共查询到20条相似文献，搜索用时 415 毫秒
1.
《International Geology Review》2012,54(5):526-533
The impact of gigantic meteorites momentarily creates extremely high pressures and temperatures, leading to the formation of distinctive objects — impact breccias and impactites — at the points where they fall. The Zhamanshin crater is one such place. This annular structure has a diameter of about 10 km, contoured by a low rim made up of a body of shattered Paleozoic rocks thrown out from the ring's center, from depths exceeding 100 - 200 m. Among these breccias have been found pieces and lenticular bodies of remelted rocks — impactites, called zhamanshinites. These thermally altered rocks from a series ranging from baked clays to cinder-like, partly recrystallized substances, glass, and black drops and spattered droplets (up to 1 - 5 cm) of isotropic glass that undoubtedly hardened as they fell through the air. The refused neogenic substances formed by selective evaporation are characterized by a considerable deficit of K and Na, excess Al2O3 and SiO2, a lack of H2O, and a sharp predominance of Fe+2 over Fe+3. Their characteristic shape and distinctive structure and composition suggests that these remelted droplets are tektites, which were called irgizites when first found in the USSR. Their occurrence in the meteorite crater confirms the idea of a genetic unity between tektites and impactites. Selective evaporation of the more volatile elements is characteristic of the surfaces of small planets lacking an atmosphere, but is not characteristic of the earth's surface. The processes and substances occurring at the impact points of gigantic meteorites are therefore unique on the earth, but highly typical of the surfaces of the Moon, Mars, Mercury, and other relatively small celestial bodies. 相似文献
2.
Richard M. Auty 《Geoforum》1986,17(3-4)
There are scale advantages in resource-based industrialization (RBI). Trinidad and Tobago's small size meant that its RBI projects resulted in: relatively low revenue retention, heavy dependence on export markets, skilled personnel shortages and severe ‘Dutch disease’ effects. However Venezuela squandered its size advantage because its RBI strategy was over-ambitious. Instead of taking advantage of its ample scope for risk-reducing diversification, Venezuela concentrated largely on metals processing in a single location. Although it captured more backward linkage than Trinidad and Tobago it did so at high cost as a result of inefficient project execution. Worse, Venezuela's metals projects greatly exceeded its sizeable domestic demand, overtaxed its human resources and exacerbated existing distortions in the economy. Since poorly implemented RBI projects can overwhelm even a large developing economy, RBI is risky and should therefore only be pursued as part of a flexible, broadly-based diversification drive. 相似文献
3.
Uzo M. Igbozurike Dr. 《GeoJournal》1978,2(5):443-449
Although polyculture or interplanting is a dominant production method used by traditional cultivators in the tropics, there has been increasing emphasis on monoculture in agricultural development planning. Analysis of the economic and ecological consequences of these two cropping alternatives in a densely-populated area of eastern Nigeria suggests that a focus on monoculture as a panacea for increasing productivity and food supply is questionable. Polyculture is held to be ecologically superior to monoculture and, in the field area examined, economically more productive as well. Thus further investigation of polycultural approaches to agricultural development would appear to be warranted. 相似文献
4.
J. S. Nicoll G. V. Gibbs M. B. Boisen Jr. R. T. Downs K. L. Bartelmehs 《Physics and Chemistry of Minerals》1994,20(8):617-624
Molecular orbital calculations completed on fluoride molecules containing first and second row cations have generated bond lengths, R, that match those observed for coordinated polyhedra in crystals to within ～0.04 Å, on average. The calculated bond lengths and those observed for fluoride crystals can be ranked with the expression R=Kp ?0.22, where p=s/r, s is the Pauling strength of the bond, r is the row number of the cation and K=1.34. The exponent -0.22 (≈ -2/9) is the same as that observed for oxide, nitride and sulfide molecules and crystals. Bonded radii for the fluoride anion, obtained from theoretical electron density maps, increase linearly with bond length. Those calculated for the cations as well as for the fluoride anion match calculated promolecule radii to within ～0.03 Å, on average, suggesting that the electron density distributions in the vicinity of the minima along the bond paths possess a significant atomic component despite bond type. Bonded radii for Si and O ions provided by experimental electron density maps measured for the oxides coesite, danburite and stishovite match those calculated for a series of monosilicic acid molecules. The resulting radii increase with bond length and coordination number with the radius of the oxide ion increasing at a faster rate than that of the Si cation. The oxide ion within danburite exhibits several distinct radii, ranging between 0.9 and 1.2 Å, rather than a single radius with each exhibiting a different radius along each of the nonequivalent bonds with B, Si and Ca. Promolecule radii calculated for the coordinated polyhedra in danburite match procrystal radii obtained in a structure analysis to within 0.002 Å. The close agreement between these two sets of radii and experimentally determined bonded radii lends credence to Slater's statement that the difference between the electron density distribution observed for a crystal and that calculated for a procrystal (IAM) model of the crystal “would be small and subtle, and very hard to determine by examination of the total charge density.” 相似文献
5.
景观格局与水土流失的尺度特征与耦合方法 总被引：11，自引：0，他引：11
景观格局与生态过程的耦合研究是景观生态学研究的核心科学问题,也是综合自然地理学深化和发展的关键.尺度广泛存在于生态学现象中,尺度效应与尺度转换是景观生态学研究面临的挑战,探讨格局与过程之间相互作用机理与尺度特征是为解决尺度问题提供理论依据的必然途径.水土流失作为一种生态过程,是国内外颇为关注的生态问题.依据多种研究手段,在不同尺度上开展景观格局与水土流失的相互关系与尺度特征的研究,在分析景观格局的时空异质性、水土流失的影响因子与尺度效应的基础上,揭示流域景观格局与水土流失的耦合机理,发展尺度转换方法和景观格局-水土流失过程耦合模型,是完善景观生态学的理论基础,是为水土流失区生态建设提供科学依据的重要途径. 相似文献
6.
Morgan D. Thomas 《Geoforum》1981,12(1):1-17
Regional economic development is largely influenced by technical progress, and innovative manufacturing firms are important in this context. Large, fast growing, innovative firms contribute significantly to growth by direct and indirect employment and income-generating impacts, and these are likely to be extended through time if the firms are capable of developing new product lines and markets. Unfortunately, ‘orthodox’ theories of the firm provide a poor basis for understanding ‘how’ and ‘why’ innovative firms come into existence, grow, change, and operate over time and geographic space. Behavioral—managerial notions, on the other hand, do appear to provide a useful basis for conceptualization. This paper examines some of these concepts and goes on to provide a framework for understanding growth and change in innovative, multiproduct, multiregional firms. 相似文献
7.
8.
Results of numerical analyses of boundary value problems in geomechanics include output of three‐dimensional stress and strain states. Two‐dimensional plots of stress–stress or stress–strain quantities, often used to represent such output, do not fully communicate the evolution of stress and strain states. This paper describes the use of glyphs and hyperstreamlines for the visual representation of three dimensional stress and strain tensors in geomechanics applications. Glyphs can be used to represent principal stress states as well as normal stresses at a point. The application of these glyphs is extended in this paper to represent strain states. The paper introduces a new glyph, called HWY glyph for the representation of shear tensor components. A load step‐based hyperstreamline is developed to show the evolution of a stress or strain tensor under a general state of loading. The evolution of stress–strain states from simulated laboratory tests and a general boundary value problem of a deep braced excavation are represented using these advanced visual techniques. These visual representations facilitate the understanding of complex multidimensional stress–strain soil constitutive relationships. The visual objects introduced in this paper can be applied to stress and strain tensors from general boundary value problems. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
Spatial and Temporal Distribution of Au and Pb-Zn Mineralization: Phenomenon, Mechanism and Implication 总被引：1，自引：0，他引：1
WANG Dongbo SHAO Shicai XU Yong LIU Guoping Beijing Institute of Geology for Mineral Resources Beijing State Nonferrous Metals Industry Administration Beijing 《《地质学报》英文版》2000,74(3):504-510
In the 1990s, some median-large gold deposits have been discovered in several lead-zinc metalloge-netic belts (e.g. the Qinling lead-zinc metallogenetic belt, Shanxi Province and Gansu Province and the Qingchengzi lead-zinc ore field, Liaoning Province) in China. Gold deposits and lead-zinc deposits spatially co-exist in the same tectonic setting; lead-zinc orebodies are commonly located below gold ore bodies. The host rocks of lead-zinc ore-bodies are conformably overlain by those of gold ore bodies. The age of gold mineralization is obviously younger than that of lead-zinc mineralization. Preliminary geochemical research has demonstrated the following: lead-zinc mineralization took place in a marine sedimentary-exhalative system, which had the characteristics of a high fluid/rock ratio, a high salinity and a high halide activity; meanwhile, most of gold was transported into the low-temperature hydrothermal plume and primarily enriched in sediments. During later (magmatism-) metamorphism-tectonism, gol 相似文献
10.
自由对流及其对成岩作用和烃类运移的影响 总被引：2，自引：1，他引：1
自由对流是一种由于流体的密度变化而产生的流体的运动。在沉积盆地,随深度增加,流体的温度也升高,升高的温度可引起流体的热膨胀作用,从而导致地下流体密度随深度而降低,产生垂向密度差。在一定的条件下,该密度差可导致流体产生自由对流。自由对流的流体在运动过程中搬运了大量的矿物质和烃类。由于这些矿物质和烃类的溶解度几乎都与温度有关,因此在对流圈的高温和低温部位,将出现一些矿物质和烃类的溶解、析出或沉淀,从而对成岩作用和烃类运移、聚集构成重要的影响。 相似文献
11.
Katy A. Boon Paul D. Taylor Michael H. Ramsey 《Geostandards and Geoanalytical Research》2007,31(3):237-249
Measurements taken to characterise environmental contamination contain uncertainty, which is generated by both field sampling and chemical analyses. Recently devised techniques have been applied for the first time to estimate this uncertainty in the commercial monitoring and assessment of contaminated land. The uncertainty reduces the reliability of the classification of the land that is made following a site investigation. The possible misclassification of areas of land, as a result of measurement uncertainty, can lead to substantial financial penalties, resulting from litigation or unnecessary remediation. Previous studies have developed methods for the estimation and financial optimisation of measurement uncertainty. These methods have now been applied to a series of six contrasting site investigations, which were conducted by various commercial organisations. The previous uses of these sites included a gas works, a tin mine and railway sidings. The measurement uncertainty was successfully estimated for each of the six investigations, showing its applicability to a wide range of different sampling methods, such as trial pits, window sampling and augering. The measurement uncertainty ranged widely between sites from 25% to 158%, indicating that investigations can differ widely in their reliability. The field sampling tended to generate the largest component of the measurement uncertainty when compared to the contribution from the chemical analysis. The Optimised Contaminated Land Investigation (OCLI) method was applied to each site, with the initial aim of estimating the financial losses that could be incurred as a result of misclassifying the land, due to the uncertainty. It showed that the expectation of loss value per sampling location ranged from only £58 at one site to over £ 11 000 at another. The optimal level of uncertainty that produced the minimal financial loss was then calculated for each site. It provided a reduction in the expectation of loss for the whole site of over £ 10 000 at two of the sites and over £90 000 at two others. These findings demonstrate that implementing concepts of uncertainty can have practical benefits in environmental monitoring, and can enable improvements to be made in the quality of sampling and hence of measurements in general. 相似文献
12.
根据地层层序特征 ,叠加在东秦岭造山带之上的泌阳凹陷伸展作用可以划分出 6个伸展作用幕。核二段沉积前泌阳凹陷以北东—南西向的伸展作用为主 ,构造变形受以正断层为主兼具左旋走滑分量的唐河—栗园断裂控制。核二段沉积期——廖庄组沉积末期构造应力场发生转变 ,以北西—南东向伸展作用为主 ,构造变形主要受以正断层为主兼具右旋走滑分量的泌阳—栗园断裂控制。断裂活动引起上盘构造变形 ,对先成构造进行改造。廖庄组沉积末期发生区域性的隆升作用 ,北西—南东向的伸展作用导致边界断裂上盘发生断块掀斜 ,地层遭受强烈剥蚀。核二段沉积以来尤其是廖庄组沉积末期 ,受北西—南东向不均匀伸展作用的影响 ,北西向走滑断层活动并影响盖层构造样式 相似文献
13.
介质中热质输运-反应体系对于热质成矿、污物迁移等十分重要。这里利用热质流体输运动力学模型与石英溶解与沉淀的化学动力学模型,以及多孔介质的本构关系,建立了一个热质输运、反应动力学藕合模型。并使用此模型研究了局部的温度变化和颗粒半径不均一分布对研究区域内温度场和浓度场的变化情况,其结论是它们之间的耦合可能打破系统的平衡,驱使系统长时间持续进行流体输运-反应动力学过程。 相似文献
14.
Radan Květ 《GeoJournal》1990,22(4):387-390
Conclusion The suggested application of hierarchical systems to geology and geography offers a new view on the evolution of the Earth and a new classification of geosciences. The application of these systems allows the individual fields of geosciences to be connected with each other and also with other disciplines (e.g. physics, astronomy, biology). Hierarchical systems including periodicity can aid future advances in natural sciences because they can be regarded as a uniting principle and key to new approaches to research in natural sciences. 相似文献
15.
为解决5000 m地质岩芯钻探基础准则与依据缺失问题，提高钻探装备的自动化、智能化水平，启动了5000 m智能地质钻探技术装备研发工作，通过钻机装备、钻探器具研制，钻探工艺技术研究并经试验示范验证，取得多项创新成果，形成了5000 m地质岩芯钻探技术体系。通过特深孔钻孔口径与管柱规格优化研究、钻杆规格设计、装备性能参数选配，形成了5000 m地质岩芯钻探技术规范体系；基于5000 m特深孔地质岩芯钻机、孔口自动化作业装置等关键设备研制，实现了绳索取芯钻进的孔口作业全流程自动化，形成了轻量化钻机孔口管柱柔顺控制技术；基于复杂地层孔内工况判别、钻进参数优化与轨迹优化控制等技术问题研究，形成了多源信息融合的地面与孔底一体化钻进过程智能控制技术；基于高性能薄壁绳索取芯钻杆和系列小口径高效钻具研制，形成了大深度绳索取芯系列钻杆钻具技术；研发了耐高温环保型冲洗液、生物破胶废浆处理技术、“广谱型”双浆堵漏技术，形成了绿色环保型冲洗液体系与护壁堵漏技术。 相似文献
16.
为解决5000 m地质岩芯钻探基础准则与依据缺失问题，提高钻探装备的自动化、智能化水平，启动了5000 m智能地质钻探技术装备研发工作，通过钻机装备、钻探器具研制，钻探工艺技术研究并经试验示范验证，取得多项创新成果，形成了5000 m地质岩芯钻探技术体系。通过特深孔钻孔口径与管柱规格优化研究、钻杆规格设计、装备性能参数选配，形成了5000 m地质岩芯钻探技术规范体系；基于5000 m特深孔地质岩芯钻机、孔口自动化作业装置等关键设备研制，实现了绳索取芯钻进的孔口作业全流程自动化，形成了轻量化钻机孔口管柱柔顺控制技术；基于复杂地层孔内工况判别、钻进参数优化与轨迹优化控制等技术问题研究，形成了多源信息融合的地面与孔底一体化钻进过程智能控制技术；基于高性能薄壁绳索取芯钻杆和系列小口径高效钻具研制，形成了大深度绳索取芯系列钻杆钻具技术；研发了耐高温环保型冲洗液、生物破胶废浆处理技术、“广谱型”双浆堵漏技术，形成了绿色环保型冲洗液体系与护壁堵漏技术。 相似文献
17.
西藏冈底斯带花岗岩的时空分布特征及地壳生长演化信息 总被引：159，自引：1，他引：158
花岗岩是大陆特有的重要组成部分,同时与矿产资源有密切的关系。西藏花岗岩约占西藏自治区面积的12％,其中,80％分布在冈底斯岩浆岩带。在空间上,冈底斯花岗岩带大致可以分为3个亚带：北带、中带和南带;在时间上,以印度一亚洲大陆碰撞事件为标尺,可将青藏高原构造一岩浆事件划分为碰撞前（〉65Ma）、碰撞期（65～45Ma）、后碰撞（〈45Ma）3大阶段。在这3个阶段中,冈底斯带都产生了具有各自特点的花岗岩构造一岩浆类型。冈底斯花岗岩类的形成演化与新特提斯班公湖一怒江洋及雅鲁藏布洋的形成演化,有密切的关系。因此,其岩石的Nd,Sr同位素资料,对地壳生长与演化有重要的指示意义。冈底斯南带的大部分地区的花岗岩,均具有εNd（t）（＋）值（＋1．64～＋5．21）,模式年龄tDM也很年青（〈500Ma）,具有初生（juvenile）地壳的特征。在花岗岩成因中地幔物质有重要的贡献。而冈底斯中带、北带及南带西段的花岗岩类以εNd（t）（-）值为特征（-5．3～-17．3）,模式年龄tDM有两组值1．2Ga及2．0～2．5Ga,暗示这些地区的地壳具有古元古代一中元古代基底在花岗岩成因中,地壳组分具有主要贡献。 相似文献
18.
通过分析、对比发达国家场地污染调查与风险评价技术流程的大量信息,结合工作实践,充分考虑我国的实际情况,视土壤和地下水为相互联系的一个整体,提出了我国现阶段场地尺度土壤和地下水污染调查与风险评价的技术程序和工作内容。 相似文献
19.
《Russian Geology and Geophysics》2007,48(8):668-674
In dividing supracrustal strata, formation and horizon have been and are basic stratigraphic units. Stratigraphic boundaries of a formation, a natural geologic body, are drawn mostly on the basis of its composition. Paleontological remains constrain the formation in time and spatially locate it in the Earth's crust. Boundaries between formations can be of three types: strictly stratigraphic, parastratigraphic, and allostratographic. The stratigraphic interval can range from a fraction of a horizon or chronozone to several stages. At the boundary between two systems the adjacent parts of the formation can relate to both systems. The main stratigraphic characteristics for recognizing horizons are paleontologic (biostratigraphic) features, revealed by zonal, paleoecosystemic (ecostratigraphic), bioeventual, and other methods to make a basis for their immanent signature. Horizon can be characterized by boundaries of only two types: strictly stratigraphic and allostratigraphic. The stratigraphic interval of a horizon can vary from a single chronozone to a stage. Boundaries of neighboring horizons at the contact between two stages or systems should coincide with the latter. The stratigraphic units of the International Stratigraphic Chart, in contrary to formation and horizon, are characterized by borders of only one type — strictly stratigraphic. 相似文献
20.
黔南桂西早中三叠世碳酸盐台地边缘和斜坡沉积模式及其演化 总被引：3，自引：0，他引：3
牟传龙 《沉积与特提斯地质》1989,9(2):1-10
黔南桂西地区(东经105°-107°,北纬24°20＇-26°40＇)地跨扬子准地台和加里东褶皱带(华南褶皱带)两个一级大地构造单元。属于南盘江沉积盆地的北部或西北边缘。区内早、中三叠世碳酸盐地层出露良好、层序完整,为台地边缘和斜坡沉积。详细研究该区碳酸盐台地边缘和斜坡沉积,对了解台地边缘特征和演化、海平面变化以及边缘的构造作用等有着重要的理论意义,为确定三叠糸南盘江沉积盆地的西北或北部边缘的构造性质提供可靠的沉积学依据。 相似文献