On the orientation of tensile dikes in a ridge-centered plume

We present three-dimensional numerical models of the ascent of a plume under a spreading ridge and the concomitant melt generation and crust formation using a mantle viscosity which depends on pressure, temperature, melt content, and, optionally, water content. From the velocity field of these convection models we compute the viscous stress tensor in the mantle. Assuming that melt-rich channels or melt-filled dikes are oriented parallel to the maximum compressional stress, we calculate the orientation of such dikes in the partially molten zone of the plume head and beneath the ridge. For the central part of the plume we find dike orientations parallel to the ridge in shallow parts of the plume head, while they are ridge-perpendicular at greater depth. The boundary between these two regimes is shifted downwards for a water-rich plume which dehydrates upon melting. The two regimes of different dike or melt channel orientations seem to be in good agreement with seismic observations on depth-dependent seismic anisotropy, indicating a preference of our wet model. We find a modest focusing of melt towards the spreading center beneath normal ridge in both models, but also in the fully dehydrated parts of the plume head in the model where water was included; those are regions where upwelling is essentially passive. In contrast, the plume in the water-free model and the only partly dehydrated parts of the plume in the water-bearing model tend to develop a dike orientation which moves melt away from the spreading center; these regions are characterized by active upwelling. The defocusing of melt in actively upwelling plume mantle has radial symmetry about the plume axis, i.e. an outward orientation of the dikes is not only visible in planes perpendicular to the ridge, but also along the ridge.     

Deep-rooted piercement structures in deep sedimentary basins — Manifestations of supercritical water generation at depth?

Deep-rooted enigmatic piercement structures in sedimentary basins, including ‘mud volcanoes’, ‘shale diapirs’, ‘salt diapirs’, and ‘asphalt volcanoes’, range in size from less than 1 km², surface area, up to 64 km², and have often an unknown depth of penetration due to incomplete imaging. We propose that they form a family associated with fluid flow. Our argument is based partly on their inferred location (above deep faults) and on the chemical analysis of emitted products, which includes liquid clays, brines and other substances from salt diapirs, and asphalt and light oils from the asphalt volcanoes. We explain these compositions by chemical alteration caused partly by supercritical water, a phase of water existent at high pressure and temperature, locally and temporarily achieved at depths generally beyond 10 km below surface, i.e., at the sediment–crust boundary. Our hypothesis overcomes some of the problems with interpreting fluid flow products, which are otherwise very difficult to explain. In case this hypothesis can be further verified, the family could perhaps be called ‘hydrothermally associated piercement structures’.     

On the velocity covariance for steady flows in heterogeneous porous formations and its application to contaminants transport

We consider groundwater steady flow in a heterogeneous porous formation of random and stationary log-conductivity Y = ln K, characterized by the mean 〈Y〉, and the two point correlation function C _Y which in turn has finite, and different horizontal and vertical integral scales I and I _v , respectively. The fluid velocity V, driven by a given head drop applied at the boundary, has constant mean value U ≡ (U, 0, 0). Approximate explicit analytical expressions for transverse velocity covariances are derived. The adopted methodology follows the approach developed by Dagan and Cvetkovic (Spatial moments of kinetically sorbing plume in a heterogeneous aquifers, Water Resour. Res. 29 (1993) 4053) to obtain a similar result for the longitudinal velocity covariance. Indeed, the approximate covariances of transverse velocities are determined by requiring that they have the exact first order variances as well as zero integral scale (G. Dagan, Flow and Transport in Porous Formations (Springer, 1989)) , and provide the exact asymptotic limits of the displacement covariance of the fluid particles obtained by Russo (On the velocity covariance and transport modeling in heterogeneous anisotropic porous formations 1. Saturated flow, Water Resour. Res., 31 (1995) 129). Comparisons with numerical results show that the proposed expressions compare quite well in the early time regime, and for Ut/I >100. Since most of the applications, like assessing the effective mobility of contaminants or quantifying the potential hazards of nuclear repositories, require predictions over higher times the proposed approximate expressions provide acceptable results. The main advantage related to such expressions is that they allow obtaining closed analytical forms of spatial moments pertaining to kinetically sorbing contaminant plumes avoiding the very heavy computational effort which is generally demanded. For illustration purposes, we consider the movement of one contaminant species, and show how our approximate spatial moments compare with the numerical simulations.     

中国小岩体镍铜(铂族)矿床的区域成矿规律

文章进一步提出中国小岩体镍铜(铂族)矿床产出于三种地质背景,即古大陆内的小侵入体、造山带内小侵入体和与大陆溢流玄武岩有关的小侵入体,分别介绍了金川、喀拉通克和白马寨三个典型矿床的地质情况。从成矿的三个必要条件(①岩浆应达到硫化物饱和;②硫化物与岩浆之间应有足够的质量比;③硫化物聚集到有限的空间成矿)出发,结合矿床实例,阐述了成矿的深部过程和深部熔离-贯入成矿模式。论述了不同尺度的区域成矿规律:①三种地质背景;②邻近深大断裂;③三种岩体-矿床的分布结构形式;④矿集区往往是由一个同源多期次上侵的岩体群组成;⑤矿床由含矿岩浆上侵的终端岩浆房组成;⑥含矿岩浆贯入成矿往往伴随一定的流动分异作用或重力分异作用。     

淮北刘桥二矿七含涌(突)水机理研究

刘桥二矿在开采4煤过程中，七含突水次数达38次之多，严重影响煤矿安全生产。文章在系统地分析刘桥二矿七含涌突水概况的基础上，提出了该矿七含涌突水的主要机理为断裂构造的控制作用和矿山压力的促进作用；指出了砂岩含水层的裂隙发育程度和富水性强弱、煤层的厚度、断层的作用以及4煤与含水层之间隔水层厚度的大小等，是影响工作面涌水的主要因素。研究结果对煤矿砂岩水害的有效防治具有重要的指导意义。     

软弱泥质砂岩地层中输水隧洞稳定性研究

泥质砂岩属于黏土岩,具有典型的遇水软化特征。在泥质砂岩富水地层中进行隧道开挖是地下工程的一个挑战性问题。研究了围岩软化与未软化条件下泥质砂岩地层中输水隧洞的稳定性和支护时间。首先,介绍了泥质砂岩遇水软化的力学试验结果;然后,采用基于Hoek-Brown强度准则的岩体参数评价方法,评估泥质砂岩在围岩软化与未软化条件下的力学参数;再后,以兰州水源地引水隧洞为依托工程,采用数值模拟方法对泥质砂岩隧洞软化与未软化工况的围岩稳定性进行了计算分析,得出泥质砂岩遇水软化对隧洞安全性存在显著影响;最后,采用位移收敛法,研究了泥质砂岩软化与未软化工况中,保障隧洞施工安全的合理支护时机。研究表明,泥质砂岩未软化工况中,可考虑隧道围岩初期支护在距掌子面4～5 m位置实施;而在泥质砂岩遇水软化工况中,初期支护建议在掌子面开挖后立刻支护。研究成果可为泥质砂岩地层隧洞的安全施工提供依据。     

Lateral and vertical juxtaposition of matrix‐rich and matrix‐poor lithologies caused by particle settling in mixed mud–sand deep‐marine sediment suspensions

Sandy sedimentary rocks rich in detrital matrix (>10% silt/clay) have long been recognized in the ancient sedimentary record, and nowhere more commonly than in deep‐marine turbidite systems. Despite this, their depositional mechanisms remain poorly understood, in part because these rocks, which are enriched in fine‐grained sediment, are often poorly exposed in outcrop or are confined to observation in core. Matrix‐rich strata in the Neoproterozoic Windermere Supergroup, in contrast, are very well‐exposed and show systematic changes in lithofacies over distances of several tens to a few hundreds of metres along‐strike. Notably, these strata are observed in both basin floor and continental slope deposits, suggesting that their occurrence and systematic lithological arrangement is related to mechanistic, rather than palaeogeographic, controls. Specifically, the facies transect consists of structureless, clayey sandstone that transforms along‐strike to a two‐layer deposit with the development of an upper, planar‐based, markedly more matrix‐rich layer. Further along‐strike, the basal clayey sandstone thins and eventually pinches out, leaving only the (upper) sandy claystone layer, which in turn thins along‐strike and then pinches out. These systematic changes in lithology, but more specifically the distribution of clay, is interpreted to form a depositional continuum related to particle settling in a horizontally advecting, high concentration particle suspension formed along the margins of an avulsion‐related high‐energy turbulent suspension.     

内蒙古赤峰地区上二叠统砂(页)岩型铜(金)矿的发现及其地质意义

2007年至2010年原赤峰市金田矿业有限责任公司在勘查巴林右旗馒头沟铜(金)矿时,发现该矿成因类型属于砂(页)岩型铜(金)矿,容矿岩石是上二叠统林西组砂页岩。矿区构造简单,林西组地层为一向SE倾的单斜构造。矿区林西组地层厚度大于600 m,目前已发现含矿地层厚度约214.7 m,含8个矿层,矿体呈层状、似层状、透镜状,矿石矿物以他形粒状黄铜矿和自然金为主,均呈微细浸染状散布于砂页岩中,局部有成岩期后形成的细脉状,地层普遍含黄铁矿。此类矿床在内蒙古乃至北方属首次发现,其研究成果不仅及时指导了馒头沟矿床的勘查,而且对内蒙古乃至北方上二叠统寻找同类矿床具有重要的意义。     

Impact of vertical structure on water mass circulation in a tropical lagoon (Ebrié, Ivory Coast)

A one-dimensional vertical model has been developed to simulate the water mass circulation along the vertical structure in all deep coastal areas. The model has hydrodynamic and transport components solved using finite difference scheme. The one-dimensional vertical model results are coupled to the vertically averaged two-dimensional model results at each point of a horizontal grid. A theoretical salinity profile is introduced for each vertically integrated value obtained from the 2DH model results. A viscosity profile, simulating a viscosity value close to zero at the surface and with large viscosity gradients, is applied along the water column. The model is applied to the Vridi channel, connecting the Ebrié lagoon to the sea (Ivory Coast).The response of the Ebrié lagoon is studied in terms of inflow and outflow of water in the system through the Vridi channel. Due to the abrupt variation of the surface slope, vertical velocities along the water column show an anticlockwise spiral from bottom to surface during a tidal cycle. Due to the bottom friction and to the vertical viscosity profile, velocities decrease from surface to bottom. However, the freshwater inflow slows down the tidal propagation during the flood and causes the surface velocity to be smaller than the bottom velocity at mid-tide. Close to the bottom, velocities follow an anticlockwise movement due to the tidal propagation. At the water surface, velocities follow only an alternative movement of either ebb or flood, along the channel direction. No cross shore velocities can develop at the surface in the channel.     

P–T–t evidence for mechanisms of vertical tectonic motion in a contractional orogen: north-western US and Canadian Cordillera

The >1800 km long Coast Mountains–North Cascades orogen of the Canadian Cordillera and north-western US developed as a continental magmatic arc. Metamorphic rocks in the orogen contain widespread evidence for burial of supracrustal rocks to depths of c. 40 km, followed by nearly isothermal decompression to depths of <10 km. Near many shallowly-emplaced, mid-Cretaceous plutons, low-pressure contact metamorphic effects were overprinted by high-pressure regional metamorphic minerals and textures, as evidenced by kyanite±staurolite pseudomorphs after andalusite in metapelitic rocks. Therefore, near-pluton rocks record the loading history of the orogen. Metapelitic rocks not associated with plutons only preserve evidence for high-pressure conditions and/or high-temperature decompression, as indicated, for example, by sillimanite and cordierite after kyanite and garnet, respectively. Petrological evidence for burial and decompression is therefore recorded in different rocks. Various regions of the orogen differ in timing of metamorphism, the overall shape of P–T paths and the relative timing and regional extent of the high-pressure event, but most of these data and observations are consistent with thrusting and/or pure shear thickening as primary loading mechanisms throughout the orogen, as opposed to magma-dominated loading. This interpretation is further supported by comparison with thermal models, which demonstrate that the P–T paths are consistent with simultaneous thrusting and folding at a high initial geothermal gradient (35–40 °C km^?1) in much of the orogen. A high geothermal gradient supports tectonic models invoking intra-arc contraction and suggests that magmatism played an important role in regional temperature-time paths. This tectonic-thermal history may be typical of other contractional orogens and illustrates the importance of large vertical displacement of crust in magmatic arcs.     

废旧金属拆解场地浅层地下水芘污染特征与分析

在分析废旧金属拆解场地浅层地下水中芘的检出和分布特征的基础上,对地下水中芘的污染来源、污染途径和污染控制因素进行了探讨.研究结果表明,场地中心和地下水下游2km范围内芘污染明显,垂直于地下水流向芘迁移距离较小,一般小于0.5km.芘在地下水中的迁移转化受地下水中pH、Eh及DO等因素的控制,弱酸性或中性环境以及厌氧强还原条件下,芘易于检出和迁移,一般难以生物降解.     

Analysis, in a free surface steady flow, of the interstitial velocity field inside a sedimentary bed

The objective of our study is to exploit ultrasonic Doppler velocimetry (UDV) to analyze the velocity field within a steady flow on a porous sedimentary bottom. Velocities are measured for several sedimentary beds, as well within the fluid vein as within the sediment. Our results highlight an exponential distribution of the velocities inside the sediment and a discontinuity of the velocity at the interface water–sediment, between the velocity in the free flow and the velocity within the sediment. These results highlight the need to base the analysis of sedimentary transport on the reality of the physical processes at the interface water–sediment.     

新疆库木库里盆地砂(砾)岩型铜矿地质特征及其控矿条件分析

新疆库木库里盆地砂(砾)岩型铜矿位于东昆仑造山带西段,含矿地层为古近系渐新统石马沟组、新近系中新统石壁梁组与上新统红石梁组。铜矿带东西长约170km,南北宽10～60km。已发现铜矿体20多条,矿化体70多条。铜矿化主要受构造、岩性、岩相古地理、古气候等因素控制。矿床属陆相砂砾岩型铜矿。     

Numerical investigation of the performance of micropiled rafts in sand

The micropiled raft (MPR) offers an efficient foundation system that combines the advantages of micropiles and piled rafts that can be used as primary foundation system or to enhance an existing raft foundation. In this paper, a calibrated and verified finite element model (FEM) with centrifuge tests was used to carry out a numerical investigation on the performance of MPR in sand. A total of 78 different cases were analyzed in this study to assess the behavior of MPR in sand taking into account a number of factors that may influence its behavior such as: the number of micropiles (MPs), the spacing to micropile diameter (S/D_mp), the raft thickness, type of loading and soil density. The outcomes of this investigation should help in understanding the effect of these factors on the MPR axial stiffness, including; differential settlement; load sharing between the MPs and the raft; and the raft bending moment. Moreover, the ability of the PDR method to evaluate the axial stiffness of a MPR for the preliminary design stage is examined. It was found that the MPR system has the ability to increase the tolerable bearing pressure by 190% compared to an isolated raft system. In addition, an adjustment factor (ω_PR) for PDR method was introduced to account for the raft flexibility.     

Source and genesis of sulphate and phosphate–sulphate minerals in a quartz‐sandstone cave environment

Gypsum (CaSO₄·2H₂O), alunite (KAl₃(SO₄)₂(OH)₆), and rare phosphate–sulphate sanjuanite Al₂(PO₄)(SO₄)(OH) 9(H₂O) and rossiantonite (Al₃(PO₄)(SO₄) 2(OH)₂(H₂O)₁₄) have recently been identified as secondary mineral deposits in different quartz‐sandstone caves in the Gran Sabana region, Venezuela. Due to the extended time scale required for speleogenesis in the hard and barely soluble quartz‐sandstone lithology, these caves are considered to be as old as 20 to 30 My. The study of these peculiar secondary mineral deposits potentially reveals important insights for understanding the interaction between deep, superficial and atmospheric processes over thousands to perhaps millions of years. In this study, chemical and petrographic analyses of potential host rock sources, sulphur and oxygen isotope ratios, and meteorological, hydrological and geographical data are used to investigate the origin of sulphates and phospho–sulphates. The results suggest that the deposition of sulphates in these caves is not linked to the quartz‐sandstone host rock. Rather, these mineral deposits originate from an external atmospheric sulphate source, with potential contributions of marine non‐sea salt sulphates, terrestrial dimethyl sulphide and microbially reduced H₂S from the forests or peatbogs within the watershed. Air currents within the caves are the most plausible means of transport for aerosols, driving the accumulation of sulphates and other secondary minerals in specific locations. Moreover, the studied sulphate minerals often co‐occur with silica speleothems of biological origin. Although this association would suggest a possible biogenic origin for the sulphates as well, direct evidence proving that microbes are involved in their formation is absent. Nonetheless, this study demonstrates that these quartz‐sandstone caves accumulate and preserve allogenic sulphates, playing a yet unrecognized role in the sulphur cycle of tropical environments.     

From free good to commodity: Universalizing the provision of water in Paris (1830–1930)

This article focuses on the water distribution network in Paris, from the 1830s, when most Parisians got their water from public fountains and private wells, to the 1930s, by which time almost all of the capital’s inhabitants had been connected to the same network and enjoyed a standard service. It contributes, by a detailed analysis of the entire chain of mediators and mediation, to specify how the modern infrastructure ideal actually took form. In that aim, we analyze the manner in which each actor (public as well as private), in accordance with his/her constraints and resources, which depend on his/her position in the social space, was able to conceive of his/her environment, define objectives, confront problems, make choices and deploy a whole range of frequently innovative practices. In order to understand the underlying factors, our task consists in identifying the actors, modi operandi, progress and phases involved in universalizing water services. Spatially analyzing the extension of the water network, this article demonstrates that the process of universalization, far from being the inexorable and linear outcome of the action of a small number of “major historical forces”, was the upshot of the actions of a whole range of actors acting in specific different geographical, social, economic and technical contexts. The achievement of the “modern infrastructural ideal” as a macro-social phenomenon was ultimately down to a long accumulation process of a multitude of actions, interactions, conflicts and learning processes.     

南昌市突发性应急供水水源地模拟研究

根据研究区水文地质条件,在地下水极丰富区选定尤口、谢埠、桃花三个地段作为突发性应急供水水源地.在现状开采情况下,以满足2020年研究区生活用水量(69.3×104m3/d)3个月为目标,应用GMS软件模拟三个水源地在最不利降水条件下应急供水情况.应急供水3个月之后,桃花有7口井疏干含水层厚度超过原厚度的2/3,最大为78.67％,最小为35.22％,平均为56.48％,基本能满足应急供水要求;谢埠与尤口最大疏干含水层厚度均未超出2/3,平均分别为41.06％和26.30％,均能满足应急供水要求.应急开采时,含水层疏干提供水量所占比重均在90％以上.当3个月应急供水结束后,维持现状开采,在年末桃花、谢埠、尤口含水层厚度分别可恢复至原厚度的89.82％ 、82.57％、85.45％,具有良好的恢复性能.可见,桃花、谢埠、尤口适合作为应急水源地.     

Dynamic responses of a pile embedded in a layered poroelastic half‐space to harmonic lateral loads

A single pile embedded in a layered poroelastic half‐space subjected to a harmonic lateral load is investigated in this study. Based on Biot's theory, the frequency domain fundamental solution for a horizontal circular patch load applied in the layered poroelastic half‐space is derived via the transmission and reflection matrices method. Utilizing Muki and Sternberg's method, the second kind of Fredholm integral equation describing the dynamic interaction between the layered half‐space and the pile subjected to a top harmonic lateral load is constructed. The proposed methodology is validated by comparing results of this paper with some existing results. Numerical results show that for a two‐layered half‐space, the thickness of the upper softer layer has pronounced influences on the dynamic response of the pile and the half‐space. For a three‐layered half‐space, the presence of a softer middle layer in the layered half‐space will enhance the compliance for the pile significantly, while a stiffer middle layer will diminish the dynamic compliance of the pile considerably. Copyright © 2009 John Wiley & Sons, Ltd.     

Geochemistry of hydroxy acids in sediments—I. Some freshwater and brackish water lakes in Japan

Series of α, β, ω and (ω-1) hydroxy fatty acids (FAOHs) were determined in several freshwater and brackish water lacustrine sediments in Japan. Analytical procedure used was digestion of the solvent-extracted sediment with HF/HCl followed by solvent and saponification extraction of the residue. Abundances of α/β and ω-FAOH determined by this procedure were 2–3 times higher than those obtained by single alkaline saponification and of the same order with those provided by HCl hydrolysis. Major portion of α/β-FAOH was obtained by solvent extraction of the acid-treated sediments, while subsequent alkaline saponification was needed for the majority of ω-FAOH to be recovered. Thus determined FAOHs comprised 33–61% (Av. = 42%) of the “bound” acid constituents in the lacustrine surface sediments. The α/β and ω-FAOH composition was principally the same among the samples examined, except for relative proportions of the iso to anteiso C₁₅ and C₁₇ ß(α)-FAOH, which showed significant variations in the ranges of 0.30–1.1 and 0.46–1.5, respectively. In the holomictic lakes, the ratios together with the same ratios of the “bound” branched monocarboxylic acids tended to decrease with increasing water depth of the lakes, suggesting that the ratios may indicate an extent of the early diagenetic alteration of the bacteria-derived lipids either in water column or in surface sediment.