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1.
The Three Kings Ridge has been reinterpreted as a west-facing island arc under which a significant amount of Norfolk Basin lithosphere may have been subducted. Examination of additional seismic reflection profiles adds credence to this interpretation and suggests the presence of a north-south transition from subduction under the northern half of the ridge, evidenced by well-preserved island-arc morphology, to obduction along the southern half of the ridge. This obduction probably obliterated the trench, resulting in overthrusting and severe deformation of the forearc basin as well as intense faulting of the volcanic arc.  相似文献   

2.
The Philippine Fault Zone, a system of left-lateral strike-slip faults traversing the length of the Philippine Islands, is associated with the oblique convergence between the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). Although it is a major deformational structure within the diffuse PSP–EP convergent boundary, some of its segments, particularly its marine extensions, are not well studied. To investigate the crustal deformation in the marine prolongation of the Philippine Fault Zone offshore Luzon Island, multi-channel seismic (MCS) data, gravity data and centroid moment tensor solutions were used in this study. Focal mechanism solutions from the Global CMT catalog were inverted to determine the average principal stress directions and consequently understand the prevailing stress regime in the study area. The stress inversion results indicate that the direction of maximum compression (σ1) is 321°N, which coincides with the PSP–EP convergence direction. From the MCS profiles, the study area was subdivided into deformation zone and a relatively stable zone. Thrust faulting, folding and general uplift are observed in the deformation zone. This zone is further subdivided into the active and inactive segments. In the active segment, uplift is occurring in the submarine ridge. This deformation pattern can be related to the ongoing uplift in some regions bisected by the PFZ. The inactive segment, characterized by intense folding of the sequences and faulting of the basement and overlying sequences, is suggested as the precursor of the Philippine Fault Zone. Deformation appears to be recently shifted to the east as delineated by an uplifted N-NW trending submarine ridge offshore NW Luzon Island.  相似文献   

3.
Several mechanisms have been proposed to account for the rotation of the nearly north-south abyssal hill fabric formed on the East Pacific Rise north of the Easter Microplate to the nearly east-west trends in the northern microplate interior. Proposed mechanisms include rigid microplate rotation, transform fault – parallel shear, and bookshelf faulting during the transfer of lithosphere from the Nazca Plate to the microplate. We used a submersible magnetometer on a NAUTILE dive program to measure the magnetic vector rotation of a pillow basalt and dike spur near Pito Deep, the present location of the tip of the propagating rift system that created the microplate. Our results, although too limited to draw strong conclusions from, suggest clockwise rotations of the seafloor magnetic vectors inconsistent with the transform-parallel shear model, and larger than can be explained solely by rigid microplate rotation.  相似文献   

4.
华北板块东部新生代断裂构造特征与盆地成因   总被引：22，自引：3，他引：19  
华北板块东部新生代的构造特征及动力学演化主要受左行郯庐断裂带和右行兰考-聊城-台安-大洼-法哈牛断裂带的控制。这两条断裂都是新生代岩石圈断裂。在兰考-聊城-台安-大洼-法哈牛断裂带以西,新生代伸展盆地为NNE走向的铲形正断层控制的箕状断陷;两断裂之间为北断南超的NWW走向的断陷盆地;郯庐断裂以东的北黄海盆地为南断北超的Nww走向的断陷盆地。这些构造特征继承了该区中生代的构造格局,但其构造性质发生了根本变化,在这两条走滑方向相反的断裂带控制下,这两条断裂带内古近纪以张扭作用下的裂陷为主,随后以伸展断陷为主,第四纪沿两断裂带局部发生挤压,而鲁西地块和渤海湾盆地区仍然为伸展正断。渤海湾盆地及邻区这些新生代复杂的断块或断裂构造格局受控于应力-应变-基底格局3个基本要素。  相似文献   

5.
南海南部海域新生代万安运动的构造意义及其油气资源效应   总被引：15，自引：2，他引：13  
南海南部海域在中中新世末发生了一次区域构造运动,被命名为万安构造运动。这次构造运动在新生代沉积中的表现是断裂、块断、挤压背斜和向斜。部分地区发育逆冲构造等。根据南海区域构造分析产生这次构造运动的起因可能与菲律宾海板块和欧亚板块于13MaBP在民都洛岛处发生碰撞．以及澳大利亚板块和欧亚板块在苏拉威西岛处发生碰撞(10MaBP)有关。这两次碰撞事件均对南海南部海域产生挤压,尤其是第一次碰撞挤压(向西方向)很强烈,是这次构造事件的主导因素。万安构造运动在南海南部海域沉积盆地中产生了许多挤压构造;而该海域沉积盆地中生烃的关键时刻是6MaBP,构造形成时间在生烃关键时间之前。因此,该海域形成了极其丰富的油气资源。  相似文献   

6.
Analysis of airgun seismic profiles from the Alboran Sea reveals a complex morphostructure with margins, basins, and structural highs. North of the Alboran Ridge, south-facing margins have a passive style of evolution, with thick progradational sequences of post-Messinian deposits, whereas north-facing margins are tectonized along structural highs with reduced sediment cover. Basins are extensional features developed since the Early Miocene by mechanisms of tectonic escape and pull-apart, under generalized northwest-southeast to north-south compression. Depositional sequences in this semi-land-locked sea were controlled by the local tectonism and influenced by global sea-level oscillations.  相似文献   

7.
Fault patterns at outer trench walls   总被引：1，自引：0，他引：1  
Profiles across subduction-related trenches commonly show normal faulting of the outer trench wall. Such faulting is generally parallel or sub-parallel to the trench and is ascribed to tension in the upper part of the oceanic plate as it is bent into the subduction zone. A number of authors have noted that outer trench wall faulting may involve re-activation of the oceanic spreading fabric of the subducting plate, even when the trend of this fabric is noticeably oblique to the extensional stress direction. However, one previous review of outer trench wall fault patterns questioned the occurrence of a consistent link between fault orientation and such controlling factors. This latter study predated the widespread availability of swath bathymetry and longrange sidescan sonar data over trenches. Based only on profile data, it was unable to analyse fault patterns with the accuracy now possible. This paper therefore re-examines the relationship between outer trench wall faulting and the structure of the subduction zone and subducting plate using GLORIA and Seabeam swath mapping data from several locations around the Pacific and Indian Oceans. The principal conclusions is that the trend of outer trench wall faults is almost always controlled by either the subducting slab strike or by the inherited oceanic spreading fabric in the subducting plate. The latter control operates when the spreading fabric is oblique to the subducting slab strike by less than 25–30°; in all other cases the faults are parallel to slab strike (and parallel or sub-parallel to the trench). Where the angle between spreading fabric and slab strike is close to 30°, two fault trends may coexist; evidence from the Aleutian Trench indicates a gradual change from spreading fabric to slab strike control of fault trend as the angle between the two increases from 25 to 30°. The only observed exception to the above rule of fault control comes from the western Aleutian Trench, where outer trench wall faults are oblique to the slab strike, almost perpendicular to the spreading fabric, and parallel to the convergence direction. Re-orientation of the extensional stress direction due to right-lateral shear at this highly oblique plate boundary is the best explanation of this apparently anomalous observation.  相似文献   

8.
The Omo basin in south western Ethiopia at the Kenyan boundary is a northern extension of the trans- boundary Turkana rift. It is an Early Pliocene north-south trending depression bounded on either side by normal faulting. The Omo river flows in the middle of the basin and empties itself at its southern end into Lake Turkana.The structural pattern of the Omo basin is determined from 2D and 3D analyses of the gravity field. The basin is an asymmetric half-graben formed by and localized within the NS/NNE trending Early Pliocene normal faults. It is built up on the older NW trending structures that were reactivated and affected the recent NS faults. Automatic depth determination techniques and 3D inversion are used to estimate depth to the basement and determine the sedimentary thickness. The results indicate over 4 km thick sediments were deposited over the graben.The Omo basin lies within the East African Rift system and appears to connect the generally NW trending oil-rich Muglad-Melut basins of south Sudan and the highly prospective and similarly trending Anza graben of Kenya. The Omo basin contains thick sequence of sediments and appears to be a promising future site of intensive hydrocarbon exploration.  相似文献   

9.
The steep Antipodes Scarp, along the eastern boundary of the Campbell Plateau south‐east of New Zealand, is attributed to dextral tear‐faulting within a NE‐SW belt, the Antipodes Fracture Zone, which also truncates the eastern end of the Chatham Rise. A complementary zone of sinistral movement, the Waipounamu Fracture, separates the Campbell Plateau and Chatham Rise from mainland New Zealand.

The origin of these fracture zones is linked with that of the parallel Alpine Fault of South Island, and is related to a phase of NE‐SW crustal compression that dominated the New Zealand region during the Mesozoic era. It is suggested that this compression resulted from the north‐eastward “drift” of the Australian craton and the simultaneous elevation of the Darwin Rise in the central Pacific.  相似文献   

10.
The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.  相似文献   

11.
This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the Eastern Venezuelan Basin and the main conclusions about shale tectonic mechanisms in the area. The deformation of the foreland-fold-belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs. Three contractional episodes are proposed for the Eastern Venezuelan Basin: 1) Oligocene to middle Miocene, 2) late Miocene to Pliocene and 3) Pleistocene. The first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying Cretaceous units. The second episode produced the deformation of the Cenozoic strata into overlapping east-west-trending, convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide, break-through normal faults product of a high sedimentary load that overcomes contraction and the formation of short-displacement blind thrusts in the underlying Cretaceous units. The last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and NW-SE strike. The role of the shale tectonics in the evolution implies that shale deforms in two stages: 1) folding and 2) normal faulting of the crest of the anticline (Break through normal faulting). Folding controlled the sediment distribution during most of the Neogene strata, while the normal faulting of the anticlines represent basin potential for hydrocarbon. The best potential hydrocarbon plays in the basin are related to oblique-collision restricted basins and controlled by break-through normal faults and the presence of NW-SE strike faults that connect the HC source with the reservoirs. Results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds.  相似文献   

12.
Water level observations from tide stations and current observations from current-meter moorings in South San Francisco Bay (South Bay), California have been harmonically analysed. At each tide station, 13 harmonic constituents have been computed by a least-squares regression without inference. Tides in South Bay are typically mixed; there is a phase lag of approximately 1 h and an amplification of 1·5 from north to south for a mean semi-diurnal tide. Because most of the current-meter records are between 14 and 29 days, only the five most important harmonics have been solved for east-west and north-south velocity components. The eccentricity of tidal-current ellipse is generally very small, which indicates that the tidal current in South Bay is strongly bidirectional. The analyses further show that the principal direction and the magnitude of tidal current are well correlated with the basin bathymetry. Patterns of Eulerian residual circulation deduced from the current-meter data show an anticlockwise gyre to the west and a clockwise gyre to the east of the main channel in the summer months due to the prevailing westerly wind. Opposite trends have been observed during winter when the wind was variable.  相似文献   

13.
The Shabwa Basin is the northeastern extension of the Marib-Al Jawf-Shabwa system of Mesozoic grabens, located onshore in the Republic of Yemen. An evaporitic sequence with an estimated maximum depositional thickness of 300 metres was deposited during the Tithonian. It is designated the Sabatayn Formation and exerts significant control on most of the play elements in the principal hydrocarbon play systems anticipated in the northeastern part of the basin. Migration of hydrocarbons from pre-salt source rocks into intra-and post-salt reservoirs is restricted by the evaporites. Localised heat flow perturbations introduced by the salt, increase the maturity of post-salt source rocks. Post and intra-salt reservoirs are structured by listric faulting on a salt detachment, salt pillowing due to post-depositional loading, by local salt dissolution and by late folding due to gravity sliding of the post-salt section on a salt detachment. Early dissolution and reprecipitation of salt is responsible for occlusion of porosity in intra-salt clastic reservoirs.  相似文献   

14.
Reservoirs where tectonic fractures significantly impact fluid flow are widespread. Industrial-level shale gas production has been established from the Lower Cambrian Niutitang Formation in the Cen'gong block, South China; the practice of exploration and development of shale gas in the Cen'gong block shows that the abundance of gas in different layers and wells is closely related to the degree of development of fractures. In this study, the data obtained from outcrop, cores, and logs were used to determine the developmental characteristics of such tectonic fractures. By doing an analysis of structural evolution, acoustic emission, burial history, logging evaluation, seismic inversion, and rock mechanics tests, 3-D heterogeneous geomechanical models were established by using a finite element method (FEM) stress analysis approach to simulate paleotectonic stress fields during the Late Hercynian—Early Indo-Chinese and Middle-Late Yanshanian periods. The effects of faulting, folding, and variations of mechanical parameters on the development of fractures could then be identified. A fracture density calculation model was established to determine the quantitative development of fractures in different stages and layers. Favorable areas for shale gas exploration were determined by examining the relationship between fracture density and gas content of three wells. The simulation results indicate the magnitude of minimum principal stress during the Late Hercynian — Early Indo-Chinese period within the Cen'gong block is −100 ∼ −110 MPa with a direction of SE-NW (140°–320°), and the magnitude of the maximum principal stress during the Middle-Late Yanshanian period within the Cen'gong block is 150–170 MPa with a direction of NNW-SSE (345°–165°). During the Late Hercynian — Early Indo-Chinese period, the mechanical parameters and faults play an important role in the development of fractures, and fractures at the downthrown side of the fault are more developed than those at the uplifted side; folding plays an important role in the development of fractures in the Middle-Late Yanshanian period, and faulting is a secondary control. This 3-D heterogeneous geomechanical modelling method and fracture density calculation modelling are not only significant for prediction of shale fractures in complex structural areas, but also have a practical significance for the prediction of other reservoir fractures.  相似文献   

15.
Two field observations were conducted around the Lembeh Strait in September 2015 and 2016, respectively.Evidences indicate that seawater around the Lembeh Strait is consisted of North Pacific Tropical Water(NPTW),North Pacific Intermediate Water(NPIW), North Pacific Tropical Intermediate Water(NPTIW) and Antarctic Intermediate Water(AAIW). Around the Lembeh Strait, there exist some north-south differences in terms of water mass properties. NPTIW is only found in the southern Lembeh Strait. Water mass with the salinity of 34.6 is only detected at 200–240 m between NPTW and NPTIW in the southern Lembeh Strait, and results from the process of mixing between the saltier water transported from the South Pacific Ocean and the lighter water from the North Pacific Ocean and Sulawesi Sea. According to the analysis on mixing layer depth, it is indicated that there exists an onshore surface current in the northern Lembeh Strait and the surface current in the Lembeh Strait is southward.These dramatic differences of water masses demonstrate that the less water exchange has been occurred between the north and south of Lembeh Strait. In 2015, the positive wind stress curl covering the northern Lembeh Strait induces the shoaling of thermocline and deepening of NPIW, which show that the north-south difference of airsea system is possible of inducing north-south differences of seawater properties.  相似文献   

16.
The Cenozoic seismic stratigraphy and geological development of the south Vøring margin are analyzed to understand their relation to fluid flow and margin stability. The regional stratigraphy and palaeomorphology of the Møre and Vøring basins indicate gradual changes in depositional environment and tectonic compression between 55 Ma to 2.8 Ma during Brygge and Kai periods, and abrupt changes associated with glacial/interglacial cycles from last 2.8 Ma during Naust period. These changes resulted in deposition of various types of sediments and led to processes such as polygonal faulting and dewatering, inter-fingering of contouritic, stratified and glacigenic sediments, and margin progradation.A gas hydrate related bottom simulating reflector (BSR) occurs at Nyegga and within the central Vøring Basin while pockmarks are observed at Nyegga only. Diagentic reflectors due to Opal A - Opal CT conversion (DBSRs) occur along a wider area beyond the shelf edge. The DBSRs are located in oozes within the Kai and late Brygge Formations. The gas hydrate BSR occurrence is concentrated above Eocene depocenters in hemipelagic and contouritic sediments deposited during Late Plio-Pleistocene. The BSR overlies polygonal faults and DBSRs but are confined to the slope of anticlines indicating its formation being related to fluid pathways from methanogenic rocks through focused fluid flow. Microbial gas production in Kai, Brygge and deeper formations may have supplied the gas for gas hydrate formation. Fluid expulsion due to DBSR formation and polygonal faulting in oozes may have created overpressure development in permeable layers belonging to the overlying Naust Formation. Slide headwalls are also located close to the anticlines in the study area, implying that over pressured oozes and focussed fluid flow may have been important in creating weak surfaces in the overlying Naust sediments, promoting conditions for failures to occur.  相似文献   

17.
A regional geophysical traverse of the Mid-Atlantic Ridge in the northern South Atlantic was obtained during CIRCE cruise of the Scripps Institution of Oceanography. During the traverse, four detailed surveys were made of small areas on the crest and east flank. The geomagnetic anomaly profile can be used as a time base for the interpretation of tectonic events of the ridge. The profile also suggests that the rate of sea-floor spreading in this part of the South Atlantic accelerated twice, approximately 40 and 4.5 million years ago, and decelerated at least twice, 38 and 10 million years ago. Accelerations were probably accompanied by uplift and normal faulting of the central part of the ridge, while decelerations produced subsidence with modest contraction, reflected in reverse faulting and folding. The effects of uplift are clearly present in the reflection seismic records, which are, however, not well suited to detect reverse faulting.Spreading without creation of significant relief occurred on the ridge until approximately 5 million years ago. This process produced a low relief with small rifts, strongly reminiscent of the present crestal topography of the East Pacific Rise. A markedly linear secondary relief of 100–200 m, parallel to the ridge axis, developed later by faulting of the flanks. Portions of the crust that were near the crest during periods of uplift are more intensely faulted than those that were remote at all times. The importance of the last uplift of the crest and associated faulting on the flanks is reflected by a decrease in the density of faulting away from the ridge crest.The present crestal zone is very different from the flanks and from the older crests; the relief is nearly ten times greater, transverse disturbances are common, and there is conflicting evidence regarding its age. This striking change in character indicates either a recent change in the spreading process or a recent period of strong deformation which has affected only the crestal zone.Contribution from Scripps Institution of Oceanography, University of California, San Diego.  相似文献   

18.
印尼附近海域地震海啸发生的构造背景综述   总被引：3，自引：0，他引：3  
2004年12月26日在印度尼西亚苏门答腊岛以西海域发生的里氏9级地震,引发了历史上第五大地震海啸,引起了地学界的高度关注。印度尼西亚西部位于环太平洋地震带和地中海-喜马拉雅地震带结合部位,处于洋壳和陆壳的汇聚边界以及弧状压缩构造格局中。苏门答腊陆缘NW—SE向延伸约1600km,苏门答腊俯冲带源于印度-澳大利亚和欧亚板块3°N的汇聚。苏门答腊弧前区沿着平行于俯冲海沟的两大走滑断裂——苏门答腊大断裂和明打威断裂向北运动。本文对印度尼西亚苏门答腊岛附近海域的地质背景、大地构造特征和地震活动评估等进行了综述,对该海域产生大地震的深部动力学机制进行了分析,并从地质、地球物理资料的获取与分析角度出发,对区域灾害模型进行了探讨。  相似文献   

19.
黄、渤海表层沉积物中钙质超微化石有较广泛分布,属种较大洋和开阔海少而单调。黄海南部见有14个种,北黄海及渤海海峡4～5个种,渤海沿岸区2～3个种。钙质超微化石分异度D_H以及主要化石种相对百分含量的高值区的主轴线的走向与现代黄海暖流的流路密切相关。得出黄海暖流由南黄海东南部流入北黄海,通过渤海海峡的北侧进入渤海,在渤海中部呈南北向伸展。  相似文献   

20.
Recently, analysis of organochlorines in sediment and in pike from Lake Vänern, Sweden, showed a north-south gradient of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). In the present study, good correlations were found between muscle 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents and liver ethoxyresorufin-O-deethylase (EROD) activities (and P4501A levels) in pike caught at three sampling sites along the north-south gradient in the lake. This comparison between tissue levels of PCDD/PCDF and EROD activity (and P4501A) may indicate that TCDD or structural analogs could be responsible for the observed induction of the pike P450 system. It must, however, be taken into account that the analysed contaminants often do not appear alone but are, rather, accompanied by a range of other substances which may be inducers or antagonists.  相似文献   

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