The Lac Cornu retrograded eclogites (Aiguilles Rouges massif,Western Alps,France): evidence of crustal origin and metasomatic alteration     

Jean-Paul Liégeois  Jean-Clair Duchesne 《Lithos》1981,14(1):35-48

Metabasic rocks interbedded in amphibolite facies supracrustal gneisses outcrop around Lac Carnu in the Aiguilles Rouges massif (Western Alps). The cores of the thickest boudinaged lenses are made up of eclogitic amphibolites grading outwards into amphibolites. The common assemblage is unzoned garnet + symplectitic clinopyroxebe + hornblende + plagioclase. In a slightly amphibolitized sample, minimum P and T conditions of equilibrium between garnet and omphacite inclusions are 780°C and 11 Kb. A polymetamorphic pre-Alpine evolution of the massif is thus demonstrated. Eclogitic amphibolites show variations in major element composition similar to the Skaergaard evolution in the Al₂O₃ ? FeO + Fe₂O₃ ? MgO triangle. Variation diagrams in which Zr is taken as differentiation index also indicate magmatic trends for Mn, Ti, P, Ni, Co, Y, V and Cr, Ca, K, Na, Sr, Rb and Si were mobile during the evolution of the rocks. The igneous trend can be described by a quantitative model of fractional crystallization in which a noritic assemblage separated in the initial stage. This provides evidence of crustal P, T conditions of differentiation for the original materoal and in situ evolution for the eclogites. A second group of amphibolites shows banded structure and transitional terms with the surrounding gneisses. A volcano-sedimentary origin is suggested though the process cannot be modelled. The rocks may result from complex interactions of magnetic, metasomatic and sedimentary processes. It is concluded that Lac Cornu metabasites were originally continental tholeiites, though several geochemical criteria tend to indicate an oceanic origin. This casts some doubt on the validity of these criteria, when applied to metamorphic rocks.  相似文献   

Les rhyolites hyperalcalines (pantellérites) du lac Tchad. Composition et signification tectonomagmatiqueThe peralkaline rhyolites (pantellerites) of the Lake Chad. Composition and tectonomagmatic significance     

Jean-Paul Vicat  André Pouclet  Yves Bellion  Jean-Claude Doumnang 《Comptes Rendus Geoscience》2002,334(12):885-891

Remnants of rhyolite lava-dome and of alkaline microgranite extrusions emerge, as inselbergs, in the alluvial plain, south of Lake Chad. The peralkaline, arfvedsonite- and acmite-bearing rhyolites are determined as pantellerites. They can be related to a tectonomagmatic stage, dated of the Late Cretaceous, of the western central Africa rift system. They may constitute the NNE extension of a N50° to 30° elongated succession of small alkaline complexes, from the Gulf of Guinea to the North-Cameroon, which initiated the magmatic activity of the Cameroon Line. To cite this article: J.-P. Vicat et al., C. R. Geoscience 334 (2002) 885–891.  相似文献   

Signification du signal isotopique (δ18O, δ13C) des carbonates néritiques : composante diagénétique et composante originelle (Jurassique supérieur de l'Est du bassin de Paris,France)     

Benoı̂t Vincent  Laurent Emmanuel  Jean-Paul Loreau 《Comptes Rendus Geoscience》2004,336(1):29-39

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Effets de la vitesse d'écoulement sur le transport et la cinétique de dépôt de particules en suspension en milieu poreux saturé     

Ahmed Benamar  HuaQing Wang  Nasre-dine Ahfir  Abdellah Alem  Nicolas Masséi  Jean-Paul Dupont 《Comptes Rendus Geoscience》2005,337(5):497-504

We study in this paper the transport and deposition of suspended particles in saturated porous media. Some chromatographic short-pulse tests were performed in a laboratory column with a tracer and two types of suspended particles. A mathematical model was used to determine the hydrodispersive parameters and deposition rates from the breakthrough curves. The results show that the fitted parameters obtained vary with the flow rate and the characteristics of the suspended particles. We also observe, at high flow rates, that particles have a migration velocity higher than that of the conservative tracer. To cite this article: A. Benamar et al., C. R. Geoscience 337 (2005).  相似文献   

Ash layers in deep-sea sediments as tracers of arc volcanic activity: Japan and Central America as case studies     

Herve  Cambray Jean-Paul  Cadet André  Pouclet 《Island Arc》1993,2(2):72-86

Abstract Arc volcanic activity on opposite sides of the Pacific Ocean (Japan and Central America) has been investigated by examining the number of volcanic ash layers recorded in Neogene and Quaternary deep-sea sediments. The data suggest that ash layers counted in deep-sea sediments may provide a reliable record of arc volcanism. The study is based on a quantitative analysis of arc volcanic activity using cores collected on DSDP (Deep-Sea Drilling Project) and ODP (Ocean Drilling Program) legs. Five distinct parameters which might affect ash distribution in marine sediments were reviewed: nature of the eruption, wind influence, settling conditions, diagenesis, and plate motion. Of these five, past atmospheric circulation was the most significant. The main constraint on the analysis is that temporal scattering of ash is not directly related to wind pattern variations. Results of this analysis are correlated with dating of terrestrial volcanic sequences. Although marine tephra records for individual regions reveal minor differences in the episodes of volcanic activity, a general correlation exists between activity of arc volcanism in Japan and in Central America. Two important pulses of arc volcanism occurred during Middle Miocene times (18–13 Ma) and Plio-Quaternary times (5–0 Ma). These episodes of intense volcanism are separated by a well recorded quiescent period during Late Miocene times. These correlating episodes of the volcanic record indicate a direct link between arc volcanism and the global tectonic evolution of the Pacific ocean margins.  相似文献   

Radiative surface temperature and convective flux calculation over crop canopies     

Jean-Paul Lhomme  Nader Katerji  Alain Perrier  Jean-Michel Bertolini 《Boundary-Layer Meteorology》1988,43(4):383-392

The analysis presented in this paper aims at a better understanding of the potential role of radiative temperature, as measured by a radiometer over crops, in sensible heat flux calculation. Defining radiative temperature as the mean temperature of the surfaces viewed by the radiometer (leaves and soil surface) and assuming that an Ohm's law type formula can be used to express sensible heat flux as a function of the difference between air temperature and radiative temperature, the aerodynamic resistance which divides this temperature difference has been analytically defined. The parameters which appear in the resistance expression depend essentially on wind velocity and canopy structure but also on the inclination angle of the radiometer. Finally an experimental verification is presented with data obtained over a potato crop.  相似文献   

Preface to the Proceedings of ENS''93 Conference     

Michael Elliott  Jean-Paul Ducrotoy 《Marine pollution bulletin》1994,29(6-12):253-254

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The 3100 BP eruption of the Soufrière of Guadeloupe     

Pascale Besson  Jean-Paul Poirier 《Bulletin of Volcanology》1994,56(3):184-192

Fragments of unaltered andesite found at all levels in the deposits of the catastrophic flank-failure, directed-blast eruption of the Soufrière of Guadeloupe in 3100 bp are thought to be remnants of the cryptodome. They were observed in analytical transmission electron microscopy for clues to the evolution of the intrusion prior to the eruption. Several features that could potentially be used as temperature markers were identified, among which the angle between microexsolutions of magnetite in augite phenocrysts was used to find an upper boundary of the temperature of the intrusion before the eruption: 600–700°C. Calculation of the time a dyke or sphere-shaped intrusion may have taken to cool from the emplacement temperature down to the temperature of exsolution of the magnetite leads to an estimate of the time between emplacement of the intrusion and the eruption, which could not have been less than a few tens of years. It therefore seems probable that the emplacement of the magmatic intrusion was not the immediate cause of the flank destabilization and catastrophic eruption of the Soufrière in 3100 bp.  相似文献   

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3     

Jean-Paul Cadet  Kazuo Kobayashi  Jean Aubouin  Jacques Boulgue  Christine Deplus  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kinichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km² and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary?  相似文献   

A model of the diagenetic evolution of coaly sedimentary organic matter     

Jean-Paul Boudou  Régis Pelet  René Letolle 《Geochimica et cosmochimica acta》1984,48(6):1357-1362

Elemental composition was used to calculate the amounts of compounds produced during the diagenetic evolution of a coal series from the Mahakam delta (Kalimantan, Indonesia). These calculations were based on the following hypotheses: organic nitrogen does not take part in reactions and remains unchanged in the residual organic matter, the only compounds produced are water, carbon dioxide and hydrocarbons.This approach shows that carbon loss during diagenesis is mainly as CO₂, and hydrogen loss is mainly as H₂O. Hydrocarbon production is negligible, in accordance with absence of bacterial methane accumulations in the Mahakam delta.The δ¹³C of coals in the sequence becomes about 2 per mil more positive over the diagenetic depth range of coal evolution. Accounting for the coal δ¹³C change in terms of CO₂ loss requires that the CO₂ given off have δ¹³C of about ?40%.. Such negative CO₂ has not been observed in natural systems, except when CH₄ is undergoing oxidation. Several plausible causes for this effect are discussed.  相似文献