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31.
Résumé Cet article décrit la façon dont ont été calculés les débits journaliers de l'Amazone à Óbidos. La relation hauteur-débit est univoque en basses et moyennes eaux. En période de hautes eaux la dispersion des jaugeages par rapport à la courbe de tarage univoque amène à corriger les débits en fonction des niveaux à Santarém puis à Parintins. La méthode de la “dénivelée normale” n'étant pas bien adaptée pour Óbidos: elle a été remplacée par une “dénivelée à géométrie variable” fonction de la hauteur d'eau à Óbidos. En utilisant seulement la station de Santarém, l'application de cette nouvelle méthode ramène la dispersion à 3.0% sur la totalité de la courbe de tarage. 相似文献
32.
Abstract Since 1995, hydrologists of the HiBAm (Hydrology and Geochemistry of the Amazon Basin) Research Program carried out several hundred discharge measurements in the Amazon basin. Implementation of modern discharge measurement techniques using ultrasonic devices (ADCP), give evidence of a systematic error linked to the displacement of the river bottom due to high water velocity close to the bottom. This error leads to an underestimation of discharge value. It was possible to establish a correlation between the water velocity close to the river bottom and the error between real position and position computed by ADCP when the boat returns to its starting point after a two-way crossing of the river. When there is no bottom displacement, i.e. during low flow period, this return position error is weak (less than 50 m). This has allowed quantification of river bed load speed, or bottom displacement speed. A correction method was developed on the basis of this correlation. This method, systematically applied to ADCP discharge measurements obtained at Óbidos hydrometric station, allowed all measured discharges to be corrected, especially for 1997 and 1999 floods. Another method, based on the analysis of real trajectory of the boat (obtained from topographic measurement or GPS positioning) compared with the ADCP computed trajectory, is under study. 相似文献
33.
“缓变型地球化学灾害”是通过长期积累而存在于土壤或沉积物中的包括重金属和有机污染物在内的环境污染物,因环境物理化学条件(例如温度、pH值、湿度、有机质含量等)的改变减小了环境容量,某种或某些形态的污染物大量地被重新活化和突然释放出来并造成严重生态和环境损害的灾害现象。这种灾害具有明显的特征,其定量数学模型可较完整地概括出环境系统从“干净”到“污染”再到“灾害”的整个过程,可以用于灾害的风险概率评估、预测、灾害爆发轨迹等方面的研究,为土壤污染防治和灾害预警提供了定量研究工具和可供实际采用的基本手段,对当前国土资源调查中的“生态环境地球化学评价”具有重要的借鉴意义。 相似文献
34.
35.
Lithospheric Mantle Evolution during Continental Break-Up: The West Iberia Non-Volcanic Passive Margin 总被引：6，自引：0，他引：6
CHAZOT GILLES; CHARPENTIER SOPHIE; KORNPROBST JACQUES; VANNUCCI RICCARDO; LUAIS BEATRICE 《Journal of Petrology》2005,46(12):2527-2568
Ultramafic (lherzolites, metasomatized peridotites, harzburgites,websterites and clinopyroxenites) and mafic igneous (basalts,dolerites, diorites and gabbros) rocks exposed at the sea-flooralong the West Iberia continental margin represent a rare opportunityto study the transition zone between continental and oceaniclithosphere. The igneous rocks are enriched in LREE, unlikeNorth Atlantic MORB. A correlation between their 143Nd/144Ndisotopic composition and Ce/Yb ratio suggests that they originatefrom mixing between partial melts of a depleted mantle sourcesimilar to DMM and of an enriched mantle source which may residewithin the continental lithosphere. Clinopyroxenes and amphibolesin the ultramafic rocks are LREE depleted and have flat HREEpatterns with concentrations higher than those of abyssal peridotites.Clinopyroxenes in the harzburgites are less LREE depleted buthave lower HREE concentrations. The clinopyroxenes in the GaliciaBank (GB) lherzolites have radiogenic Nd (143Nd/144Nd rangingfrom 0·512937 to 0·513402) and unradiogenic Sr(87Sr/86Sr ranging from 0·702100 to 0·702311)isotopic ratios similar to, or higher than, DMM (Depleted MORBMantle) whereas the clinopyroxenes in the Iberia Abyssal Plainwebsterites have low-Nd isotopic compositions (143Nd/144Nd rangingfrom 0·512283 to 0·512553) with high-Sr isotopicratios (87Sr/86Sr ranging from 0·704170 to 0·705919).Amphiboles in Galicia Bank lherzolites and diorites have Nd–Srisotopic compositions (143Nd/144Nd from 0·512804 to 0·512938and 87Sr/86Sr from 0·703243 to 0·703887) intermediatebetween those of the clinopyroxenes from the Galicia Bank andthe Iberia Abyssal Plain, but similar to the clinopyroxenesin the 5100 Hill harzburgite (143Nd/144Nd = 0·512865and 87Sr/86Sr = 0·703591) and to the igneous rocks (143Nd/144Ndranging from 0·512729 to 0·513121 and 87Sr/86Srranging from 0·702255 to 0·705109). The majorand trace element compositions of cpx in the Galicia Bank spinellherzolites provide evidence for large-scale refertilizationof the lithospheric upper mantle by MORB-like tholeiitic melts.The associated harzburgites did not undergo partial meltingduring the rifting stage, but, in earlier times, probably during,or even before, the Hercynian orogeny. Iberia Abyssal Plainwebsterites are interpreted as high-pressure cumulates formedin the mantle. Their high Sm/Nd ratios (from 0·43 to0·67) coupled with very low-Nd isotopic compositionsare best explained by a two-stage history: formation of thecumulates from the percolation of enriched melts long beforethe rifting, followed by low-degree partial melting of the pyroxenites,accounting for their LREE depletion. This last event probablyoccurs during the rifting episode, 122 Myr ago. The isotopicheterogeneities observed in the ultramafic rocks of the Iberiamargin were already present at the time of the rifting event.They reflect a long and complex history of depletion and enrichmentevents in an old part of the mantle, and provide strong argumentsfor a sub-continental origin of this part of the upper mantle. KEY WORDS: Iberia margin; mantle peridotites; igneous rocks; petrology; geochemistry 相似文献
36.
Major palaeohydrographic changes in Alpine foreland during the Pliocene - Pleistocene 总被引：1，自引：0，他引：1
CHRISTOPHE PETIT MICHEL CAMPY JEAN CHALINE JACQUES BONVALOT 《Boreas: An International Journal of Quaternary Research》1996,25(2):131-143
The changing palaeogeographical pattern of Alpine deposits across the European forelands can be traced by identifying mineral assemblages and establishing the chronology of Pliocene-Pleistocene deposits in Alpine foreland. In the late Miocene, the upper courses of the Rhine and the Aar flowed east from the Swiss molasse plain towards the Danube. In the early Pliocene (Brunssumian, 5-3.2 Ma), these same rivers headed north wards towards the Rhine Graben of Alsace. In the early Reuverian, these streams were captured south of the Rhine Graben by the Doubs. They ceased their northward flow and headed west to feed the Bresse Graben. This phase is dated to the Lower and Middle Reuverian (3.2-2.6 Ma). From the Upper Reuverian (2.6 Ma) to the present day, the Rhine has adapted approximately its present course towards the North Sea, south to north along the Rhine Graben and across the Rhine Schist Massif to feed the Dutch Grabens. This changing pattern of capture and alteration of the hydrographic system of the upper reaches of the Rhine and the Aar can be explained by local tectonic movements. 相似文献
37.
Oxygen Thermobarometry of Orogenic Lherzolite Massifs 总被引：5，自引：1，他引：4
The oxidation state has been determined for spinel peridotitesfrom 13 orogenic lherzolite massifs including Beni Bousera,Ronda, and 11 smaller massifs in the French Pyrenees. The oxygenfugacity (fo2) was calculated for 67 samples from microprobeanalyses using a set of secondary spinel standards to correctthe ferric iron content in the spinels. The utility of thismethod is confirmed by the good agreement between the calculatedvalues and those determined by Mossbauer spectroscopy on 28samples. The spinel peridotites of Ronda and Beni Bousera are relativelyreduced, averaging -11 and -1.5 log units relative to fayalite-magnetite-quartz(FMQ) respectively, which is in agreement with values from abyssalperidotites and mid-ocean ridge basalt (MORB) glasses. The Pyreneanmassifs are relatively oxidized and are intermediate between the abyssal peridotites and continentalxenolith suites. No systematic gradients are observable. Instead,variations of up to 2 log units in fo2 occur at a localizedscale. This type of variation is also observed for trace elementsand radiogenic isotopes. The harzburgites at Beni Bousera recordthe most reduced conditions. Local oxidation coincides withthe appearance of amphibolc, indicating that metasomatizingfluids or melts are generally oxidized compared with the hostperidotites. Partial re-equilibration in the plagioclase peridotitefades has occurred at Ronda, causing the spinels to become Crrich. Re-equilibration is extremely heterogeneous. Mild oxidationappears to attend the crystallization of fine-grained plagioclase. The similarity in fo2 values at Beni Bousera and Ronda indicatesa fairly uniform oxidation state at a scale of {small tilde}200 km. This scale of homogeneity is also observed in the Pyrenees,where no significant variation in fo2 is apparent along 200km of strike in the Northern Pyrenean Zone. 相似文献
38.
The Four Plutonic Belts of the Transhimalaya-Himalaya: a Chemical, Mineralogical, Isotopic, and Chronological Synthesis along a Tibet-Nepal Section 总被引：31，自引：0，他引：31
DEBON FRANCOIS; FORT PATRICK LE; SHEPPARD SIMON M. F.; SONET JACQUES 《Journal of Petrology》1986,27(1):219-250
The geochemistry (major, trace element, O- and Sr-isotope ratios)and petrology of the Transhimalaya, North Himalaya, High Himalayaand ‘Lesser Himalaya’ plutonic belts are comparedbased on the analyses of up to 492 samples. The composite Transhimalaya batholith is subalkaline or monzoniticin character rather than calc-alkaline. Its genesis was probablyclosely related to subduction processes associated with strike-slipmovement. It was emplaced on both sides of the boundary betweenan earlier metavolcanic arc and a continental margin. Two principalperiods of magmatic activity occurred: Upper Cretaceous and,particularly in this region, Eocene at the time of the India-Eurasiacollision when sediments may have become involved in the subductionprocess. Magmatic differentiation, characterized by two superimposedstages of evolution, and hybridization processes, involvingboth basic and acidic magmas, can account for the genesis ofthe different plutonic units. Although a continental contributionis implied, the isotopic data (6.8 < 18O < 9?2; 0?704< 87Sr/86Sr, < 0?707) preclude a significant contributionfrom either old crust or surface derived sediments. The North, High and ‘Lesser’ Himalaya plutonic beltsare fundamentally different and correspond to aluminous associationsof two groups of ages (Lower Palaeozoic for the ‘LesserHimalaya’ and part of the North Himalaya; Upper Cenozoicfor the High Himalaya and part of the North Himalaya). Theyare all high-18O (9 < 18O < 14) granites and adamelliteswith high initial 87Sr/86Sr, ratios (0?709 to < 0?740). TheLower Palaeozoic group was generated within the Gondwana continentalcrust, independent of any true orogenesis, with a probable butlimited contribution from the mantle. High Himalaya and NorthHimalaya Cenozoic plutons are directly linked to the activityof the Main Central Thrust. They were derived by similar anatecticprocesses of the same continental source rocks. The small butdistinct chemical and mineralogical differences among the plutonsare related to the increase in the intensity of anatexis ongoing towards the north and the east. 相似文献
39.
An extension of TOPMODEL was developed for rainfall–runoff simulation in agricultural watersheds equipped with tile drains. Tile drain functions are incorporated into the framework of TOPMODEL. Nine possible flow generation scenarios are suggested for tile-drained watersheds and applied in the modelling procedure. In the model development, two methods of simulation of the flow in the unsaturated zone were compared: the traditional, physically based storage approach and a new approach using a transfer function. A regionalized sensitivity analysis was used to determine the sensitivity of parameters and to compare the behaviour of the transfer function with that of the simple storage-related formulation. The number of accepted combinations of parameter values, on average, was higher for the transfer function approach than when using a Monte Carlo method of parameter estimation. Since the rainfall–runoff response pattern tends to vary seasonally, seven events distributed throughout a year were used in the sensitivity analysis to investigate the seasonal variation of the hydrological characteristics. © 1997 John Wiley & Sons, Ltd. 相似文献
40.
JACQUES CALLEDE EURIDES DE OLIVEIRA VALDEMAR S. GUIMARÃES MAURO S. RODRIGUES 《水文科学杂志》2013,58(6):903-913
Abstract The difficulties of exploiting the huge Brazilian hydrometeorological network led hydrologists of the Departamento Nacional de Águas e Energie Elétrica (DNAEE—Brazilian Department of Water and Electric Power) to use real time satellite telecommunications to improve network management. Data-gathering satellites, which are perfectly adapted to this network, were first used in 1975 and have interested DNAEE since 1980. Collaboration with ORSTOM permitted an initial evaluation of the technique in 1982. In 1984 DNAEE, together with ORSTOM, was able to set up a 20-station network in the Amazon. The results have been so encouraging that a scheme for 200 stations equipped with telecommunications facilities which use the Brazilian Satélite de Colecta de Dados number 1 (SCD1) satellite is in the final stages. This network will cover the entire country. 相似文献