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   

苏北盘石山、练山地幔捕虏体的PGE地球化学   总被引：3，自引：0，他引：3  

杨雪英  孙亚莉  孙卫东  徐夕生 《地球化学》2008,37(3):197-205

通过锍镍火试金预富集法,分析了位于郯庐断裂带东侧的盘石山、练山地幔橄榄岩包体中铂族元素(PGE)和Au含量.不同于部分熔融残留成因地幔橄榄岩中通常所观察到的负斜率型或平坦型的分布模式,这两地的地幔橄榄岩以Pt、Pd、Ru相对富集,Ir、Rh相对亏损的"燕子型"分布模式为特征.Pt、Pd等不相容元素富集说明上地幔除经历过早期的部分熔融外,还经历了后期富Pt、Pd的高熔/岩比的熔(流)体的层析分离交代作用影响.盘石山地幔橄榄岩的PGE总量比练山高,Os的含量也比原始地幔值高;而练山地幔橄榄岩的Os含量比原始地幔值低,说明交代作用带走了练山地幔橄榄岩中的Os,却没有很大改变盘石山地幔橄榄岩中的Os含量,这可能与交代熔(流)体含硫量饱和程度有关.Rh的负异常可能与部分熔融过程中熔体较低的fo2有关.  相似文献   

地幔岩中流体包裹体研究   总被引：5，自引：2，他引：3  

卢焕章 《岩石学报》2008,24(9):1954-1960

地幔岩石中的流体包裹体代表地幔流体的样品。地幔流体包裹体可以存在从地幔来的金刚石,地幔捕虏体和岩浆碳酸岩中。研究这些岩石和矿物中的流体包裹体可以得出其所代表的地幔流体的温度、压力、成分和同位素。我们目前见到的这三类地幔岩石的包裹体主要可在橄榄石、辉石、金刚石、方解石和磷灰石中见到。这些包裹体可以粗略地分为CO2包襄体和硅酸盐熔融体包裹体。又可细分为四类包裹体：（1）富碳酸盐的硅酸盐熔融包裹体。这种包裹体在金刚石、地幔岩捕虏体和岩浆碳酸盐岩中见到,它又可分为结晶质熔融包裹体和玻璃包裹体。（2）CO2包裹体。这种包裹体大多见于地幔捕虏体中,在金刚石和岩浆碳酸岩中也可见到。（3）含硫化物的包裹体。这种包裹体见于地幔捕虏体中,与纯CO2包裹体和含CO2的熔融包裹体共存。（4）高密度的流体包裹体。这种包裹体见于金刚石中,是一种高盐度、高密度的含K、Cl和H2O的流体包裹体,又可分为高卤水包裹体和含卤水的富硅的碳酸盐岩浆包裹体。从对金刚石、地幔捕虏体和岩浆碳酸盐岩中流体包裹体的研究表明,地幔流体存在不均匀性和不混溶性。  相似文献   

Origin and evolution of alkali basaltic magma in the Okinawa Trough     

Zhang Jiaqiang  Sun Yongfu  Jiang Xiaoli 《海洋学报(英文版)》2000,19(3):115-129

I~IOXThe Okinawa Trough is an extending back--arc basin between the East China Sea Shelf andthe Ry'Ukyu Island Arc of Japan. There are widespreadly distributing acid pumice in the troughand a little basalt just in some area of the extending center. There have been some detailed rePOrtsabout the mineralogy and petrochemical feature of the subalkali tholeiite and alkali trachyte in thetrough (Zhai and Gan, 1995; Li et al., 1997; Qin and Zhai, 1988). This paper mainly reportselectron mic…  相似文献   

A map series of the Southern East Pacific Rise and its flanks, 15° S to 19° S     

Daniel S. Scheirer  Ken C. Macdonald  Donald W. Forsyth  Stephen P. Miller  Dawn J. Wright  Marie-Hélène Cormier  Charles M. Weiland 《Marine Geophysical Researches》1996,18(1):1-12

Four large-scale bathymetric maps of the Southern East Pacific Rise and its flanks between 15° S and 19° S display many of the unique features of this superfast spreading environment including abundant seamounts (the Rano Rahi Field), axial discontinuities, discontinuity migration, and abyssal hill variation. Along with a summary of the regional geology, these maps will provide a valuable reference for other sea-going programs on-and off-axis in this area, including the Mantle ELectromagnetic and Tomography (MELT) experiment.  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   

Pb and other ore metals in modern seafloor tectonic environments: Evidence from melt inclusions   总被引：1，自引：0，他引：1  

Yannick Beaudoin  Steven D. Scott  Zoltan Zajacz 《Marine Geology》2007,242(4):271-289

Many modern seafloor tectonic environments are host to hydrothermal systems and associated polymetallic sulfide deposits. Metal transport and precipitation are controlled by magmatic processes such as pre-eruptive degassing and the hydrothermal cycle. The original availability of Pb and other ore metals in a given setting is dependent on concentrations in the original magmatic source or additional enrichment processes. We have examined the Pb budget of melt inclusions from nine modern seafloor settings representing back-arcs, mid-ocean ridges and seamounts. Melt inclusions provide information on the characteristics of parental magmas, including insights into metal budgets. Trace element data in melt inclusions hosted in plagioclase, olivine and pyroxene were obtained by laser-ablation inductively-coupled mass-spectrometry.Results from back-arcs emphasize the impact of slab-subduction and dehydration processes on the chemical characteristics of generated magmas. Volatile- and fluid-mobile element-rich melt inclusions at Manus basin and Okinawa trough reflect a robust contribution of elements from the subducting slab as evidenced by relatively low Ce/Pb ratios. At Bransfield strait, on the other hand, melt inclusions are volatile poor, and fluid-mobile element ratios are similar to mid-ocean ridge values indicating little or no contribution from the slab. High Cu concentrations at Manus basin and Okinawa trough can be explained by fluxing of ferric iron from the subducting slab benefiting the production of sulfate over sulfide.Metal budgets for seamounts located on and nearby the axis of mid-ocean ridge segments appear to be independent of any input of mantle plume material. Results from the southern Explorer ridge (strong lower mantle influence, transitional- and enriched-MORBs), Pito and Axial seamounts (moderate lower mantle influence, transitional-MORBs) and a Foundation near-ridge seamount (little to no mantle influence, normal-MORB) show that, despite similar tectonic environments and varying contributions of mantle plume material, Cu, Zn and Pb values do not vary significantly between the enriched and non-enriched magma components of a given setting.  相似文献   

Estimating Influence of Crystallizing Latent Heat on Cooling-Crystallizing Process of a Granitic Melt and Its Geological Implications     

ZHANG Bangtong  WU Junqi  LING Hongfei  CHEN Peirong 《《地质学报》英文版》2008,82(2):438-443

Based on the theory of thermal conductivity, in this paper we derived a formula to estimate the prolongation period （AtL） of cooling-crystallization process of a granitic melt caused by latent heat of crystallization as follows：△tL=QL×△tcol/（TM-TC）×CP where TM is initial temperature of the granite melt, Tc crystallization temperature of the granite melt, Cp specific heat, △tcol cooling period of a granite melt from its initial temperature （TM） to its crystallization temperature （Tc）, QL latent heat of the granite melt.
The cooling period of the melt for the Fanshan granodiorite from its initial temperature （900℃） to crystallization temperature （600℃） could be estimated -210,000 years if latent heat was not considered. Calculation for the Fanshan melt using the above formula yields a AtL value of -190,000 years, which implies that the actual cooling period within the temperature range of 900°-600℃ should be 400,000 years. This demonstrates that the latent heat produced from crystallization of the granitic melt is a key factor influencing the cooling-crystallization process of a granitic melt, prolongating the period of crystallization and resulting in the large emplacement-crystallization time difference （ECTD） in granite batholith.  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   

The transition from peraluminous to peralkaline granitic melts: Evidence from melt inclusions and accessory minerals     

R. Thomas  J.D. Webster  D. Rhede  W. Seifert  K. Rickers  H.-J. Frster  W. Heinrich  P. Davidson 《Lithos》2006,91(1-4):137-149

Fractional crystallization of peraluminous F- and H₂O-rich granite magmas progressively enriches the remaining melt with volatiles. We show that, at saturation, the melt may separate into two immiscible conjugate melt fractions, one of the fractions shows increasing peraluminosity and the other increasing peralkalinity. These melt fractions also fractionate the incompatible elements to significantly different degrees. Coexisting melt fractions have differing chemical and physical properties and, due to their high density and viscosity contrasts, they will tend to separate readily from each other. Once separated, each melt fraction evolves independently in response to changing T/P/X conditions and further immiscibility events may occur, each generating its own conjugate pair of melt fractions. The strongly peralkaline melt fractions in particular are very reactive and commonly react until equilibrium is attained. Consequently, the peralkaline melt fraction is commonly preserved only in the isolated melt and mineral inclusions.

We demonstrate that the differences between melt fractions that can be seen most clearly in differing melt inclusion compositions are also visible in the composition of the resulting ore-forming and accessory minerals, and are visible on scales from a few micrometers to hundreds of meters.  相似文献