Carbonaceous micrometeorites from Antarctica     

CCILE ENGRAND  MICHEL MAURETTE 《Meteoritics & planetary science》1998,33(4):565-580

Abstract— Over 100 000 large interplanetary dust particles in the 50–500 μm size range have been recovered in clean conditions from ～600 tons of Antarctic melt ice water as both unmelted and partially melted/dehydrated micrometeorites and cosmic spherules. Flux measurements in both the Greenland and Antarctica ice sheets indicate that the micrometeorites deliver to the Earth's surface ～2000× more extraterrestrial material than brought by meteorites. Mineralogical and chemical studies of Antarctic micrometeorites indicate that they are only related to the relatively rare CM and CR carbonaceous chondrite groups, being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals. However, there are also marked differences between these two families of solar system objects, including higher C/O ratios and a very marked depletion of chondrules in micrometeorite matter; hence, they are “chondrites-without-chondrules.” Thus, the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects, probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles, comets. One of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early Earth, and more recently, with the early history of the solar system.  相似文献   

Actual and potential skill of seasonal predictions using the CNRM contribution to DEMETER: coupled versus uncoupled model     

JEAN-FRANÇOIS GUÉRÉMY  MICHEL DÉQUÉ  ALAIN BRAUN  JEAN-PHILIPPE PIEDELIÈVRE 《地球，A辑:动力气象学与海洋学》2005,57(3):308-319

  相似文献   

Geochemical and Isotopic Evidence for Crustal Assimilation Beneath Krafla, Iceland   总被引：7，自引：3，他引：7  

NICHOLSON  HUGH; CONDOMINES  MICHEL; FITTON  J. GODFREY; FALLICK  ANTHONY E.; GR?NVOLD  KARL; ROGERS  GRAEME 《Journal of Petrology》1991,32(5):1005-1020

The Krafla volcanic system consists of a central volcano andassociated fissure swarm in the NE axial rift zone of Iceland.Lavas spanning the whole of Krafla's exposed volcanic history(estimated to be 0-> 300 ka) have been analysed and rangein composition from olivine tholeiite to rhyolite. Major-elementcompositions suggest that fractional crystallization exertsthe main control over the differentiation process. However,K₂O and the very incompatible trace elements, Rb, Th, and U,are all enriched beyond the extent expected by closed-systemfractional crystallization. Fractionation coupled with periodicreplenishment and tapping of the reservoir is unlikely to beresponsible for this enrichment, despite the geophysical evidencesuggesting a large number of inflations and deflations of ashallow magma reservoir (Tryggvason, 1986). Th- and O-isotope results confirm the work of previous authorsthat crustal assimilation is operating on a local scale beneathKrafla. A model is suggested, fitting both the Th- and O-isotopicdata, which involves the partial melting and incorporation ofa hydrothermally altered wall-rock contaminant during fractionalcrystallization (i. e., AFC processes). This process of partialmelting is likely to enhance the most highly incompatible elementconcentrations (e. g., increasing Rb/Zr) more than expectedby closed-system fractional crystallization.  相似文献   

E) Non Governmental International Organizations Organisations Internationales non gouvernementales     

MICHEL DANIS  MICHEL QUINTARD 《水文科学杂志》2013,58(1):105-110

RESUME

La méthode classique de simulation d'une nappe captive consiste à résoudre le problème en régime transitoire à partir de la situation originelle. Dans cet article est présentée une méthode qui permet de déterminer directement l'état de la nappe à un instant donné si l'on peut connaître la chute piézométrique à cet instant.  相似文献   

Position of the palaeontological site Aven I des Abîmes de La Fage, at Noailles (Corrèze, France), in the European Pleistocene chronology     

CÉCILE MOURER-CHAUVIRÈ  MICHEL PHILIPPE  YVES QUINIF  JEAN CHALINE  EVELYNE DEBARD  CLAUDE GUÉRIN  MARGUERITE HUGUENEY 《Boreas: An International Journal of Quaternary Research》2003,32(3):521-531

Mourer-Chauviré, C., Philippe, M., Quinif, Y., Chaline, J., Debard, E., Guérin, C. & Hugueney, M. 2003 (September): Position of the palaeontological site Aven I des Abîmes de La Fage, at Noailles (Corrèze, France), in the European Pleistocene chronology. Boreas , Vol. 32, pp. 521–531. Oslo. ISSN 0300–9483.
The palaeontological locality of Aven I des Abîmes de La Fage, at Noailles, Corrèze, France, is a limestone swallow hole filling which includes a rich fauna of micro- and macromammals, and one of the most complete Pleistocene avifaunas in the Palearctic. According to the mammal fauna and to the sedimentological study, the filling was previously assigned to the penultimate, Saalian, glaciation. U/Th datings made on a stalagmitic floor deposited in a lateral gallery on top of the filling confirm this previous attribution. Revised lists of the mammal and bird faunas are provided. The comparison of the La Fage fauna with that of other European localities, radiochronologically or biostratigraphically dated, leads to the conclusion that most of the fossiliferous layers were deposited during the Marine Isotope Stage (MIS) 8 (242 to 301 ka).  相似文献   

Climate of the last millennium: a sensitivity study   总被引：2，自引：0，他引：2  

CÉDRIC BERTRAND  MARIE-FRANCE LOUTRE  MICHEL CRUCIFIX  ANDRÉ BERGER 《地球，A辑:动力气象学与海洋学》2002,54(3):221-244

Seventy-one sensitivity experiments have been performed using a two-dimensional sector-averaged global climate model to assess the potential impact of six different factors on the last millennium climate and in particular on the surface air temperature evolution. Both natural (i.e, solar and volcanism) and anthropogenically-induced (i.e. deforestation, additional greenhouse gases, and tropospheric aerosol burden) climate forcings have been considered.
Comparisons of climate reconstructions with model results indicate that all the investigated forcings are needed to simulate the surface air temperature evolution. Due to uncertainties in historical climate forcings and temperature reconstructions, the relative importance of a particular forcing in the explanation of the recorded temperature variance is largely function of the forcing time series used. Nevertheless, our results indicate that whatever the historical solar and volcanic reconstructions may be, these externally driven natural climate forcings are unable to give climate responses comparable in magnitude and time to the late–20th-century temperature warming while for earlier periods combination of solar and volcanic forcings can explain the Little Ice Age and the Medieval Warm Period. Only the greenhouse gas forcing allows the model to simulate an accelerated warming rate during the last three decades. The best guess simulation (largest similarity with the reconstruction) for the period starting 1850 AD requires however to include anthropogenic sulphate forcing as well as the impact of deforestation to constrain the magnitude of the greenhouse gas twentieth century warming to better fit the observation. On the contrary, prior to 1850 AD mid-latitude land clearance tends to reinforce the Little Ice age in our simulations.  相似文献   

The origin and glaciodynamic significance of sandstone ridge networks from the Hirnantian glaciation of the Djado Basin (Niger)     

MICHAËL DENIS  JEAN-FRANÇOIS BUONCRISTIANI  MOUSSA KONATɆ  MICHEL GUIRAUD 《Sedimentology》2007,54(6):1225-1243

The Djado Basin (Niger) was located beneath the inner part of the Late Ordovician ice sheet. The Felar‐Felar Formation consists mainly of glaciomarine deposits, associated with the major ice sheet recession within the glaciation, and is bounded by two glacial unconformities. Structures corresponding to sandstone ridges are found within the Felar‐Felar Formation. Sandstone ridges are several metres high, about 10 m wide and hundreds of metres long. These structures are organized in extensive anastomosed to sub‐polygonal networks. The association of sandstone ridge networks with the later glacial unconformity and with other glacial evidence suggests sub‐glacial conditions for their origin. Sandstone ridge sedimentological characteristics indicate that sandstone ridges result from the scouring of the Felar‐Felar Formation by sub‐glacial, turbulent and pressurized meltwater; then sub‐glacial cavities were infilled with sand derived from glacial abrasion. Sandstone ridge networks are comparable with tunnel channels and document unusual drainage structures of the inner part of the palaeo‐ice sheet.  相似文献   

Petrological and Experimental Constraints on the Pre-eruption Conditions of Holocene Dacite from Volcan San Pedro (36{degrees}S, Chilean Andes) and the Importance of Sulphur in Silicic Subduction-related Magmas   总被引：3，自引：0，他引：3  

COSTA  FIDEL; SCAILLET  BRUNO; PICHAVANT  MICHEL 《Journal of Petrology》2004,45(4):855-881

We present an experimental and petrological study aimed at estimatingthe pre-eruptive conditions of a Holocene dacitic lava fromVolcán San Pedro (36°S, Chilean Andes). Phase-equilibriumexperiments were performed at temperatures (T) from 800 to 950°C,and mainly at 200 MPa, but also at 55, 150, and 406 MPa. Oxygenfugacity (fO₂) ranged from the Ni–NiO buffer (NNO) to3·5 log units above (NNO + 3·5), and water contentsfrom  相似文献   

Reversal of Fe-Mg Partitioning Between Garnet and Staurolite in Eclogite-facies Metapelites from the Champtoceaux Nappe (Brittany, France)     

BALLEVRE  MICHEL; PINARDON  JEAN-LUC; KIENAST  JEAN-ROBERT; VUICHARD  JEAN-PAUL 《Journal of Petrology》1989,30(6):1321-1349

This paper concentrates on the petrology of eclogite-faciesmetapelites and, particularly, the significance of staurolitein these rocks. A natural example of staurolite-bearing eclogitic micaschistsfrom the Champtoceaux nappe (Brittany, France) is first described.The Champtoceaux metapelites present, in addition to quartz,phengite, and rutile, two successive parageneses: (1) chloritoid+staurolite+garnetcores, and (2) garnet rims+kyanite?chloritoid. Detailed microprobe analyses show that garnet and chloritoidevolve towards more magnesian compositions and that stauroliteis more Fe-rich than coexisting garnet. A comparison of thestudied rocks with other known occurrences of eclogitic metapelitesshows that whereas staurolite is always more Fe-rich than garnetin high-pressure eclogites, the reverse is true in low- to medium-pressuremicaschists. Phase relations between garnet, staurolite, chloritoid, biotite,and chlorite are analysed in the KFMASH system (with excessquartz, phengite, rutile, and H₂O). The topology of univariantreactions is depicted for a normal and a reverse Fe-Mg partitioningbetween garnet and staurolite. Mineral compositional changesare also predicted for varying bulk-rock chemistries. In the studied micaschists, the zonal arrangement of garnetinclusions and the progressive compositional changes of ferromagnesianphases record part of the prograde P–T path, before theattainment of ‘peak’ metamorphic conditions (atabout 65O–7OO?C, 18–20 kb). The retrograde path,which records the uplift of the Champtoceaux nappe, occurs underdecreasing temperatures.  相似文献   

MIGRATION TO ZERO OFFSET (DMO) FOR A CONSTANT VELOCITY GRADIENT: AN ANALYTICAL FORMULATION1     

MICHEL DIETRICH  JACK K. COHEN 《Geophysical Prospecting》1993,41(5):621-643

Migration to zero offset (MZO) is a prestack partial migration process that transforms finite-offset seismic data into a close approximation to zero-offset data, regardless of the reflector dips that are present in the data. MZO is an important step in the standard processing sequence of seismic data, but is usually restricted to constant velocity media. Thus, most MZO algorithms are unable to correct for the reflection point dispersal caused by ray bending in inhomogeneous media. We present an analytical formulation of the MZO operator for the simple possible variation of velocity within the earth, i.e. a constant gradient in the vertical direction. The derivation of the MZO operator is carried out in two steps. We first derive the equation of the constant traveltime surface for linear V(z) velocity functions and show that the isochron can be represented by a fourth-degree polynomial in x, y and z. This surface reduces to the well-known ellipsoid in the constant-velocity case, and to the spherical wavefront obtained by Slotnick in the coincident source-receiver case. We then derive the kinematic and dynamic zero-offset corrections in parametric form by using the equation of the isochron. The weighting factors are obtained in the high-frequency limit by means of a simple geometric spreading correction. Our analytical results show that the MZO operator is a multivalued, saddle-shaped operator with marked dip moveout effects in the cross-line direction. However, the amplitude analysis and the distribution of dips along the MZO impulse response show that the most important contributions of the MZO operator are concentrated in a narrow zone along the in-line direction. In practice, MZO processing requires approximately the same trace spacing in the in-line and cross-line directions to avoid spatial aliasing effects.  相似文献