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1.
New paleomagnetic data from 11 sites in layered gabbros and lava flows from the Oman Ophiolite indicate stable, early remagnetizations and suggest that the southern portion of the ophiolite (the Wadi Tayin, Sumail, Nakhl-Rustaq and Haylayn massifs) is relatively unrotated since detachment near the paleoridge. The gabbros possess a magnetization carried by a combination of primary and secondary magnetites derived from hydrothermal alteration. Evidence from positive tilt tests, constancy of remanence directions in differing magnetic mineralogies and agreement with previous paleomagnetic data, however, suggests that this remagnetization was acquired early – analogous to the remagnetization of the V2 volcanic series. Thus, the evidence implies that the southern portion of the ophiolite has been primarily translated from the paleoridge since the time of V2 remagnetization, and 120° of clockwise rotation affecting the northern Oman Ophiolite is internal to the ophiolite, rather than a combination of internal and global rotation as previously hypothesized. Given this evidence, we propose a simplified model of a rapid, active microplate rotation of a portion of the ophiolite resulting from spreading at an EPR-type propagating ridge at a high angle to the previous spreading direction. Paleomagnetic data from this and previous studies can be well explained by a rapidly rotating microplate, similar to the kinematic evolution documented for the Juan Fernandez microplate in the modern setting. 相似文献
2.
Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan. 相似文献
3.
The Orange Basin records the development of the Late Jurassic to present day volcanic-rifted passive margin of Namibia. Regional extension is recorded by a Late Jurassic to Lower Cretaceous Syn-rift Megasequence, which is separated from a Cretaceous to present day post-rift Megasequence by the Late Hauterivian (ca. 130 Ma) break-up unconformity. The Late Cretaceous Post-rift evolution of the basin is characterized by episodic gravitational collapse of the margin. Gravitational collapse is recorded as a series of shale-detached gravity slide systems, consisting of an up-dip extensional domain that is linked to a down-dip zone of contraction domain along a thin basal detachment of Turonian age. The extensional domain is characterized by basinward-dipping listric faults that sole into the basal detachment. The contractional domain consists of landward-dipping listric faults and strongly asymmetric basinward-verging thrust-related folds. Growth stratal patterns suggest that the gravitational collapse of the margin was short-lived, spanning from the Coniacian (ca. 90 Ma) to the Santonian (ca. 83 Ma). Structural restorations of the main gravity-driven system show a lack of balance between up-dip extension (24 km) and down-dip shortening (16 km). Gravity sliding in the Namibian margin is interpreted to have occurred as a series of episodic short-lived gravity sliding between the Cenomanian (ca. 100 Ma) and the Campanian (ca. 80 Ma). Gravity sliding and spreading are interpreted to be the result of episodic cratonic uplift combined with differential thermal subsidence. Sliding may have also been favoured by the presence of an efficient detachment layer in Turonian source rocks. 相似文献
4.
Perrin Mireille Plenier Guillaume Dautria Jean-Marie Cocuaud Emmanuel Prévot Michel 《Marine Geophysical Researches》2000,21(3-4):181-194
Thirty-two flows (247 cores) were sampled in the V1 (Geotimes) and V2 (Lasail) volcanic units of the Semail ophiolite, Oman (Aswad, Fizh, Hilti, Sarami, Wuqbah, and Tayin massifs). Paleomagnetic analysis of the samples was complicated by a large overlap of the two components of magnetization carried by the rocks: a crystalline remanent magnetization (CRM) acquired in the present day field, probably during weathering, and an older CRM probably produced by oxidation of the original titanomagnetites during hydrothermal event(s). If the magnetization carried by the V1 samples was acquired during the hydrothermal event related to the emplacement of these lava, e.g., during and/or shortly after cooling, the tectonic unity of the northern domain has to be questioned and a differential rotation considered between the Aswad and Hilti-Sarami massifs but, by the time of emplacement of the V2 series, this northern area seems to behave as one large unit. As only one set of data is available for the southern Tayin-Sumail massif, it is premature but a possible relative rotation on the order of 90° can be suspected between the Hilti-Sarami and Tayin-Sumail massifs, rotation which would have occurred after emplacement of the V2 series. 相似文献
5.
The central part of the Zagros Fold-Thrust Belt is characterized by a series of right-lateral and left-lateral transverse tear fault systems, some of them being ornamented by salt diapirs of the Late Precambrian–Early Cambrian Hormuz evaporitic series. Many deep-seated extensional faults, mainly along N–S and few along NW–SE and NE–SW, were formed or reactivated during the Late Precambrian–Early Cambrian and generated horsts and grabens. The extensional faults controlled deposition, distribution and thickness of the Hormuz series. Salt walls and diapirs initiated by the Early Paleozoic especially along the extensional faults. Long-term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks. They created weak zones in the sedimentary cover, located approximately above the former and inactive deep-seated extensional faults. The N–S to NNE–SSW direction of tectonic shortening during the Neogene Zagros folding was sub-parallel with the strikes of the salt walls and rows of diapirs. Variations in thickness of the Hormuz series prepared differences in the basal friction on both sides of the Precambrian–Cambrian extensional faults, which facilitated the Zagros deformation front to advance faster wherever the salt layer was thicker. Consequently, a series of tear fault systems developed along the rows of salt diapirs approximately above the Precambrian–Cambrian extensional faults. Therefore, the present surface expressions of the tear fault systems developed within the sedimentary cover during the Zagros orogeny. Although the direction of the Zagros shortening could also potentially reactivate the basement faults as strike-slip structures, subsurface data and majority of the moderate-large earthquakes do not support basement involvement. This suggests that the tear fault systems are detached on top of the Hormuz series from the deep-seated Precambrian–Cambrian extensional faults in the basement. 相似文献
6.
7.
The Gebel Yelleg area includes a number of folds belonging to the northern Sinai Syrian Arc structures. Detailed surface structural mapping and subsurface (seismic and borehole) data show that the Gebel Yelleg structures are related to Late Cretaceous-Early Tertiary inversion of a Jurassic asymmetric (or half) graben formed during the opening of Neotethys. The inversion structures include a large (45-km long) asymmetric fold (Yelleg Anticline) with a steep flank overlying the southeastern (main) bounding fault of the inverted half graben as well as some right-stepped en echelon folds overlying the northwestern bounding fault of the half graben. The large inversion anticline is dissected by a large number of long, nearly orthogonal normal faults whereas the en echelon folds are dissected by transverse normal faults and two sets of oblique-slip faults. Inversion of the northern Sinai extensional basins is related to Africa-Eurasia convergence and was probably transpressional with a small component of dextral slip. This study shows that the magnitude of inversion in the northern Sinai fold belt decreases toward the southern boundary of the Jurassic extensional province. 相似文献
8.
Cuimei Zhang Zhenfeng Wang Zhipeng Sun Zhen Sun Jianbao Liu Zhangwen Wang 《Marine Geophysical Researches》2013,34(3-4):309-323
Located at the intersection between a NW-trending slip system and NE-trending rift system in the northern South China Sea, the Qiongdongnan Basin provides key clues for us to understand the proposed extrusion of the Indochina Block along with Red River Fault Zone and extensional margins. In this paper we for the first time systematically reveal the striking structural differences between the western and eastern sector of the Qiongdongnan Basin. Influenced by the NW-trending slip faults, the western Qiongdongnan Basin developed E–W-trending faults, and was subsequently inverted at 30–21 Ma. The eastern sector was dominated by faults with NE orientation before 30 Ma, and thereafter with various orientations from NE, to EW and NW during the period 30–21 Ma; rifting display composite symmetric graben instead of the composite half graben or asymmetric graben in the west. The deep and thermal structures in turn are invoked to account for such deformation differences. The lithosphere of the eastern Qiongdongnan Basin is very hot and thinned because of mantle upwelling and heating, composite symmetric grabens formed and the faults varied with the basal plate boundary. However, the Southern and Northern Uplift area and middle of the central depression is located on normal lithosphere and formed half grabens or simple grabens. The lithosphere in the western sector is transitional from very hot to normal. Eventually, the Paleogene tectonic development of the Qiongdongnan Basin may be summarized into three stages with dominating influences, the retreat of the West Pacific subduction zone (44–36 Ma), slow Indochina block extrusion together with slab-pull of the Proto-South China Sea (36–30 Ma), rapid Indochina block extrusion together with the South China Sea seafloor spreading (30–21 Ma). 相似文献
9.
The Goliat field consists of Middle to Late Triassic reservoirs which exploit an elongate anticline (the Goliat anticline) in the hanging wall of the Troms-Finnmark Fault Complex (TFFC), offshore Norway. The area is affected by a dense network of multiple trending fault populations which historically have inhibited seismic resolution owing to persistent fault shadow. Seismic investigations utilising a multi-azimuth three-dimensional survey (EN0901) allow much crisper delineation of seismic features previously unattainable by vintage single-azimuth surveys. Three dominant fault populations are identified in the area, two of which parallel TFFC segments, the Alke–Goliat (WSW–ENE) and the Goliat–Tornerose (NNE–SSW) segments. The Goliat field is located within a zone of intersection between both segments. A third E–W trending fault population, the Hammerfest Regional population, is likely influenced by the offshore extension of the Trollfjord-Komagelv Fault Complex (TKFZ). A local NW–SE trending fault population, the Goliat Central, affects the Goliat anticline and partitions Alke–Goliat and Goliat–Tornerose subsidiary faults resulting in curvilinear traces. Several cross-cutting relationships between fault populations are observed and may provide fluid compartmentalisation in the reservoirs. Compilation of regional transects and the EN0901 survey provides new insight into the evolution of the Goliat anticline which is underlain by a fault-bound basement terrace that became established in the Late Palaeozoic. The structure is interpreted to have formed due to vertical segmentation of the TFFC and cores the overlying broad anticline. The western limb of the Goliat anticline likely formed by differential compaction, whereas the eastern limb is primarily a result of hanging wall roll-over linked to variable listric to ramp-flat-ramp fault geometry. Rifting took place in the Palaeozoic (Carboniferous to Permian?), and in the Mesozoic, possibly as early as the Late Triassic, with a major event in the Late Jurassic to Early Cretaceous. Minor reactivations continued into the Late Cretaceous, and possibly the Early Cenozoic. Mesozoic syn-kinematic geometries in the hanging wall of the Goliat–Tornerose TFFC segment are consistent with deposition during up section propagation of a blind fault, over which, a monocline was established and later breached. Jogs (abrupt orientation changes) in fault traces, transverse folds (associated with displacement maxima/minima) and vertical fault jogs suggest the TFFC existed as a greater number of segments prior to amalgamation during the Late Triassic to Jurassic. A phase of Barremian inversion created local compression structures above blind extensional faults, and deeper seated buttressing against large faults. Polygonal faults affect the Late Cretaceous to Early Cenozoic successions. 相似文献
10.
Stuart Hardy 《Marine and Petroleum Geology》2011,28(5):966-972
A discrete element model is used to investigate progressive cover deformation above a steep (70°), basement normal fault. The cover materials are homogenous with frictional material behavior. In the model shown here both normal and reverse faults in the cover accommodate displacement on the underlying basement fault. The earliest faults are curved, reverse faults which propagate upwards from the basement fault tip into the proto hanging wall. These are replaced, progressively towards the footwall, by subvertical to steep normal faults and finally by a normal fault which dips at an angle predicted by Mohr-Coulomb theory. Thus, most early, secondary structures are located in the hanging-wall of the final, through-going, fault. This structural evolution produces an asymmetric, triangular zone of deformation above the basement fault tip which superficially resembles that associated with trishear; however, its progressive development is quite different. Results also emphasize that the occurrence of reverse faults in extensional settings is not diagnostic of inversion. 相似文献
11.
Cenozoic structures in the Bohai Bay basin province can be subdivided into eleven extensional systems and three strike-slip systems. The extensional systems consist of normal faults and transfer faults. The normal faults predominantly trend NNE and NE, and their attitudes vary in different tectonic settings. Paleogene rifting sub-basins were developed in the hanging walls of the normal faults that were most likely growth faults. Neogene–Quaternary sequences were deposited in both the rifting sub-basins and horsts to form a unified basin province. The extensional systems were overprinted by three NNE-trending, right-lateral strike-slip systems (fault zones). Although the principal displacement zones (PDZ) of the strike-slip fault zones are developed only in the basement and lower basin sequences in some cross sections, the structural deformation characteristics of the upper basin sequences also indicate that they are basement-involved, right-lateral strike-slip fault zones. According to the relationships between faults and sedimentary sequences, the extensional systems were mainly developed from the middle Paleocene to the late Oligocene, whereas the strike-slip systems were mainly developed from the Oligocene to the Miocene. Strike-slip deformation was intensified as extensional deformation was weakened. Extensional deformation was derived from horizontal tension induced by upwelling of hot mantle material, whereas strike-slip deformation was probably related to a regional stress field induced by plate movement. 相似文献
12.
The Oman Mountains preserve Permo-Mesozoic sedimentary rocks of the Arabian passive margin that were overridden during Late Cretaceous time by deep-water sediments of the Hawasina units and by the Semail Ophiolite, a portion of the Neo-Tethyan oceanic crust and upper mantle. Passive margin sequences are exposed in the Jabal Akhdar Culmination (JAC) and in the Jabal Salakh Range at the Oman Mountains thrust front. Samples of these sequences were investigated by X-ray diffraction of the clay size fraction to evaluate the thermal evolution of the subophiolite rocks and estimate the thickness and extent of the obducted ophiolites.The sedimentary succession from the northern flank of the JAC shows a clay mineral assemblage characterized by long-range ordered mixed layer I-S with an illite content between 85% and 92% and the occurrence of pyrophyllite and/or paragonite, suggesting maximum paleotemperatures between 150° and 200 °C in deep diagenetic conditions. On the southern flank of the JAC, temperature dependent clay minerals indicate maximum paleotemperatures, ranging between 120° and 150 °C, indicating a reduced ophiolite thickness towards the south. Ooid strain analyses of the subophiolite rocks from the northern flank of JAC show a component of flattening and stretching in the z-x plane as a result of plastic deformation and pressure solution. On the southern flank, such ductile deformation is absent, suggesting a brittle rheology for the subophiolite carbonates and a reduced overburden. 1D thermal modeling reveals that the sub-ophiolite units of the JAC were overthrust by 4.5 km-thick Semail Ophiolite and Hawasina units during the Coniacian, and exhumed since the Campanian. The subophiolite rocks of the Jabal Salakh Range were buried under 1.35 km of synobduction clastics and overthrust by 2 km-thick Hawasina units, suggesting a decrease of the thickness of allochthonous units from NE to SW, consistent with strain analysis and their direction of emplacement. 相似文献
13.
Metalliferous and pelagic sediments are exposed within and above the extrusive successions of the Upper Cretaceous Oman ophiolite which, on the basis of mostly geochemical evidence, is believed to have formed in an incipient marginal basin setting located above a NE-dipping subduction zone. The ophiolitic extrusives document various volcano-tectonic settings which include the axial zones of a spreading ridge, fault-controlled seamounts and off-axis volcanic edifices. Most of the Fe, Mn and trace metal-enriched sediments studied are interpreted as precipitates formed by oxidation of solutions derived from high-temperature sulphide-precipitating vents. The trace element content (e.g. REE and Sr) was largely scavenged from seawater. The sediments are similar to the dispersed metalliferous sediments on the flanks of modern spreading ridges, and the ‘basal’ sediments of DSDP wells and of other ophiolite complexes (e.g. Troodos, Cyprus).Distinctive mound structures located low in the lavas are attributed to percolation of sulphide-rich solutions into already deposited metalliferous oxide sediments. The resulting iron-silica rock was probably originally precipitated as ferruginous silicates.Major massive sulphides formed off-axis at the base of intermediate-basic edifices of volcanic arc affinities. Fe, Mn and trace metal enrichment in the sediment cover of a flat-topped seamount of axial lavas is interpreted as a dispersion halo around the largest massive sulphide orebody which is situated 5 km away (Lasail). Small massive sulphide bodies are common in the axial lavas particularly along major seafloor fault zones. The metalliferous sediments, locally precipitated near these vents, are ferromanganiferous, but trace metal-depleted.The metalliferous and pelagic sediment cover of the extrusive successions, generally, documents waning hydrothermal input after volcanism ended in the area.A model is discussed in which the ophiolite was created at a spreading axis above a subduction zone dipping away from the Arabian continental margin. With progressive subduction this crust approached the margin. Initially, calcareous sediment accumulated above the calcite compensation depth (CCD), but then non-calcareous radiolarites were deposited as the ophiolitic crust approached the continental margin where the CCD was higher and marginal upwelling possibly enhanced productivity. As the edge of the Arabian continental margin entered the trench, the over-riding ophiolite was regionally uplifted allowing short-lived chalk accumulation above the CCD. This was followed by volcaniclastic deposition related to the tectonic emplacement. 相似文献
14.
Structural analysis of the Indian Merge 3D seismic survey identified three populations of normal faults within the Exmouth Sub-basin of the North West Shelf volcanic margin of Australia. They comprise (1) latest-Triassic to Middle Jurassic N-NNE-trending normal faults (Fault Population I); (2) Late Jurassic to Early Cretaceous NE-trending normal faults (Fault Population II); and (3) latest-Triassic to Early Cretaceous N-NNE faults (Fault Population III). Quantitative evaluation of >100 faults demonstrates that fault displacement occurred during two time periods (210–163 and 145–138 Ma) separated by ∼20 Myr of tectonic quiescence. Latest Jurassic to Early Cretaceous (145–138 Ma) evolution comprises magmatic addition and contemporaneous domal uplift ∼70 km wide characterised by ≥ 900 m of denudation. The areally restricted subcircular uplift centred on the southern edge of the extended continental promontory of the southern Exmouth Sub-basin supports latest Jurassic mantle plume upwelling that initiated progradation of the Barrow Delta. This polyphase and bimodal structural evolution impacts current hydrocarbon exploration rationale by defining the nature of latest Jurassic to Early Cretaceous fault nucleation and reactivation within the southern Exmouth Sub-basin. 相似文献
15.
In this paper, the diagenesis from either side of a major Cenozoic reverse fault in the Northern Oman Mountains is documented. Detailed petrographical and geochemical analysis of calcite-filled fractures in carbonate strata of Late Triassic and Early Cretaceous age in the hanging wall and footwall in Wadi Ghalilah reflect a different diagenetic history. In both hanging wall and footwall most of the fractures are pre-burial, extensional in origin, formed by a crack-seal mechanism, and the calcite vein infill has a host-rock buffered signature. In the hanging wall, the fluid responsible for calcite precipitation of these extensional fractures was a marine fluid at 60 °C. These veins predate deep burial and contractional tectonic deformation and consequently do not provide any information about syntectonic fluid flow. Neither do the pre-burial extension fractures in the footwall which are also host-rock buffered. The fractures post-dating the tectonic stylolitization in the footwall, by contrast, show evidence of syntectonic migration of saline formation waters at temperatures between 80 and 160 °C during contractional deformation. These fluids probably were sourced from the subsurface via the reverse fault, which acted as a fluid conduit. At the same time, however, this fault functioned as a permeability barrier towards the hanging wall, since no evidence of syntectonic fluid flow is present here. In this way compartmentalization of the hanging wall and footwall block was realized. 相似文献
16.
Controls on turbidite sand deposition during gravity-driven extension of a passive margin: examples from Miocene sediments in Block 4, Angola 总被引：1，自引：0，他引：1
In recent years, exploration of the Lower Congo Basin in Angola has focused on the Neogene turbidite sand play of the Malembo Formation. Gravity tectonics has played an important role during deposition of the Malembo Formation and has imparted a well-documented structural style to the post-rift sediments. An oceanward transition from thin-skinned extension through mobile salt and eventually to thin-skinned compressional structures characterises the post-rift sediments. There has been little discussion, however, regarding the influence of these structures on the deposition of the Malembo Formation turbidite sands. Block 4 lies at the southern margin of the Lower Congo Basin and is dominated by the thin-skinned extensional structural style. Using a multidisciplinary approach we trace the post-rift structural and stratigraphic evolution of this block to study the structural controls on Neogene turbidite sand deposition.In the Lower Congo Basin the transition from terrestrial rift basin to fully marine passive margin is recorded by late Aptian evaporites of the Loeme Formation. Extension of the overlying post-rift sequences has occurred where the Loeme Formation has been utilised as a detachment surface for extensional faults. Since the late Cretaceous, the passive margin sediments have moved down-slope on the Loeme detachment. This history of gravity-driven extension is recorded in the post-rift sediments of Block 4. Extension commenced in the Albian in the east of the block and migrated westwards with time. In the west, the extension occurred mainly in the Miocene and generated allochthonous fault blocks or “rafts”, separated by deep grabens. The Miocene extension occurred in two main phases with contrasting slip vectors; in the early Miocene the extension vector was to the west, switching to southwest-directed extension in the late Miocene. Early Miocene faults and half-grabens trend north–south whereas late Miocene structures trend northwest–southeast. The contrast in slip vectors between these two phases emphasises the differences in driving mechanisms: the early Miocene faulting was driven by basinward tilting of the passive margin, but gravity loading due to sedimentary progradation is considered the main driver for the late Miocene extension. The geological evolution of the late Miocene grabens is consistent with southwest-directed extension due to southwest progradation of the Congo fan.High-resolution biostratigraphic data identifies the turbidite sands in Block 4 as early Miocene (17.5–15.5 Ma) and late Miocene (10.5–5.5 Ma) in age. Deposition of these sands occurred during the two main phases of gravity-driven extension. Conditions of low sedimentation rates relative to high fault displacement rates were prevalent in the early Miocene. Seafloor depressions were generated in the hangingwalls of the main extensional faults, ultimately leading to capture of the turbidity currents. Lower Miocene turbidite sand bodies therefore trend north–south, parallel to the active faults. Cross-faults and relay ramps created local topographic highs capable of deflecting turbidite flows within the half grabens. Flow-stripping of turbidity currents across these features caused preferential deposition of sands across, and adjacent to, the highs. Turbidite sands deposited in the early part of the late Miocene were influenced by both the old north–south fault trends and by the new northwest–southeast fault trends. By latest Miocene times turbidite channels crosscut the active northwest–southeast-trending faults. These latest Miocene faults had limited potential to capture turbidity currents because the associated hangingwall grabens were rapidly filled as pro-delta sediments of the Congo fan prograded across the area from the northeast. 相似文献
17.
This study proposed a new reconstruction of the tectono-sedimentary evolution of the Lake Albert Rift based on a biostratigraphical, sedimentological and structural re-evaluation of the outcropping data and on an exceptional subsurface dataset. The infilling of the rift consists of lacustrine deposits wherein two major unconformities dated at 6.2 Ma and 2.7 Ma were characterized, coeval with major subsidence and climatic changes. Combined with the fault analysis, the evolution and distribution of the subsidence highlights a four-steps evolution of the rift after its initiation dated at 17.0 Ma. The first phase (17.0 – 6.2 Ma) consists of low and diffuse extension associated with low accommodation rates ranging from 150 to 200 m/Ma. Restricted in the southern part of the basin, the depocenter location is poorly controlled by faults, meaning that the basin extension was potentially larger at this time. The second time interval (6.2 – 2.7 Ma) shows an increase of accommodation rates with values reaching more than 800 m/Ma. These high rates combined with the location of the major depocenters down the bounding faults argue for a first true rifting phase. Between 2.7 Ma and 0.4 Ma, the accommodation rates decreases to reach less than 400 m/Ma and the individualization of major depocenters continue down the major fault in the southern and northwestern parts of the basin. Finally, between 0.4 Ma and present-day, a late uplift led the formation of the Ugandan scarp. Comparison of the Lake Albert Rift evolution with the data available in the rifts of both branches of the East African Rift System shows that most of the sedimentary basins experienced the same geometrical evolution from large basins with limited fault control during Late Miocene to narrow true rift in Late Pleistocene. 相似文献
18.
The NW-SE striking Otway Basin in southeastern Australia is part of the continental rift system that formed during the separation of Australia from Antarctica. The development of this sedimentary basin occurred in two phases of Late Jurassic-Early Cretaceous and Late Cretaceous rifting. The evolution of this basin is mainly associated with extensional processes that took place in a pre-existing basement of Archean, Proterozoic to Paleozoic age. In this study, the total amounts of extension and stretching factor (β factor) have been measured for six transects across the entire passive margin of the Otway Basin region. The results show significant variation in extensional stretching along the basin, with the smallest stretching factors in the easternmost (β = 1.73, 1.9) and westernmost part of the basin (β = 2.09), and the largest stretching factors in the central part (β = 2.14 to 2.44). The domain with the lowest β factor is underlain mostly by thicker lithosphere of the Delamerian Orogen and older crustal fragments of the Selwyn Block. In contrast, the region with the largest β factor and amount of extension is related to younger and thinner lithosphere of the Lachlan Orogen. The main basement structures have been mapped throughout eastern South Australia and Victoria to examine the possible relationships between the younger pattern of extensional faults and the older basement fabrics. The pattern of normal faults varies considerably along onshore and offshore components of the Otway Basin from west to east. It appears that the orientation of pre-existing structures in the basement has some control on the geometry of the younger normal faults across the Otway Basin, but only in a limited number of places. In most areas the basement fabric has no control on the younger faulting pattern. Basement structure such as the north-south Coorong Shear Zone seems to affect the geometry of normal faults by changing their strike from E-W to NW-SE and also, in the easternmost part of the basin, the Bambra Fault changes the strike of normal faults from NW-SE to the NE-SW. Our results imply that the properties of the continental lithosphere exert a major influence on the β factor and amount of crustal extension but only a minor influence on the geometry of extensional faults. 相似文献
19.
对琼东南盆地陆架区晚中新世以来的断层活动性进行研究, 有助于理解南海西北部晚中新世以来的构造演化, 也对该区钻井平台的安全性评估、海洋工程勘查以及区域稳定性评价等有重要意义。研究区断层走向主要为NWW向, 多数断层在晚中新世时期停止活动。通过对断层几何形态的统计分析以及使用高分辨率断层落差图法(T-Z图示法)对断层活动性进行量化分析, 结果显示: 断层活动性在晚中新世末期(5.5Ma)发生转变; 研究区南部的断层落差值大于北部; 南部断层停止活动的时间较北部断层稍晚。这些研究成果表明, 晚中新世末期研究区断层受构造应力变化的影响, 在生长发育过程中断层活动性质发生了改变, 由逆断层转为正断层。红河断裂带对琼东南盆地的构造演化起着重要的控制作用, 文章推测研究区断层活动性变化是由红河断裂带的构造反转所导致, 因为红河断裂带在5.5Ma时发生了走滑运动的反转, 与研究区的断层活动性变化在时间和性质上相耦合。 相似文献
20.
琼东南盆地深水区东区凹陷带,即松南—宝岛—长昌凹陷,位于琼东南盆地中央坳陷东端。在大量地震资料解释的基础上,对38条主要断层进行了详细分析。获得以下认识:(1)琼东南盆地深水区东区凹陷带平面上表现为近EW向展布的平行四边形,剖面结构表现为自西向东由半地堑—不对称的地堑—半地堑有规律变化。(2)琼东南盆地深水区东区凹陷带断裂系统可划分控制凹陷边界断层、控制洼陷沉积中心断层和调节性断层3类。(3)琼东南盆地深水区东区凹陷带古近纪时期受到太平洋板块俯冲和南海海盆扩张的双重影响,构造应力场发生NW—SE→SN转变。构造演化可划分为3个阶段:～32Ma,应力场以区域性NW—SE向伸展为主,断裂系统以NE—SW向为主,控制凹陷边界;32～26Ma,以南海海盆近SN向拉张应力场为主,断裂系统以NWW—SEE向为主,断层活动控制凹陷沉积中心;26～Ma,区域性伸展与南海海盆扩张应力均逐渐减弱,NE—SW向和NWW—SEE向断裂继承性发育。(4)琼东南盆地深水区东区凹陷带内部主要断层在渐新统崖城组和陵水组沉积时期活动速率快,地形高差大、沉积水体深、沉积厚度大,控制了崖城组和陵水组的大规模沉积,有利于烃源岩的发育。圈闭以受断层控制的断鼻和断块为主,长昌主洼凹中隆起带发育2个最为理想的构造圈闭。 相似文献