Climate simulation of the twenty-first century with interactive land-use changes   总被引：5，自引：0，他引：5  

Aurore Voldoire  Bas Eickhout  Michiel Schaeffer  Jean-François Royer  Fabrice Chauvin 《Climate Dynamics》2007,29(2-3):177-193

To include land-use dynamics in a general circulation model (GCM), the physical system has to be linked to a system that represents socio-economy. This issue is addressed by coupling an integrated assessment model, IMAGE2.2, to an ocean–atmosphere GCM, CNRM-CM3. In the new system, IMAGE2.2 provides CNRM-CM3 with all the external forcings that are scenario dependent: greenhouse gas (GHGs) concentrations, sulfate aerosols charge and land cover. Conversely, the GCM gives IMAGE changes in mean temperature and precipitation. With this new system, we have run an adapted scenario of the IPCC SRES scenario family. We have chosen a single scenario with maximum land-use changes (SRES A2), to illustrate some important feedback issues. Even in this two-way coupled model set-up, land use in this scenario is mainly driven by demographic and agricultural practices, which overpowers a potential influence of climate feedbacks on land-use patterns. This suggests that for scenarios in which socio-economically driven land-use change is very large, land-use changes can be incorporated in GCM simulations as a one-way driving force, without taking into account climate feedbacks. The dynamics of natural vegetation is more closely linked to climate but the time-scale of changes is of the order of a century. Thus, the coupling between natural vegetation and climate could generate important feedbacks but these effects are relevant mainly for multi-centennial simulations.  相似文献   

The construction of the Total Alkali-Silica chemical classification of volcanic rocks   总被引：4，自引：0，他引：4  

Dr. M. J. Le Bas  Dr. R. W. Le Maitre  Dr. A. R. Woolley 《Mineralogy and Petrology》1992,46(1):1-22

Summary This paper describes the reasoning that lies behind the construction of the field boundaries in the Total Alkali-Silica diagram (TAS) for the chemical classification of volcanic rocks. It shows that by utilizing nomenclature in common use by petrologists in combination with a large computer database of geochemical analytical information derived from the published literature, it was possible to construct a Total Alkali-Silica diagram for volcanic rocks of only 15 fields, which has straight-line boundaries and necessitates the definition of only 11 points to construct the diagram. One of the principal constraints on the positioning of the boundaries between the various named fields was to minimize the degree of overlap between adjacent fields.

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Die chemische Einteilung vulkanischer Gesteine auf der Basis von Gesamtalkali und SiO₂

Zusammenfassung Diese Arbeit beschreibt die Überlegungen die zur Konstruktion des Total Alkali-SilicaDiagramms (TAS) zur chemischen Klassifikation der Vulkanite führten. Es wird gezeigt, daß durch die Kombination der geläufigen petrographischen Nomenklatur mit der geochemischen Information einer grossen computerisierten Datensammlung publizierter Gesteinsanalysen ein Alkali-Kieselsäurediagramm mit nur 15 Namensfeldern für vulkanische Gesteine konstruiert werden konnte. Die Felder haben gerade Begrenzungslinien und benötigen nur 11 definierte Punkte zur Einteilung. Eine der

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With 28 Figures

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formerly: University of Melbourne, Parkville, Victoria, Australia

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As approved by the IUGS Subcommission on the Systematics of Igneous Rocks.  相似文献   

Age and nature of carbonatite emplacement in North Pakistan     

M. J. Le Bas  I. Mian  D. C. Rex 《International Journal of Earth Sciences》1987,76(2):317-323

The N Pakistan carbonatites of Loe Shilman, Silai Patti and those within the Ambela complex were formerly considered as comprising one alkaline igneous province associated with a Peshawar rift valley. New data show that these alkaline rocks occur in two distinct periods, Carboniferous and Tertiary, and are not related to any Tertiary rift faulting. K-Ar dates determined on biotites from the Loe Shilman and Silai Patti carbonatites reveal that the carbonatites were emplaced at 31±2 Ma, and along thrust planes, not rift faults. Subsequent movement of the thrusts reset the argon contents in some biotites to indicate a deformation age of 24±2 Ma for the carbonatites at both localities.The Koga carbonatite in the Ambela complex occurs as a plug associated with nepheline syenites and ijolites, and Rb-Sr isotope determinations on the silicate rocks give dates of approximately 297–315 Ma.The study implies that there were thrust movements associated with the Indian — Asian plate collision more than 31 Ma ago, which is much earlier than the 20 Ma date previously advocated for the initiation of thrusting.

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Zusammenfassung Die nordpakistanischen Karbonatite Loe Shilman, Silai Patti und jene aus dem Ambela-Komplex wurden bisher zusammen mit einer Alkaligesteins-Provinz betrachtet, deren Bildung mit dem Peshawar Riff zusammenhÄngt. Neue Daten zeigen auf, da\ die Alkaligesteine von Shilman und Silai Patti dem Karbon zuzuordnen sind und jene aus dem Ambela-Komplex dem TertiÄr. Beide Gesteinserien gehören keiner tertiÄren Riff-Faltung an. K-Ar Altersdaten, bestimmt an Biotiten aus den Karbonatiten von Loe Shilman und Silai Patti, ergeben ein Alter von 31±2 Ma für die Platznahme der Karbonatite entlang einer überschiebungszone. Nachfolgende Bewegungen in der überschiebungsbahn verÄnderten den Argongehalt in einigen Biotiten, so da\ sich ein Deformationsalter von 24±2 Ma ergibt. Die Koga Karbonatite aus dem Ambela Komplex kommen dagegen als Propfen vor. Sie sind assoziiert mit Nephelinsyeniten und Ijoliten. Rb-Sr Bestimmungen an diesen Silikatgesteinen ergeben ein Alter zwischen 297–315 Ma.Diese Untersuchung zeigt, da\ die Indisch-Asiatische Plattenkollision vor 31±2 Ma Jahren stattfand, da sie mit der überschiebungsbewegung assoziiert werden kann. Bisher wurde für diese Kollision ein Alter von 20 Ma angenommen.

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Résumé Les carbonatites du Pakistan septentrional, situées à Loe Shilman, Silai Patti et dans le complexe d'Ambela, ont été regardées jusqu'ici comme appartenant à une seule province magmatique alcaline associée au fossé de Peshawar. Des données nouvelles démontrent que ces roches alcalines appartiennent à deux périodes différentes, le Carbonifère et le Tertiaire, et qu'elles ne sont associées à aucun fossé tertiaire. Des datations K-Ar, effectuées sur les biotites des carbonatites de Loe Shilman et de Silai Patti, montrent que ces roches se sont mises en place il y a 31±2 Ma et ce, le long de failles de charriage et non de failles radiales. Des mouvements plus récents le long de ces charriages ont modifié la teneur en argon de certaines biotites, qui fournissent pour cette déformation un âge des 24±2 Ma dans les carbonatites des deux localités.La carbonatite de Koga dans le complexe d'Ambela est un culot associé à des syénites à néphéline et à des ijolites sur lesquelles les déterminations Rb-Sr donnent des aes approximatifs de 297 à 315 Ma.Cette étude montre que des mouvements de charriage, associés à la collision des plaques indienne et asiatique, ont eu lieu avant 31±2 Ma, c'est-à-dire beaucoup plus tÔt que les 20 Ma admis jusqu'ici.

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Loe Shilman, Silai Patti Ambela , , Peshawar. , Shilman Silai Patti , Ambela — . . Loe Shilman Silai Patti, K/, 31±2 . , 24 ± 2 . Koga Ambela «». - ; , Rb/Sr, 297–315 . , 31 ± 2 , . . , . , 20 .

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Atmospheric turbidity at athens observatory     

Bas Katsoulis 《Pure and Applied Geophysics》1977,115(3):583-591

Summary In this study, values of the Ångström turbidity coefficient () determined from Solar radiation observations at the National Observatory of Athens over the period 1955–1972 are analysed. Mean daily turbidity lies between 0.020–0.100. Turbidity is higher in summer than in winter. The main factor determining the turbidity is the air mass type. The scavenging by rainfall probably has a considerable effect in determining this distribution. There is some evidence of a trend of increasing turbidity during the period.  相似文献   

Carbonatite dykes at bayan Obo,inner Mongolia,China   总被引：17，自引：0，他引：17  

M. J. Le Bas  J. Kellere  Tao Kejie  F. Wall  C. T. William  Zhang Peishan 《Mineralogy and Petrology》1992,46(3):195-228

Summary Calcite-rich dykes occur in the thrust fold belt near the Bayan Obo rare earth element (REE) deposit. They cut a thrust inlier of granitic migmatite within folded Bayan Obo Group sediments of Proterozoic age. Cathodoluminescence, X-ray fluorescence and microprobe studies show that the rock is a calcite carbonatite with Sr-Mn-bearing calcite, magnesio-riebeckite, apatite, pyrochlore, K-feldspar and biotite. One dyke was chosen for detailed analysis. Its margin is strongly REE-mineralized with much monazite developed adjacent to zoned apatite. Secondary alteration is marked by the introduction of Fe and Mn. The adjacent migmatite is fenitized to a magnesio-riebeckite-albite rock. The sedimentary dolomite of the Bayan Obo Group is composed mainly of Mn-Sr-RE-hearing ferroan dolomite and contains bands of opaque grains, apatite, monazite, fluorite and taeniolite. Many trace element and isotope similarities between the carbonatite dyke and the sedimentary dolomite are revealed, and the evidence supports the possibility that the dolomite is a dolomitized carbonatite tuff. The Bayan Obo REE mineralization also shows geochemical similarities with the mineralization seen in the carbonatites, and a possible genetic connection is presented.

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Die Karbonatit-Gänge von Bayan Obo, Innere Mongolei, China

Zusammenfassung Kalzit-reiche Gänge kommen im Faltengürtel in der Nähe der Seltenen-Erd-Lagerstätte Bayan Obo vor. Es handelt sich um hellbräunliche, 1–2 m mächtige Gänge, die migmatitische Orthogneise von granitischer Zusammensetzung innerhalb der gefalteten Sedimente der Bayan Obo Gruppe durchsetzen. Chemische Daten, die auf Kathoden-Lumineszenz, Röntgen-Fluoreszenz und Mikrosondenuntersuchungen beruhen, zeigen, daß es sich hier um einen Kalzit-KazhooudimdSr-Mo-führeodem Kalzit, Magnesio-Riebeckit Apatit, Pyrochlor Alkalifelds und Biotit handelt. Einer dieser Gänge wurde für eine eingehende Untersuchung ausgewählt. Seine randlichen Partien sind stark mit SEE mineralisiert, und viel Monazit kommt in der Nähe von zonar gebautem Apatit vor. Sekundäre Umwandlung wird durch die Zufuhr von Fe und Mn markiert. Der benachbarte Migmatit ist fenitisiert und dadurch in ein Magnesio-Riebeckit-Gestein umgewandelt. Der sedimentäre Dolomit der Bayan-Obo-Gruppe besteht hauptsächlich aus Mn-Sr-SE-führenden eisenhaltigen Dolomit und enthält Lagen von opaken Mineralen, Apatit, Monazit, Fluorit und Taeniolit. Karbonatitgänge und der sedimentäre Dolomit zeigen Ähnlichkeiten, was den Spurenelementgehalt und die isotopische Zusammensetzung betrifft. Diese Daten weisen auf die Möglichkeit hin, daß der Dolomit ein dolomitisiert Karbonatit-Tuff ist. Die SEE-Vererzung von Bayan Obo zeigt auch geochemische Ähnlichkeiten mit der Vererzung der Karbonatite, und ein möglicher genetischer Zusammenhang wird diskutiert.

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With 16 Figures  相似文献   

Unlocking paleo-environmental information from Early Cretaceous shelf sediments in the Helvetic Alps: stratigraphy is the key!     

Karl B. Föllmi  Stéphane Bodin  Alexis Godet  Pascal Linder  Bas van de Schootbrugge 《Swiss Journal of Geoscience》2007,100(3):349-369

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Grazing on microcystin-producing and microcystin-free phytoplankters by different filter-feeders: implications for lake restoration     

Luis M. Dionisio Pires  Babette M. Bontes  Larysa Samchyshyna  Jacco Jong  Ellen Van Donk  Bas W. Ibelings 《Aquatic Sciences - Research Across Boundaries》2007,69(4):534-543

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Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China   总被引：1，自引：2，他引：1  

Le Bas MJ 《岩石学报》2006,22(2):517-518

Recent ce-valuation of the dating of the carbonatite dykes associated with the REE-Re-Nb giant deposit at Bayan Obo has  相似文献   

A combined central- and fissure-type phonolitic volcano in western Kenya     

M. J. Le Bas 《Bulletin of Volcanology》1970,34(2):518-536

The Nyamaji volcano is a small eruptive complex of late Miocene age associated with the nearby Usaki ijolite and Sokolo carbonatite intrusion of Homa Bay in the Kavirondo Rift valley of Kenya. It is probably a satellite volcano to the major volcanic structure of Kisingiri - Rangwa which lies 25 km to the west. The Nyamaji volcanic complex is composed of agglomerates, breccias and tuffs erupted from a central vent, whilst at much the same time lavas were extruded from fissures which are now occupied by dykes. These two contemporaneous events gave rise to an interdigitated sequence of pyroclastic deposits and effusive lavas. The pyroclastic rocks of Vulcanian origin cover an area at least 30 km² in extent, are poorly bedded, and usually are about 25 m (80ft.) thick though they often thin to zero over topographic highs in the pre-existing landscape. At Nyamaji itself, the Strombolian style pyroclastic pile exceeds 330 m (1100 ft.) in thickness over an area of 1 km², and this marks the position of the original central vent. The fragmental material in the pyroclastic rocks includes ijolite, phonolite, nephelinite, trachyte, carbonatite, granite, and feldspathic and aegirine-bearing fenites; the matrix is sometimes calcareous, sometimes feldspathic. Nephelinitic lavas occur amongst the lowest lavas, but the lavas above are nearly all phonolitic. The oldest dykes are nephelinitic and are rare; the youngest dykes are phonolitic and are abundantly exposed. Both lavas and dykes contain xenoliths similar to those in the pyroclastic rocks. A series of volcanic plugs pierce the lavas. These plugs, mostly non-conduit type, average 200–500 m diameter, are mainly composed of glassy to very fine-grained phonolites, and show good flow structures. The plugs, especially those near the Ruri hills, tend to lie along N - S and E - W lines. The majority of the dykes also lie along these directions. The dominant structural directions within the nearby Usaki ijolite complex and the Wasaki carbonatite are also N - S and E - W, respectively. These directions are quite different from the axis of the Kavirondo rift valley which here is NE - SW, and from the strike of the Precambrian basement. The Nyamaji volcanic structure differs from nearly all the other East African volcanoes by its dominant phonolitic petrochemistry.  相似文献   

Estimating Travel Time in Bank Filtration Systems from a Numerical Model Based on DTS Measurements          下载免费PDF全文

Bas F. des Tombe  Mark Bakker  Frans Schaars  Kees‐Jan van der Made 《Ground water》2018,56(2):288-299

An approach is presented to determine the seasonal variations in travel time in a bank filtration system using a passive heat tracer test. The temperature in the aquifer varies seasonally because of temperature variations of the infiltrating surface water and at the soil surface. Temperature was measured with distributed temperature sensing along fiber optic cables that were inserted vertically into the aquifer with direct push equipment. The approach was applied to a bank filtration system consisting of a sequence of alternating, elongated recharge basins and rows of recovery wells. A SEAWAT model was developed to simulate coupled flow and heat transport. The model of a two‐dimensional vertical cross section is able to simulate the temperature of the water at the well and the measured vertical temperature profiles reasonably well. MODPATH was used to compute flowpaths and the travel time distribution. At the study site, temporal variation of the pumping discharge was the dominant factor influencing the travel time distribution. For an equivalent system with a constant pumping rate, variations in the travel time distribution are caused by variations in the temperature‐dependent viscosity. As a result, travel times increase in the winter, when a larger fraction of the water travels through the warmer, lower part of the aquifer, and decrease in the summer, when the upper part of the aquifer is warmer.  相似文献