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排序方式: 共有170条查询结果,搜索用时 46 毫秒
81.
82.
N. Kukowski R. von Huene J. Malavieille S. E. Lallemand 《International Journal of Earth Sciences》1994,83(4):822-831
Reflection seismic data from the Peruvian continental margin at 12° S clearly reveal an accretionary wedge and buttress. Sandbox experiments applying the physical concept of the Coulomb theory allow the systematic investigation of the growth and deformation of such an accretionary structure. The style of deformation of the buttress and the internal structure of the wedge is observed in the sandbox models. The possibility of underplating material beneath the buttress and the amount of tectonic erosion depend on the physical properties of the materials, mainly internal friction, cohesion and basal friction. Boundary conditions such as the height of the subduction gate and the thickness of incoming sand also constrain the style of growth of the model accretionary structure.The configurations of two experiments were closely scaled to reflection seismic depth sections across the Peruvian margin. A deformable buttress constructed of compacted rock powder is introduced to replicate the basement rock which allows deformation similar to that in the seismic data. With the sandbox models it is possible to verify a proposed accretionary history derived from seismic and borehole data. The models also help in understanding the mechanisms which control the amount of accretion, subduction and underplating as a function of physical properties, boundary conditions and the duration of convergence. 相似文献
83.
Relative importance of strain rate and rheology for the mode of continental extension 总被引:3,自引:0,他引:3
G. Bassi 《Geophysical Journal International》1995,122(1):195-210
84.
C. J. Greenroyd C. Peirce M. Rodger A. B. Watts R. W. Hobbs 《Geophysical Journal International》2007,169(3):964-987
Geophysical data from the Amazon Cone Experiment are used to determine the structure and evolution of the French Guiana and Northeast Brazil continental margin, and to better understand the origin and development of along-margin segmentation. A 427-km-long combined multichannel reflection and wide-angle refraction seismic profile acquired across the southern French Guiana margin is interpreted, where plate reconstructions suggest a rift-type setting.
The resulting model shows a crustal structure in which 35–37-km-thick pre-rift continental crust is thinned by a factor of 6.4 over a distance of ∼70 km associated with continental break-up and the initiation and establishment of seafloor spreading. The ocean–continent boundary is a transition zone up to 45 km in width, in which the two-layered oceanic-type crustal structure develops. Although relatively thin at 3.5–5.0 km, such thin oceanic crust appears characteristic of the margin as a whole.
There is no evidence of rift-related magmatism, either as seaward-dipping sequences in the reflection data or as a high velocity region in the lower crust in the P -wave velocity model, and as a such the margin is identified as non-volcanic in type. However, there is also no evidence of the rotated fault block and graben structures characteristic of rifted margins. Consequently, the thin oceanic crust, the rapidity of continental crustal thinning and the absence of characteristic rift-related structures leads to the conclusion that the southern French Guiana margin has instead developed in an oblique rift setting, in which transform motion also played a significant role in the evolution of the resulting crustal structure and along-margin segmentation in structural style. 相似文献
The resulting model shows a crustal structure in which 35–37-km-thick pre-rift continental crust is thinned by a factor of 6.4 over a distance of ∼70 km associated with continental break-up and the initiation and establishment of seafloor spreading. The ocean–continent boundary is a transition zone up to 45 km in width, in which the two-layered oceanic-type crustal structure develops. Although relatively thin at 3.5–5.0 km, such thin oceanic crust appears characteristic of the margin as a whole.
There is no evidence of rift-related magmatism, either as seaward-dipping sequences in the reflection data or as a high velocity region in the lower crust in the P -wave velocity model, and as a such the margin is identified as non-volcanic in type. However, there is also no evidence of the rotated fault block and graben structures characteristic of rifted margins. Consequently, the thin oceanic crust, the rapidity of continental crustal thinning and the absence of characteristic rift-related structures leads to the conclusion that the southern French Guiana margin has instead developed in an oblique rift setting, in which transform motion also played a significant role in the evolution of the resulting crustal structure and along-margin segmentation in structural style. 相似文献
85.
Crustal structure of the Newfoundland rifted continental margin from constrained 3-D gravity inversion 总被引:1,自引:0,他引:1
The rifting history of the Atlantic continental margin of Newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2-D seismic surveys. While informative, the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin. A 3-D gravity inversion of the free air data over the Newfoundland margin allows us to generate a 3-D density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage. Results of the gravity inversion show good correspondence with Moho depths from seismic results. A shallowing of the Moho to 12 km depth is resolved on the shelf at the northern edge of the Grand Banks, in a region poorly sampled by other methods. Comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends. Such insights must act as constraints for future palaeoreconstructions of North Atlantic rifting. 相似文献
86.
87.
T. Nielsen L. De Santis K.I.T. Dahlgren A. Kuijpers J.S. Laberg A. Nygrd D. Praeg M.S. Stoker 《Marine and Petroleum Geology》2005,22(9-10):1149
The present paper provides an overview of glacial related seabed features and sedimentary sequences found along the formerly glaciated NW European margin and compare it with those found on contemporary glaciated margins from both the Southern and Northern Hemispheres. A brief review of the seabed physiography and strata architecture of the margins under consideration is followed by comparison of the most relevant similarities and differences. Comparison of the present-day bathymetric setting of both former and contemporary glaciated margins reveals no clear link to the effect of neither ice sheet or sediment load. Three different types of glacially eroded shelf transverse troughs have been identified, while marginal troughs seem connected to similar geological settings everywhere. Beyond the shelf edge interaction between downslope and alongslope processes has occurred resulting, amongst others, in the formation of large sedimentary mounds on the rise. More frequent large-scale mass wasting occurs on the former glaciated NW European margin than the Greenland and Antarctic margins in the latest Neogene to recent times. A two-stage evolution of the shelf prograding wedges is observed on all margins under consideration, which may reflect a general development of an ice cover from an initial phase of non- to restricted glaciation, evolving to a mature stage of expansive glaciation. 相似文献
88.
We have obtained improved images of a debris flow deposit through the reprocessing of multichannel seismic reflection data
between Drifts 6 and 7 of the continental rise of the Pacific margin of the Antarctic Peninsula. The reprocessing, primarily
aimed at the reduction of noise, relative to amplitude preservation, deconvolution, also included accurate velocity analyses.
The deposit is dated as upper Pliocene (nearly 3.0 Ma) via correlation to Sites 1095 and 1096 of the Ocean Drilling Program
(ODP) Leg 178. The estimated volume is about 1800 km3 and the inferred provenance from the continental slope implies a run out distance exceeding 250 km. The dramatic mass-wasting
event that produced this deposit, unique in the sedimentary history of this margin, is related to widespread late Pliocene
margin erosion. This was associated with a catastrophic continental margin collapse, following the Antarctic ice sheet expansion
in response to global cooling. The seismic data analysis also allowed us to identify diffractions and amplitude anomalies
interpreted as expressions of sedimentary mounds at the seafloor overlying narrow high-velocity zones that we interpret as
conduits of fluid expulsion hosting either methane hydrates or authigenic carbonates. Fluid expulsion was triggered by loading
of underlying sediments by the debris flow deposits and may have continued until today by input of fluids from sediment compaction
following the deep diagenesis of biogenic silica. 相似文献
89.
Hölker Andreas B. Manatschal Gianreto Holliger Klaus Bernoulli Daniel 《Marine Geophysical Researches》2002,23(4):319-334
The tectonic interpretation of basement structures in seismic reflection profiles from ocean-continent transitions (OCT) of magma-poor rifted margins is notoriously difficult due to the scarcity of borehole information. Low-angle intra-basement reflections are frequently interpreted as detachment faults, and in certain locations the drilled top of the basement is interpreted as exhumed detachment fault. The seismic expression of such detachment faults is, however, poorly understood. We address this problem by comparing synthetic seismic data from the Tasna OCT, an exposed remnant of a Tethyan margin, with seismic reflection data from Hobby High, a drilled basement high within the west Iberian margin. Both sites are widely considered as being representative of OCT zones. Their geological similarity and the complementary nature of the data enable us to perform a detailed investigation of the seismic structure and response of these OCT zones. This provides insights into the seismic imaging of OCT zones in general and the tectonic evolution of the associated detachment systems in particular. On the basis of the Tasna OCT models and their seismic responses we have identified some potential characteristics of intra- and top-basement detachments: (i) variable amplitudes and numerous diffractions from the top of exhumed subcontinental mantle, (ii) a continuous and strong reflection imaging the top of exhumed lower crustal rocks, and (iii) a weak and discontinuous reflection of inverse polarity representing a shallow intra-basement crust-mantle detachment. Similar features are consistently observed at geologically equivalent positions in the seismic data from Hobby High and may thus serve as guidelines for interpretation of seismic data from un-drilled OCT zones. 相似文献
90.
大洋和大陆边缘岩石圈有效弹性厚度的研究意义 总被引:4,自引:1,他引:4
大洋岩石圈有效弹性厚度分布在 (45 0± 15 0 )℃等温面内 ,并且随着加载时岩石圈年龄的增加而增加。因此 ,大洋岩石圈的挠曲刚度强烈地依赖岩石圈的热结构。一些海隆下岩石圈有效弹性厚度的降低 ,可能是岩石圈经历过热活化 ,岩石圈热年龄降低的结果。大西洋一些群岛的岩石圈有效弹性厚度小于理论值 ,则反映了岩石圈结构的不同。在海沟 ,板块的挠曲也是影响岩石圈有效弹性厚度的因素 ,它降低了岩石圈的强度。在被动大陆边缘海陆岩石圈交界处 ,向陆的方向 ,岩石圈弹性厚度比同年龄的大陆或大洋岩石圈的小 ,表明强度明显降低 ;向大洋方向 ,岩石圈的弹性厚度与正常的大洋岩石圈弹性厚度吻合。在活动大陆边缘的挠曲前陆盆地和造山带 ,岩石圈有效弹性厚度变化较大 ,部分地区受先前的岩石圈低强度影响 ,而表现出岩石圈强度的弱化。同时 ,这种方法还广泛地用于大洋中脊岩浆侵位、地幔流动、南太平洋超级海隆的动力学机制、大陆边缘的变形和构造演化、新生岩石圈的力学性质和流变学性质的研究 相似文献