Constraining diamond metasomatic growth using C- and N-stable isotopes: examples from Namibia     

Pierre Cartigny  Thomas Stachel  Jeff.W. Harris  Marc Javoy 《Lithos》2004,77(1-4):359-373

The present paper provides C- and N-stable isotope characteristics, N-contents and N-aggregation states for alluvial diamonds of known paragenesis from placers along the Namibian coast. The sample set includes diamonds with typical peridotitic and eclogitic inclusions and the recently reported “undetermined” suite of Leost et al. [Contrib. Mineral. Petrol. 145 (2003) 15] which resulted from infiltration of high temperature, carbonate-rich melts. δ¹³C-values range from −20.3‰ to −0.5‰ (n=48) for peridotitic diamonds and from −38.5‰ to −1.6‰ (n=45) for eclogitic diamonds. Diamonds belonging to the “undetermined” suite span a narrower range in δ¹³C from −8.5‰ to −2.7‰ (n=13). When compared with previous studies, diamonds from Namibia are characterised by unusually low proportions of N-free (i.e. Type II) peridotitic and eclogitic diamonds (3% and 2%, respectively) and an unprecedented high proportion of N-rich diamonds (15% and 73%, respectively, have N-contents >600 ppm). δ¹⁵N-values for diamonds of the peridotitic, eclogitic and “undetermined” suites range from −10‰ to +13‰ without correlations with either N-content or δ¹³C. The similarity in N-isotopic composition and the N-rich character of diamonds belonging to the eclogitic, peridotitic and “undetermined” suites is striking and suggests a close genetic relationship. We propose that a large part of the diamonds mined in Namibia formed during metasomatic events of similar style that introduced carbon and nitrogen into a range of different host lithologies.  相似文献   

Kyril. Ya. Kondratyev and A. P. Cracknell: 1998, Observing Global Climate Change, Taylor and Francis Ltd., London, 562 pp.     

Pierre Morel 《Climatic change》2001,48(4):647-648

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Analyse quantitative des faciès carbonatés et cycles T–R de haute fréquence dans le Barrémien du Prébalkan central (Bulgarie)     

Viara Minkovska  Bernard Peybernès  Pierre Cugny  Todor Nikolov 《Comptes Rendus Geoscience》2004,336(10):931-938

Within the Emerici zone–Barremense zone biostratigraphic interval, the Barremian deposits of Central Fore-Balkan (Lovech–Veliko Tarnovo shelf) consist of a succession of several formations where alternate terrigenous argillaceous/sandy-dominated facies (Kormjansko Fm., Balgarene Fm.) and carbonate-dominated (‘Urgonian’) facies (Krushevo Fm., Emen Fm.). The qualitative and, particularly, quantitative facies analysis of the carbonate successions observed along 13 detailed cross-sections and in one drill hole show the stacking of about 40 fifth-order T–R cycles induced by numerous eustatic jerks contributing to the progressive settlement of this shelf. These high-frequency cycles of about 100 000 years must be regarded as valuable correlation tools for the subsurface hydrocarbon research. To cite this article: V. Minkovska et al., C. R. Geoscience 336 (2004).  相似文献   

Solutions for Exterior Orientation in Photogrammetry: A Review     

Pierre Grussenmeyer  & Omar Al Khalil 《The Photogrammetric Record》2002,17(100):615-634

The determination of the attitude, the position and the intrinsic geometric characteristics of the camera is recognised as the fundamental photogrammetric problem. It can be summarised as the determination of camera interior and exterior orientation parameters, as well as the determination of 3D coordinates of object points. The term "exterior orientation"of an image refers to its position and orientation related to an exterior (object space) coordinate system. Several methods can be applied to determine the parameters of the orientation of one, two or more photos. The orientation can be processed in steps (as relative and absolute orientation) but simultaneous methods (such as bundle adjustments) are now available in many software packages. Several methods have also been developed for the orientation of single images. They are based in general on geometric and topological characteristics of imaged objects.
This paper presents a survey of classical and modern methods for the determination of the exterior parameters in photogrammetry, some of which are available as software packages (with practical examples) on the Internet. The methods presented are classified in three principal groups. In the first, a selection of approximate methods for applications that do not require great accuracy is presented. Such methods are also used to calculate values required for iterative processes. In the second group, standard point–based methods derived from collinearity, coplanarity or coangularity conditions are briefly reviewed, followed by line–based approaches. The third group represents orientation methods based on constraints and on concepts of projective geometry, which are becoming of increasing interest for photogrammetrists. In the last section, the paper gives a summary of existing strategies for automatic exterior orientation in aerial photogrammetry.  相似文献   

Small valley bottom deposits in the sandy districts of the Sarthe basin (France): climatic and/or human origin?     

Jean Pierre Larue   《Geomorphology》2002,45(3-4)

The study of the small valley bottom deposits in a sandy district where several recent erosional events have occurred makes it possible to distinguish deposits, which are caused by climatic oscillations from those induced by both climate and human activities. The coarse alluvium with flints, which reached the main valleys prior to the Subboreal, was transported by greater flows than those which resulted from later human-induced flood discharges, where flints were not evacuated from the small valleys. Radiocarbon dates of peat set those deposits in the Iron Age, in the transition from Antiquity to the Medieval period, at the end of the “optimum climatique de l'an Mil” and during the Little Ice Age. At the present time, human-induced flood discharges reach again the main valleys.  相似文献   

Compartmentalisation of fluid migration pathways in the sub-Andean Zone, Bolivia     

Isabelle Moretti  Pierre Labaume  Simon M. F. Sheppard  Jacques Boulgue 《Tectonophysics》2002,348(1-3)

Numerous observations indicate that faults play a major role on the migration pathways of fluids in the Bolivian sub-Andean Zone. Most oil seeps in the foothills are located on faults, but oil fields in the foredeep are closed by faults. In the foothills, analysis of cements in fractures inside and around fault zones indicates that the faults act as barriers for transversal migration but can be preferential lateral migration pathways for both hydrocarbons and water. A detailed study of these apparent contradictions suggests that the hydraulic behaviour of faults changes with depth in relation with sandstone diagenesis, but it is strain-independent. From microstructural analyses of fault zones, we suggest that the main controlling factor is temperature, which facilitates or inhibits quartz precipitation. This result implies that the same fault is a barrier for lateral and transversal migration at depths >3 km, due to sealing of fractures by authigenic quartz at T>80 °C, and is a lateral drain in its shallower parts. As a result, the various thrust sheets are isolated from a hydraulic point of view, whereas migration in the foreland may take place over long distances (>100 km).  相似文献   

Non-ionic surfactants adsorption: structure and thermodynamicsAdsorption des tensioactifs non ioniques : structure et thermodynamique     

Pierre E. Levitz 《Comptes Rendus Geoscience》2002,334(9):665-673

Adsorption of non-ionic surfactants from aqueous solutions has been studied for years because of its industrial relevance. These surfactants, made of an aliphatic part attached to a hydrophilic and polar chain, play an important role in diverse applications. Modelling of the adsorption mechanisms of surfactants has traditionally been based on the interpretation of adsorption isotherms. However, this first level of investigation is not sufficient for a complete understanding. Direct inspection of the adsorbed layer of non-ionic surfactant molecules at the solid–liquid interface is needed. This is an active field of research for almost 15 years, even if the subject is not completely settled down. The aim of this paper is to present a short review of this topic. I will restrict this paper to the case of non-ionic adsorption onto hydrophilic or polar solid interfaces. In the first part, I comment some experimental studies of non-ionic adsorption layer, including fluorescence spectroscopy, neutron scattering and atomic force microscopy. In the second part, a theoretical discussion about thermodynamics of adsorption is presented. A model involving an aggregative adsorption process is proposed. This last part will permit to raise some interesting questions concerning the role of the so-called ‘normal interaction’ (surfactant/solid interaction) to select the optimal surface aggregate curvature. To cite this article: P.E. Levitz, C. R. Geoscience 334 (2002) 665–673.  相似文献   

Origine et évolution du soufre au sein de l'aquifère des Sables infra-molassiques du Bassin aquitainOrigin and evolution of sulphur in the Infra-Molassic Sands Aquifer from the Aquitaine Basin     

Laurent André  Michel Franceschi  Pierre Pouchan  Olivier Atteia 《Comptes Rendus Geoscience》2002,334(10):749-756

New data on isotopic composition of sulphur and oxygen in dissolved sulphates are used to determine the origin of sulphate ions (SO₄^2?) in the water of the Infra-Molassic Sands Eocene aquifer. Two very distinct origins appear: one is the gypsum dissolution, from the molasse, and the second is the pyrite oxidation, present at the bottom of and within the aquifer. These isotopic analyses helped, in agreement with hydrogeology, to identify geochemical basins whose properties modify the chemical water composition. They also highlight the existence of bioreduction areas. To cite this article: L. André et al., C. R. Geoscience 334 (2002) 749–756.  相似文献   

A three-dimensional model of the Pyrenean deep structure based on gravity modelling, seismic images and petrological constraints     

Pierre Vacher  Annie Souriau 《Geophysical Journal International》2001,145(2):460-470

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Paper 2. agricultural impacts of and responses to climate change in the Missouri-Iowa-Nebraska-Kansas (MINK) region     

William E. Easterling III  Pierre R. Crosson  Norman J. Rosenberg  Mary S. McKenney  Laura A. Katz  Kathleen M. Lemon 《Climatic change》1993,24(1-2):23-61

The climate of the 1930s was used as an analog of the climate that might occur in Missouri, Iowa, Nebraska and Kansas (the MINK region) as a consequence of global warming. The analog climate was imposed on the agriculture of the region under technological and economic conditions prevailing in 1984/87 and again under a scenario of conditions that might prevail in 2030. The EPIC model of Williamset al. (1984), modified to allow consideration of the yield enhancing effects of CO₂ enrichment, was used to evaluate the impacts of the analog climate on the productivity and water use of some 50 representative farm enterprises. Before farm level adjustments and adaptations to the changed climate, and absent CO₂ enrichment (from 350 to 450 ppm), production of corn, sorghum and soybeans was depressed by the analog climate in about the same percent under both current and 2030 conditions. Production of dryland wheat was unaffected. Irrigated wheat production actually increased. Farm level adjustments using low-cost currently available technologies, combined with CO₂ enrichment, eliminated about 80% of the negative impact of the analog climate on 1984/87 baseline crop production. The same farm level adjustments, plus new technologies developed in response to the analog climate, when combined with CO₂ enrichment, converted the negative impact on 2030 crop production to a small increase. The analog climate would have little direct effect on animal production in MINK. The effect, if any, would be by way of the impact on production of feed-grains and soybeans. Since this impact would be small after on-farm adjustments and CO₂ enrichment, animal production in MINK would be little affected by the analog climate.  相似文献