南海大陆边缘动力学:科学实验与研究进展   总被引：13，自引：4，他引：9       下载免费PDF全文

李家彪 《地球物理学报》2011,54(12):2993-3003

国家重点基础研究发展计划(973)项目(2007CB411700)首次在南海南部大陆边缘及西南次海盆开展长排列大震源多道地震、海底地震仪(OBS)折射/反射地震等的综合地球物理探测,结合地质构造、地球化学、动力模拟等的综合研究,形成如下重要认识:南海海盆新生代发生了早、晚两期海底扩张.早期扩张发生于33.5～25 Ma...  相似文献   

南海西南次海盆北缘海底地震仪测线深部地壳结构研究   总被引：7，自引：4，他引：3       下载免费PDF全文

吕川川  郝天珧  丘学林  赵明辉  游庆瑜 《地球物理学报》2011,54(12):3129-3138

基于2009年和2011年采集的海底地震仪数据,辅以多道地震数据,对南海西南次海盆北缘的地壳结构进行了探索.利用二维射线追踪的反演方法建立测线上的模型.利用声学基底面的反射波,下地壳顶界面的反射波和莫霍面的反射波走时的反演勾绘了地层中的不连续界面,利用自声学基底面下的折射波和来自上地幔的首波来反演整条测线的P波速度结构...  相似文献   

Eocene to Miocene geometry of the West Antarctic Rift System     

R. D. Müller  K. Gohl  S. C. Cande  A. Goncharov  A. V. Golynsky 《Australian Journal of Earth Sciences》2013,60(8):1033-1045

Tectonic models for the Late Cretaceous/Tertiary evolution of the West Antarctic Rift System range from hundreds of kilometres of extension to negligible strike-slip displacement and are based on a variety of observations, as well as kinematic and geodynamic models. Most data constraining these models originate from the Ross Sea/Adare Trough area and the Transantarctic Mountains. We use a new Antarctic continental crustal-thinning grid, combined with a revised plate-kinematic model based on East Antarctic – Australia – Pacific – West Antarctic plate circuit closure, to trace the geometry and extensional style of the Eocene – Oligocene West Antarctic Rift from the Ross Sea to the South Shetland Trench. The combined data suggest that from chron 21 (48 Ma) to chron 8 (26 Ma), the West Antarctic Rift System was characterised by extension in the west to dextral strike-slip in the east, where it was connected to the Pacific – Phoenix – East Antarctic triple junction via the Byrd Subglacial Basin and the Bentley Subglacial Trench, interpreted as pullapart basins. Seismic-reflection profiles crossing the De Gerlache Gravity Anomaly, a tectonic scar from a former spreading ridge jump in the Bellingshausen Sea, suggest Late Tertiary reactivation in a dextral strike-slip mode. This is supported by seismic-reflection profiles crossing the De Gerlache Gravity Anomaly in the Bellingshausen Sea, which show incised narrow sediment troughs and vertical faults indicating strike-slip movement along a north – south direction. Using pre-48 Ma plate circuit closure, we test the hypothesis that the Lord Howe Rise was attached to the Pacific Plate during the opening of the Tasman Sea. We show that this plate geometry may be plausible at least between 74 and 48 Ma, but further work especially on Australian – Antarctic relative plate motions is required to test this hypothesis.  相似文献   

Comparison of four techniques for estimating temporal change of seismic velocity with passive image interferometry          下载免费PDF全文

Zhikun Liu  Jinli Huang  Jiaojiao Li 《地震科学（英文版）》2010,23(5):511-518

Passive image interferometry (PII) is becoming a powerful tool for detecting the temporal variations in the Earth's structure,which applies coda wave interferometry to the waveforms from the cross-correlation of seismic ambient noise.There are four techniques for estimating temporal change of seismic velocity with PII:moving-window cross-correlation technique (MWCCT),moving-window cross-spectrum technique (MWCST),stretching technique (ST) and moving-window stretching technique (MWST).In this paper,we use the continuous seismic records from a typical station pair near the Wenchuan MS8.0 earthquake fault zone and generate three sets of waveforms by stacking cross-correlation function of ambient noise with different numbers of days,and then apply four techniques to processing the three sets of waveforms and compare their results.Our results indicate that the techniques based on moving-window (MWCCT,MWCST and MWST) are superior in detecting the change of seismic velocity,and the MWCST can give a better estimate of velocity change than the other moving-window techniques due to measurement error.We also investigate the clock errors and their influences on measuring velocity change.We find that when the clock errors are not very large,they have limited impact on the estimate of the velocity change with the moving-window techniques.  相似文献   

大别山及邻区若干重要基础地质问题的再认识:再论大别造山带非板块碰撞造山过程   总被引：1，自引：0，他引：1  

汤家富  侯明金 《地学前缘》2016,23(4):1-21

就大别山及邻区若干重要基础地质问题作了较深入阐述,并据前人资料与新近调查成果,进一步明确：(1)北淮阳地区属扬子地块北缘,与华北地块南缘的分界为固始-肥中断裂以北。(2)超高压变质带内新元古代浅变质岩层确系存在,并与榴辉岩及其他超高压岩石,共同经受两期褶皱变形,形成早期为伸展拆离,主期为收缩挤压叠加褶皱变形带,而非外来构造残片,或俯冲过程被铲刮下来的“构造加积楔”。(3)蓝片岩形成于伸展拆离构造带内。榴辉岩为地幔岩,属岩浆成因。其他超高压岩石与“柯石英”可在“地壳异常压力”与“高压釜”机制联合作用下,在地壳较浅层次的伸展拆离构造环境下形成。(4)广泛分布的新元古代火山岩系及侵入岩,代表了晋宁期地壳被强烈拉伸裂解扩张事件,但未形成洋壳盆地。(5)详细描述了大别山及邻区构造变形及拉伸与生长线理特征以及形成机制,认为是由“地幔差速环流”所引发的岩石圈与地壳各分层间伸展拆离滑断剪切过程中形成。大别造山带经历了裂解成盆、伸展拆离、收缩挤压、热隆成山,由多阶段构造运动所完成,而非板块碰撞造山。  相似文献   

Crustal Structure and Extension from Slope to Deepsea Basin in the Northern South China Sea     

Hu Dengke  Zhou Di  Wu Xiangjie  He Min  Pang Xiong  Wang Yuwei 《中国地质大学学报(英文版)》2009,20(1)

The newly acquired long-cable multi-channel seismic (MCS) lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 Van strip from the slope to the deepsea basin in the northern South China Sea (SCS).These profdes are of good penetration that Moho is recognizable in ～70% length of the lines.Seismostrattgraphic interpretation and time-depth conversion were conducted.A power function D = atb+ c was used in the time-depth conversion,which avoided the under-or over-estimation of the depths of deep-seated interfaces by cubic or quadratic polynomial functions.Contour maps of basement depth,Moho depth,crustal thickness,and crustal stretching factor were obtained for the study area.In the dip direction,the Moho depth decreases stepwisely from 28 km in the outer shelf southwards to 19,15,and 12 km in the deepsea basin,with ramps at the shelf break,lower slope,and the continent ocean boundary (COB),respectively.Accordingly,the crustal thickness decreased southwards from 3,and 7 km spectively.Under the center of the Balynn (白云) sag,the crust thins significantly to ＜ 7 kin.The crustal stretching factor βc was calculated by assuming the original crust thickness of 30 km.In the centers of the Baiyun sag,βc exceeds 5.Tertiary and Quaternary volcanic activities show a general trend of intensifying towards the COB.An important finding of this study is the along-strike variation of the crustal structure.A Moho rise extends from the COB NW-ward until the shelf break,about 170 km long and 50-100 km wide,with Moho depth ＜ 20 kin.This is called the Balyun Moho Nose,which is bounded to the east,west,and north by belts of high Moho gradients indicative of crustal or even lithospheric faults.The doming of Moho in the nose area might he the cause of the W-E segmentation of the crustal and geological structures along the slope of the northern South China Sea,and the cause of the strong crustal stretching in the Baiyun and Liwan (荔湾) sags.  相似文献   

Tilting separation flows: a mechanism for intense vertical mixing in the coastal ocean     

D. Farmer  R. Pawlowicz  R. Jiang   《Dynamics of Atmospheres and Oceans》2002,36(1-3)

Observations of a front associated with boundary layer separation from a headland illustrate a mechanism by which horizontal density gradients create intense turbulence and vertical mixing, thus, contributing to water property modification in the coastal zone. Tidal current past an island separates from the coast, creating a shear zone between the primary flow and the slowly moving water in the lee of the island. The density structure on either side of the front may differ due to different origins or degrees of prior mixing. Consequently, there can be horizontal density gradients across the front. Boundary layer separation from the headland begins as a vertical vortex sheet on which instabilities grow to form a sequence of eddies. The presence of horizontal density gradients causes the shear layer to tilt. Tilting and stretching of the sheared flow generates intense circulation. Whirlpools and boils appear at the surface accompanied by vertical motions in which broad areas of upwelling alternate with narrow areas of downwelling. These mix the water throughout its depth; bubbles entrained at the surface reach depths of over 120 m. Such violent mixing weakens stratification associated with the estuarine circulation and aerates water masses passing through the area.  相似文献   

Transpressional deformation in northwestern Sardinia (Italy): insights on the tectonic evolution of the Variscan BeltDéformation transpressive dans le Nord-Ouest de la Sardaigne (Italie) : considérations sur l'évolution tectonique de la chaı̂ne Varisque     

Rodolfo Carosi  Giacomo Oggiano 《Comptes Rendus Geoscience》2002,334(4):287-294

Structural investigations in northwestern Sardinia highlight the occurrence of a regional D2 transpressional deformation related both to NNE–SSW direction of compression and to a NW–SE shear displacement. The deformation is continuous and heterogeneous, showing a northward strain increase, indicated by progressively tighter folds and occurrence of F2 sheath folds. D2 transpression is characterised by the presence of a crustal-scale shear deformation overprinting previous D1 structures, related to nappe stacking and top-to-the-south and southwest thrusting. The L2 prominent stretching lineation points to an orogen-parallel extension and to a change in the tectonic transport from D1 to D2. It is attributed to the position of Sardinia close to the northeastern part of the Cantabrian indenter during the progressive evolution of the Ibero-Armorican Arc. D1 phase developed during initial frontal collision, whereas D2 deformation characterised the progressive effect of horizontal displacement during the increasing curvature of the arc. To cite this article: R. Carosi, G. Oggiano, C. R. Geoscience 334 (2002) 287–294.  相似文献   

Subsidence and strike-slip tectonism of the upper continental slope off Manzanillo, Mexico     

William L. Bandy  Franois Michaud  Jacques Bourgois  Thierry Calmus  Jrme Dyment  Carlos A. Mortera-Gutirrez  Jose Ortega-Ramírez  Bernard Pontoise  Jean-Yves Royer  Bertrand Sichler  Marc Sosson  Mario Rebolledo-Vieyra  Florence Bigot-Cormier  Oscar Díaz-Molina  Angel D. Hurtado-Artunduaga  Guillermo Pardo-Castro  Corrine Trouillard-Perrot 《Tectonophysics》2005,398(3-4):115-140

The direction of convergence between the Rivera and North American plates becomes progressively more oblique (in a counter-clockwise sense as measured relative to the trench-normal direction) northwestward along the Jalisco subduction zone. By analogy to other subduction zones, the forces resulting from this distribution of convergence directions are expected to produce a NW moving, fore-arc sliver and a NW–SE stretching of the fore-arc area. Also, a series of roughly arc parallel strike-slip faults may form in the fore-arc area, both onshore and offshore, as is observed in the Aleutian arc.In the Jalisco subduction zone, the Jalisco block has been proposed to represent such a fore-arc sliver. However, this proposal has encountered one major problem. Namely, right-lateral strike-slip faulting within the fore-arc sliver, and between the fore-arc sliver and the North American plate, should be observed. However, evidence for the expected right-lateral strike-slip faulting is sparse. Some evidence for right-lateral strike-slip faulting along the Jalisco block–North American plate boundary (the Tepic–Zacoalco rift system) has been reported, although some disagreement exists. Right-lateral strike-slip faulting has also been reported within the interior of the Jalisco block and in the southern Colima rift, which forms the SE boundary of the Jalisco block.Threefold, multi-channel seismic reflection data were collected in the offshore area of the Jalisco subduction zone off Manzanillo in April 2002 during the FAMEX campaign of the N/O L'Atalante. These data provide additional evidence for recent strike-slip motion within the fore-arc region of the Jalisco subduction zone. This faulting offsets right-laterally a prominent horst block within the southern Colima rift, from which we conclude that the sense of motion along the faulting is dextral. These data also provide additional evidence for recent subsidence within the area offshore of Manzanillo, as has been proposed.  相似文献   

Rheology and seismotectonic regime in the northern central Mediterranean   总被引：4，自引：0，他引：4  

V. Pasquale  M. Verdoya  P. Chiozzi  G. Ranalli 《Tectonophysics》1997,270(3-4):239-257

The connection between thermal field and mechanical properties is analysed in the northern central Mediterranean region, extending from the Ligurian-Provençal basin to the Adriatic foredeep. As the thermal regime is still far from equilibrium in most of the tectonic units, transient thermal models are used. The temperature-depth distribution is estimated in four areas affected by the volcanic activity, which from the Neogene to the Present shifted from Corsica to the Apenninic arc. In the Adriatic foredeep, the thermal effects of the recent thrust-faulting phase in the buried sectors of the northern Apennines are taken into account.

The general context consists of convergence involving westward subduction of the Adriatic plate. This process caused anti-clockwise rotation of Corsica and Sardinia, which led to formation of the Ligurian marginal basin, and also resulted in crustal doubling and overthrusting in the northern Apennines and rifting in the northern Tyrrhenian.

Seismic activity is focused in the internal and external zones of the Apenninic arc, where low surface heat flux is observed, and in the western margin of the Ligurian-Provençal basin. This is a consequence not only of lateral variations in the thermal field but also of the different tectonic settings. Regional extensional patterns in the shallow crust, with minimum principal stress axes trending N60°E and E-W, are observed in the northern and in the southern sectors of the Apenninic arc, respectively. A compressional regime at depths greater than 30 km is observed below the northern sector of the arc, while to the south a change in the structure of the lithosphere is marked by a decrease in deeper seismic activity. Thrust faults and strike-slip faults with a thrust component support a compressional regime along the western margin of the Ligurian basin with maximum principal stress axis oriented N120°E.

Two lithospheric cross-sections across the study region are constructed, based on structural, thermal, gravity, rheological and seismic data. There is clear evidence of the presence of the subducting slab of the Adriatic plate, corresponding to a thickening of the uppermost brittle layer. The crustal seismicity cut-off corresponds to temperatures of 320–390°C. A brittle layer of considerable thickness is present in the uppermost mantle beneath Variscan Corsica and the Adriatic foredeep, with estimated seismic cut-off temperature of about 550 ± 50°C.  相似文献