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991.
Allen P. Nutman Vickie C. Bennett Clark R. L. Friend Kenji Horie Hiroshi Hidaka 《Contributions to Mineralogy and Petrology》2007,154(4):385-408
The Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a
complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single
phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and
granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon,
oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses
and laser ablation ICP-MS depth profiling show that thin (usually < 10 μm) younger (3,660–3,590 Ma and Neoarchaean) shells
of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population
occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than
one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples
with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites
from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted,
respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110–140 ppm Zr in the
tonalites and likely magmatic temperatures of >850°C, zircon solubility–melt composition relationships show that they were
only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined
with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the
melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma
quartzo–feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon
with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites
and as inherited grains in some 3,660 Ma granites (sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally
derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved
c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions
from melting of hydrated mafic crust to the earliest Archaean. Five c. 3,850 Ma tonalites were selected as the best preserved
on the basis of field criteria and zircon petrology. Four of these samples have overlapping initial ɛNd (3,850 Ma) values from +2.9 to +3.6± 0.5, with the fourth having a slightly lower value of +0.6. These data provide additional
evidence for a markedly LREE-depleted early terrestrial mantle reservoir. The role of c. 3,850 Ma crust should be considered
in interpreting isotope signatures of the younger (3,800–3,600 Ma) rocks of the Itsaq Gneiss Complex.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
992.
Citizens as sensors: the world of volunteered geography 总被引:62,自引:0,他引:62
Michael F. Goodchild 《GeoJournal》2007,69(4):211-221
In recent months there has been an explosion of interest in using the Web to create, assemble, and disseminate geographic information provided voluntarily by individuals. Sites such as Wikimapia and OpenStreetMap are empowering citizens to create a global patchwork of geographic information, while Google Earth and other virtual globes are encouraging volunteers to develop interesting applications using their own data. I review this phenomenon, and examine associated issues: what drives people to do this, how accurate are the results, will they threaten individual privacy, and how can they augment more conventional sources? I compare this new phenomenon to more traditional citizen science and the role of the amateur in geographic observation. 相似文献
993.
Åsa Fransson 《Hydrogeology Journal》2007,15(2):307-313
Two methods, both using data from fixed-interval-length hydraulic tests and geological mapping on different scales, have been
utilised to estimate transmissivity distributions of individual fractures. Individual fracture properties are of importance
in estimating transport of water and solutes; they influence the spreading of grout when sealing tunnels. One of the methods
is non-parametric, while the other is based on combinatorics and the multiplication principle. The study verified the usefulness
of both methods for estimating the probability of conductive and non-conductive fractures, and the transmissivity distributions.
Data for estimating transmissivity distributions originate from flow logging of a borehole in Sweden. Fracture frequency data
are from core logging and images using a borehole image processing system (BIPS). Estimated transmissivity distributions,
based on flow log data from 3-m sections (test scale length, L: 3 m, and step length, dL: 3 m), were compared with transmissivities
obtained directly from detailed, overlapping flow logging which identify individual conductive fractures (test scale, L: 0.5 m,
step length, dL: 0.1 m). The latter data are considered to be an acceptable approximation of the individual fracture transmissivities;
the agreement, compared with the calculated transmissivity distributions based on 3-m section data, is good for both methods.
Resumen Se han utilizado dos métodos, ambos procesando datos de pruebas hidráulicas de longitud e intervalo fijo y mapas geológicos en distintas escalas, para estimar las distribuciones de transmisividad de fracturas individuales. Las propiedades de fracturas individuales son de importancia para estimar el transporte de agua y solutos; las propiedades influyen en la propagación de lechada al sellar túneles. Uno de los métodos es no paramétrico mientras que el otro se basa en el principio de multiplicación y combinatorio. El estudio verifica la utilidad de ambos métodos para estimar la probabilidad de fracturas conductivas y no conductivas y las distribuciones de transmisividad. Los datos para estimar las distribuciones de transmisividad se originan del registro de flujo de un pozo en Suecia. Los datos de frecuencia de fracturas provienen de registros de núcleo e imágenes usando un Sistema de Procesamiento de Imágenes de Pozo (BIPS). Se compararon las distribuciones estimadas de transmisividad basadas en datos del registro de flujo en secciones de 3 m (longitud de escala de la prueba L: 3 m, y escalón de longitud dL: 3 m), con transmisividades obtenidas directamente de registros detallados de flujo superpuesto el cual identifica fracturas conductivas individuales (escala de la prueba, L: 0.5 m, escalón de longitud, dL: 0.1 m). Los últimos datos se consideran una aproximación aceptable de las transmisividades de fracturas individuales; la consistencia, comparada con las distribuciones de transmisividad calculada basadas en datos de sección de 3 m, es buena para ambos métodos.
Résumé Deux méthodes ont été testées afin d’estimer la distribution des transmissivités de fractures unitaires; toutes deux utilisent des données issues de tests hydrauliques effectués à intervalles réguliers et de cartographies géologiques à plusieurs échelles. La connaissance des propriétés des fractures unitaires est importante pour estimer le transport d’eau et de solutés; elles influencent en outre l’étalement du coulis lors du scellement des tunnels. La première méthode est non-paramétrique, et la seconde repose sur l’analyse combinatoire et le principe de multiplication. Cette étude a vérifié l’utilité des deux méthodes pour estimer la probabilité d’occurrence de fractures conductrices et non-conductrices, et la distribution des transmissivités. Les distributions des transmissivités ont été estimées à partir de diagraphies effectuées sur un forage situé en Suède. Les densités de fracturation proviennent de carottages et d’imagerie BIPS (Borehole Image Processing System). Les distributions estimées des transmissivités, basées sur des diagraphies de flux effectuées sur des sections de 3 m (échelle du test L:3 m; pas dL:3 m), ont été comparées aux transmissivités obtenues sur des diagraphies de flux détaillées et se chevauchant, identifiant les fractures conductrices unitaires (échelle du test L: 0.5 m ; pas dL: 0.1 m). Il est admis que ces dernières données représentent une approximation satisfaisante des transmissivités des fractures unitaires; les deux méthodes sont en accord avec les distributions des transmissivités calculées à partir des données acquises sur des sections de 3 m.相似文献
994.
Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA 总被引:1,自引:2,他引:1
Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m3/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms. 相似文献
995.
Pantelis Soupios Nikos Papadopoulos Ilias Papadopoulos Maria Kouli Filippos Vallianatos Apostolos Sarris Thrassyvoulos Manios 《Environmental Geology》2007,53(3):661-675
An integrated suite of environmental methods was used to characterize the hydrogeological, geological and tectonic regime
of the largest waste disposal landfill of Crete Island, the Fodele municipal solid waste site (MSW), to determine the geometry
of the landfill (depth and spatial extent of electrically conductive anomalies), to define the anisotropy caused by bedrock
fabric fractures and to locate potential zones of electrically conductive contamination. A combination of geophysical methods
and chemical analysis was implemented for the characterization and management of the landfill. Five different types of geophysical
surveys were performed: (1) 2D electrical resistance tomography (ERT), (2) electromagnetic measurements using very low frequencies
(VLF), (3) electromagnetic conductivity (EM31), (4) seismic refraction measurements (SR), and (5) ambient noise measurements
(HVSR). The above geophysical methods were used with the aim of studying the subsurface properties of the landfill and to
define the exact geometrical characteristics of the site under investigation. 相似文献
996.
997.
Sitharam G. Thallak Sireesh Saride Sujit Kumar Dash 《Geotechnical and Geological Engineering》2007,25(5):509-524
This paper presents the results of laboratory model tests carried out to develop an understanding of the behaviour of geocell-reinforced
soft clay foundations under circular loading. Natural silty clay was used in this study. The geocells were prepared using
biaxial polymer grid. The performance of the reinforced bed is quantified using non-dimensional factors i.e., Bearing capacity
improvement factor (If) and Percentage reduction in footing settlement (PRS). The test results demonstrate that the geocell mattress redistributes
the footing load over a wider area thereby improving the performance of the footing. The load carrying capacity of the clay
bed is increased by a factor of up to about 4.5 times that of unreinforced bed. From the pressure-settlement responses, it
is observed that the geocell-reinforced foundation bed behaves as a much stiffer system compared to the unreinforced case
indicating that a substantial reduction in footing settlement can be achieved by providing geocell reinforcement in the soft
clay bed. The maximum reduction in footing settlement obtained with the provision of geocell mattress of optimum size placed
close to the footing is around 90%. Further improvement in performance is obtained with provision of an additional planar
geogrid layer at the base of the geocell mattress. 相似文献
998.
999.
Amber J. Roesler Christopher H. Gammons Gregory K. Druschel Harry Oduro Simon R. Poulson 《Aquatic Geochemistry》2007,13(3):211-235
Unlike the majority of the water in the flooded mine complex of Butte Montana, which includes the highly acidic Berkeley pit
lake, groundwater in the flooded West Camp underground mine workings has a circum-neutral pH and contains at least 8 μM aqueous
sulfide. This article examines the geochemistry and stable isotope composition of this unusual H2S-rich mine water, and also discusses problems related to the colorimetric analysis of sulfide in waters that contain FeS(aq) cluster compounds. The West Camp mine pool is maintained at a constant elevation by continuous pumping, with discharge water
that contains elevated Mn (90 μM), Fe (16 μM), and As (1.3 μM) but otherwise low metal concentrations. Dissolved inorganic
carbon in the mine water is in chemical and isotopic equilibrium with rhodochrosite in the mineralized veins. The mine water
is under-saturated with mackinawite and amorphous FeS, but is supersaturated with Cu- and Zn-sulfides. However, voltammetry
studies show that much of the dissolved sulfide and ferrous iron are present as FeS(aq) cluster molecules: as a result, the free
concentration of the West Camp water is poorly constrained. Concentrations of dissolved sulfide determined by colorimetry
were lower than gravimetric assays obtained by AgNO3 addition, implying that the FeS(aq) clusters are not completely extracted by the Methylene Blue reagent. In contrast, the clusters are quantitatively extracted
as Ag2S after addition of AgNO3. Isotopic analysis of co-existing aqueous sulfide and sulfate confirms that the sulfide was produced by sulfate-reducing
bacteria (SRB). The H2S-rich mine water is not confined to the immediate vicinity of the extraction well, but is also present in flooded mine shafts
up to 3 km away, and in samples bailed from mine shafts at depths up to 300 m below static water level. This illustrates that
SRB are well established throughout the southwestern portion of the extensive (>15 km3) Butte flooded mine complex. 相似文献
1000.
Many tens of severe earthquake damage patterns were revealed at the ancient city of Ayla. The seismic deformation patterns
are of various types, including systematic tilting of walls, systematic shifting and rotation of wall fragments and individual
stones, arch deformations and joints crossing two or more stones. Features of later repair, supporting walls and secondary
use of building stones suggest that the damage patterns can be explained by two historical devastating earthquakes: (I) revealed
in the constructions built during the late Rashidun period (644–656 A.D.); (II) revealed in the structures restored and/or
built during the Fatimid period (1050–1116 A.D.). The maximum observed intensity of both earthquakes at the studied site was
not less than IX (EMS98 scale). The sources of the seismic events were probably the Dead Sea Transform and Wadi Araba Faults
that cross the site obliquely. The last 1995 Nuweiba earthquake with maximum observed intensity VIII has also left its clear
traces in the excavated ancient Ayla buildings. The severity of the destruction was significantly increased because of site
effects. 相似文献