Un nouveau gisement de granite orbiculaire dans le Massif Central français: le granite du Signal de Randon (Lozère)     

Jean -Pierre Couturié 《Contributions to Mineralogy and Petrology》1973,42(4):305-312

This orbicular granite contains ovoïds of an exceptional composition, comprising a core of biotite, surrounded by an envelope of plagioclase, enclosed in turn by an envelope of potassium feldspar. The latter also occurs as isolated idiomorphic megacristals between the ovoïds.Because of the spectacularly clear mineralogical relationships of the rock, it is possible to work out the order of crystallization of the minerals, the magmatic differentiation of syenitic orbicules and that of the leucogranitic groundmass with an aplito-pegmatitic texture.A magmatic process is proposed to explain the origin of the rock.

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Les déterminations de l'indice de triclinicité des feldspaths potassiques ont été effectuées par Yves Blanc, Clermont-Ferrand (diffractométrie X, d'après G. Sabatier, 1963).  相似文献   

Education challenges in the North Sea area     

Ducrotoy JP 《Marine pollution bulletin》2003,47(1-6):246-252

This paper introduces the North Sea as a fast evolving coastal ecosystem. The variability of natural conditions relates to the global climatic change and to human disturbances, which originate regionally. Education is an integral part of the strategy to improve environmental awareness. Considering contemporary challenges for educating the wider public about the main issues of environmental concern, attention is paid to various plans, which are being developed in North-Western Europe from primary schools to universities. "Learning for life" relies on an opening of the vocation of traditional universities and on the creation of a European university. Sharing resources in a competitive environment is one response given by British universities in the framework of a Discipline Network in Coastal Sciences and Management in 1996-2000. Networking is truly the key to a fast evolving teaching and learning context, notably in relation to ever developing information and communication technologies. The dissemination of scientific information is primordial in this context; a case study relating to the European project "Marine biodiversity in Europe" (BIOMARE) demonstrates the need for an elaborated strategy leading to socio-economic considerations. Empowering communities and governance are the main possible outcomes of such an enlarged approach to education, involving teachers, students, researchers, professionals, and volunteers. Proposals are made for amplifying the involvement of non-scientists into scientific research and its applications to management. Finally, a case is made for facilitating the mobility of all concerned, with a view to annihilate language and cultural barriers.  相似文献   

Assessment of gully erosion rates through interviews and measurements: a case study from northern Ethiopia   总被引：3，自引：0，他引：3  

Jan Nyssen  Jean Poesen  Maude Veyret‐Picot  Jan Moeyersons  Mitiku Haile  Jozef Deckers  Joke Dewit  Jozef Naudts  Kassa Teka  Gerard Govers 《地球表面变化过程与地形》2006,31(2):167-185

Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha^?1 a^?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha^?1 a^?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure?   总被引：1，自引：0，他引：1  

Gert Verstraeten  Jean Poesen  Katleen Gillijns  Gerard Govers 《水文研究》2006,20(20):4259-4267

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Runoff and water erosion modelling using WEPP on a Mediterranean cultivated catchment   总被引：1，自引：0，他引：1  

Damien Raclot  Jean Albergel 《Physics and Chemistry of the Earth》2006,31(17):1038-1047

Soil erosion due to water is a major environmental problem in many parts of the world. Most of Mediterranean countries are concerned because of their specific climate and soils sensitivity, but also because of the recent intensification of human activities and agricultural practices. Accurate estimation of soil water erosion for various land-use and climate scenarios is so an important key to define sustainable management policies. In the last decades, several studies have been carried out to build models suitable for quantifying soil erosion. Among these models, the Water Erosion Prediction Project (WEPP, Flanagan, D.C., Nearing, M.A., 1995. USDA-Water Erosion Prediction Project: Hillslope profile and watershed model documentation. NSERL Report 10, USDA-ARS National Soil Erosion Research Laboratory, West Lafayette, IN, USA.) is a physically based, distributed-parameter model that has been developed and mainly validated in USA. Only few studies have investigated its applicability to environmental conditions that differs from those where the model was developed. The aim of this work is to test the efficiency of WEPP model to predict soil erosion at catchment scale in a Mediterranean semi-arid area. Continuous simulations have been conducted between 1995 and 2002 on an cultivated experimental catchment located upstream from a hill reservoir (Kamech catchment, 2.45 km², Cap Bon, Tunisia) where runoff and soil erosion measurements are available at the outlet. Comparison between predictions and measurements shows significant differences. Processes related to seasonal effects (as cracking soils) are pointed out as a weakness of WEPP model for Mediterranean conditions.  相似文献   

Estimating Crustal Heterogeneity from Double-difference Tomography     

Jean -Luc Got  Vadim Monteiller  Jean Virieux  Paul Okubo 《Pure and Applied Geophysics》2006,163(2-3):405-430

Seismic velocity parameters in limited, but heterogeneous volumes can be inferred using a double-difference tomographic algorithm, but to obtain meaningful results accuracy must be maintained at every step of the computation. MONTEILLER et al. (2005) have devised a double-difference tomographic algorithm that takes full advantage of the accuracy of cross-spectral time-delays of large correlated event sets. This algorithm performs an accurate computation of theoretical travel-time delays in heterogeneous media and applies a suitable inversion scheme based on optimization theory. When applied to Kilauea Volcano, in Hawaii, the double-difference tomography approach shows significant and coherent changes to the velocity model in the well-resolved volumes beneath the Kilauea caldera and the upper east rift. In this paper, we first compare the results obtained using MONTEILLER et al.'s algorithm with those obtained using the classic travel-time tomographic approach. Then, we evaluated the effect of using data series of different accuracies, such as handpicked arrival-time differences (``picking differences'), on the results produced by double-difference tomographic algorithms. We show that picking differences have a non-Gaussian probability density function (pdf). Using a hyperbolic secant pdf instead of a Gaussian pdf allows improvement of the double-difference tomographic result when using picking difference data. We completed our study by investigating the use of spatially discontinuous time-delay data.  相似文献   

Perspectives on present-day sea level change: a tribute to Christian le Provost     

Alix Lombard  Anny Cazenave  Pierre Yves Le Traon  Stephanie Guinehut  Cécile Cabanes 《Ocean Dynamics》2006,56(5-6):445-451

In this paper, we first discuss the controversial result of the work by Cabanes et al. (Science 294:840–842, 2001), who suggested that the rate of past century sea level rise may have been overestimated, considering the limited and heterogeneous location of historical tide gauges and the high regional variability of thermal expansion which was supposed to dominate the observed sea level. If correct, this conclusion would have solved the problem raised by the IPCC third assessment report [Church et al, Cambridge University Press, Cambridge, pp 881, 2001], namely, the factor two difference between the 20th century observed sea level rise and the computed climatic contributions. However, recent investigations based on new ocean temperature data sets indicate that thermal expansion only explains part (about 0.4 mm/year) of the 1.8 mm/year observed sea level rise of the past few decades. In fact, the Cabanes et al.’s conclusion was incorrect due to a contamination of abnormally high ocean temperature data in the Gulf Stream area that led to an overestimate of thermal expansion in this region. In this paper, we also estimate thermal expansion over the last decade (1993–2003), using a new ocean temperature and salinity database. We compare our result with three other estimates, two being based on global gridded data sets, and one based on an approach similar to that developed here. It is found that the mean rate of thermosteric sea level rise over the past decade is 1.5±0.3 mm/year, i.e. 50% of the observed 3 mm/year by satellite altimetry. For both time spans, past few decades and last decade, a contribution of 1.4 mm/year is not explained by thermal expansion, thus needs to be of water mass origin. Direct estimates of land ice melt for the recent years account for about 1 mm/year sea level rise. Thus, at least for the last decade, we have moved closer to explaining the observed rate of sea level rise than the IPCC third assessment report.  相似文献   

The glacial inception as recorded in the NorthGRIP Greenland ice core: timing, structure and associated abrupt temperature changes     

Amaelle Landais  Valérie Masson-Delmotte  Jean Jouzel  Dominique Raynaud  Sigfus Johnsen  Christof Huber  Markus Leuenberger  Jakob Schwander  Bénédicte Minster 《Climate Dynamics》2006,26(2-3):273-284

The mechanisms involved in the glacial inception are still poorly constrained due to a lack of high resolution and cross-dated climate records at various locations. Using air isotopic measurements in the recently drilled NorthGRIP ice core, we show that no evidence exists for stratigraphic disturbance of the climate record of the last glacial inception (∼123–100 kyears BP) encompassing Dansgaard–Oeschger events (DO) 25, 24 and 23, even if we lack sufficient resolution to completely rule out disturbance over DO 25. We quantify the rapid surface temperature variability over DO 23 and 24 with associated warmings of 10±2.5 and 16±2.5°C, amplitudes which mimic those observed in full glacial conditions. We use records of δ¹⁸O of O₂ to propose a common timescale for the NorthGRIP and the Antarctic Vostok ice cores, with a maximum uncertainty of 2,500 years, and to examine the interhemispheric sequence of events over this period. After a synchronous North–South temperature decrease, the onset of rapid events is triggered in the North through DO 25. As for later events, DO 24 and 23 have a clear Antarctic counterpart which does not seem to be the case for the very first abrupt warming (DO 25). This information, when added to intermediate levels of CO₂ and to the absence of clear ice rafting associated with DO 25, highlights the uniqueness of this first event, while DO 24 and 23 appear similar to typical full glacial DO events.  相似文献   

Holographic interferometry study of the dissolution and diffusion of gypsum in water     

Jean Colombani  Jacques Bert 《Geochimica et cosmochimica acta》2007,71(8):1913-1920

We have performed holographic interferometry measurements of the dissolution of the (0 1 0) plane of a cleaved gypsum single crystal in pure water. These experiments have provided the value of the dissolution rate constant k of gypsum in water and the value of the interdiffusion coefficient D of its aqueous species in water. D is 1.0 × 10⁻⁹ m² s⁻¹, a value close to the theoretical value generally used in dissolution studies. k is 4 × 10⁻⁵ mol m⁻² s⁻¹. It directly characterizes the microscopic transfer rate at the solid-liquid interface, and is not an averaged value deduced from quantities measured far from the surface as in macroscopic dissolution experiments. It is found to be two times lower than the value obtained from macroscopic experiments.  相似文献   

The Stannern trend eucrites: Contamination of main group eucritic magmas by crustal partial melts     

J.A. Barrat  A. Yamaguchi  M. Bohn  M. Benoit 《Geochimica et cosmochimica acta》2007,71(16):4108-4124

We report on the petrology of a new eucrite belonging to the Stannern trend and discuss the origin of this trend. The eucrite Northwest Africa 4523 (NWA 4523) is an equilibrated eucrite consisting of dark clasts embedded in a fine-grained crystallized matrix. Two types of clasts have been observed: medium-grained ophitic/subophitic clasts, and very fine-grained clasts. Despite textural differences, the clasts display the same mineralogy, in particular the same kind of pyroxenes with pigeonitic cores containing sparse exsolution lamellae, and augitic rims, zoned plagioclases and the occurrence of K-feldspar. The major and trace element abundances of a large medium-grained clast are very similar to Stannern or Bouvante.The Stannern trend eucrites are characterized by high incompatible trace element abundances. Their trace element patterns normalized to a representative Main Group eucrite, exhibit significant Eu, Sr and Be negative anomalies. In this paper, we show that contamination of Main Group eucritic magmas by melts derived by partial melting of the asteroid’s crust can successfully explain both the high incompatible trace elements concentrations and the distinctive Eu, Sr, Be anomalies shown by the Stannern trend eucrites. This model is in agreement with the view that Stannern and some Main Group-Nuevo Laredo trend eucrites have been contemporaneously erupted, and with the probable assumption that Stannern trend eucrites formed rather late in the history of the 4-Vesta’s crust.  相似文献