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 15 毫秒
1.
The segment of the Interandean Depression of Ecuador between Ambato and Quito is characterized by an uppermost Pliocene–Quaternary basin, which is located between two N-S trending reverse basement faults: the Victoria Fault to the west, and the Pisayambo Fault to the east. The clear evidence of E-W shortening for the early Pleistocene (between 1.85 and 1.21 Ma) favours a compressional basin interpretation. The morphology (river deviations, landslides, folded and flexure structures) demonstrates continuous shortening during the late Quaternary. The late Pliocene-Quaternary shortening reached 3400 ± 600 m with a rate of 1.4 ± 0.3 mm yr−1. The E-W shortening is kinematically consistent with the current right-lateral reverse motion along the NE-SW trending Pallatanga Fault. The Quito-Ambato zone appears to act as a N-S restraining bend in a system of large right-lateral strike-slip faults. The compressive deformation which affects the Interandean Depression during the Pliocene is apparently coeval to the beginning subduction of very young oceanic lithosphere north of the Gulf of Guayaquil. The relatively buoyant new crust may have significantly increased the mechanical coupling in the subduction zone from Pliocene to Present.  相似文献   

2.
BILL Higgs 《Basin Research》1988,1(3):155-165
Abstract The Plio-Quaternary history of the Gulf of Corinth Basin has been controlled by dominantly north-south extension. The basin has an asymmetric graben geometry that is, at the present time, controlled by a master fault (the Gulf of Corinth Fault) downthrowing to the north and running offshore from the north Peloponnese coast.
Detailed structural interpretation of single-channel seismic data collected during RRS 'Shackleton' cruise 1/82 combined with onshore structural studies indicates that the basin geometry is not controlled simply by the main Gulf of Corinth Fault. The subsidence history for the uppermost 1 km of sediment can be documented using time-structure contour maps and isochron maps. These indicate that there is a general narrowing in the size of the basin with time, achieved by fault-controlled subsidence switching to antithetic faults concentrated towards the basin centre. It can also be demonstrated that growth of sediments into topographic lows is not only controlled by sea bed rupture but also by more passive sea bed flexure over 'blind' faults at depth.
The main conclusion of this study is that the 3D geometry of the Gulf of Corinth Basin changes not only spatially but also temporally. Active growth faulting and, therefore, the position of depocentres can switch across the basin and the relative importance of synthetic and antithetic faults controls the geometry of the basin, forming grabens, asymmetric grabens and half-grabens throughout the basin history.  相似文献   

3.
The Central Graben in the Danish North Sea sector consists of a series of N–S to NW–SE trending, eastward‐tilted half‐grabens, bound to the east by the Coffee Soil Fault zone. This fault zone has a complex Jurassic history that encompasses at least two fault populations; N–S to NNW–SSE striking faults active in the Late Aalenian–Early Oxfordian, and NNW–SSE to WNW–ESE striking faults forming in Late Kimmeridgian time (sensu gallico), following a short period of tectonic quiescence. Sediment transport across the Coffee Soil Fault zone was controlled by fault array evolution, and in particular the development of relay ramps that formed potential entry points for antecedent drainage systems from the Ringkøbing–Fyn High east of the rift. Fault and isochore trends of the Upper Kimmeridgian–Lower Volgian succession in the northeast Danish Central Graben show that accommodation space was initially generated close to several minor, isolated or overlapping faults. Subsidence became focused along a few master faults in the Early Volgian through progressive linkage of selected faults. Seismic time isochore geometries, seismic facies, amplitude trends and well ties indicate the presence of coarse clastic lithologies locally along the fault zone. The deposits probably represent submarine mass flow deposits supplied from footwall degradation and possibly also from the graben hinterland via a relay ramp. The latter source appears to have been cut off as the relay ramp was breached and the footwall block are uplifted. Fault growth and linkage processes thus controlled the spatial and temporal trends of accommodation space generation and sediment supply to the rift basin.  相似文献   

4.
A regional Magnetotelluric (MT) study, was carried out with 55 MT soundings, distributed along five traverses, across the Kutch Mainland Unit (KMU), on the west coast of India, a region characterized by a series of successive uplifts and intervening depressions in the form of half graben, bounded by master faults. We obtain the deeper electrical structure of the crust beneath Kutch, from 2-D modelling of MT data along the 5 traverses, in order to evaluate the geo-electrical signatures, if any, of the known primary tectonic structures in this region. The results show that the deeper electrical structure in the Kutch region presents a mosaic of high resistive crustal blocks separated by deep-rooted conductive features. Two such crustal conductive features spatially correlate with the known tectonic features, viz., the Kutch Mainland Fault (KMF), and the Katrol Hill Fault (KHF).
An impressive feature of the geo-electrical sections is an additional, well-defined conductive feature, running between Jakhau and Mundra, located at the southern end of each of the five MT traverses and interpreted to be the electrical signature of yet another hidden fault at the southern margin of the KMU. This new feature is named as Jakhau–Mundra Fault (JMF). It is inferred that the presence of JMF together with the Kathiawar Fault (NKF), further south, located at the northern boundary of the Saurashtra Horst, would enhance the possibility of occurrence of a thick sedimentary column in the Gulf of Kutch. The region between the newly delineated fault (JMF) and the Kathiawar fault (NKF) could thus be significant for Hydrocarbon Exploration.  相似文献   

5.
The Zambapala Fault Zone (ZFZ) is located at the link between the offshore structures of the Gulf of Guayaquil and the Guayaquil Caracas Megashear (GCM) that accommodates the northeastward motion of the North Andean Block. We use morphological observations of drainage offset to assess the active motion of the Zambapala Fault. The relation between the horizontal offset amount D of the stream channel and the upstream length L from the offset segment, and offset of beach morphology provide a measurement of the average slip rate of the motion of the fault to an accuracy of a fraction of millimeters per year. The drainage network is short, running down the southeastern slopes of the Zambapala Cordillera (297 m), a Quaternary dome uplifted along a positive flower structure. We measure the D (drainage offset along the fault)/L (drainage length from the fault) relation for the upper and more recent part of the drainage network. The relation suggests that the fault is active at present. Capture occurs along the middle slopes and channel straightening near the littoral plain, hiding part or most of the fault offset. The fault trace crosses the littoral plain, showing 35–40 m offset of the inner beach ridge, and delimiting variations of the beach morphology. The attribution of a maximum age of 5000–6000 years to the oldest beach ridge (the postglacial transgression) allows us to calculate a minimal mean slip rate of 5.8–8 mm year−1. This result confirms that the Guayaquil Caracas Megashear extends to the Gulf of Guayaquil through the Zambapala Fault Zone, which accommodate at least 60–80% of the slip motion of the Guayaquil Carcas Megashear.  相似文献   

6.
The Lake Izabal Basin in Guatemala is a major pull-apart basin along the sinistral Polochic Fault, which is part of the North American and Caribbean plate boundary. The basin infill contains information about the tectonic and sedimentological processes that have imparted a significant control on its sedimentary section. The inception of the basin has been linked to the relative importance of the Polochic Fault in the tectonic history of the plate boundary; yet, its sedimentological record and its inception age have been poorly documented. This study integrates diverse datasets, including industry reports, well logs and reports, well cuttings, vintage seismic data, outcrop observations and geochronological data to constrain the initial infill and age of inception of the basin. The integrated data show that during the Oligocene–Miocene, a marine carbonate platform was established in the region which was later uplifted and eroded in the early Miocene. The fluvial–lacustrine deposits above this carbonate platform are part of the initial infill of the basin and are constrained with zircon weighted-mean 206Pb/238U ages of 12.060 ± 0.008 from a volcanic tuff ~30 m above the unconformity. Sandstone, mudstone and coal dominate the interval from 12 to 4 Ma, with an increase in conglomerate correlating to the uplift of the Mico Mountains and San Gil Hill at 4 Ma. Fault switch activity between the Polochic and Motagua faults has been hypothesized to explain total offset along the Polochic Fault and the geologic and geodetic slip rates along the two faults. The 12 Ma age determined for the initial infill of the basin confirms this hypothesis. Consequently, our study confirms that at ~12 Ma the Polochic Fault served as the main fault of the plate boundary with inferred slip rates ranging from 13 to 21 mm/yr with a strong possibility that the Polochic Fault was, at some point between 15 Ma and 7 Ma, the only active fault of the plate boundary. The results of this study show that tectonic records preserved in sediments of strike-slip basins improve the understanding of the relative significance of individual faults and the implications with respect to strain partitioning throughout its tectonic history.  相似文献   

7.
Summary. The pole positions obtained from Upper Cretaceous and Eocene tuffs and dykes of the Mesudiye region, which is located between the north of the North Anatolian Fault Zone and eastern Black Sea coast, are at 75.3° N, 275.4° E and 41.7° N, 138.6° E respectively. These results, taken together with the results of previous studies of Turkish rocks, suggest that rotational movements of Turkey have been 45–50° counterclockwise to Europe since the Upper Cretaceous.  相似文献   

8.
Formed during an early compressional period in the opening of North Atlantic Ocean, a Tertiary fold-thrust belt extends along the mid-to- southern part of the western coast of Spitsbergen. Complex thrust structures involve the basement (Caledonian and older) and many shallow dipping thrust faults dissect the overlying cover rocks (Devonian and younger) in Oscar II Land in the northern part of the belt. Some of these faults occur within the basement rocks with slivers or fault blocks of the cover rocks from south-western Brøggerhalvøya to innermost St. Jonsfjorden in north-eastern Oscar II Land. Six of the slivers contain Carboniferous rocks and one is a fault-bounded block with Devonian rocks. These steeply west-dipping faults form a complex fault system- EOFC (Engelskbukta-Osbornbreen Fault Complex) - within the basement area. The lithological units of the basement are separated by faults within the EOFC, which is structurally continuous with the Brøggerhalvøya fold-thrust zone to the north and is thought to continue to the fold-thrust zone on the south-eastern coast of St. Jonsfjorden. Some previous authors considered that the two lithologically contrasting Vendian diamictites and intervening Moefjellet Formation are stratigraphically continuous and defined two separate tilloid successions in the present area. This interpretation has been extended over the whole of western Spitsbergen. However, the present study indicates that these two tilloid formations and the Moefjellet Formation are separated by the faults, probably thrusts, within the EOFC and are not in a continuous stratigraphic relation. Therefore, the two-stage history of Vendian glaciation seems questionable.  相似文献   

9.
The Hazar Basin is a 25 km‐long, 7 km‐wide and 216 m‐deep depression located on the central section of the East Anatolian Fault zone (eastern Turkey) and predominantly overlain by Lake Hazar. This basin has been described previously as a pull‐apart basin because of its rhombic shape and an apparent fault step‐over between the main fault traces situated at the southwestern and northeastern ends of the lake. However, detailed structural investigation beneath Lake Hazar has not been undertaken previously to verify this interpretation. Geophysical and sedimentological data from Lake Hazar were collected during field campaigns in 2006 and 2007. The analysis of this data reveals that the main strand of the East Anatolian Fault (the Master Fault) is continuous across the Hazar Basin, connecting the two segments previously assumed to be the sidewall faults of a pull‐apart structure. In the northeastern part of the lake, an asymmetrical subsiding sub‐basin, bounded by two major faults, is cross‐cut by the Master Fault, which forms a releasing bend within the lake. Comparison of the structure revealed by this study with analogue models produced for transtensional step‐overs suggests that the Hazar Basin structure represents a highly evolved pull‐apart basin, to the extent that the previous asperity has been bypassed by a linking fault. The absence of a step‐over structure at the Hazar Basin means that no significant segmentation boundary is recognised on the East Anatolian Fault between Palu and Sincik. Therefore, this fault segment is capable of causing larger earthquakes than recognised previously.  相似文献   

10.
Microseismicity and faulting geometry in the Gulf of Corinth (Greece)   总被引：7，自引：0，他引：7  
During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al . (1985 ) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 ( Rigo et al . 1996 ), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes ( Hatzfeld et al . 1996 ; Bernard et al . 1997 ) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).  相似文献   

11.
Our understanding of continental rifting is, in large parts, derived from the stratigraphic record. This record is, however, incomplete as it does not often capture the geomorphic and erosional signal of rifting. New 3D seismic reflection data reveal a Late Permian-Early Triassic landscape incised into the pre-rift basement of the northern North Sea. This landscape, which covers at least 542 km2, preserves a drainage system bound by two major tectonic faults. A quantitative geomorphic analysis of the drainage system reveals 68 catchments, with channel steepness and knickpoint analysis of catchment-hosted palaeo-rivers showing that the landscape preserved a >2 Myr long period of transient tectonics. We interpret that this landscape records a punctuated uplift of the footwall of a major rift-related normal fault (Vette Fault) at the onset of rifting. The landscape was preserved by a combination of relatively rapid subsidence in the hangingwall of a younger fault (Øygarden Fault) and burial by post-incision sediments. As such, we show how and why erosional landscapes are preserved in the stratigraphic record, and how they can help us understand the tectono-stratigraphic evolution of ancient continental rifts.  相似文献   

12.
Extensional tectonic regimes in the Aegean basins during the Cenozoic   总被引：4，自引：0，他引：4  
Abstract Kinematics of faults in the Northern Aegean show three extensional tectonic regimes the tensional directions of which trend (1) WNW-ESE, (2) NE-SW and (3) N-S. These were active during the Upper Miocene, Pliocene-Lower Pleistocene and Mid Pleistocene-Present day, respectively. The main characteristics of the stress patterns (1) and (2) on the overall Aegean is tentatively explained by variations of the horizontal lithospheric stress value σzz due to the slab push and of the vertical lithospheric stress value σzz due to mass heterogeneities. During the Mid Pleistocene-Present, due to the slab push, tectonics were compressional along the arc boundary: σzz was σ1. In the Aegean basins, tectonics were extensional, c2Z was σ1 as a consequence of the thickness of the continental crust and, possibly of an updoming asthenosphere; thus σzz became σ2, allowing tension σ3 to be orthogonal to the compression along the arc, i.e. to be roughly parallel to the arc trend. During the Pliocene-Lower Pleistocene, the extensional regime was distinctly different. The tensional directions were roughly radial to the arc. It is suggested that σzz was weakly compressional, or eventually tensional, due a seaward migration of the slab so that σzz became σ3. In the Northern Aegean, the stress pattern has been also controlled by the westward push of the Anatolian landmass. During the Mid Pleistocene-Present day, this was typically extensional (al was vertical) and the right lateral strike-slip motion on the North Anatolian Fault transformed into a N-S-stretching, E-W-shortening of the Northern Aegean. Dextral strike-slip motions along the North Aegean Trough fault zone were possible on NE-SW-striking faults. During the Pliocene-Lower Pleistocene, normal fault components were higher; however, because the angle between the NE-SW trend of the tensional axis and the strike of the fault zone was acute, dextral strike-slip components were possible on all the faults striking NE-SW to E-W. A clockwise 15o rotation of Limnos with respect to Samothraki, Thraki and Thassos, suggested by structural data, was probably associated with these dextral motions. The WNW-ESE trending tension during the Upper Miocene indicates that the dextral North Anatolian Fault had not yet merged into the North Aegean Trough fault zone at that time. We propose that the formation of Aegean basins during the Cenozoic was related to the activity of two major Hellenic arcs. The ‘Pelagonian-Pindic Arc’ resulted in the formation of the subsident Aegean basins of Middle Eocene-Lower Miocene age and of the older Northern Aegean orogenic volcanism. The ‘Aegean Arc’ resulted in the formation of the subsident Aegean basins of Middle Miocene to Present day age and of the Southern Aegean orogenic volcanism. Were these arcs associated with a unique subduction zone or with two such zones ? In the first case, the slab is no more than 16 Myr old, in the second it may be as old as 45–50 Myr. The answer depends on the accuracy of the seismic tomography profiles.  相似文献   

13.
Summary. Three-component seismograms of small local earthquakes recorded in the Peter the First Range of mountains near Garm, Tadzhikistan SSR, display shear-wave splitting similar to that previously observed near the North Anatolian Fault in Turkey. The Peter the First Range is in a region of compressional tectonics, whereas the North Anatolian Fault is a comparatively simple strike-slip fault. Detailed analysis of the Turkish records suggests that the splitting is diagnostic of crack-induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression. Preliminary examination of paper records from Garm shows that most shear waves arriving within the shear-wave window display shear-wave splitting, and that the polarizations of leading shear-waves are consistently aligned in a NE/SW direction. The area is complicated and the tectonics are not well-understood, but the NE/SW direction is approximately perpendicular to the compressional axis in many of the fault-plane mechanisms of the earthquakes. These earthquakes are usually at depths between 5 and 12 km, although there are some deeper events nearby.
Parallel shear-wave polarizations, such as those observed, are expected to indicate the strike of nearly vertical parallel microcracks, which would be aligned parallel to the direction of maximum compression. Thus the shear-wave polarizations in the Peter the First Range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place.  相似文献   

14.
The Gulf of Corinth is one of the most active extensional regions in the Mediterranean area characterized by a high rate of seismicity. However, there are still open questions concerning the role and the geometry of the numerous active faults bordering the basin, as well as the mechanisms governing the seismicity. In this paper, we use a 2-D plane strain finite element analysis to constrain the upper crust rheology by modelling the available deformation data (GPS and geomorphology). We consider a SSW–NNE cross-section of the rift cutting the main active normal faults (Aigion, West Eliki and Off-Shore faults). The models run for 650 Kyr assuming an elasto-viscoplastic rheology and 1.3 cm yr−1 horizontal extension as boundary condition (resulting from GPS data). We model the horizontal and vertical deformation rates and the accumulation of plastic strain at depth, and we compare them with GPS data, with long term uplift rates inferred from geomorphology and with the distribution of seismicity, respectively. Our modelling results demonstrate that dislocation on high-angle normal faults in a plastic crustal layer plays a key role in explaining the extremely localized strain within the Gulf of Corinth. Conversely, the contribution of structures such as the antithetic Trizonia fault or the buried hypothetical subhorizontal discontinuity are not necessary to model observed data.  相似文献   

15.
《Basin Research》2018,30(4):688-707
Investigations of syn‐sedimentary growth faults in the Last Chance delta (Ferron Sandstone, Utah, USA) show that fault‐bounded half‐grabens arrested high amounts of sand in the mouth bar and/or distributary channel areas. Fault‐controlled morphology causes changes in routing of the delta top to delta front drainage towards the long axis of half‐grabens. Faulting was spatially and temporally non‐systematic, and polyphase, with 3D cusp/listric fault geometries instigated by linkage of variously oriented segments. Hanging wall rollover folds consisting of wedge‐shaped syn‐kinematic sand attest to rapid <1‐m slip increments on faults followed by mild erosion along crests of fault blocks and sedimentary infill of adjacent accommodation. Triangle‐zones in prodelta to delta front muds are located underneath steeper faults and interconnected rotated fault‐flats. Their geometry is that of antiformal stack duplexes, in an arrangement of low‐angle‐to‐bedding normal faults at the base, replaced by folded thrusts upwards. These faults show a brittle, frictional flow deformation mechanism ascribed to early compaction of mud. For syn‐kinematic sand, there is a change from general granular/hydroplastic flow in shear zones to later brittle failure and cataclasis, a transition instigated by precipitation of calcite cement. Extensional faulting in the Last Chance delta was likely controlled by gravity driven collapse towards the delta slope and prodelta, as is commonly observed in collapsing deltas. The trigger and driving mechanism is envisioned as localized loads from sand deposited within distributary channels/mouth bars and fault‐controlled basins along the delta top. A regional tilt and especially displacement of compacted mud below sand bodies towards less compacted muds also contributed to the faulting.  相似文献   

16.
The Corinth rift (Greece) is one of the world's most active rifts. The early Plio‐Pleistocene rift is preserved in the northern Peloponnese peninsula, south of the active Corinth rift. Although chronostratigraphic resolution is limited, new structural, stratigraphic and sedimentological data for an area >400 km2 record early rift evolution in three phases separated by distinct episodes of extension rate acceleration and northward fault migration associated with major erosion. Minimum total N–S extension is estimated at 6.4–7.7 km. The earliest asymmetrical, broad rift accommodated slow extension (0.6–1 mm a?1) over >3 Myrs and closed to the west. North‐dipping faults with throws of 1000–2200 m defined narrow blocks (4–7 km) with little footwall relief. A N‐NE flowing antecedent river system infilled significant inherited relief (Lower group). In the earliest Pleistocene, significant fluvial incision coincided with a 15 km northward rift margin migration. Extension rates increased to 2–2.5 mm a?1. The antecedent rivers then built giant Gilbert‐type fan deltas (Middle group) north into a deepening lacustrine/marine basin. N‐dipping, basin margin faults accommodated throws <1500 m. Delta architecture records initiation, growth and death of this fault system over ca. 800 ka. In the Middle Pleistocene, the rift margin again migrated 5 km north. Extension rate increased to 3.4–4.8 mm a?1. This transition may correspond to an unconformity in offshore lithostratigraphy. Middle group deltas were uplifted and incised as new hangingwall deltas built into the Gulf (Upper group). A final increase to present‐day extension rates (11–16 mm a?1) probably occurred in the Holocene. Fault and fault block dimensions did not change significantly with time suggesting control by crustal rheological layering. Extension rate acceleration may be due to strain softening or to regional tectonic factors.  相似文献   

17.
《Basin Research》2018,30(Z1):382-400
High‐resolution acoustic and seismic data acquired 100 km offshore Cape São Vicente, image with unprecedented detail one of the largest active reverse faults of the SW Iberian Margin, the Horseshoe Fault (HF). The HF region is an area seismogenically active, source of the largest magnitude instrumental and historical earthquake (Mw > 6) occurred in the SW Iberian Margin. The HF corresponds to a N40 trending, 110 km long, and NW‐verging active thrust that affects the whole sedimentary sequence and reaches up to the seafloor, generating a relief of more than 1 km. The along‐strike structural variability as well as fault trend suggests that the HF is composed by three main sub‐segments: North (N25), Central (N50) and South (N45). Swath‐bathymetry, TOBI sidescan sonar backscatter and parametric echosounder TOPAS profiles reveal the surface morphology of the HF block, characterized by several, steep (20°) small scarps located on the hangingwall, and a succession of mass transport deposits (i.e. turbidites) on its footwall, located in the Horseshoe Abyssal Plain. A succession of pre‐stack depth‐migrated multichannel seismic reflection profiles across the HF and neighbouring areas allowed us to constrain their seismo‐stratigraphy, structural geometry, tectono‐sedimentary evolution from Upper Jurassic to present‐day, and to calculate their fault parameters. Finally, on the basis of segment length, surface fault area and seismogenic depth we evaluated the seismic potential of the HF, which in the worst‐case scenario may generate an earthquake of magnitude Mw 7.8 ± 0.1. Thus, considering the tectonic behaviour and near‐shore location, the HF should be recognized in seismic and tsunami hazard assessment models of Western Europe and North Africa.  相似文献   

18.
Deeply incised drainage networks are thought to be robust and not easily modified, and are commonly used as passive markers of horizontal strain. Yet, reorganizations (rearrangements) appear in the geologic record. We provide field evidence of the reorganization of a Miocene drainage network in response to strike–slip and vertical displacements in Guatemala. The drainage was deeply incised into a 50‐km‐wide orogen located along the North America–Caribbean plate boundary. It rearranged twice, first during the Late Miocene in response to transpressional uplift along the Polochic fault, and again in the Quaternary in response to transtensional uplift along secondary faults. The pattern of reorganization resembles that produced by the tectonic defeat of rivers that cross growing tectonic structures. Compilation of remote sensing data, field mapping, sediment provenance study, grain‐size analysis and Ar40/Ar39 dating from paleovalleys and their fill reveals that the classic mechanisms of river diversion, such as river avulsion over bedrock, or capture driven by surface runoff, are not sufficient to produce the observed diversions. The sites of diversion coincide spatially with limestone belts and reactivated fault zones, suggesting that solution‐triggered or deformation‐triggered permeability have helped breaching of interfluves. The diversions are also related temporally and spatially to the accumulation of sediment fills in the valleys, upstream of the rising structures. We infer that the breaching of the interfluves was achieved by headward erosion along tributaries fed by groundwater flow tracking from the valleys soon to be captured. Fault zones and limestone belts provided the pathways, and the aquifers occupying the valley fills provided the head pressure that enhanced groundwater circulation. The defeat of rivers crossing the rising structures results essentially from the tectonically enhanced activation of groundwater flow between catchments.  相似文献   

19.
The Billefjorden Fault Zone represents a major lineament on Spitsbergen with a history of tectonic activity going back into the Devonian and possibly earlier. Recent structural, sedimcntological and stratigraphical investigations indicate that most of the stratigraphic thickness variations within the Mesozoic strata along the Billefjorden Fault Zone south of Isfjordcn are due to Tertiary compressional tectonics related to the transpressive Eocene West-Spitsbergen Orogeny. No convincing evidence of distinct Mesozoic extensional events, as suggested by previous workers, has been recognized. Tertiary compressional tectonics are characterized by a combined thin-skinned/thick-skinned structural style. Decollement zones arc recognized in the Triassic Sassendalen Group (tower Décollement Zone) and in the Jurassic/Cretaceous Janusfjellet Subgroup (Upper Décollement Zone). East-vergent folding and reverse faulting associated with these decollement' zones have resulted in the development of compressional structures, of which the major arc the Skolten and Tronfjellct Anticlines and the Advcntelva Duplex. Movements on one or more high angle east-dipping reverse faults in the pre-Mesozoic basement have resulted in the development of the Juvdalskampcn Monocline, and are responsible for out-of-sequence thrusting and thinning of the Mesozoic sequence across the Billefjorden Fault Zone. Preliminary shortening calculations indicate an eastward displacement of minimum 3-4 km, possibly as much as 10 km for the Lower Cretaceous and younger rocks across the Billefjorden Fault Zone.  相似文献   

20.
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   

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