Beaver dam analogues drive heterogeneous groundwater–surface water interactions     

Jeffrey Wade  Laura Lautz  Christa Kelleher  Philippe Vidon  Julianne Davis  Julio Beltran  Casey Pearce 《水文研究》2020,34(26):5340-5353

Beaver dam analogues (BDAs) are a cost-effective stream restoration approach that leverages the recognized environmental benefits of natural beaver dams on channel stability and local hydrology. Although natural beaver dams are known to exert considerable influence on the hydrologic conditions of a stream system by mediating geomorphic processes, nutrient cycling, and groundwater–surface water interactions, the impacts of beaver-derived restoration methods on groundwater–surface water exchange are poorly characterized. To address this deficit, we monitored hyporheic exchange fluxes and streambed porewater biogeochemistry across a sequence of BDAs installed along a central Wyoming stream during the summer of 2019. Streambed fluxes were quantified by heat tracing methods and vertical hydraulic gradients. Biogeochemical activity was evaluated using major ion porewater chemistry and principal component analysis. Vertical fluxes of approximately 1.0 m/day were observed around the BDAs, as was the development of spatially heterogeneous zones of nitrate production, groundwater upwelling, and anaerobic reduction. Strong contrasts in hyporheic zone processes were observed across BDAs of differing sizes. This suggests that structures may function with size-dependent behaviour, only altering groundwater–surface water interactions after a threshold hydraulic step height is exceeded. Patterns of hyporheic exchange and biogeochemical cycling around the studied BDAs resemble those around natural beaver dams, suggesting that BDAs may provide comparable benefits to channel complexity and near-stream function over a 1-year period.  相似文献   

Influence of large-diameter pipe pile driving on surrounding marine soils and adjacent submarine pipelines     

Jinzhong Dou  Zhong-Jie Zhang 《Marine Georesources & Geotechnology》2021,39(1):15-33

Abstract

With the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing.  相似文献   

Geochemistry of the Mian-Lue ophiolites in the Qinling Mountains, central China: Constraints on the evolution of the Qinling orogenic belt and collision of the North and South China Cratons   总被引：3，自引：0，他引：3  

Ji-feng Xu  Ben-ren Zhang  Yin-wen Han 《Journal of Asian Earth Sciences》2008,32(5-6):336

The Anzishan ophiolite, a typical ophiolitic block of early Carboniferous age in the Mian-Lue suture zone of the Qinling Mountains, central China, consists of amphibolites/metabasalts, gabbros and gabbroic cumulates. All of these rocks, as well as those in the Hunshuiguan-Zhuangke (HZ) block, have compositions similar to normal MORB and back-arc basin basalts (BABB) with high ε_Nd(t) values, indicating that they were derived from a depleted mantle source. The Mian-Lue suture zone also contains blocks of other lithologies, e.g., rift volcanic rocks in the Heigouxia block and arc volcanic rocks in the Sanchazi block. Although they are in fault contact with each other, the presence of these different blocks in the Mian-Lue suture zone may represent a complete Wilson cycle, from initial rifting to open ocean basin to final subduction and continent-continent collision, during the late Paleozoic-early Triassic. In this region, the North and South China Cratons were separated by Paleo-Tethys at least until the early Carboniferous, and final amalgamation of both cratons along the Qinling orogenic belt took place in the Triassic.  相似文献   

Mais comment s'écoule donc un glacier ? Aperçu historique     

Frédérique Rémy  Laurent Testut 《Comptes Rendus Geoscience》2006,338(5):368-385

Ice and snow have often helped physicists understand the world. On the contrary it has taken them a very long time to understand the flow of the glaciers. Naturalists only began to take an interest in glaciers at the beginning of the 19th century during the last phase of glacier advances. When the glacier flow from the upslope direction became obvious, it was then necessary to understand how it flowed. It was only in 1840, the year of the Antarctica ice sheet discovery by Dumont d'Urville, that two books laid the basis for the future field of glaciology: one by Agassiz on the ice age and glaciers, the other one by canon Rendu on glacier theory. During the 19th century, ice flow theories, adopted by most of the leading scientists, were based on melting/refreezing processes. Even though the word ‘fluid’ was first used in 1773 to describe ice, more the 130 years would have to go by before the laws of fluid mechanics were applied to ice. Even now, the parameter of Glen's law, which is used by glaciologists to model ice deformation, can take a very wide range of values, so that no unique ice flow law has yet been defined. To cite this article: F. Rémy, L. Testut, C. R. Geoscience 338 (2006).  相似文献   

大别造山带地壳泊松比结构与超高压变质带—来自宽角反射与近垂直反射剖面的启示   总被引：3，自引：0，他引：3  

李英康  董树文等 《地质论评》2002,48(1):15-23

综合宽角反射、近垂直反射的探测结果和有关地质资料，对大别造山带地壳结构和超高压变质带研究显示：大别造山带地壳具有层块结构特征。沿安义－庄墓剖面，上地壳有7个弹性块体，中地壳有5个，下地壳有4个。扬子与华北地块的主缝合带是超高压变质带，扬子地块与大别造山带的现今分界线是与郯庐断裂相交的太湖－马庙断裂，磨子潭－晓天断裂是大别造山带的北界，北淮阳构造带呈楔状向下插入，它与华北地块的分界是肥中断裂。郯庐断裂在中、上地壳近于直立，下地壳向西倾斜。超高压变质带的厚度为5－7km，产状向北插入到北大别块体之下，折返过程是构造就位，不是大别山的均匀抬升，折返的主运动面是水吼－五河高温剪切带。  相似文献   

中生代羌塘前陆盆地充填序列及演化过程   总被引：40，自引：1，他引：40  

李勇  王成善  伊海生 《地层学杂志》2002,26(1):62-67,79

中生代羌塘前陆盆地位于青藏高原巨型造山带内 ,夹于金沙江缝合带与班公湖—怒江缝合带之间 ,是一个与两侧缝合带逆冲作用相关的沉积盆地 ,由羌北盆地 (对应于金沙江缝合带 )、羌南盆地 (对应于班公湖—怒江缝合带 )和中央隆起带构成 ,其中中央隆起是北部前陆盆地和南部前陆盆地共有的前陆隆起 ,显示为对称型复合前陆盆地 ;该盆地形成于晚三叠世 ,并持续发育至早白垩世 ,盆地中充填了巨厚的同构造期的复理石和磨拉石 ,具有总体向上变粗变浅的充填序列 ,以不整合面可将其划分为 5个由顶底不整合面限制的构造层序 ,其中晚三叠世诺利期构造层序对应于金沙江缝合带主碰撞期 ,晚三叠世瑞替期构造层序对应于金沙江缝合带碰撞闭合后冲断抬升 ,早侏罗世构造层序对应于班公湖—怒江缝合带初始逆冲推覆 ,中侏罗世—早白垩世构造层序对应于班公湖—怒江缝合带主碰撞期 ,中白垩世构造层序为班公湖—怒江缝合带碰撞闭合后冲断抬升与金沙江缝合带冲断抬升的产物 ,为中生代羌塘盆地关闭后的磨拉石建造  相似文献   

秦岭造山带勉略缝合带构造变形与造山过程   总被引：23，自引：4，他引：23  

李三忠  李亚林等 《地质学报》2002,76(4):469-483

秦岭晚古生代以来造山过程中的构造变形研究对建立华北板块与华南板块之间的最终拼合过程尤为重要。为此，选择勉略带进行了详细的野外调查，对其物质组成，几何学结构，变形序列，运动学和动力学作了系统解剖，认为：勉略带是有一定宽度，由一定实体组成的蛇构造混杂岩带，它包括不同时代，不同构造背景，不同起源的一系列构造岩片，如：基底岩片组，洋壳岩片组，岛弧岩片组，碰撞构造沉积楔形体，大陆边缘岩片组，它们被一系列的北倾南冲的断裂分割。勉略带到－高川段的北倾南冲逆冲断裂和勉略带北部南倾北冲的逆冲断裂组合成为现今不对称的正花状几何学结构，但勉略带的北界状元碑断裂和南界 到－略阳断裂走滑特征明显。结合勉略带邻区的构造特征，分别对带内重要断裂及岩片的构造解析表明，除主造山的大地构造演化阶段外，可将勉略带构造变形序列及演化历程总体归纳为三大阶段：俯冲变形阶段，主造山碰撞变形阶段的陆内造山调整变形阶段，并对不同变表阶段的时限，变形特征，运动学和动力学分别作了描述；最后针对该区复杂的楔入，挤出（逃逸）走滑，逆冲过程，提出了一个统一的动力学演化模式。  相似文献   

A Cordilleran model for the evolution of Avalonia   总被引：2，自引：0，他引：2  

R. Damian Nance  J. Brendan Murphy  J. Duncan Keppie 《Tectonophysics》2002,352(1-2)

Striking similarities between the late Mesoproterozoic–Early Paleozoic record of Avalonia and the Late Paleozoic–Cenozoic history of western North America suggest that the North American Cordillera provides a modern analogue for the evolution of Avalonia and other peri-Gondwanan terranes during the late Precambrian. Thus: (1) The evolution of primitive Avalonian arcs (proto-Avalonia) at 1.2–1.0 Ga coincides with the amalgamation of Rodinia, just as the evolution of primitive Cordilleran arcs in Panthalassa coincided with the Late Paleozoic amalgamation of Pangea. (2) The development of mature oceanic arcs at 750–650 Ma (early Avalonian magmatism), their accretion to Gondwana at ca. 650 Ma, and continental margin arc development at 635–570 Ma (main Avalonian magmatism) followed the breakup of Rodinia at ca. 755 Ma in the same way that the accretion of mature Cordilleran arcs to western North America and the development of the main phase of Cordilleran arc magmatism followed the Early Mesozoic breakup of Pangea. (3) In the absence of evidence for continental collision, the diachronous termination of subduction and its transition to an intracontinental wrench regime at 590–540 Ma is interpreted to record ridge–trench collision in the same way that North America's collision with the East Pacific Rise in the Oligocene led to the diachronous initiation of a transform margin. (4) The separation of Avalonia from Gondwana in the Early Ordovician resembles that brought about in Baja California by the Pliocene propagation of the East Pacific Rise into the continental margin. (5) The Late Ordovician–Early Silurian sinistral accretion of Avalonia to eastern Laurentia emulates the Cenozoic dispersal of Cordilleran terranes and may mimic the paths of future terranes transferred to the Pacific plate.This close similarity in tectonothermal histories suggests that a geodynamic coupling like that linking the evolution of the Cordillera with the assembly and breakup of Pangea, may have existed between Avalonia and the late Precambrian supercontinent Rodinia. Hence, the North American Cordillera is considered to provide an actualistic model for the evolution of Avalonia and other peri-Gondwanan terranes, the histories of which afford a proxy record of supercontinent assembly and breakup in the late Precambrian.  相似文献   

Timanian orogenic deformation along the northeastern margin of Baltica, Northwest Russia and Northeast Norway, and Avalonian–Cadomian connections     

D. Roberts  A. Siedlecka 《Tectonophysics》2002,352(1-2)

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吉林延边开山屯地区蓝片岩相变质作用——来自硬绿泥石＋纤锰柱石＋多硅白云母组合的证据   总被引：5，自引：4，他引：5  

李存有吴汉泉  唐克东 《地质通报》2003,22(9):651-654

吉林延边开山屯低级变质作用发育于兴凯地块西南晚古生代活动大陆边缘，这里产出二叠纪末的消减增生杂岩。低级变质作用矿物除冻蓝闪石、阳起石、玉髓、黝帘石、多硅白云母、绿泥石、钠长石外，还在灰黑色变泥质岩中发现硬绿泥石 纤锰柱石 多硅白云母组合。这是国内首次报道的以泥质岩为原岩并具有硬绿泥石 纤锰柱石标志矿物组合的蓝片岩相岩石。研究表明，该组合的形成温度290．14(或370．8)℃，具明显的低温特征。  相似文献