Regional geochemical anomalies related to plate tectonic models for the Northwestern Canadian shield     

R.J. Allan   《Journal of Geochemical Exploration》1978,10(3):203-218

Regional geochemical maps of a 97,000-km² area of the northwestern Canadian Shield were based on analysis of lake sediment samples collected at 5-km grid points. The maps revealed three global-scale geochemical features: (1) a major anomaly of refractory and chalcophile elements associated with a Proterozoic volcanic-plutonic belt of previously proposed Andean are affinities; (2) a dramatic increase in Ba concentrations on crossing a proposed Precambrian suture zone; and (3) another major anomaly of refractory and chalcophile elements associated with the Archean greenstone belt closest to the supposed suture zone.The regional geochemical anomaly in the Proterozoic volcanic-plutonic belt is considered to have originated during an island-arc-type evolution of the belt by intrusion of magma formed by stages of partial melting of subducted oceanic basalts contaminated by subducted ocean floor sediments. The increase in Ba concentration found on crossing the proposed Precambrian suture is attributed to exposure of deep crust by the post-collision erosion of the uplifted edge of one of the proto-continents. The multielement, geochemical signature of the Archean greenstone belt is tentatively attributed to Archean subduction of oceanic crust and ocean sediments.The regional, multielement anomalies delineated are associated with known or suspected base metal and uranium mineralization. If the geotectonic relationships proposed above are valid, routine geochemical mapping of the Precambrian Canadian Shield will not only be of use in prospecting and mineral potential evaluation but may indirectly assist in metallogenic interpretations. Further, there is a possibility that routine geochemical mapping of the Canadian Shield may define other subduction and suture zones.  相似文献   

The use of oxygen isotope geothermometry on the granulites and related intrusives,Musgrave Ranges,central Australia     

Allan F. Wilson  David C. Green  Lawrence E. Davidson 《Contributions to Mineralogy and Petrology》1970,27(2):166-178

Oxygen isotope equilibration involving quartz, feldspar and magnetite has taken place within the granulites of the metamorphic aureole of the intrusive charnockitic Ernabella Adamellite, and a temperature of approximately 550° C is indicated by ¹⁸O/¹⁶O values from quartz-magnetite and plagioclase-magnetite pairs. Pyroxene-magnetite fractionations are larger than equilibrium fractionations at this temperature, and demonstrate that caution is necessary in assigning estimates of temperature to highly metamorphosed rocks.The intrusive adamellite and related fine-grained and pegmatitic phases appear to have attained oxygen isotope equilibrium with the granulites at a similar temperature (approx. 550° C) which is here regarded as a late metamorphic equilibration temperature rather than the maximum temperature (estimated to be about 780° C) reached within the aureole.Oxygen was extracted from the minerals by means of bromine pentafluoride, and the isotopes were successfully measured without the normal prior conversion of oxygen to carbon dioxide.  相似文献   

Natural resources as national fantasies     

J.A. Allan 《Geoforum》1983,14(3):243-247

The development of agriculture is recognised to be an essential preliminary and on-going element in the economic development strategies of most developing countries. The contribution of agricultural production to gross domestic product, food self-sufficiency and export income are amongst the major development goals exercising the governments of such countries. In addition, in many countries the agricultural sector is regarded as one with a potential for generating a surplus to sustain other economic activities and to have an important stabilising role in reducing the movement of population from rural areas. This article discusses renewable natural resources, soil and water, as the basis for agricultural development and especially of irrigated farming. A number of case studies will be referred to which illustrate the idea that many national governments attribute quite unreal qualities to soil and water resources. Once development schemes were launched appropriate rhetoric was mobilised to invest the reclamation of ‘virgin lands’ and ‘new lands’, with the character of ‘green revolutions’. These ventures have been sustained not because of their success but because the ‘fantasies’ have been circulated amongst ill-formed urban populations, remote from the arduous realities of land reclamation. Case studies in the Soviet Union and the Middle East are discussed.  相似文献   

Comparison of macrobenthos collected with cores and suction sampler in vegetated and unvegetated marine habitas     

Allan W. Stoner  Holly S. Greening  Joseph D. Ryan  Robert J. Livingston 《Estuaries and Coasts》1983,6(1):76-82

A comparison of shallow water benthic macrofauna collected with hand-held cores and a suction sampler shoed that the core method provided the best estimate of macrofaunal density and composition. In a bare sand habitat, suction methods collected 72.8% fewer individuals per unit surface area of sediment. The difference was 32.6% in a seagrass (Halodule wrightii) habitat. At each site the number of species collected with the two devices was similar; however, population densities of numerically important species were underestimated with the suction device resulting in effects on community statistics. In addition to high sampling efficiency and statistical advantages associated with the use of the multiple cores, ease of operation and low construction cost make simple core tubes the preferred gear for sampling small macrobenthos in soft sediments, with or without vegetation.  相似文献   

Animating ground water levels with Excel     

Shikaze SG  Crowe AS 《Ground water》2003,41(4):548-549

This note describes the use of Microsoft Excel macros (programs written in Excel's internal language, Visual Basic for Applications) to create simple onscreen animations of transient ground water data within Excel. Compared to many specialized visualization software packages, the use of Excel macros is much cheaper, much simpler, and can rapidly be learned. The Excel macro can also be used to create individual GIF files for each animation frame. This series of frames can then be used to create an AVI video file using any of a number of graphics packages, such as Corel PhotoPaint. The technique is demonstrated through a macro that animates changes in the elevation of a water table along a transect over several years.  相似文献   

Preface: Bruce Chappell     

Allan J. R. White 《Resource Geology》2006,56(3):197-202

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Observed thermal pollution and post-development simulations of low-temperature geothermal systems in Winnipeg, Canada     

Grant Ferguson  Allan D. Woodbury 《Hydrogeology Journal》2006,14(7):1206-1215

Two issues arise in the long-term use of groundwater for thermal purposes: (1) the sustainability of an individual system; and (2) the effect of neighbouring systems on each other. Both of these effects are observed in an area of the Carbonate Rock Aquifer beneath Winnipeg in Manitoba, Canada, where groundwater has been exploited in thermal applications since 1965. In this area, there are four systems that utilize groundwater for cooling purposes that are closely spaced. The current temperatures observed in this area of the Carbonate Rock Aquifer and the results of the numerical modeling conducted in this study confirm that in each system, temperatures at the production well have risen as a result of breakthrough of injected water. The results of numerical modeling also indicate that interference effects are present in three of the four systems examined in this study. The influence of these systems on each other implies that these systems have a spacing that is smaller than the optimum spacing for such systems, and indicates that there is a limit to the density of development that can occur in a given aquifer.Contaminación termal y simulaciones post-desarrollo de sistemas geotermales de baja temperatura en Winnipeg, Canadá  相似文献   

Water and Radioactive Tracer Flow in a Heterogeneous Field-Scale System   总被引：1，自引：0，他引：1  

Frank M. Dunnivant  Meredith E. Newman  Carolyn W. Bishop  Dave Burgess  John R. Giles  Brian D. Higgs  Joel M. Hubbell  Erick Neher  Greg T. Norrell  M. Cathy Pfiefer  Indrek Porro  Robert C. Starr  Allan H. Wylie 《Ground water》1998,36(6):949-958

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The origin of the cosmic soft X-ray background: optical identification of an extremely deep ROSAT survey     

MHardy  Jones  Merrifield  Mason  Newsam  Abraham  Dalton  Carrera  Smith  Rowan-Robinson  Wegner  Ponman  Lehto  Branduardi-Raymont  Luppino  Efstathiou  Allan  & Quenby 《Monthly notices of the Royal Astronomical Society》1998,295(3):641-671

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Shock compression and isentropic release of granite     

Toshimori Sekine  Thomas S. Duffy  Allan M. Rubin  William W. Anderson  Thomas J. Ahrens 《Geophysical Journal International》1995,120(2):247-261

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