‐apart) basins. The traits include combinations of oblique, strike‐slip and normal faults with common steps and bends, buttress unconformities between the fault steps and beyond the ends of faults, a common facies pattern of terrestrial strata changing upward and away from the faults into marine strata, small fault blocks within the basin that result in complex lateral facies relations, common Gilbert deltas, dramatic termination of the margin of the basin by means of fault reorganization and boundary faults dying and an overall short basin history (few million years). Similar transtensional fault‐termination basins are present in Death Valley and other parts of the Eastern California shear zone of the western United States, northern Aegean Sea and along ancient strike‐slip faults.  相似文献   

4.
High resolution seismic reflection surveys over one of the most active and rapidly extending regions in the world, the Gulf of Corinth, have revealed that the gulf is a complex asymmetric graben whose geometry varies significantly along its length. A detailed map of the offshore faults in the gulf shows that a major fault system of nine distinct faults limits the basin to the south. The northern Gulf appears to be undergoing regional subsidence and is affected by an antithetic major fault system consisting of eight faults. All these major faults have been active during the Quaternary. Uplifted coastlines along their footwalls, growth fault patterns and thickening of sediment strata toward the fault planes indicate that some of these offshore faults on both sides of the graben are active up to present. Our data ground‐truth recent models and provides actual observations of the distribution of variable deformation rates in the Gulf of Corinth. Furthermore they suggest that the offshore faults should be taken into consideration in explaining the high extension rates and the uplift scenarios of the northern Peloponnesos coast. The observed coastal uplift appears to be the result of the cumulative effect of deformation accommodated by more than one fault and therefore, average uplift rates deduced from raised fossil shorelines, should be treated with caution when used to infer individual fault slip rates. Seismic reflection profiling is a vital tool in assessing seismic hazard and basin‐formation in areas of active extension.  相似文献   

5.
Quantifying the extent to which geomorphic features can be used to extract tectonic signals is a key challenge in the Earth Sciences. Here we analyse the drainage patterns, geomorphic impact, and long profiles of bedrock rivers that drain across and around normal faults in a regionally significant oblique-extensional graben (Hatay Graben) in southern Turkey that has been mapped geologically, but for which there are poor constraints on the activity, slip rates and Plio–Pleistocene evolution of basin-bounding faults. We show that drainage in the Hatay Graben is strongly asymmetric, and by mapping the distribution of wind gaps, we are able to evaluate how the drainage network has evolved through time. By comparing the presence, size, and distribution of long profile convexities, we demonstrate that the northern margin of the graben is tectonically quiescent, whereas the southern margin is bounded by active faults. Our analysis suggests that rivers crossing these latter faults are undergoing a transient response to ongoing tectonic uplift, and this interpretation is supported by classic signals of transience such as gorge formation and hill slope rejuvenation within the convex reach. Additionally, we show that the height of long profile convexities varies systematically along the strike of the southern margin faults, and we argue that this effect is best explained if fault linkage has led to an increase in slip rate on the faults through time from  0.1 to 0.45 mm/yr. By measuring the average length of the original fault segments, we estimate the slip rate enhancement along the faults, and thus calculate the range of times for which fault acceleration could have occurred, given geological estimates of fault throw. These values are compared with the times and slip rates required to grow the documented long-profile convexities enabling us to quantify both the present-day slip rate on the fault (0.45 ± 0.05 mm/yr) and the timing of fault acceleration (1.4 ± 0.2 Ma). Our results have substantial implications for predicting earthquake hazard in this densely populated area (calculated potential Mw = 6.0–6.6), enable us to constrain the tectonic evolution of the graben through time, and more widely, demonstrate that geomorphic analysis can be used as an effective tool for estimating fault slip rates over time periods > 106 years, even in the absence of direct geodetic constraints.  相似文献   

6.
In areas of broadly distributed extensional strain, the back‐tilted edges of a wider than normal horst block may create a synclinal‐horst basin. Three Neogene synclinal‐horst basins are described from the southern Rio Grande rift and southern Transition Zone of southwestern New Mexico, USA. The late Miocene–Quaternary Uvas Valley basin developed between two fault blocks that dip 6–8° toward one another. Containing a maximum of 200 m of sediment, the Uvas Valley basin has a nearly symmetrical distribution of sediment thickness and appears to have been hydrologically closed throughout its history. The Miocene Gila Wilderness synclinal‐horst basin is bordered on three sides by gently tilted (10°, 15°, 20°) fault blocks. Despite evidence of an axial drainage that may have exited the northern edge of the basin, 200–300 m of sediment accumulated in the basin, probably as a result of high sediment yields from the large, high‐relief catchments. The Jornada del Muerto synclinal‐horst basin is positioned between the east‐tilted Caballo and west‐tilted San Andres fault blocks. Despite uplift and probable tilting of the adjacent fault blocks in the latest Oligocene and Miocene time, sediment was transported off the horst and deposited in an adjacent basin to the south. Sediment only began to accumulate in the Jornada del Muerto basin in Pliocene and Quaternary time, when an east‐dipping normal fault along the axis of the syncline created a small half graben. Overall, synclinal‐horst basins are rare, because horsts wide enough to develop broad synclines are uncommon in extensional terrains. Synclinal‐horst basins may be most common along the margins of extensional terrains, where thicker, colder crust results in wider fault spacing.  相似文献   

7.
Relationships between tectonic framework and gravity-driven phenomena have been investigated in an area of the Central Apennines (Italy) characterised by high relief. The north–south, half-dome shaped Maiella anticline lies in the easternmost part of the Apennine fold-and-thrust belt. Its backlimb is bordered by the Caramanico Fault, a normal fault with a maximum downthrown of about 3.5 km that separates the western slope of the Maiella Massif from the Caramanico Valley. The southwestern Maiella area is affected by deep-seated gravitational slope deformation indicated by major double crest lines, down-hill and up-hill facing scarps, a pattern of crossing trenches, bulging at the base of slopes and the presence of different types of landslide and talus slope deposits.The onset and development of deep-seated gravitational slope deformations and the location of Quaternary, massive rockslope failures have been strongly influenced by the structural framework and tectonic pattern of the anticline. Deep-seated gravitational slope deformation at Mt. Macellaro–Mt. Amaro ridge has developed along the Maiella western, reverse slope in correspondence with the anticline axial culmination; it is bordered at the rear by a NNW–SSE oriented, dextral, strike-slip fault zone and has an E–W direction of rock mass deformation. Closer to the southern plunging area of the anticline, gravity-driven phenomena show instead a N–S and NW–SE direction, influenced by bedding attitude.3D topographic models illustrate the relationship between deep-seated gravitational slope deformation and massive rockslope failures. The Campo di Giove rock avalanche, a huge Quaternary failure event, was the result of an instantaneous collapse on a mountaine slope affected by a long-term gravity-driven deformation.  相似文献   

8.
We present a new tectonic map focused upon the extensional style accompanying the formation of the Tyrrhenian back‐arc basin. Our basin‐wide analysis synthetizes the interpretation of vintage multichannel and single‐channel seismic profiles, integrated with modern seismic images, P‐wave velocity models, and high‐resolution morpho‐bathymetric data. Four distinct evolutionary phases of the Tyrrhenian back‐arc basin opening are further constrained, redefining the initial opening to Langhian/Serravallian time. Listric and planar normal faults and their conjugates bound a series of horst and graben, half‐graben and triangular basins. Distribution of extensional faults, active throughout the basin since Middle Miocene, allows us to define an arrangement of faults in the northern/central Tyrrhenian mainly related to a pure shear which evolved to a simple shear opening. At depth, faults accommodate over a Ductile‐Brittle Transitional zone cut by a low‐angle detachment fault. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variation throughout the back‐arc basin combined with wide‐angle seismic velocity models allows to explore the relationships between shallow deformation, faults distribution throughout the basin, and crustal‐scale processes as thinning and exhumation.  相似文献   

9.
The Gödöllő Hills, a low-relief terrain within the Central Pannonian Basin in Hungary, is characterised by moderate tectonic deformation rates. Although typical tectonic landforms are not clearly recognisable in the study area, this paper succeeded in discriminating between tectonically controlled landforms and features shaped by fluvial erosion or deflation with no tectonic control.DEM-based morphometric parameters including elevation, slope and surface roughness, enabled the delineation of two NW–SE trending spearhead-shaped ridges separated by a wide rectilinear valley of the same strike. Although directional statistics suggested possible tectonic control of NW–SE striking landforms, precise morphometry completed with an analysis of subsurface structures rejected their tectonic preformation. Deflation plays a significant role in shaping the area, and the presence of two large-scale yardangs separated by a wind channel is proposed. In temperate-continental areas of Europe, no deflational landforms of such scale have been described so far, suggesting that Pleistocene wind power in periglacial areas was more significant than it was previously thought.Characteristic drainage patterns and longitudinal valley profiles enabled the recognition of areas probably affected by neotectonic deformation. A good agreement was observed between locations of Quaternary warping predicted by the morphometric study and subsurface structures revealed by the tectonic analysis. Zones of surface uplift and subsidence corresponded to anticlinal and synclinal hinges of fault-related folds. In low-relief and slowly-deforming areas, where exogenous forces may override tectonic deformation, only the integrated application of morphometric and subsurface-structural indications could assure correct interpretation of the origin of various landforms, while a morphometric study alone could have led to misinterpretation of some morphometric indices apparently suggesting tectonic preformation. On the other hand, the described morphological expression of subsurface structures could verify Quaternary age of the deformation.  相似文献   

10.
The Sagaing Fault zone is the largest active fault in SE Asia, whose current displacement rate of around 1.8 cm year?1 is well‐established from GPS data. Yet determining the timing of initiation and total displacement on the fault zone has proven controversial. The timing problem can potentially be resolved through a newly identified syn‐kinematic sedimentary section directly related to displacement on the Sagaing Fault in the northern Minwun Ranges. The northern part of the western strand of the Sagaing Fault has a releasing splay geometry that sets up a syn‐kinematic oblique‐extensional basin in its hangingwall, here called the North Minwun Basin. A series of thick ridges probably composed of alluvial fan and fluvial sandstones dipping between 20 and 70° to the north, and younging northwards comprise the basin fill over a distance of 40 km. Total stratigraphic thickness (not vertical thickness) is estimated at 25 km. The basin in terms of depositional geometries, large displacements, and large stratigraphic thickness and appearance on satellite images has parallels with the extensional Hornelen basin, Norway and the strike‐slip Ridge Basin, California. Minimum likely displacement on the fault strand is 40 km, and may possibly be in excess of 100 km. The remote and inaccessible basin has yet to be properly dated, likely ages range between Eocene and Miocene. When dated the basin will provide an important constraint on the timing of deformation. The potential for this basin to constrain the timing and displacement along the northern part of the Sagaing Fault has not been previously recognised.  相似文献   

11.
《Geomorphology》2006,73(1-2):16-32
Well-constrained case studies of transient landscape response to external forcing are needed to improve our understanding of erosion processes in tectonically active mountain belts. The Peninsular Ranges portion of the San Jacinto fault zone (SJFZ) is an excellent location for such a study because it displays pronounced geomorphic disequilibrium resulting from initiation of a major strike-slip fault in the past 1.0 to 2.5 million years. We recognize two geomorphic domains in this region: (1) a relict low-relief upland domain consisting of broad flat valleys and low-gradient streams and (2) very steep, rough topography with deeply incised canyons and retreating erosional knickpoints. Pleistocene sediments exposed along and near the SJFZ include fluvial conglomerate, sandstone, and mudstone, with weak paleosols and west- to NW-directed paleocurrents. These sediments accumulated in a low-gradient stream system (represented by domain 1) during an early phase of slip in the SJFZ, prior to the modern phase of erosion and degradation (domain 2). Late Pliocene or early Pleistocene initiation of the SJFZ triggered a wave of headward erosion and stream capture that is still migrating NW along the fault zone. Using the total distance that capture points have migrated along the fault zone and a range of possible ages for fault initiation, the rate of knickpoint retreat is estimated at ∼ 12 to 44 km/my.To explore the signal of transient geomorphic response to fault initiation, we analyzed 23 tributaries along an ∼ 20-km portion of the main fault valley within domain 2. The analysis reveals three zones with distinctive morphologies: (1) strongly convex longitudinal profiles in the NW, (2) a large (ca. 5–6 km2) landslide in the central zone, and (3) concave tributaries in the SE with profile complexity decreasing and catchment area increasing from NW to SE. The distribution of these zones suggests close spatial and temporal association of active fault slip, bedrock incision, deep-seated landslides, and erosional modification. The fundamental driving force behind these processes is profound geomorphic disequilibrium resulting from initiation of the SJFZ. We suggest that landslides may have played a significant role in shaping the morphology of this fault zone, and that the influence of landslides may be underestimated in areas where characteristic landforms and deposits are obscured by later erosion and faulting.  相似文献   

12.
P. Haughton 《Basin Research》2001,13(2):117-139
ABSTRACT The mechanisms driving subsidence in late orogenic basins are often not easily resolved on account of later fault reactivation and a rapidly changing stress field. Contained turbidites in such basins provide a unique opportunity of monitoring sea bed deformation and evolving bathymetry and hence patterns of subsidence during basin filling. A variety of interpretations have been proposed to explain subsidence in Neogene basins in SE Spain, including extensional, strike‐slip and thrust top mechanisms. Ponded turbidite sheets on the floor of the Neogene Sorbas Basin (SE Spain) were deposited by sand‐bearing currents which ran into enclosed bathymetric deeps where they underwent rapid suspension collapse. The structure and distribution of these sheets (and the thick mudstone caps which overlie them) act as a proxy for the containing sea bed bathymetry at the time of deposition. An analysis of the sheet architecture helps identify a trough‐axial zone of syndepositional faulting and reveals a westwards stepping of the ponding depocentre with time. Fault breaks at the sea bed influenced the position of flow arrest and the distribution of sandstone beds on the basin floor. Westward stepping of the deeper bathymetry was episodic and probably controlled by transverse faults. Re‐locations of the depocentre were accompanied by the destabilization of carbonate sand stores on the margins of the basin, resulting in the repeated emplacement of large‐volume carbonate megabeds and calciturbidites. The fill to the Sorbas Basin was shingled by the onset of compression in the east attributed to transfer of slip between intersecting strike‐slip fault strands. A sinistral fault (a splay of the Carboneras Fault System) propagated through the evolving basin fill from the east as the eastern part of the basin became inverted and the locus of subsidence migrated into the Tabernas area 20 km area to the west. The sedimentological analysis of the basin fill helps see through a late dextral overprint which ultimately juxtaposed basement rocks to the south against the inverted and upended basin, along a late slip‐modified unconformity. Conventional palaeostress analysis of fractures along the basin margin fails to see past this late dextral shearing event. Basin migration parallel to the E–W‐orientated basin axis, slip‐reversal (sinistral to dextral) and the active involvement of strike‐slip faults are now identified as important aspects of the evolution of the Sorbas Basin during the latestTortonian.  相似文献   

13.
ABSTRACT Geological mapping and sedimentological investigations in the Guilin region, South China, have revealed a spindle‐ to rhomb‐shaped basin filled with Devonian shallow‐ to deep‐water carbonates. This Yangshuo Basin is interpreted as a pull‐apart basin created through secondary, synthetic strike‐slip faulting induced by major NNE–SSW‐trending, sinistral strike‐slip fault zones. These fault zones were initially reactivated along intracontinental basement faults in the course of northward migration of the South China continent. The nearly N–S‐trending margins of the Yangshuo Basin, approximately coinciding with the strike of regional fault zones, were related to the master strike‐slip faults; the NW–SE‐trending margins were related to parallel, oblique‐slip extensional faults. Nine depositional sequences recognized in Givetian through Frasnian strata can be grouped into three sequence sets (Sequences 1–2, 3–5 and 6–9), reflecting three major phases of basin evolution. During basin nucleation, most basin margins were dominated by stromatoporoid biostromes and bioherms, upon a low‐gradient shelf. Only at the steep, fault‐controlled, eastern margin were thick stromatoporoid reefs developed. The subsequent progressive offset and pull‐apart of the master strike‐slip faults during the late Givetian intensified the differential subsidence and produced a spindle‐shaped basin. The accelerated subsidence of the basin centre led to sediment starvation, reduced current circulation and increased environmental stress, leading to the extensive development of microbial buildups on platform margins and laminites in the basin centre. Stromatoporoid reefs only survived along the windward, eastern margin for a short time. The architectures of the basin margins varied from aggradation (or slightly backstepping) in windward positions (eastern and northern margins) to moderate progradation in leeward positions. A relay ramp was present in the north‐west corner between the northern oblique fault zone and the proximal part of the western master fault. In the latest Givetian (corresponding to the top of Sequence 5), a sudden subsidence of the basin induced by further offset of the strike‐slip faults was accompanied by the rapid uplift of surrounding carbonate platforms, causing considerable platform‐margin collapse, slope erosion, basin deepening and the demise of the microbialites. Afterwards, stromatoporoid reefs were only locally restored on topographic highs along the windward margin. However, a subsequent, more intense basin subsidence in the early Frasnian (top of Sequence 6), which was accompanied by a further sharp uplift of platforms, caused more profound slope erosion and platform backstepping. Poor circulation and oxygen‐depleted waters in the now much deeper basin centre led to the deposition of chert, with silica supplied by hydrothermal fluids through deep‐seated faults. Two ‘subdeeps’ were diagonally arranged in the distal parts of the master faults, and the relay ramp was destroyed. At this time, all basin margins except the western one evolved into erosional types with gullies through which granular platform sediments were transported by gravity flows to the basin. This situation persisted into the latest Frasnian. This case history shows that the carbonate platform architecture and evolution in a pull‐apart basin were not only strongly controlled by the tectonic activity, but also influenced by the oceanographic setting (i.e. windward vs. leeward) and environmental factors.  相似文献   

14.
The Pakuashan anticline is uniquely suited for study of the forward and lateral growth of fault-related folds. The Pakuashan ridge development arises from the late Quaternary uplift of the most external thrust zone of the western foothills of Taiwan. From Kaoshiung to Taichung, recent and active westward thrusting occurs at the front of the foothills. The Pakuashan anticline, trending N 150°E in the northern part to N 000° in the southern part, has been active throughout the Quaternary period. This activity is marked by geological structures, tectonic geomorphology and seismicity. A multisource and multiscale approach to study of the continental collision setting has been undertaken to combine tectonics, sedimentology and geomorphology. Studies of fracture patterns allow identification of two main features of stress orientations: a WNW/ESE compression direction, and E–W and N–S extension directions. Quantitative geomorphic parameters have been used to define the morphotectonic evolution and to infer tectonic style along the mountain front. Geomorphic evidence provides significant information on the processes that govern lateral propagation of an active anticline. Quaternary terraces are uplifted, tilted and folded over the Pakuashan ridge. Drainage systems in areas of active compression give information on the thrust zone structures and their development. Steep drainage and high local relief indicate that the Pakuashan anticline forms a well-defined zone of high uplift, especially in the southern part. The two main controls on drainage in that area are rock strength in the hanging wall and propagation of the deformation towards the south.  相似文献   

15.
We present a study on the impact of litho-structural setting and neotectonic activity on meso- and macro-scale relief production in Alpine areas. The topography of the high alpine Triglav Lakes Valley, NW Slovenia, was studied by means of detailed mapping and stratigraphic study of the valley. The Triglav Lakes Valley is characterised by a generally asymmetric transverse (E–W) profile: a very steep eastern slope, a relatively flat valley and a relatively gentle western slope. On the transverse profile the valley floor is essentially flat, gently dipping towards the east. In the longitudinal cross-section, however, the valley floor is marked by sharply-defined fault blocks extending in a W–E to NW–SE direction. Additionally, the highest block (elevations  2100 m) is in the northern part of the valley, the lowest (elevations  1600 m) in the southern part of the valley. Our research shows that the Triglav Lakes Valley directly represents the topographic expression of Paleogene–Neogene thrusting and faulting, having recorded the following geomorphologic evolutionary stages: 1. an Oligocene to early Miocene W-vergent thrusting phase, with steep W-facing slopes of the eastern part of the valley directly representing the thrusting front; and 2. a Neogene-to-present strike–slip faulting in NNE–SSW direction with two bifurcating right-lateral strike–slip systems. We show that the Triglav Lakes Valley almost perfectly mimics the wedge-shaped damage zone located between these faults.  相似文献   

16.
秦岭北麓断裂带晚第四纪活动的地貌表现   总被引：3，自引：0，他引：3  
侯建  柴宝龙 《地理学报》1995,50(2):138-146
本区地貌特征反映秦岭北麓断裂带的活动特点是：①第四纪以来主要发生垂直运动，其活动性质与程度有差异性、阶段性。第一、二级阶地的形态和年代资料表征秦岭北麓断裂带晚更新世和全新世垂直位错幅度和平均速率。②河流阶地在上升盘出口处高度大，而向上游逐渐减小，反映第四纪以来，秦岭断块山地继续发生由北向南的掀斜运动。③被断层切割的冲洪积扇体的结构和堆积层的产状特征，反映出山麓带多发育铲形断层。  相似文献   

17.
The geodynamic processes in the western Mediterranean are driven by both deep (mantle) processes such as slab‐rollback or delamination, oblique plate convergence and inherited structures. The present‐day deformation of the Alboran Sea and in particular the Nekor basin area is linked to these coeval effects. The seismically active Nekor basin is an extensional basin formed in a convergent setting at the eastern part of the Rif Chain whose boundaries extend both onshore and offshore Morocco. We propose a new structural model of the Nekor basin based on high‐resolution offshore data compiled from recent seismic reflection profiles, swath bathymetry acquisitions and industrial seismic reflection profiles. The new data set shows that the northern limit of the basin is oriented N49° with right‐stepping faults from the Bousekkour–Aghbal fault to the sinistral Bokkoya fault zone. This pattern indicates the presence of an inherited left‐lateral basement fault parallel to the major inherited Nekor fault. This fault has been interpreted as a Quaternary active left‐lateral transfer fault localized on weak structural discontinuities inherited from the orogenic period. Onshore and offshore active faults enclose a rhombohedral tectonic Nekor Basin. Normal faults oriented N155° offset the most recent Quaternary deposits in the Nekor basin, and indicate the transtensional behaviour of this basin. The geometry of these faults suggests a likely rollover structure and the presence at depth of a crustal detachment. Inactive Plio‐Quaternary normal faults to the east of the Ras Tarf promontory and geometries of depocentres seem to indicate the migration of deformation from east to west. The local orientations of horizontal stress directions deduced from normal fault orientations are compatible with the extrusion of the Rifian units and coherent with the westward rollback of the Tethyan slab and the localization of the present‐day slab detachment or delamination.  相似文献   

18.
The landscape of today's central Iberian Peninsula has been shaped by ongoing tectonic activity since the Tertiary. This landscape comprises a mountain ridge trending E–W to NW–SE, the Central System, separating two regions of smooth topography: the basins of the rivers Duero and Tajo. In this study, we explore interrelationships between topography and tectonics in the central Iberian Peninsula. Regional landscape features were analysed using a digital elevation model (DEM). Slope gradients and slope orientations derived from the DEM were combined to describe topographic surface roughness. Topography trend-surfaces inferred from harmonic analysis were used to define regional topographic features. Low roughness emphasizes the smooth nature of the basins' topography, where surfaces of homogeneous slope gradient and orientation dominate. High roughness was associated with abrupt changes in gradient and slope orientation such as those affecting crests, valley bottoms and scarp edges present in the mountain chain and in some deep incised valleys in the basins. One of the applications of roughness mapping was its capacity to isolate incised valley segments. The area distribution of incised rivers shows their prevalence in the east. On a regional scale, the topographic surface can be described as a train of NE–SW undulations or waves of 20 km wavelength. These undulations undergo changes in direction and interruptions limited by N–S-trending breaks. E–W and NE–SW troughs and ridges clearly mark structural uplifts and depressions within the Central System. These structures are transverse to the compressive NW–SE stress field that controlled the deformation of the central Iberian Peninsula from the Neogene to the present. They represent the upper crustal folding that accommodates Alpine shortening. N–S breaks coincide with Late Miocene faults that control the basins' sedimentation. Further, associated palaeoseismic structures suggest the recent tectonic activity of N–S faults in the eastern part of the Tajo Basin. Apatite fission track analysis data for this area suggest the occurrence of a significant uplift episode from 7 to 10 Ma which induced the river incisions appearing in the roughness map. N–S and NE–SW faults could be seismogenic sources for the current moderate to low seismic activity of the east Tajo Basin and southeast Central System. Although N–S fault activity has already been established, we propose its significant contribution to shaping the landscape.  相似文献   

19.
The Dien Bien Phu fault zone (DBP), orientated NNE to N, is one of the most seismically active zones in Indochina. In NW Vietnam, this zone is 160 km long and 6–10 km wide, cutting sedimentary and metamorphic rocks of the Late Proterozoic, Palaeozoic and Mesozoic age, as well as Palaeozoic and Late Triassic granitoids. Along the DBP relatively small, narrow pull-apart basins occur, the three largest of which (Chan Nua, Lai Chau and Dien Bien Phu) have been studied in detail. All of them are bounded by sinistral and sinistral-normal faults, responsible for offset and deflected drainage, presence of numerous shutter ridges and displaced terraces and alluvial fans. The normal component of motion is testified to by well-preserved triangular facets on fault scarps, highly elevated straths in river watergaps, overhanging tributary valleys, as well as high and uneven river-bed gradients.Our observations indicate a minimum recent sinistral offset ranging from 6–8 to 150 m for Holocene valleys to 1.2–9.75 km for middle–late Pleistocene valleys in different fault segments. The thickness of Quaternary sediments varies from 5–25 m in the Lai Chau area to some 130 m in the Dien Bien Phu Basin. In the Lai Chau Basin, the middle terrace (23 m) alluvia of Nam Na River at Muong Te bridge have been optically stimulated luminescence/single aliquot regenerative dose technique (OSL-SAR) dated at 23–40 to 13 ka. These sediments were normal-faulted by some 11 m after 13 ka, and mantled by vari-coloured slope loams, 8–12 m thick, containing colluvial wedges composed of angular debris. These wedges were probably formed due to at least three palaeoseismic events postdating 6 ka. In the Dien Bien Phu Basin, in turn, alluvium of the upper Holocene terraces has been OSL-SAR dated to 6.5–7 and 1.7–1.0 ka, whereas the younger (sub-recent) terrace sediments give ages of 0.5–0.2 ka.Displaced terraces and alluvial fans allow us to suppose that the sinistral and sinistral-normal faults bounding narrow pull-apart basins in the southern portion of the DBP fault reveal minimum rates of left-lateral strike-slip ranging from 0.6 to 2 mm/year in Holocene and 0.5–3.8 mm/year in Pleistocene times, whereas rates of Holocene uplift tend to attain 1 mm/year north of Lai Chau and 0.4–0.6 mm/year west of Dien Bien Phu. More precise estimations, however, are difficult to obtain due to poor age control of the displaced drainage. Rates of Quaternary strike-slip are comparable with those of the Red River fault; the sense of movement being, however, opposite. Taking into account the presence of two phases of Late Cenozoic strike-slip of contrasting sense of motion, as well as the geometry of the two fault zones, we hypothesize that the Red River and Dien Bien Phu faults are conjugate faults capable of generating relatively strong earthquakes in the future.  相似文献   

20.
Integration of landform and structural analysis allowed the identification of Late Pleistocene–Holocene pulses of tectonic activity in the Campos do Jordão Plateau with ages and regimes similar to the ones from the continental rift. Fault reactivation along Precambrian shear zones give rise to a series of conspicuous morphotectonic features, determine the formation of stream piracy phenomena, and divide the plateau into smaller blocks. Recognition of these tectonic pulses as well as of their effects in landform development—particularly clear on the Campos de São Francisco at the highest area of the SE edge of the plateau—show that besides the climate-related Quaternary environmental changes significant neotectonic instability should be considered in the geomorphic evolution of the Campos do Jordão Plateau.  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