Thermal rejuvenation of the Yermak Plateau

The Yermak Plateau, bordering the Arctic Ocean and the Norwegian-Greenland Sea, and adjacent to the continental Svalbard Archipelago, is characterized by high heat flow relative to its surrounding region. South of and parallel to the trend of the plateau lies the formerly active-Spitsbergen Shear Zone (De Geer Zone), which is now occupied by the slowly spreading Knipovich and Molloy Ridges. An analysis of these heat flow data suggest that asymmetric spreading within the Norwegian-Greenland Sea propagated northwards along one of the faults associated with the Spitsbergen Shear Zone. The broad zone of faults, once associated with this paleo-shear zone, extends throughout Svalbard as well as on and to the west of the Knipovich Ridge. This network of faults may comprise a complex system of detachment surfaces along which magma may rise from a deep-seated source and across which simple shear extension may develop. Dike injection into the Yermak Plateau, north of the propagating ridge may have been initiated by the thermal response of the highly fractured lithosphere to this propagating asthenospheric front. We suggest that one of these faults, acting as a secondary detachment to the main fault underlying the Knipovich Ridge, may be dissecting the Yermak Plateau. Based on an analysis of the thermal data, simple shear extension may have been taking place along a broad zone of intrusion. This region has undergone and is probably still undergoing thermal rejuvenation. Multiple zones of intrusion may be a common phenomena along newly rifted continental margins especially when they have been substantially faulted prior to rifting.     

A geophysical survey of the Spitsbergen Margin and surrounding areas

New geophysical information including multichannel seismic profiling data obtained by the PGO Sevmorgeologia Ministry of Geology of the former USSR, Murmansk during 1984–1988 is discussed and interpreted in this study. The deep structure, sedimentary cover and stratigraphy of the Spitsbergen Continental Margin, considered to be a passive margin, i.e. divergent in the northern part and strike-slip in the western part, is described.Two genetically different types of plateaus on the continental margin, Yermak in the north and Spitsbergen (Vestnesa) in the west, have been identified.The entire extent of the continental slope of the northern part of the Spitsbergen Continental Margin in the Eurasia Basin is underlain by attenuated continental crust, while at the base of the Southwest Continental Margin, the oceanic crust along almost the entire extent is observed. The sedimentary cover, up to 10 km thick within the West Spitsbergen Continental Margin, is likewise observed. Within the North Spitsbergen Margin, however, it does not exceed 3.5 km in thickness.The extension and deposition within the West Spitsbergen Margin began in early Oligocene, while the rifting with accompanying sedimentation within the North Spitsbergen Continental Margin started probably in Early Cretaceous.     

Characteristics of gravity anomalies and tectonic analysis of Enderby Land in East Antarctica and its adjacent areas

Enderby Land in East Antarctica and its adjacent areas, which are closely related to the Indian Plate in their geological evolution, have become one of the key zones for studies on how the Antarctic continent evolves. Based on the isostasy and flexure theories of the lithosphere and using the CRUST1.0 model as the depth constraint, this paper uses the gravity field model EIGEN-6C4 and topographic data to calculate the isostatic gravity anomalies of Enderby Land and its adjacent areas. Then, the ...     

Lithospheric structure below the eastern Arabian Sea and adjoining West Coast of India based on integrated analysis of gravity and seismic data

Four uniformly spaced regional gravity traverses and the available seismic data across the western continental margin of India, starting from the western Indian shield extending into the deep oceanic areas of the eastern Arabian Sea, have been utilized to delineate the lithospheric structure. The seismically constrained gravity models along these four traverses suggest that the crustal structure below the northern part of the margin within the Deccan Volcanic Province (DVP) is significantly different from the margin outside the DVP. The lithosphere thickness, in general, varies from 110–120 km in the central and southern part of the margin to as much as 85–90 km below the Deccan Plateau and Cambay rift basin in the north. The Eastern basin is characterised by thinned rift stage continental crust which extends as far as Laxmi basin in the north and the Laccadive ridge in the south. At the ocean–continent transition (OCT), crustal density differences between the Laxmi ridge and the Laxmi basin are not sufficient to distinguish continental as against an oceanic crust through gravity modeling. However, 5-6 km thick oceanic crust below the Laxmi basin is a consistent gravity option. Significantly, the models indicate the presence of a high density layer of 3.0 g/cm³ in the lower crust in almost whole of the northern part of the region between the Laxmi ridge and the pericontinental northwest shield region in the DVP, and also below Laccadive ridge in the southern part. The Laxmi ridge is underlain by continental crust upto a depth of 11 km and a thick high density material (3.0 g/cm³) between 11–26 km. The Pratap ridge is indicated as a shallow basement high in the upper part of the crust formed during rifting. The 15 –17 km thick oceanic crust below Laccadive ridge is seen further thickened by high density underplated material down to Moho depths of 24–25 km which indicate formation of the ridge along Reunion hotspot trace.     

Geodynamic Settings of the Formation of Microcontinents,Submerged Plateaus,and Nonvolcanic Islands within Continental Margins

During breakup of the continental lithosphere, partial or complete separation of small continental blocks from the mainland frequently occurs, leading to the formation of microcontinents or partially separated submerged plateaus that advance toward the ocean, as well as to emergent nonvolcanic islands. The article reviews the geodynamic settings in which isolated blocks of continental crust can form. Depending on the thermomechanical conditions of continental rifting, such blocks may be preserved as emergent islands or as submerged blocks of continental crust.     

The role of rifting in the development of the continental margins of the southwest subbasin,South China Sea: Insights from an OBS experiment

The continental margins of the southwest subbasin in the South China Sea mark a unique transition from multi-stages magma-poor continental rifting to seafloor spreading. We used reflection and refraction profiles across the margins to investigate the rifting process of the crust. Combining with the other seismic profiles acquired earlier, we focused on the comparative geological interpretation from the result of multichannel seismic analysis and wide-angle seismic tomography. Our result provides the evidence of upper crustal layer with abundant fractures below the acoustic basement with a P-wave velocity from 4.0 to 5.5 km s^?1. It indicates extensive deformation of the brittle crust during the continental rifting and can make a good explanation for the observed extension discrepancy in the rift margins of the South China Sea. The seismic chronostratigraphic result shows the possibility of the intra-continental extension center stayed focused for quite a long time in Eocene. Additionally, our evidence suggested that continental margin of the southwest subbasin had experienced at least three rifting stages and the existence of the rigid blocks is an appropriate explanation to the asymmetric rifting of the South China Sea.     

The final rifting evolution in the South China Sea

Seismic reflection data imaging conjugate crustal sections at the South China Sea margins result in a conceptual model for rift-evolution at conjugate magma-poor margins in time and space.The wide Early Cenozoic South China Sea rift preserves the initial rift architecture at the distal margins. Most distinct are regular undulations in the crust–mantle boundary. Individual rift basins are bounded to crustal blocks by listric normal faults on either side. Moho uplifts are distinct beneath major rift basins, while the Moho is downbended beneath crustal blocks, with a wavelength of undulations in the crust–mantle boundary that approximately equals the thickness of the continental crust. Most of the basin-bounding faults sole out within the middle crust. At the distal margins, detachment faults are located at a mid-crustal level where a weak zone decouples crust and mantle lithosphere during rifting. The lower crust in contrast is interpreted as being strong. Only in the region within about 50 km from the Continent–Ocean Transition (COT) we suggest that normal faults reach the mantle, enabling potentially a coupling between the crust and the mantle. Here, at the proximal margins detachment fault dip either seaward or landward. This may indicate the presence of exhumed mantle bordering the continental margins.Post-rift shallow-water platform carbonates indicate a delay in subsidence during rifting in the South China Sea. We propose that this is an inherent process in highly extended continental margins and a common origin may be the influx of warm asthenospheric material into initially cool sub-lithospheric mantle.On a crustal-scale largely symmetric process predominate in the initial rifting stage. At the future COT either of the rift basin-bounding faults subsequently penetrates the entire crust, resulting in asymmetry at this location. However, asymmetric deformation which is controlled by large scale detachment faulting is confined to narrow areas and does not result in a margin-wide simple-shear model. Rather considerable along-margin variations are suggested resulting in alternating “upper and lower plate” margins.     

Oblique rifting in the Havre Trough and its propagation into the continental margin of New Zealand: Comparison with analogue experiments

The Havre Trough is opening by oblique back-arc rifting which is propagating into the continental margin of New Zealand at the Taupo Volcanic Zone. Variations of deformational style along the rift axis have been investigated by comparison with analogue experiments which incorporate brittle and ductile rheologies and are scaled for gravity. Based on the results of the analogue experiments, we present a tectonic model for oblique rifting in the Havre Trough, which involves the rheological contrast between oceanic and continental lithosphere and the oblique geometry of the continental margin of New Zealand with respect to the regional rift trend. The model shows that the continental margin, which is weaker than both oceanic and continental lithosphere, cannot support large shear stresses. The two lithospheres can be decoupled during extensional events along the marginal shear and, depending on the continental margin orientation, this shear can modify the regional stress field. A heterogeneous stress field will rotate normal stresses to be perpendicular or parallel to the margin. As the two lithospheres decouple during extension, the rift grabens and internal faults of the oblique rift system propagate normal to the marginal shear. This model explains the oblique trend of the Havre Trough's tectonic fabric and its relationships to the Vening Meinesz Fracture Zone which represents the oceanic/continental lithospheric boundary.As the Havre Trough rift propagates into the continental margin, rheological differences between oceanic and continental lithosphere result in variations in distribution of strain along the rift axis. Extension of oceanic sub-arc lithosphere is localized into a single rift graben. At the transition into continental rifting, the zone of extension widens into a number of rift grabens forming complex indentations into the margin. This change in deformation style is consistent with analogue experiments as well as other natural examples and results from the contrast in lithospheric rheology and its influence on the process of strain localization.     

Geologic structure and neotectonics of the North African Continental Margin south of Sicily

Marine geological and geophysical data together with drilling information indicate that the North African passive continental margin has been subjected to extension and wrenching after it collided with the northern part of Sicily. The area of the Tripolitania Basin, Jarrafa Trough, Melita and Medina Bank and the Ragusa-Malta Plateau has formed part of a sinking passive margin since the dispersal of Gondwanaland at about 180 My ago as observed from geohistory diagrams. A record of rifting in a NW-SE direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data. The rifting started during the Neocomian and lasted until the Eocene when activity became minor. A pre-Middle Miocene period of northward subduction of oceanic crust is inferred from the geology in NE Sicily. Uplift of the northern part of the African margin after collision in the Middle Miocene is seen in wells in southern Sicily. After the Messinian a rift and dextral shear zone established itself across the African Margin from the Strait of Sicily to the Medina Ridge in the lonian Basin. The zone is marked by up to 1.7 km deep grabens, narrow active wrench faulted channels, volcanic fissures and local uplifted ‘Keilhorsts’ such as Malta. This zone, which varies in width from 100 to 35 km, forms the southern boundary of a microplate which includes Sicily. We speculate that the present motion of this microplate is partly due to the eastward movement of the Calabrian Arc with the Sicilian block over the last remaining oceanic lithosphere in the Eastern Mediterranean.     

南海北部陆缘张裂--岩石圈拆沉的地壳响应

南海北部陆缘在中生代晚期曾形成宏伟的华夏陆缘造山带。火成岩岩石学、岩相古地理学和地球物理学证据显示，该造山带不仅具有巨厚(50～60 km)的陆壳，而且还有巨厚(160～180 km)的岩石圈根，在地势上曾出现过高3 500～4 000 m 的华夏山系。陆缘裂陷盆地的形成发育历史、地壳-岩石圈深部结构、火成岩地球化学特征及理论计算均表明，南海北部陆缘从晚白垩世以来发生的张裂作用起始于华夏陆缘造山带的拉伸塌陷，岩石圈拆沉是南海北部陆缘张裂的重要的引发机制。因此，南海北部陆缘张裂既不同于弧后扩张，也不受控于大西洋式的海底扩张，而是该区大陆构造演化和深部壳幔相互作用的结果。     

Benthic activity and biomass on the Yermak Plateau and in adjacent deep-sea regions northwest of Svålbard

Sediment samples collected during expedition ARK XIII/2 in summer 1997 with the German ice-breaker R/V POLARSTERN were investigated to estimate benthic microbial activity and total biomass of the smallest sediment-inhabiting organisms (size range from bacteria to meiofauna) from the Yermak Plateau northwest of Spitsbergen and adjacent deep-sea areas. Stations covered water depths from about 500 m north of Svålbard and on top of the Yermak Plateau to 3250–4250 m in the Fram Strait and the Nansen Basin. The area of investigations is located in a region with permanent ice-coverage, but in summer 1997 stations along the southern transect crossing the Yermak Plateau at about 81°N lay 50–100 km from the ice-edge. The hydrography of the area is characterized by the inflow of relatively warm, nutrient-rich and particle-laden Atlantic Water into the Arctic Ocean. The input of organic matter from primary production was estimated by measuring concentrations of sediment-bound chloroplastic pigments. Benthic activities and biomasses were evaluated by analyzing a series of biogenic compounds (i.e. bacterial exoenzymes, total adenylates, phospholipids, particulate proteins) in the sediments. Bacterial numbers and biomasses, meiofauna abundances, and nematode biomasses were determined for direct comparison with biochemical parameters. Faunal and biochemical data suggest a high current-driven lateral input of particulate organic matter from the South associated with increased sedimentation rates along the western slope of the Yermak Plateau.     

Seismic stratigraphy and structure of the Northland Plateau and the development of the Vening Meinesz transform margin,SW Pacific Ocean

The Northland Plateau and the Vening Meinesz “Fracture” Zone (VMFZ), separating southwest Pacific backarc basins from New Zealand Mesozoic crust, are investigated with new data. The 12–16 km thick Plateau comprises a volcanic outer plateau and an inner plateau sedimentary basin. The outer plateau has a positive magnetic anomaly like that of the Three Kings Ridge. A rift margin was found between the Three Kings Ridge and the South Fiji Basin. Beneath the inner plateau basin, is a thin body interpreted as allochthon and parautochthon, which probably includes basalt. The basin appears to have been created by Early Miocene mainly transtensive faulting, which closely followed obduction of the allochthon and was coeval with arc volcanism. VMFZ faulting was eventually concentrated along the edge of the continental shelf and upper slope. Consequently arc volcanoes in a chain dividing the inner and outer plateau are undeformed whereas volcanoes, in various stages of burial, within the basin and along the base of the upper slope are generally faulted. Deformed and flat-lying Lower Miocene volcanogenic sedimentary rocks are intimately associated with the volcanoes and the top of the allochthon; Middle Miocene to Recent units are, respectively, mildly deformed to flat-lying, calcareous and turbiditic. Many parts of the inner plateau basin were at or above sea level in the Early Miocene, apparently as isolated highs that later subsided differentially to 500–2,000 m below sea level. A mild, Middle Miocene compressive phase might correlate with events of the Reinga and Wanganella ridges to the west. Our results agree with both arc collision and arc unzipping regional kinematic models. We present a continental margin model that begins at the end of the obduction phase. Eastward rifting of the Norfolk Basin, orthogonal to the strike of the Norfolk and Three Kings ridges, caused the Northland Plateau to tear obliquely from the Reinga Ridge portion of the margin, initiating the inner plateau basin and the Cavalli core complex. Subsequent N115° extension and spreading parallel with the Cook Fracture Zone completed the southeastward translation of the Three Kings Ridge and Northland Plateau and further opened the inner plateau basin, leaving a complex dextral transform volcanic margin.     

Seismic stratigraphy and structural setting of the Adventure Plateau (Sicily Channel)

Within the central Mediterranean, the northwestern sector of the Sicily Channel is the unique area where two independent tectonic processes can be analyzed: the building of the Sicilian–Maghrebian Chain occurred in Late Miocene and the continental lithospheric rifting of the northern African margin occurred since Early Pliocene. These two geodynamic processes generated a peculiar structural style that is largely recognizable in the Adventure Plateau. This plateau is the shallowest part of the Sicily Channel, where water depths do not generally exceed 150 m. It hosts several areas of geomorphic relief, which in some cases rise up to less than 20 m beneath sea-level. A series of submarine magmatic manifestations occur in this area, mainly associated with the extensional phase which produced the rift-related depressions of Pantelleria, Malta and Linosa. Seismic-stratigraphic and structural analyses, based on a large set of multichannel seismic reflection profiles and well information acquired mostly for commercial purposes in the 1970s and 1980s, have allowed us to reconstruct the Triassic-Quaternary sedimentary succession of the Adventure Plateau and define its structural setting. A broad lithological distinction can be made between the successions ranging from Triassic to Paleogene, predominantly carbonate, and the successions ranging from Miocene to Quaternary, predominantly siliciclastic. Three main structural belts have been identified within the Adventure Plateau: (1) the northern belt, affected during Late Miocene time by ESE-verging thrusts belonging to the External Thrust System orogenic domain, which represents the lowermost structural level of the Sicilian–Maghrebian Orogen; (2) the Apenninic–Maghrebian domain of the Sicilian–Maghrebian Orogen, which occupies the northwestern sector of the Adventure Plateau, and that is overthrusted on the External Thrust System orogenic domain during the Late Miocene; (3) the extensional belt of the southwestern sector of the Adventure Plateau, affected by broad NW-trending, high-angle normal faults associated with the Early Pliocene continental rifting phase. The eastern boundary of the Adventure Plateau corresponds to a broadly N–S trending lithospheric transfer zone separating two sectors of the Sicily Channel characterized by a different tectonic evolution.     

Different expressions of rifting on the South China Sea margins

Rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces, but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin. Being opened quite recently in the Tertiary in a scissor-shape manner, the South China Sea (SCS) offers an image of the rifting structures which varies along strike the basin margins. The SCS has a long history of extension, which dates back from the Late Cretaceous, and allows us to observe an early stretching on the northern margin onshore and offshore South China, with large low angle faults which detach the Mesozoic sediments either over Triassic to Early Cretaceous granites, or along the short limbs of broad folds affecting Palaeozoic to Early Cretaceous series. These early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone. Because these low-angle faults reactivate older trends, they vary in geometry according to the direction of the folds or the granite boundaries. A later set of faults, characterized by generally E–W low and high angle normal faults was dominant during the Eocene. Associated half-graben basement deepened as the basins were filling with continental or very shallow marine sediments. This subsequent direction is well expressed both in the north and the SW of the South China Sea and often reactivated earlier detachments. At places, the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the Phu Khanh Basin East of the Vietnam fault. A third direction of faults, which rarely reactivates the detachments is NE–SW and well developed near the oceanic crust in the southern and southwestern part of the basin. This direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part, and ended by the Late Miocene after the onset of the regional Mid Miocene unconformity known as MMU and dated around 15.5 Ma. Latest Miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast. The SE margin of the South China Sea does not show the extensional features as well as the Northern margin. Detachments are common in the Dangerous Grounds and Reed Bank area and may occasionally lead to mantle exhumation. The sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the Late Miocene, when it suddenly deepened. This period also corresponds to the cessation of the shortening of the NW Borneo wedge in Palawan, Sabah, and Sarawak. We correlate the variation of margin structure and composition of the margin; mainly the occurrence of granitic batholiths and Mesozoic broad folds, with the location of the detachments and major normal faults which condition the style of rifting, the crustal boudinage and therefore the crustal thickness.     

Crustal transect across the North Atlantic

Two dimensional crustal models derived from four different ocean bottom seismographic (OBS) surveys have been compiled into a 1,580 km long transect across the North Atlantic, from the Norwegian Møre coast, across the extinct Aegir Ridge, the continental Jan Mayen Ridge, the presently active Kolbeinsey Ridge north of Iceland, into Scoresby Sund in East Greenland. Backstripping of the transect suggests that the continental break-up at ca. 55 Ma occurred along a west-dipping detachment localized near the western end of a ca. 300 km wide basin thinned to less than 20 km crustal thickness. It is likely that an east-dipping detachment near the present day Liverpool Land Escarpment was active during the late stages of continental rifting. A lower crustal high-velocity layer (7.2–7.4 km/s) interpreted as mafic intrusions/underplating, was present beneath the entire basin. The observations are consistent with the plume hypothesis, involving the Early Tertiary arrival of a mantle plume beneath central Greenland and focused decompression melting beneath the thinnest portions of the lithosphere. The mid-Eocene to Oligocene continental extension in East Greenland is interpreted as fairly symmetric and strongly concentrated in the lower crustal layer. Continental break-up which rifted off the Jan Mayen Ridge, occurred at ca. 25 Ma, when the Aegir Ridge became extinct. The first ca. 2 m.y. of oceanic accretion along the Kolbeinsey Ridge was characterized by thin magmatic crust (ca. 5.5 km), whereas the oceanic crustal formation since ca. 23 Ma documents ca. 8 km thick crust and high magma budget.     

冲绳海槽断裂、岩浆构造活动和洋壳化进程

讨论了冲绳海槽断裂、岩浆构造活动特征和它们之间的关系,认为雁行排列的地堑斜交于陆架外缘隆起带,海槽北段断块隆脊、龙王构造带和海槽南段"棉花构造带"可能保留了海槽各幕断陷前的火山岩浆活动特征,而现在活动的吐噶喇火山岛弧可沿海槽南段岛坡追踪到台湾。吕宋岛向台湾的碰撞挤压引起的旋张活动加强了海槽南段的地壳拉张,诱发了地堑内火山岩浆活动,在洋壳化进程中起关键作用,其中最典型的八重山地堑已经形成洋壳。断裂和岩浆活动主要是单向地向岛弧侧迁移,由洋中脊扩张产生的对称条带状磁异常模式难以解释冲绳海槽的洋壳化进程。     

Deep Crustal Structure of the Continental Margin off the Explora Escarpment and in the Lazarev Sea, East Antarctica

This study presents the results of a seismic refraction experiment that was carried out off Dronning Maud Land (East Antarctica) along the Explora Escarpment (14° W–12° W) and close to Astrid Ridge (6°E). Oceanic crust of about 10 km thickness is observed northwest of the Explora Escarpment. Stretched continental crust, observed southeast of the escarpment, is most likely intruded by volcanic material at all crustal levels. Seismic velocities of 7.0–7.4 km/s are modelled for the lower crust. The northern boundary of this high velocity body coincides approximately with the Explora Escarpment. The upper crystalline crust is overlain by a 4-km thick and 70-km wide wedge of volcanic material: the Explora Wedge. Seismic velocities for the oceanic crust north of the Explora Escarpment are in good agreement with global studies. The oceanic crust in the region of the Lazarev Sea is also up to 10-km thick. The lower crystalline crust shows seismic velocities of up to 7.4 km/s. This, together with the larger crustal thickness might point to higher mantle temperatures during the formation of the oceanic crust. The more southerly rifted continental crust is up to 25-km thick, and also has seismic velocities of 7.4 km/s in the lower crystalline crust. This section is interpreted to consist of stretched continental crust, which is heavily intruded by volcanic material up to approximately 8-km depth. Multichannel seismic data indicate that, in this region, two volcanic wedges are present. The wedges are interpreted to have evolved during different time/rift periods. The wedges have a total width of at least 180 km in the Lazarev Sea. Our results support previous findings that the continental margin off Dronning Maud Land between ≈2°E and ≈13°E had a complex and long-lived rift history. Both continental margins can be classified as rifted volcanic continental margins that were formed during break-up of Gondwana.     

From strike-slip faulting to oblique subduction: A survey of the Alpine Fault-Puysegur Trench transition,New Zealand,results of cruise Geodynz-sud leg 2

The Geodynz-sud cruise on board the R/V l'Atalante collected bathymetric, side-scan sonar and seismic reflection data along the obliquely convergent boundary between the Australian and Pacific plates southwest of the South Island, New Zealand. The survey area extended from 44°05 S to 49°40 S, covering the transition zone between the offshore extension of the Alpine Fault and the Puysegur Trench and Puysegur Ridge. Based on variations in the nature and structure of the crust on either side of the margin, the plate boundary zone can be divided into three domains with distinctive structural and sedimentary characteristics. The northern domain involves subduction of probably thinned continental crust of the southern Challenger Plateau beneath the continental crust of Fiordland. It is characterized by thick sediments on the downgoing slab and a steep continental slope disrupted by fault scarps and canyons. The middle domain marks the transition between subduction of likely continental and oceanic crust defined by a series of en echelon ridges on the downgoing slab. This domain is characterized by a large collapse terrace on the continental slope which appears to be due to the collision of the en echelon ridges with the plate margin. The southern domain involves subduction of oceanic crust beneath continental and oceanic crust. This domain is characterized by exposed fabric of seafloor spreading on the downgoing slab, a steep inner trench wall and linear ridges and valleys on the Puysegur ridge crest. The data collected on this cruise provide insights into the nature and history of both plates, and factors influencing the distribution of strike-slip and compressive strain and the evolution of subduction processes along a highly oblique convergent margin.     

Tectonic subsidence history and thermal evolution of the Orange Basin

The Orange Basin offshore southwest Africa appears to represent a classical example of continental rifting and break up associated with large-scale, transient volcanism. The presence of lower crustal bodies of high seismic velocities indicates that large volumes of igneous crust formed as a consequence of lithospheric extension.     

南海北部新生代的构造运动特征

新生代以来,南海北部陆架陆坡区及其邻区的地壳构造运动是在统一的区域构造应力场和总体区域性张裂沉降背景之下发生的,构造运动具有多旋回振荡式发生的特点,并贯穿了晚白垩世末之后的整个新生代.它的发生与太平洋板块的构造运动密切相关,这是由于太平洋板块之下的软流层流动方向和强度的振荡式改变而引发的.