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1.
A recent swath-bathymetry and geophysical survey of the R/V L'Atalante in the Fairway Basin between Australia and New Caledonia allowed to confirm the Cretaceous age of the creation of the basin by continental stretching. This first stage of opening of the Fairway Basin is associated with the deposition of a continuous salt/mud layer feeding today numerous diapirs, some of them piercing the 3 to 4 km thick sedimentary cover and reaching the seafloor. In close link with this salt/mud layer a Bottom Simulating Reflector indicator of gas hydrates level occupies a 70000 km2 surface at about 500 to 600 m-depth beneath the sea floor. The coexistence of both BSR and diapirs suggests a thermogenic better than biogenic origin for the gas hydrates horizon.  相似文献   

2.
The Edremit Gulf, which developed during the Neogene-Quaternary, is a seismically active graben in NW Anatolia (Turkey) surrounded by the Sakarya continent. The sedimentary deposits in the gulf overlie the bedrock unconformably and can be separated into two parts as upper and lower deposits based on similarity of their seismic characteristics, and because the contact between them is clear. The lower deposits are characterized in the seismic profiles by the absence of well defined, continuous reflectors and are strongly disturbed by faults. A tectonic map and structural model of the Edremit Gulf was derived from interpreting 21 deep seismic profiles trending NE–SW and NW–SE within the gulf. Two fault systems were distinguished on the basis of this compilation. The NNW–SSE trending parallel faults are low-angle normal faults formed after compression. They controlled and deformed the lower basin deposits. A syncline and anticline with a broad fold-curvature length resulted in folds that developed parallel to basin boundaries in the lower basin deposits. The ENE–WSW trending high-angle faults have controlled and deformed the northern basin of the Edremit Gulf. The folds developed within the northern lower deposits originated from the listric geometry of the faults. These faults are normal faults associated with regional N–S extension in western Anatolia. The Edremit Gulf began to open under the control of low-angle NNW–SSE trending faults that developed after the compression of western Anatolia in an E–W direction in the early Neogene. Subsequently, regional N–S extensional stress and high-angle normal faults cut the previous structures, opened the northern basin, and controlled and deformed the lower basin deposits in the gulf. As a result, the Edremit Gulf has not been controlled by any strike-slip faults or the Northern Anatolian Fault. The basin developed in the two different tectonic regimes of western Anatolia as an Aegean type cross-graben from the Neogene to Holocene.  相似文献   

3.
法尔维海盆位于西南太平洋海域豪勋爵海丘东侧、新喀里多尼亚岛西侧，是全球油气勘探的前沿地区。但目前对于该海盆的构造演化研究较为薄弱，限制了该海盆油气资源的进一步勘探开发。本文通过从新西兰塔斯曼海数据库搜集到大量地球物理资料，使用2D Move软件，通过平衡剖面技术进行构造演化模拟，结合区域动力学机制将海盆北部和南部的构造演化分为7个阶段:(1)早白垩世至晚白垩世陆内裂谷阶段；(2)晚白垩世断坳过渡阶段；(3)始新世早期坳陷阶段；(4)始新世晚期一次构造反转阶段；(5)始新世至渐新世热沉降阶段；(6)渐新世至中新世二次构造反转阶段；(7)中新世至今海洋沉降阶段。由于海盆中部未发现有明显的二次构造反转阶段，所以将海盆中部的构造演化划分为5个阶段:(1)早白垩世至晚白垩世陆内裂谷阶段；(2)晚白垩世断坳过渡阶段；(3)始新世早期坳陷阶段；(4)始新世晚期构造反转阶段；(5)中新世至今海洋沉降阶段。此阶段海盆整体下坳，逐渐形成现今样貌。法尔维海盆北部受到区域构造活动影响较大，白垩系地层发育较多的断裂构造；海盆中部晚白垩统地层发生较多的底辟构造；海盆南部从形成至今，受到构造活动影响较小，发育地层完整，前新生代地层较厚。整个法尔维海盆北部构造活动较强，中部较弱，南部较小。沉积地层从北到南由厚变薄。  相似文献   

4.
A seismic reflection survey was conducted in the proximal shelf off Atlit, western Mt. Carmel, Israel, to clarify the regional neotectonic regime. The Atlit promontory is built of late Pleistocene eolianite ridge, truncated by faults at its northern extension. The seismic survey encountered two series of faults, trending N—S and NW—SE, offsetting the upper strata by 1–5 m. Faulted escarpments of the N—S faults are barely covered by sediments, suggesting that they are tectonically active. The escarpments of the NW—SE faults are rarely exposed, suggesting their late Pleistocene age. A submerged undamaged Neolithic well near a major NW trending fault indicates that the structural stability of these faults during the last 8000 years can be presumed.  相似文献   

5.
The ZoNéCo 1 and 2 cruises of Ifremer's Research Vessel L'Atalante, collected new swath bathymetry and geophysical data over the southern and northern segments of the basins and ridges forming the Loyalty system. Between the two surveyed areas, previous studies found evidence for the resistance of the Loyalty Ridge to subduction beneath the New Hebrides trench near 22°S–169°E. On the subducted plate, except for seismicity related to the downbending of the Australian plate, recorded shallow seismicity is sparse within the Loyalty system (Ridge and Basin) where reliable focal mechanism solutions are almost absent.Swath bathymetry, seismic reflection and magnetic data acquired during the ZoNéCo 1 and 2 cruises revealed a transverse asymmetric morphology in the Loyalty system, and an along-strike horst and graben structure on the discontinuous Loyalty Ridge. South of 23°50S and at 20°S, the two WSW-ENE-trending fault systems, respectively, sinistral and dextral, that crosscut the southern and northern segments of the Loyalty system, are interpreted as due to the early effects of collision with the New Hebrides Arc. A NNW-SSE trend, evident along the whole Loyalty system and on the island of New Caledonia, is interpreted as an inherited structural trend that may have been reactivated through flexure of the Australian lithospheric plate at the subduction zone.Overall then, the morphology, structure and evolution of the southern and northern segments of the Loyalty system probably result from the combined effects of the Australian plate lithospheric bulge, the active Loyalty-New Hebrides collision and the overthrust of the New Caledonian ophiolite.  相似文献   

6.
In this paper, we demonstrate the effectiveness of steerable filters as a method of delineating the boundaries of subsurface geological structures. Steerable filters, generally used for edge detection on 2-D images, have the properties of band pass filters with certain directions and are applied to many image processing problems. We first tested the method on synthetic data and then applied it to the aeromagnetic data of İskenderun Basin and adjacent areas.İskenderun Basin is located in the Northeastern Mediterranean where African–Arabian and Anatolian plates are actively interacting. The basin fill records a complex tectonic evolution since the Early Miocene, involving ophiolite emplacement, diachronous collision of Eurasian and Arabian plates and subsequent tectonic escape related structures and associated basin formation. Geophysical investigations of the tectonic framework of İskenderun Basin of Turkey provide important insights on the regional tectonics of the Eastern Mediterranean and Middle East. In this study we show geological structures, which are responsible for the magnetic anomalies in İskenderun Basin and enlighten the structural setting of the Northeastern Mediterranean triple junction using steerable filters. We obtained a magnetic anomaly map of the region from the General Directorate of Mineral Research and Exploration as raw data and then evaluated this by steerable filters. We determined the magnetic anomaly boundaries for İskenderun Basin by using various types of steerable filters and correlated these to drilling data and seismic profiles from the Turkish Petroleum Corporation. The result of the steerable filter analysis was a clarified aeromagnetic anomaly map of İskenderun Basin. The tectonic structure of İskenderun Basin is divided into regions by an N–S trending oblique-slip fault defined by the steerable filter outputs. We propose a new tectonic structure model of İskenderun Basin and modify the direction of the East Anatolian Fault Zone. In our model, East Anatolian Fault Zone cross-cuts the basin as a narrow fault zone and continues towards the Cyprus arc.  相似文献   

7.
To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.  相似文献   

8.
The Jan Mayen microcontinent was as a result of two major North Atlantic evolutionary cornerstones—the separation of Greenland from Norway (~54 Ma), accompanied by voluminous volcanic activity, and the jump of spreading from the Aegir to the Kolbeinsey ridge (~33 Ma), which resulted in the separation of the microcontinent itself from Eastern Greenland (~24 Ma). The resulting eastern and western sides of the Jan Mayen microcontinent are respectively volcanic and non-volcanic rifted margins. Until now the northern boundary of the microcontinent was not precisely known. In order to locate this boundary, two combined refraction and reflection seismic profiles were acquired in 2006: one trending S–N and consisting of two separate segments south and north of the island of Jan Mayen respectively, and the second one trending SW–NE east of the island. Crustal P-wave velocity models were derived and constrained using gravity data collected during the same expedition. North of the West Jan Mayen Fracture Zone (WJMFZ) the models show oceanic crust that thickens from west to east. This thickening is explained by an increase in volcanic activity expressed as a bathymetric high and most likely related to the proximity of the Mohn ridge. East of the island and south of the WJMFZ, oceanic Layers 2 and 3 have normal seismic velocities but above normal average crustal thickness (~11 km). The similarity of the crustal thickness and seismic velocities to those observed on the conjugate M?re margin confirm the volcanic origin of the eastern side of the microcontinent. Thick continental crust is observed in the southern parts of both profiles. The northern boundary of the microcontinent is a continuation of the northern lineament of the East Jan Mayen Fracture Zone. It is thus located farther north than previously assumed. The crust in the middle parts of both models, around Jan Mayen island, is more enigmatic as the data suggest two possible interpretations—Icelandic type of oceanic crust or thinned and heavily intruded continental crust. We prefer the first interpretation but the latter cannot be completely ruled out. We infer that the volcanism on Jan Mayen is related to the Icelandic plume.  相似文献   

9.
The Kerguelen Province, consisting of two oceanic plateaus (Kerguelen, Broken Ridge) and three basins (Enderby, Labuan and Diamantina), covers a large area of ocean floor in the southeast Indian Ocean. As very few magnetic anomalies have been identified in this area and only a few basement ages from the Kerguelen Plateau are known, reconstruction models of the Kerguelen Province are not well constrained. In an effort to gain more understanding about the evolution of this area, we have used satellite gravity to identify additional fracture zones. As they are likely to be associated with high frequency and low amplitude gravity anomalies, we have computed the vertical derivative map instead of the regular satellite gravity map. Using this approach, we have identified a series of fracture zones in the Enderby Basin, which are aligned with the Mesozoic fracture zones in the Perth Basin and converge to the Kerguelen Fracture Zone. In the conjugate Bay of Bengal, we traced an equivalent pattern of fracture zones which, together, better constrain the early evolution of this part of the Indian Ocean. Synthesis of these images and the other available data from the Kerguelen Province, suggests that the spreading of India from both Australia and Antarctica is closely related. Spreading between the three continents appears to have begun about the same time, in the early Cretaceous and thus, the accretion of some parts of the Kerguelen Province must have occurred before the onset of the quiet magnetic period at 118 Ma. At about 96–99 Ma, when the spreading direction in the Indian Ocean had changed into a N-S direction, it also took place throughout the Kerguelen Province. We find that previously proposed slow spreading in the Diamantina Zone and Labuan Basins, between 96–99 Ma and the initiation of the Southeast Indian Ridge at 43 Ma, could not have taken place. Furthermore, we suggest that there is growing evidence that the same is true for spreading in the eastward continuation of the Diamantina Zone and Labuan Basin, between Australia and Antarctica. Initiation of spreading in this area is likely to be contemporaneous with the spreading in the Kerguelen Province and, thus, older than 96–99 Ma. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   

10.
Fractures associated with volcanic rock outcrops on the inner shelf of Alboran Island, Western Mediterranean, were mapped on the basis of a side-scan sonar mosaic. Absolute maximum fracture orientation frequency is NW–SE to NNW–SSE, with several sub-maxima oriented NNE–SSW, NE–SW and ENE–WSW. The origin of the main fracture systems in Neogene and Quaternary rocks of the Alboran Basin (south Spain) appears to be controlled by older structures, namely NE–SW and WNW–ESE to NW–SE faults which cross-cut the basement. These faults, pre-Tortonian in origin, have been reactivated since the early Neogene in the form of strike-slip and extensional movements linked to the recent stress field in this area. Fracture analysis of volcanic outcrops on the inner continental shelf of Alboran Island suggests that the shelf has been deformed into a narrow shear zone limited by two NE–SW-trending, sub-parallel high-angle faults, the main orientation and density of which have been influenced by previous WNW–ESE to NW–SE basement fractures.  相似文献   

11.
The seafloor spreading of the South China Sea (SCS) was previously believed to take place between ca. 32 and 15 Ma (magnetic anomaly C11 to C5c). New magnetic data acquired in the northernmost SCS however suggests the existence of E–W trending magnetic polarity reversal patterns. Magnetic modeling demonstrates that the oldest SCS oceanic crust could be Late Eocene (as old as 37 Ma, magnetic anomaly C17), with a half-spreading rate of 44 mm/yr. The new identified continent–ocean boundary (COB) in the northern SCS generally follows the base of the continental slope. The COB is also marked by the presence of a relatively low magnetization zone, corresponding to the thinned portion of the continental crust. We suggest that the northern extension of the SCS oceanic crust is terminated by an inactive NW–SE trending trench-trench transform fault, called the Luzon–Ryukyu Transform Plate Boundary (LRTPB). The LRTPB is suggested to be a left-lateral transform fault connecting the former southeast-dipping Manila Trench in the south and the northwest-dipping Ryukyu Trench in the north. The existence of the LRTPB is demonstrated by the different patterns of the magnetic anomalies as well as the different seafloor morphology and basement relief on both sides of the LRTPB. Particularly, the northwestern portion of the LRTPB is marked by a steep northeast-dipping escarpment, along which the Formosa Canyon has developed. The LRTPB probably became inactive at ca. 20 Ma while the former Manila Trench prolonged northeastwards and connected to the former Ryukyu Trench by another transform fault. This reorganization of the plate boundaries might cause the southwestern portion of the former Ryukyu Trench to become extinct and a piece of the Philippine Sea Plate was therefore trapped amongst the LRTPB, the Manila Trench and the continental margin.  相似文献   

12.
 Magnetic data over the eastern continental margin of India and adjacent Bengal fan demarcate two major lineaments. A high amplitude N–S-trending lineation of the Cauvery offshore Basin corresponds to the offshore fragment of the 80°E lineament recorded onland. A N–S lineation of very high amplitude anomaly off Chilka lake considered as the possible northward extension of the 85°E ridge delineated, hitherto in Bengal Fan. A subdued magnetic anomaly zone is demarcated seaward of the continent–ocean boundary (COB) in the Bengal Fan. Over the northern Bengal Fan this zone is delineated east of 85°E lineation. This quiet zone might have evolved during the Early Cretaceous period of normal magnetic polarity between M0 and 34 (120–84 Ma) anomalies. Received: 6 April 1995 / Revision received: 3 September 1996  相似文献   

13.
On the basis of new geophysical data acquired by the Federal Institute of Geosciences and Natural Resources (BGR) and the Polar Marine Geological Research Expedition (PMGRE) as well as existing data new geophysical maps were compiled for the Lazarev Sea and the Riiser-Larsen Sea between 10°W and 25°E. The new results are: – The drastic change in the strike direction of the volcanic Explora Wedge between longitudes 10°W and 5°W is accompanied with a gradual change from one major wedge, i.e. the Explora Wedge, into at least two wedge-shaped volcanic constructions, each manifested by a sequence of seaward-dipping reflectors in the seismic records. – The southern Lazarev Sea is best described as a continental margin affected by multiple rifting episodes accompanied with transient volcanism. – A distinct N80°E striking basement depression separates the volcanic-prone continental margin of the southern Lazarev Sea from oceanic crust upon which the Maud Rise rests. The southern scarp of the narrow depression was presumably aligned with the eastern scarp of the Mozambique Ridge during the Early Cretaceous. – The Astrid Ridge proper occupies the transition from the volcanic-prone continental margin of the Lazarev Sea to old oceanic crust of the Riiser -Larsen Sea, and it rests upon a large volcanic apron which covers the basement of the southwestern Riiser-Larsen Sea. – No evidence was found that prolific volcanism has affected the early opening of the Riiser-Larsen Sea. – The Lazarev Sea is a sediment-starved region.  相似文献   

14.
The Pelotas Basin is the classical example of a volcanic passive margin displaying large wedges of seaward-dipping reflectors (SDR). The SDR fill entirely its rifts throughout the basin, characterizing the abundant syn-rift magmatism (133–113 Ma). The Paraná–Etendeka Large Igneous Province (LIP), adjacent to west, constituted the pre-rift magmatism (134–132 Ma). The interpretation of ultra-deep seismic lines showed a very different geology from the adjacent Santos, Campos and Espírito Santo Basins, which constitute examples of magma-poor passive margins. Besides displaying rifts totally filled by volcanic rocks, diverse continental crustal domains were defined in the Pelotas Basin, such as an outer domain, probably constituted by highly stretched and permeated continental igneous crust, and a highly reflective lower crust probably reflecting underplating.The analysis of rifting in this portion of the South Atlantic is based on seismic interpretation and on the distribution of regional linear magnetic anomalies. The lateral accretion of SDR to the east towards the future site of the breakup and the temporal relationship between their rift and sag geometries allows the reconstitution of the evolution of rifting in the basin. Breakup propagated from south to north in three stages (130–127.5; 127.5–125; 125–113 Ma) physically separated by oceanic fracture zones (FZ). The width of the stretched, thinned and heavily intruded continental crust also showed a three-stage increase in the same direction and at the same FZ. Consequently, the Continental-Oceanic Boundary (COB) shows three marked shifts, from west to east, from south to north, resulting into rift to margin segmentation. Rifting also propagated from west to east, in the direction of the final breakup, in each of the three segments defined. The importance of the Paraná–Etendeka LIP upon the overall history of rupturing and breakup of Western Gondwanaland seems to have been restricted in time and in space only to the Pelotas Basin.  相似文献   

15.
Recent multibeam bathymetric and geophysical data recorded in the West Philippine Basin, east of Taiwan, reveal new information on the structure and the tectonic origin of the oceanic Gagua Ridge. This linear, 300 km-long, 4 km-high, north-south-trending ridge, is being subducted beneath the Ryukyu Trench along 123° E. This basement high separates two basins of different ages. Its summit is marked by two crests and an axial valley. A map of the basement top shows the region of the ridge to be composed of a set of linear and parallel ridges and troughs. All these elements suggest that the development of the ridge, and its surroundings, has been influenced by strike-slip deformation. Nevertheless, the height of the ridge indicates also an important compressive component in the deformation. Gravity models across the ridge show local compensation with a crustal root, indicating that an overthickening of the crust occurred when it was young and thus more easily deformable. This idea is strengthened with flexural modeling of the lithosphere that bends under the load of the ridge, indeed it indicates that the high probably formed when the underlying lithosphere was young. We interpret the Gagua Ridge as a fracture zone transverse ridge uplifted during a transpressive episode along a north-south -trending fracture zone in the middle Eocene time, if we accept Hilde and Lee's (1984) model of magnetic lineations. This tectonic event could be contemporaneous with a change of the pole of rotation of the West Philippine Basin which occurred about 43/45 Ma ago.  相似文献   

16.
利用高分辨率水深、重力、地磁和多道反射地震数据,综合分析了楚科奇边缘地及其周边区域的地形地貌和地球物理场特征,划分了区域构造单元。研究表明,楚科奇边缘地不仅是楚科奇大陆架外缘独特的地形单元,也是一个相对独立的构造单元,与周边的加拿大洋盆、阿尔法-门捷列夫大火山岩省、北楚科奇陆架盆地和阿拉斯加被动陆缘等构造单元在地球物理场和区域构造上具有截然不同的特征。楚科奇边缘地是一个地壳减薄的微陆块,新生代早、中期发生了大规模的E-W向构造拉伸作用,基底断块的差异性升降塑造了当前的地形地貌和沉积层的发育。边缘地可能形成于北楚科奇盆地侏罗纪-早白垩纪的张裂作用,而内部盆-脊相间排列的构造格局则可能与加拿大海盆相边缘地俯冲作用停止后的均衡调整有关。  相似文献   

17.
A New Scenario of the Parece Vela Basin Genesis   总被引：4，自引：0，他引：4  
Okino  K.  Kasuga  S.  Ohara  Y. 《Marine Geophysical Researches》1998,20(1):21-40
A new high density geophysical data set in the Parece Vela Basin north of 15°N has been obtained through surveys conducted by the Hydrographic Department of Japan. The combined analyses of the swath bathymetry, magnetic and gravity anomalies from these surveys reveal a new scenario for the genesis of this basin. The evolutionary process is as follows: rifting and crust thinning (29–26 Ma), northward propagation of east-west opening (26-23 Ma) , east-west opening together with the Shikoku Basin (23–21 Ma), and the northeast-southwest opening (20/19–15 Ma). The western part of the basin is complicated, displaying some traces of northward propagation of the spreading center. The change between early east-west opening and the final stage of northeast-southwest spreading is marked by a distinct north-south boundary in both structural and magnetic patterns. Deep and rough topography of the extinct Parece Vela Rift is due to magma starvation in the terminal phase of the spreading.  相似文献   

18.
The Philippine Basin,surrounded by a series of oceanic trenches,is an independent deep ocean basin in the West Pacific Ocean.Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges,namely,the West Philippine Basin,the Shikoku and Parece Vela Basins and the Mariana Trough.This paper,through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies,suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature,and therefore,the entire basin is of the nature of oceanic crust.The basin has developed a series of special geomorphic units with different shapes.The KPR runs through the entire Philippine Basin.From the view of geomorphologic features,the KPR is a discontinuous seamount chain (chain-shaped seamounts) and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc.At the positions of 25 N,24 N,23 N and 18 N,obvious discontinuity is shown,which belongs to natural topographic discontinuity.Therefore,the KPR is topographically discontinuous.  相似文献   

19.
Swath bathymetric, sonar imagery and seismic reflection data collected during the SOPACMAPS cruise Leg 3 over segments of the Vitiaz Trench Lineament and adjacent areas provide new insights on the geometry and the stuctural evolution of this seismically inactive lineament. The Vitiaz Trench Lineament, although largely unknown, is one of the most important tectonic feature in the SW Pacific because it separates the Cretaceous crust of the Pacific Plate to the north from the Cenozoic lithosphere of the North Fiji and Lau Basins to the south. The lineament is considered to be the convergent plate boundary between the Pacific and Australian Plates during midde to late Tertiary time when the Vitiaz Arc was a continuous east-facing are from the Tonga to the Solomon Islands before the development of the North Fiji and Lau Basins. Progressive reversal and cessation of subduction from west to east in the Late Miocene-Lower Plioene have been also proposed. However, precise structures and age of initiation and cessation of deformation along the Vitiaz Trench Lineament are unknown.The lineament consists of the Vitiaz Trench and three discontinuous and elongated troughs (Alexa, Rotuma and Horne Troughs) which connect the Vitiaz Trench to the northern end of the Tonga Trench. Our survey of the Alexa and Rotuma Troughs reveals that the lineament is composed of a series of WNW-ESE and ENE-WSW trending segments in front of large volcanic massifs belonging to the Melanesian Border Plateau, a WNW trending volcanic belt of seamounts and ridges on Pacific crust. The Plateau and Pacific plate lying immediately north of the lineament have been affected by intense normal faulting, collapse, and volcanism as evidenced by a series of tilted blocks, grabens, horsts and ridges trending N 120° to N100° and N60°–70°. This tectonism includes several normal faulting episodes, the latest being very recent and possibly still active. The trend of the fault scarps and volcanic ridges parallels the different segments of the Vitiaz Trench Lineament, suggesting that tectonics and volcanism are related to crustal motion along the lineament.Although the superficial observed features are mainly extensional, they are interpreted as the result of shortening along the Vitiaz Trench Lineament. The fabric north of the lineament would result from subduction-induced normal faulting on the outer wall of the trench and the zig-zag geometry of the Vitiaz Trench Lineament might be due to collision of large volcanic edifices of the Melanesian Border Plateau with the trench, provoking trench segmentation along left-lateral ENE-WSW trending transform zones. The newly acquired bathymetric and seismic data suggest that crustal motion (tectonism associated with volcanism) continued up to recent times along the Vitiaz Trench Lineament and was active during the development of the North Fiji Basin.  相似文献   

20.
We present previously unreported depth anomalies in the Arabian Basin, northwest Indian Ocean, to provide constraints on the evolution of the oceanic lithosphere of that basin. The depth anomaly reported in this study was calculated as the difference between the observed depth to oceanic basement (corrected for sediment load) and the calculated depth to oceanic basement of the same age. The results indicate an anomalous depth to basement of oceanic crust in the Arabian Basin in the age bracket of 63–42 Ma, suggesting that subsidence in this basin does not follow the age–depth relationship of normal oceanic crust. The depth anomalies in the basin vary from +501 to −905 m. A negative depth anomaly zone, mapped in the eastern part of the basin near the Laccadive Ridge, indicates that here the basement depth is shallower than predicted. By contrast, a positive depth anomaly zone, mapped in the western part of the basin, indicates a deeper basement depth than expected. We propose that the excess subsidence of basement of the western part of the basin is probably caused by a relatively cold mantle, compared to the nearby eastern part of the basin which is affected by the intense thermal field of the former Reunion hotspot. Here, the rise in oceanic basement is caused by the vertical upwelling of oceanic crust due to convection, followed by a lateral across-axis flow facilitated by the Reunion hotspot at the time of spreading in early Tertiary times. This interpretation is in good agreement with spreading-ridge propagation and ridge-hotspot interaction reported earlier for the basin.  相似文献   

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