Morphology, stratigraphy and oxygen isotope composition of fossil glacier ice at Ledyanaya Gora, Northwest Siberia, Russia     

REIN VAIKMÄE  FREDERICK A. MICHEL  VLADIMIR I. SOLOMATIN 《Boreas: An International Journal of Quaternary Research》1993,22(3):205-213

Studies of the stratigraphy, sedimentology, structure and isotope composition of a buried massive ice body and its encompassing sediments at Ledyanaya Gora in northwestern Siberia demonstrate that the ice is relict glacier ice, probably emplaced during the Early Weichselian. Characteristics of this ice body should serve as a guide for the identification of other relict buried glacier ice bodies in permafrost regions.  相似文献   

Corundum-bearing Garnet Clinopyroxenites at Beni Bousera (Morocco): Original Plagioclase-rich Gabbros Recrystallized at Depth within the Mantle?   总被引：7，自引：5，他引：7  

KORNPROBST  JACQUES; PIBOULE  MICHEL; RODEN  MICHAEL; TABIT  ABDELHALIM 《Journal of Petrology》1990,31(3):717-745

The Beni Bousera ultramafic massif, Morocco, is composed ofperidotite with subordinate garnet pyroxenitc units which belongto two different families: (1) the Type I pyroxenites, whichare characterized by an Fe-enrichment trend; and (2) the TypeII pyroxenites, which are characterized by high but nearly constantMg/Fe ratios and highly variable concentrations of Ca and Al;the latter family includes corundum-bearing garnet pyroxeniteswhich resemble the peraluminous eclogites and grospydites describedas xenoliths in kimberlite diatremes. The Type II pyroxenites appear as layered sheets in the peridotite,and have granuloblastic metamorphic texture. They contain aprimary association of a coarse-grained assemblage (cpx + gt;cpx + gt + sp; cpx + gt + co), and a variety of secondary andtertiary associations includ ng clinopyrox-ene, orthopyroxene,olivine, spinel, corundum, sapphirine, plagioclase, and amphibole.The primary assemblage in the corundum-bearing pyroxenite ischaracterized by clinopyroxene rich in A1₂O₃ (up to 20 wt%),and poor in Na₂O (generally less than 2 wt.%). The clinopyroxenephase is therefore richer in the Ca-Ts molecule than in thejadeite molecule. On the other hand, the composition of theprimary and secondary clinopyroxene and garnet phases showsstrong variation across the pyroxenite sheets. These variationsexpress compositional variations of the rock system across thesheets. The cpx-gt associations indicate high temperatures (1200–1350?C) in the central parts of the sheets. The crystallizationpressure may have reached at least 20 kb in the corundum-bearingassemblages. The bulk-rock composition and the compatible element's behaviourin the Type II pyroxenite sheets suggest that the modal andcryptic layering mainly resulted from igneous fractionationprocesses. The REE patterns of corundum-bearing Type II pyroxeniteare characterized by low concentrations of HREE and by significantEu anomalies. These, together with the high bulk-rock Sr/Ndratios, suggest that plagioclase segregation may have playeda significant part in the rock genesis. These geochemical featuresare similar to those described, in the literature, in some low-pressure,plagioclase-bearing adcumulates (e.g., in the crustal sequenceof the Oman ophiolite). They are quite different from thoseobserved in the Type I pyroxenite sheets in the Beni Bouseramassif, whose geochemistry suggests that plagioclase playedno part in the fractionation process, whereas garnet probablyfractionated as an early igneous phase. The Type II pyroxenitesheets have a primary isotopic signature similar to MORB, basedon the composition of leached clinopyroxene. It is concluded that the Mg-rich Type II pyroxenite sheets resultedultimately from the fractionation of a basaltic melt at lowpressure, and from the accumulation of olivine, clinopyroxene,and plagioclase along dykes cross-cutting the surrounding peridotite.The close similarities with the geochemical features in theOman ophiolite lead us to suggest that these processes may havebeen operative in an oceanic crustal environment. The high-pressureand high-temperature crystallization of the ‘primary’cpx+gt + co assemblage was achieved deep in the mantle, aftersubduction and/or dragging down in convection currents of thisparticular piece of the (oceanic?) lithosphere. Further ascentmay have resulted in partial melting of peridotite and/or pyroxenite,and in the emplacement of the Type I pyroxenite sheets.  相似文献   

Experimental Crystallization of Leucogranite Magmas   总被引：25，自引：8，他引：17  

SCAILLET  BRUNO; PICHAVANT  MICHEL; ROUX  JACQUES 《Journal of Petrology》1995,36(3):663-705

Both crystallization and melting experiments have been carriedout on two natural, biotite-muscovite (DK) and tourmaline-muscovite(GB) High Himalayan leucogranites (HHL) at 4 kbar, logfO₂ =FMQ–05, aH₂O = 1–0•03, and at five temperaturesbetween 803 and 663C H₂O contents of the quenched glasses wereanalysed by ion microprobe. Plagioclase and biotite are theliquidus phases for reduced melt H₂O contents and H₂O-rich conditions,respectively. H₂O saturation limits range from 8 to 10 wt%.DK has a wider crystallization interval than GB (150 vs 80Cfor conditions close to H₂O saturation), and a slightly higherH₂O-saturated solidus (645 compared with 630C for GB). Tourmalinenever crystallized spontaneously from the melt. Tourmaline seedsalways reacted out to biotite in the biotite-muscovite sample,whereas they remained stable in the tourmaline-muscovite sample.Biotite is replaced by hercynite as the main ferromagnesianphase at high temperature and reduced aH₂O. Muscovite crystallizationis restricted to near-solidus conditions. The compositions ofplagioclase, alkali feldspar, biotite and muscovite are givenas a function of bulk composition, temperature and aH₂O. Glasscompositions are richer in normative quartz than the 4 kbarH₂O-saturated Qz–Ab–Or eutectic, and become moreperaluminous and less mafic with increasing fractionation. Biotitecrystallization in peraluminous liquids is favoured by elevatedFe, Mg and Ti contents. Muscovite crystallization is not promotedunder H₂O-saturated conditions. Tourmaline stability is stronglydependent on aH₂O. For GB, tourmaline is present at elevatedtemperatures for intermediate values of aH₂O (803 C, 0–7),but not above 650C for H₂O-saturated conditions. Comparisonof the natural crystallization sequence with experiments suggestsinitial water contents between 5 and 75 wt % for the DK magma,and > 7 wt% for the GB magma. Plagioclase core compositionsgive minimum temperatures of 700C for GB and 750C for DK,consistent with an emplacement of these HHL as almost entirelyliquid bodies. The restricted occurrence of biotite in the GBgranite suggests that it reacted out during the magmatic evolution,owing to a marked change in fO₂ toward more oxidizing conditions.Tourmaline leucogranites can be generated from biotite leucogranitesby fractional crystallization under conditions of increasingdegree of oxidation. KEY WORDS: leucogranite; melting experiments; crystlization experiments; Himalayas; phase relations ^*Corresponding author  相似文献   

Sea‐surface hydrographical conditions off South Faeroes and within the North‐Eastern North Atlantic through MIS 2: the response of dinocysts     

CLÉMENCE CAULLE  AURÉLIE PENAUD  FRÉDÉRIQUE EYNAUD  SÉBASTIEN ZARAGOSI  DIDIER M. ROCHE  ELIZABETH MICHEL  SÉBASTIEN BOULAY  THOMAS RICHTER 《第四纪科学杂志》2013,28(3):217-228

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Col du Dôme (Mt Blanc Massif, French Alps) suitability for ice‐core studies in relation with past atmospheric chemistry over Europe     

SUSANNE PREUNKERT  DIETMAR WAGENBACH  MICHEL LEGRAND  CHRISTIAN VINCENT 《Tellus. Series B, Chemical and physical meteorology》2000,52(3):993-1012

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Using tendency errors to tune the parameterisation of unresolved dynamical scale interactions in atmospheric general circulation models     

EIGIL KAAS  ANNETTE GULDBERG  WILHELM MAY  MICHEL DÉQUÉ 《地球，A辑:动力气象学与海洋学》1999,51(5):612-629

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Podiform Chromite Ore Bodies: a Genetic Model   总被引：3，自引：0，他引：3  

LAGO  BERNARD L.; RABINOWICZ  MICHEL; NICOLAS  ADOLPHE 《Journal of Petrology》1982,23(1):103-125

This paper presents an attempt to interpret the formation ofpodiform chromite ore found in ophiolitic complexes from magmaticaccumulation inside cavities along the basalt conduits feedingthe main magma chamber. Two processes play a major role in chromite concentration: anactive upward magma flow in narrow dykes; and an active convectioninside the cavity, for which a numerical modelling has beenperformed. The physical conditions imposed by the model compare well withgeophysical and geological data.  相似文献   

Frequency spectra and intermittency of the turbulent suspension process in a sand-bed river   总被引：1，自引：0，他引：1  

MICHEL F. LAPOINTE 《Sedimentology》1996,43(3):439-449

Previous research suggests that the turbulence-driven suspension process in sand-bed channels is dominated by intermittent, energetic eddies with length scales of the order of channel depth. Because of the scarcity of data on the turbulent suspension process in alluvial channels, the possible variability in suspension intermittency and turbulent frequency content due to contrasts in flow depth, velocity or bedforms remains unclear however. The present study analyses eddy correlation suspension signals from seven deployments in varied flow conditions around a sandy meander bend. Deployment depths at near-bankfull flow stages varied from 2 to 5.5 m, velocities at 0.75–1 m height from 0.6 to 0.9 m s^?1 and local mean suspended sand concentrations ranged from 30 to 150 mg L^?1 in the intermittence and spectral content of sand suspension between the various deployments are analysed and results are compared with previously published findings. Study data suggest that the dominant eddy sizes involved in sediment mixing across the sensor level are consistently of the order of 1–5 times flow depth and lie within the ‘energy-bearing’ turbulent range. When sand suspension is analysed in the time domain in the various deployments, energetic, burst-like suspension events occupying only 1-5% of the record duration account for 20-90% of the suspension work. The degree of intermittence in the suspension process was observed to increase in deeper flows, where mixing events contributing extreme vertical sediment fluxes appear to be relatively more frequent.  相似文献   

Sequential Inductively Coupled Plasma Determination Of Some Rare-Earth Elements in Five French Geostandards   总被引：1，自引：0，他引：1  

Iwan ROELANDTS  Gilbert MICHEL 《Geostandards and Geoanalytical Research》1986,10(2):135-154

Experimental data for eleven rare-earth elements (REE) obtained by inductively coupled plasma spectrometry (ICP) in five French geochemical reference standards (BE-N, BR, DR-N, GS-N and FK-N)are presented. The method is based on acid digestion of the sample and cation-exchange separation from matrix elements.
Together with these new determinations an updated compilation of these reference materials are presented. Good agreement between the present results and previously preferred and published values obtained by various analytical techniques is observed. The values obtained in the present work corroborate the validity of the outlined method.  相似文献   

Quantitative reconstruction of mid-Holocene climatic variations in the northern Alpine foreland based on Lake Morat (Swiss Plateau) and Lake Annecy (French Pre-Alps) data     

MICHEL MAGNY  ODILE PEYRON  CAROLE BÉGEOT  JOËL GUIOT 《Boreas: An International Journal of Quaternary Research》2005,34(4):434-444

Vegetation and lake-level data from the sites of Lake Morat (Switzerland) and Lake Annecy (eastern France) are used to provide quantitative estimates of climatic variables over the period 6600-5500 cal. yr BP in the northern Subalpine zone, and to test the method of climate reconstruction based on modern pollen analogues constrained by lake-level data. The results obtained from both sites suggest: (1) that phases of higher lake level coincided with a cooling and a shortening of the growing season and an increase in annual precipitation, and (2) that during climatic reversals summer was more affected than winter. They also provide evidence of a sensitive method of reconstruction of climatic variables capable of capturing minor climatic oscillations such as reflected by weakly pronounced lake-level fluctuations. However, comparison of results obtained at Lake Morat and Lake Annecy, with each other and with results from other sites in central Europe, also clearly indicates that either anthropogenic disturbances of the vegetation cover or an overrepresentation of taxa due to particular site exposition can bias the reconstruction of variations in climatic parameters. In addition to pluri-centennial climatic oscillations, both the Lake Morat and Lake Annecy records show a general trend toward temperature cooling over the period considered. This may be related to a reduction in summer insolation induced by orbital factors. Finally, the quantitative estimates of climatic parameters reconstructed at Lake Morat and Lake Annecy help to increase our understanding of the possible impact of climatic oscillations on ancient agricultural communities.  相似文献