Variable Phanerozoic thermal history in the Southern Canadian Shield: Evidence from an apatite fission track profile at the Underground Research Laboratory (URL), Manitoba     

Shimon Feinstein  Barry Kohn  Richard Everitt 《Tectonophysics》2009,475(1):190-199

Analysis of a 1.15 km deep apatite fission track (AFT) thermochronology profile at the Underground Research Laboratory (URL), in the southwestern Canadian Shield suggests two Phanerozoic heating and cooling episodes indicating significant, previously unsuspected, Phanerozoic heat flow variations. Phanerozoic temperature and heat flow variations are temporally associated with burial and erosion of the Precambrian crystalline shield and its overlying Phanerozoic successions, which are now eroded completely. Maximum Phanerozoic temperatures occurred in the late Paleozoic when the geothermal gradient is estimated to have been ~ 40-50 °C/km (compared to a present day gradient of ~ 14 ± 2 °C/km) and the sedimentary cover was ~ 800-1100 m thick. Our thermal history models, confirm regional stratigraphic relationships that suggest that the Paleozoic succession was completely eroded prior to beginning of Mesozoic sedimentation. A second heating phase occurred during Late Cretaceous-Paleogene burial when the geothermal gradient is estimated to have been ~ 20-25 °C/km and the Mesozoic and Cenozoic succession was ~ 1200 to 1400 m thick. The Phanerozoic thermal history at the URL site shows a pattern similar to that inferred previously for the epicratonic Williston Basin, the centre of which lies several 100 km to the west. This implies a common regional thermal history for cratonic rocks underlying both the basin and the currently exposed shield. It is suggested that the morphotectonic differences between the Williston Basin and the exposed shield at the URL are due to a dissimilar thermomechanical response to a common, but more complicated than previously inferred, Phanerozoic geodynamic history. The two Phanerozoic periods of variations in geothermal gradient (heat flow) were coeval with epeirogenic movements related to the deposition and erosion of sediments. These paleogeodynamic variations are tentatively attributed to far-field effects of orogenic processes occurring at the plate margin (i.e. the Antler and the Cordilleran orogenies) and the associated accumulation of cratonic seaway sedimentary sequences (Kaskaskia and Zuni sequences).  相似文献   

Combined effect of rheology and confining boundaries on spreading of gravity currents in porous media     

《Advances in water resources》2015

One-dimensional flows of gravity currents within horizontal and inclined porous channels are investigated combining theoretical and experimental analysis to evaluate the joint effects of channel shape and fluid rheology. The parameter $\beta$ governs the shape of the channel cross section, while the fluid rheology is characterised by a power-law model with behaviour index n. Self-similar scalings for current length and height are obtained for horizontal and inclined channels when the current volume increases with time as $t^{\alpha }$.For horizontal channels, the interplay of model parameters $\alpha \text{,}n$, and $\beta$ governs the front speed, height, and aspect ratio of the current (ratio between the average height and the length). The dependency is modulated by two critical values of $\alpha \text{,}{\alpha }_{\beta }=n/(n+1)$ and ${\alpha }_n=(2\beta +1)/\beta$. For all channel shapes, ${\alpha }_{\beta }$ discriminates between currents whose height decreases ($\alpha <{\alpha }_{\beta }$) or increases ($\alpha >{\alpha }_{\beta }$) with time at a particular point. For all power-law fluids, ${\alpha }_n$ discriminates between decelerated currents, with time-decreasing aspect ratio ($\alpha <{\alpha }_n$), and accelerated currents, with time-increasing aspect ratio ($\alpha >{\alpha }_n$). Only currents with time-decreasing height ($\alpha <{\alpha }_{\beta }$) and aspect ratio ($\alpha <{\alpha }_n$) respect model assumptions asymptotically; the former constraint is more restrictive than the latter.For inclined channels, a numerical solution in self-similar form is obtained under the hypothesis that the product of the channel inclination $\theta$ and the slope of the free-surface is much smaller than unity; this produces a negligible error for $\theta >2°$, and is acceptable for $\theta >0.5°$. The action of gravity in inclined channels is modulated by both the behaviour index n and the shape factor $\beta$. For constant flux, the current reaches at long times a steady state condition with a uniform thickness profile. In steep channels and for sufficiently long currents, the free-surface slope becomes entirely negligible with respect to channel inclination, and the constant thickness profile depends only on n.Theoretical results are validated by comparison with experiments (i) in horizontal and inclined channels with triangular or semicircular cross-section, (ii) with different shear-thinning fluids, and (iii) for constant volume and constant flux conditions. The experimental results show good agreement with theoretical predictions in the long-time regime.Our analysis demonstrates that self-similar solutions are able to capture the essential long-term behaviour of gravity currents in porous media, accounting for diverse effects such as non-Newtonian rheology, presence of boundaries, and channel inclination. This provides a relatively simple framework for sensitivity analysis, and a convenient benchmark for numerical studies.  相似文献   

测绘遥感信息工程国家重点实验室十年建设与创新   总被引：1，自引：0，他引：1  

李德仁 《地球科学进展》1999,14(6):627-629

回顾了测绘遥感信息工程国家重点实验室自1989年建室以来10年的历程,重点展示了10年来的研究成果,成果产品化、人才培养与对外开放方面所做的工作。在总结经验的基础上提出了国家重点实验室的发展必须抓好5个方面的工作,对同类实验室建设具有一定的借鉴价值。  相似文献   

实验室盐度计校准结果的不确定度分析     

田锐  李扬眉 《海洋技术学报》2006,25(4):122-124

文中分析了实验室盐度计校准不确定度来源项,按不确定度的评定方法,以实例形式分析评定了校准结果的不确定度。  相似文献   

Wave interactions with multiple-row curtainwall-pile breakwaters     

Chang-Hwan Ji  Kyung-Duck Suh 《Coastal Engineering》2010

In this study, a mathematical model has been developed that can compute various hydrodynamic characteristics of a multiple-row curtainwall-pile breakwater. To examine the validity of the developed model, laboratory experiments have been conducted for double- and triple-row breakwaters with various combinations of drafts of curtain walls, porosities between piles, and distances between rows. Comparisons between measurement and prediction show that the mathematical model adequately reproduces most of the important features of the experimental results. As a whole, the transmission coefficient decreases with an increase in relative water depth, whereas the reflection coefficient, normalized run-up and force exhibit an opposite trend in their variations. With fixed values of the draft of the curtain wall and the porosity of lower perforated part of the first row of a double-row breakwater, as these values of the second row increase and decrease, respectively, the transmission coefficient decreases, as expected. On the other hand, their effects on wave reflection, run-up, and wave force change with the relative depth. As for the distance between the rows, the transmission coefficient becomes a maximum when it is about one half of the wave length, suggesting that this condition should be avoided to achieve the advantage of the breakwater in reducing wave transmission. It is shown that for prototype breakwaters, on an average, the transmission coefficient would be smaller than 0.3 for wave periods less than 6.0 s, and it would be about 0.45 even for the wave period of 9.0 s, although there would be a variation depending on the geometry of the breakwater. It is also shown that wave transmission is significantly reduced by multiple-row breakwaters compared with a single-row breakwater, while the difference between double-row and triple-row breakwaters is marginal. Finally, engineering monograms are provided for double-row breakwaters to be used in practical engineering applications of the breakwaters.  相似文献   

1984 AB—A unique Mars-crossing asteroid     

Eleanor F. Helin  R.Scott Dunbar 《Icarus》1984,60(2):404-408

Asteroid 1984 AB, discovered in January 1984, proved to be a unique object with a close dynamical relationship to Mars. A brief history of the discovery and subsequent “evolution” of the orbit as it was refined is presented. The preliminary orbit of 1984 AB indicated that it might be a Mars Trojan, and an extended discussion of this interesting possibility is presented, but this hypothesis had to be dismissed after further observations had refined the orbit. The semimajor axis and orbital eccentricity are very similar to that of Mars. No other known Mars-crossing asteroid exists with an orbit as closely associated to Mars.  相似文献   

冻土工程国家重点实验室的回顾与展望   总被引：7，自引：2，他引：5  

马巍  朱元林 《冰川冻土》1998,20(3):264-272

冻土工程国家重点实验室是我国唯一的一个以冻土工程为主要研究内容的综合性实验室,其建设和发展对促进我国冻土学的发展有非常重要的意义,在迎来兰州冰川冻土研究所建所４０周年之际,冻土工程国家重点实验室也走过了近９年的历程,回顾昨天,展望未来,只有紧紧把握粘土学科前沿,创新超前,解决国家在寒区经济和社会发展中提出的基础性,关键性和综合性的工程和资源环境问题,才能创建一流的国家重点实验室,使我国冻土工程研究  相似文献   

冰芯与寒区环境开放研究实验室的回顾与展望   总被引：1，自引：1，他引：0  

秦大河  姚檀栋 《冰川冻土》1998,20(3):273-279

对国际和国内冰芯研究的历史与现状,以及冰芯与寒区环境开放研究实验室的硬件（基础建设和仪器设备）和软件（科研力量）方面进行了简介,目前冰芯与寒区环境开研究实验室的三大研究领域：为（１）冰川与大气相互作用过程研究;２）冰芯记录研究;３）雪冰物理学研究,实验室已完成和正承担的课题有３２项,发表论文３００多篇,专著９部,有４项成果获奖,并同国际多家高水平的研究机构合作关系,实验室今后发展目标是,在寒区气候  相似文献   

Effect of advective mass transfer on field scale fluid and solute movement: Field and modeling studies at a waste disposal site in fractured rock at Oak Ridge National Laboratory, Tennessee, USA     

Jin-Ping Gwo  Philip M. Jardine  William Sanford 《Hydrogeology Journal》2005,13(4):565-583

Advective mass transfer is a pore scale mass-transfer process that affects fluid and solute movement between pore domains such as fracture and matrix in a structured porous medium. Mechanistically similar to advection in the advection-dispersion of solutes in non-structured porous medium, it redistributes solutes by moving solute and solvent simultaneously between pore domains. While there is much research on diffusive mass transfer that is often referred to as matrix diffusion, there is a lack of information and study for advective mass transfer in the literature. The objective of this research is to study the effects of advective mass transfer on fluid and solute movement between pore domains. First, field hydraulic measurements at a waste disposal site in fractured rock at Oak Ridge National Laboratory (ORNL), Tennessee, USA, are used to calibrate a fracture-matrix, two-pore-domain groundwater flow model. Latin-hypercube sensitivity analysis suggests that the uncertainty of the calibrated model parameters is small and the calibrated flow model is nearly the optimal. Fracture spacing thus obtained is used to calculate diffusive mass transfer coefficients. The individual effects of advective and diffusive mass transfer on solute movement are then quantitatively evaluated. The calculations indicate that pore structure conceptual models may significantly affect the role of advective mass transfer in field and pore-scale mass transfer. In the particular ORNL field site and with a fracture-matrix pore structure model, contribution of advective mass transfer to solute mass movement is about three to eight orders of magnitude smaller than that of diffusive mass transfer.

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Resumen La transferencia de masa advectiva es un proceso de transferencia de masa en escala intersticial que afecta el movimiento de fluido y soluto entre ámbitos porosos tal como fractura y matriz en un medio estructurado poroso. Este proceso, mecánicamente similar a la advección en la dispersión-advección de solutos de medios porosos no estructurados, redistribuye los solutos mediante el movimiento simultáneo de soluto y solvente entre ámbitos porosos. Mientras que existe bastante investigación en transferencia difusiva de masa que frecuentemente se conoce como difusión en matriz, existe falta de información y estudio de transferencia advectiva de masa en la literatura. El objetivo de esta investigación es estudiar los efectos de la transferencia advectiva de masa en el movimiento de fluido y soluto entre ámbitos porosos. Primero se utilizaron mediciones hidráulicas de campo en un sitio de depósito de residuos en roca fracturada en el Laboratorio Nacional Oak Ridge (ORNL), Tennessee, USA, para calibrar un modelo de flujo de agua subterránea de ámbito de dos poros fractura-matriz. Análisis de sensitividad hipercúbico-latino sugieren que la incertidumbre de los parámetros del modelo calibrado es pequeña y que el modelo de flujo calibrado es aproximadamente el óptimo. El espaciamiento de fracturas así obtenido se utiliza para calcular los coeficientes de transferencia de masa difusiva. Luego se evalúa cuantitativamente los efectos individuales de transferencia de masa advectiva y difusiva en el movimiento de soluto. Los cálculos indican que los modelos conceptuales de estructura porosa pueden afectar significativamente el papel de transferencia de masa advectiva en escalas de campo e intersticial de transferencia de masa. En el sitio de campo específico ORNL y con un modelo de estructura porosa de matriz-fractura, la contribución de transferencia de masa advectiva al movimiento de masa soluto es aproximadamente tres a ocho órdenes de magnitud más pequeño que la contribución por transferencia de masa difusiva.

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Résumé Résumé Le transfert advectif de masse est un processus de transfert de masse à léchelle du pore qui affecte les mouvements du fluide et du soluté entre les différents domaines de pores, tel les fractures et la matrice dans un milieu poreux structuré. Mécaniquement similaire à ladvection dans le concept advection-dispersion de solutés dans les milieux non structurés, ce transfert redistribue les solutés simultanément avec le fluide entre les différents domaines poreux. Alors que de nombreuses recherches portent sur les transferts de masse par diffusion, se référant généralement à une diffusion par la matrice, il y a un grand manquement dinformations et détudes sur les transferts de masse par advection dans la littérature. Lobjectif de cette recherche est détudier leffet du transfert advectif de masse de fluide et de soluté entre les différents domaines poreux. Premièrement, les mesures hydrauliques de terrain sur la décharge en milieu fracturé du laboratoire national dOak Ridge ORNL, Tennessee, USA, sont utilisées pour calibrer un modèle hydrogéologique à double porosité fracture-matrice. Lanalyse de sensibilité latin-hypercube suggère que lincertitude sur les paramètres du modèle est faible et que le calibrage est pratiquement optimal. Lespace de fracture résultant permet de calculer les coefficients de transfert de masse par diffusion. Les effets individuels de ladvection et de la diffusion sur les mouvements de solutés sont dés lors évalués. Les calculs indiquent que le modèle conceptuel de la structure des pores peuvent significativement affectés le rôle du transfert advectif de masse à léchelle du pore et du terrain. Dans le cas du site de lORNL et avec un modèle structuré fracture-matrice, la contribution de ladvection au transfert de masse est de lordre de trois-huitième du transfert de masse par diffusion.

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Laboratory observations of green water overtopping a fixed deck   总被引：1，自引：0，他引：1  

Daniel T. Cox  Jos Alberto Ortega 《Ocean Engineering》2002,29(14):1827-1840

A small-scale laboratory experiment was conducted to quantify a transient wave overtopping a horizontal, deck fixed above the free surface. Detailed free surface and velocity measurements were made for two cases with and without the deck structure to quantify the effect of the deck on the wave kinematics. The study showed that the structure increased the free surface above the leading edge of the deck by 20%. The velocity profile at the leading edge was fairly uniform, and the maximum horizontal velocity was similar to the maximum crest velocity measured without the deck. Immediately below the deck, the maximum velocity was 2.5 times greater than the corresponding velocity without the deck and 2.1 times greater than the maximum crest velocity without the deck. On the deck, the wave collapsed into a thin bore with velocities that exceeded 2.4 times the maximum crest velocity measured without the deck.  相似文献