Deep-sea demersal fish species richness in the Porcupine Seabight, NE Atlantic Ocean: global and regional patterns     

Imants G. Priede  Jasmin A. Godbold  Nicola J. King  Martin A. Collins  David M. Bailey  & John D. M. Gordon 《Marine Ecology》2010,31(1):247-260

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A moderate melting model for the Vøring margin (Norway) based on structural observations and a thermo-kinematical modelling: Implication for the meaning of the lower crustal bodies   总被引：2，自引：1，他引：1  

Laurent Gernigon  Francis Lucazeau  Frederic Brigaud  Jean-Claude Ringenbach  Sverre Planke  Bernard Le Gall 《Tectonophysics》2006,412(3-4):255-278

High P-wave velocities (7.1–7.8 km/s) lower crustal bodies (LCBs) imaged along volcanic margins are commonly interpreted as plume and breakup-related thick mafic underplating. This interpretation is partly challenged in this paper based on new seismic observations and modelling of the outer Vøring Basin (Norway). An exceptional strong amplitude reflection, the T Reflection, is particularly well defined below the North Gjallar Ridge (NGR) between 7and 8 s TWT. The T Reflection is located near the volcanic lava flows emplaced during the NE Atlantic breakup ( 55–54 Ma ago) and coincides with the top of the LCB, forming a mid-crustal dome. Based on structural and temporal relationships, we show that the dome clearly influences the structural development of the NGR and predates the continental breakup at least by 10–15 Ma. Using a thermo-kinematical model, we tried also to investigate and quantify the relationships between the extension, LCB and the magmatic production. Modelling suggests that significant Paleocene–Early Eocene magmatism can be produced without any temperature anomaly in the mantle if differential stretching occurs during the breakup initiation. The conclusion of 2D thermo-kinematical parametric analysis is that the magmatic model predicts, either little extension (β < 2) with no melting or high extension (β > 5) with significant melting along the outer Vøring Basin. We suggest that the continental part of the LCB could not necessarily be breakup-related and so magmatic, as has often been stated previously. It is concluded here that the continental part of the LCB observed beneath the outer Vøring Basin may be partly (or fully) attributed to inherited, high-pressure granulite/eclogite lower crustal rocks. The real amount of mafic material emplaced along the outer Vøring Basin could be 20–40% less than thought.  相似文献   

Comparison of Modern Zn-Ba-Pb Ore Deposits at Convergent Plate Margins and Fe-Cu-Zn Deposits at Divergent Plate Margins     

G. P. Glasby 《Marine Georesources & Geotechnology》2013,31(4):290-307

At divergent plate margins, black smoke forms immediately on contact of ascending hydrothermal solutions with sea water. The black smoke, consisting mainly of black ore (BO) and barite ore (BaO), is rapidly dispersed in seawater leaving behind a dominantly yellow ore (YO). At convergent plate margins, on the other hand, zinc sulfides and associated chalcophilic elements start depositing within the hydothermal mound at mesothermal temperatures, and are largely trapped there to form a mixed yellow, black and barite ore (YO-BO-BaO). The abundance of individual chalcophilic elements within the mixed ore varies by more than four orders of magnitude, with Zn-Pb-Ba-Cu-As-Sb-Cd being the elements most enriched in these deposits. The differing patterns of element deposition in these two tectonic settings is related to the temperature of the hydrothermal fluids, which is a function of water depth and therefore of tectonic setting (mid-ocean ridge vs volcanic arc). In highly sedimented basins, such as the JADE hydrothermal field in the Okinawa Trough, Pb and other chalcophilic elements are leached from the sediment by slowly migrating hydrothermal fluids to form a mixed black-yellow-barite ore (BO-YO-BaO). This type of deposit is the most enriched in Zn-Pb-Ba-As-Sb-Ag in decreasing order of element abundance. These results indicate that black ore (sphalerite plus galena) is most enriched in sedimented-hosted deposits such as the JADE deposit, is moderately enriched in submarine hydrothermal mineral deposits from convergent plate margins and is poorly enriched in submarine hydrothermal mineral deposits from divergent plate margins.  相似文献   

Slope failures and stability analysis of shallow water prodeltas in the active margins of Western Greece,northeastern Mediterranean Sea     

V. Lykousis  G. Roussakis  D. Sakellariou 《International Journal of Earth Sciences》2009,98(4):807-822

Sediment instabilities are common on the prodeltas of the seismically active continental margins of Western Greece. Sediment failures on the low-angle (0.5°–2°) prodelta slopes manifest themselves as successions of peripheral rotational block slumps restricted to the foresets of the late highstand systems tract (HST). The individual slump blocks are about 80–150 m long and are bounded by growth faults acting as curved slip planes that extend to a mean depth of 10–15 m below seafloor. Shear planes develop in the lower part of muddy and/or gas charged HST foresets. Deeper basal transparent muddy layers of the early HST bottomset, together with the late Pleistocene transgressive systems tract sequences (TST), are mostly unaffected. On the steeper (2^°–6^°) fan delta slopes of the western Gulf of Corinth debris flows and avalanches with a significant retrogressive component dominate slope destabilisation. Sediment cores taken from landslide scarps and slide planes penetrated gas bubble releasing sediments thereby indicating that failure planes are in the late HST foresets/upper part of the early HST bottomsets gas charged zone. The foresets of the HST prodelta deposits display high water content (30–80%), low bulk density (1.4–1.9 g cm⁻³) and relatively low values of undrained shear strength (3–20 kPa). The water content of the HST distal muddy bottomsets is relatively higher (50–110%) and bulk density relatively lower (1.3–1.7 g cm⁻³) with low values of shear strength (2–10 kPa). The shear strength of the gas releasing sediment layer displays lower values (2–9 kPa) relative to the overlying, post failure, muddy sediments of the late 100–300 years. Slope stability was calculated using the normalised soil parameter (NSP) method under undrained conditions for normally consolidated prodelta sediments. This analysis indicates that instabilities could be induced by critical earthquake ground accelerations of 26.6–29.6% g for the HST foresets and 12.4–14.1% g for the basal transparent layer belonging to the early HST bottomsets. Consequently the early HST bottomsets has to be considered a potentially unstable layer since the regional peak ground accelerations (PGAs) for the next 50 years are expected to range from 19 to 30% g. Moreover, our results show that new glide planes in the prodeltaic sediment bodies of the seismically active continental margins of Western Greece will likely develop from the gas charged sediments of the lower part of the HST foresets to the upper part of early HST bottomsets.  相似文献   

Turbidites and turbidity currents from Alpine 'flysch' to the exploration of continental margins   总被引：1，自引：0，他引：1  

EMILIANO MUTTI  DANIEL BERNOULLI†  FRANCO RICCI LUCCHI‡  ROBERTO TINTERRI 《Sedimentology》2009,56(1):267-318

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北亚造山区南部及其毗邻地区地壳构造分区与构造演化   总被引：58，自引：0，他引：58  

李锦轶  张进  杨天南  李亚萍  孙桂华  朱志新  王励嘉 《吉林大学学报(地球科学版)》2009,39(4)

基于板块构造理论和已有资料的综合研究,建议把北亚造山区南部及其毗邻地区地壳构造单元划分为西伯利亚、哈萨克斯坦、布列亚-佳木斯、塔里木和中朝等5个古板块,每个古板块再可以进一步划分为古陆和古陆缘区,并简要讨论了各个古板块的组成和演化以及蒙古弧、准噶尔盆地基底和北山与毗邻地区关系等几个重大地质构造问题;提出了蒙古-鄂霍茨克碰撞带不是古板块缝合带、华北北缘是一条复合造山带而不是克拉通、在晚古生代存在一个大华北古陆、北亚造山区前身洋盆包括中元古代大陆裂解形成的古太平洋和新元古代大陆裂解形成的古亚洲洋等新认识。  相似文献   

The lateglacial lakes of Glens Roy,Spean and vicinity (Lochaber district,Scottish Highlands)     

《Proceedings of the Geologists' Association. Geologists' Association》2017,128(1):32-41

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.  相似文献   

Rifted margin architecture and crustal rheology: Reviewing Iberia-Newfoundland,Central South Atlantic,and South China Sea     

《Marine and Petroleum Geology》2017

Crustal rheology controls the style of rifting and ultimately the architecture of rifted margins. Here we review the formation of three magma-poor margin pairs, Iberia-Newfoundland, the central segment of the South Atlantic Rift, and the South China Sea by integrating observational data into a numerical forward modelling framework. We utilise a 2D version of the finite element code SLIM3D, which includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology and is able to reproduce a wide range of rift-related deformation processes such as flexure, lower crustal flow, and faulting.Extension in cold, strong, or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries. Hot, weak, or thick continental crust is dominated by ductile deformation and often extends symmetrically into a wide rift system. This simple recipe provides the standard framework to understand initial rift geometry, however, it is insufficient to account for the dynamics of intermediate and late rift stages that shape the final margin architecture.Asymmetric conjugate margins where one side is wide and the other narrow can be formed via both wide and narrow rift styles, which we reproduce with weak and strong crustal rheologies, respectively. Exemplified by the Iberia-Newfoundland conjugates and the Central South Atlantic, we define three characteristic rift phases: an initial phase of simultaneous faulting, an intermediate phase of rift migration that involves sequential fault activity, and finally, the breakup phase. Crustal rheology plays an overarching role in governing the dynamics of these asymmetric margins: we illustrate that weak rheologies generally prolong the phase of simultaneous faulting, while rift migration is enabled by initial fault asymmetry as well as relatively weak crust.Formation of the predominantly symmetric and wide margins of the South China Sea was controlled by extraordinarily weak crust that extended the phase of simultaneous faulting until breakup. The weak crustal rheology of this region relates to the South China Sea's pre-rift history where plate convergence lead to crustal thickening and magmatic additions in a back-arc regime shortly before the onset of rifting.  相似文献   

An incomplete correlation between pre-salt topography,top reservoir erosion,and salt deformation in deep-water Santos Basin (SE Brazil)     

《Marine and Petroleum Geology》2017

In deep-water Santos Basin, SE Brazil, hypersaline conditions during the Aptian resulted in the accumulation of halite and carnallite over which stratified evaporites, carbonates and shales were folded, translated downslope and thrusted above syn-rift structures. As a result, high-quality 3D seismic data reveal an incomplete relationship between pre-salt topography and the development of folds and thrusts in Aptian salt and younger units. In the study area, three characteristics contrast with known postulates on passive margins’ fold-and-thrust belts: a) the largest thrusts do not necessarily occur where the salt is thicker, b) synthetic-to-antithetic fault ratios are atypically high on the distal margin, and c) regions of intense folding do not necessarily coincide with the position of the larger syn-rift horsts and ramps below the salt. Regions marked by important erosion and truncation of pre-salt strata, uplifted and exposed sub-aerially before the deposition of Aptian salt, can form structural lows at present or be part of horsts uplifted after the Aptian. This is an observation that suggests significant intra-salt shear drag above pre-salt structural highs during Aptian-Late Cretaceous gravitational gliding, but not on younger horsts and ramps reactivated after the main phase of salt movement. Either formed by drag or sub-aerial erosion, strata truncation below the Aptian salt does not correlate with the present-day pre-salt structure in terms of its magnitude and distribution. In addition, there is a marked increase in deformation towards the distal margin, where low-angle thrusts are ubiquitous on seismic data. The geometry and large synthetic-to-antithetic fault ratios of post-salt strata on the distal margin lead us to consider a combination of gravitational gliding of salt from the northwest and ridge push from the east as responsible for the observed styles of salt deformation.  相似文献   

从源到汇：大陆边缘的沉积作用   总被引：9，自引：1，他引：8  

李铁刚  曹奇原  李安春  秦蕴珊 《地球科学进展》2003,18(5):713-721

大陆边缘作为地球上沉积物堆积的主要区域,其沉积层保存着全球海平面变化、气候变化、岩石圈变形、大洋环流、地球化学循环、有机生产力和沉积物补给等重要信息。然而,尽管对大陆边缘沉积系统进行了几十年的研究,但仍有许多问题没有得到充分的解决,尤其是没能实现对大陆边缘沉积物扩散系统和相关地层的定量解释。为此,近年来国际地学界开始构思源到汇---大陆边缘沉积作用的系统过程研究,以提高对大陆边缘物质扩散系统行为的预测能力。介绍了源到汇---大陆边缘的沉积作用的研究对象、内容和拟解决的主要科学问题以及DSDP和ODP在大陆边缘沉积作用研究中的主要贡献和目前的进展情况。  相似文献