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101.
Emilie Pourtier Jean-Luc Devidal François Gibert 《Geochimica et cosmochimica acta》2010,74(6):1872-66
The solubility of synthetic NdPO4 monazite end-member was experimentally determined from 300 up to 800 °C, at 2000 bars in pure water, and in aqueous chloride or phosphate solutions. Both the classical weight-loss method and a new method based on isotope dilution coupled with thermal ionization mass spectrometer were used. In the range of temperature studied monazite showed a prograde solubility from 10−5.4 m at 300 °C up to 10−2.57 m at 800 °C. Experiments in H2O-H3PO4-NaCl-HCl solutions suggested Nd(OH)30 was the major species that was formed at high temperature and pressure. The equilibrium constants (log K) for the reaction:
102.
103.
ABSTRACT The Pan-African orogeny left a strong imprint on the basement rocks of Madagascar, which were metamorphosed up to granulite facies conditions. The supracrustal Itremo Group of central Madagascar, comprising quartzites, schists and carbonates of lower metamorphic grade, has to date been described as a folded sedimentary sequence. Despite their fine-grained 'sugary' appearance, most quartzites are plastically deformed tectonites. Quartzite microstructures are mainly of the elongate mosaic type, indicating significant grain boundary migration, and are compatible with dynamic recrystallization under lower amphibolite facies conditions. Consistent asymmetric quartz c -axis fabrics indicate a dominant top-to-the-east shear sense. Hence, the Itremo quartzites bear evidence for a major eastward-directed tectonic event of Pan-African age, possibly resulting from an early Pan-African thrust motion. Younger deformational events, responsible for localized mylonites with top-to-the-WSW sense of motion and N–S-trending folds and shear zones, were superimposed on this first fabric. 相似文献
104.
105.
The rate of climatic change estimated from the gradient of signals recorded in lake sediments may be erroneous if post-depositional perturbations are overlooked. A smear out of a pulse signal, over a variable thickness of core section, due to physical or biological mixing, is a well known phenomena. Much less attention is paid to a possible overestimation of the rate of change when a part of record is missing due to an erosion event. In this paper we show a few examples of recent lake sediment perturbations and the resulting distortions in the time scale, as documented by short-lived radionuclides.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program 相似文献
106.
Jean-Luc Schneider Claude Fourquin Jean-Claude Paicheler 《Journal of Volcanology and Geothermal Research》1992,49(3-4)
Pyroclastic deposits interpreted as subaqueous ash-flow tuff have been recognized within Archean to Recent marine and lacustrine sequences. Several authors proposed a high-temperature emplacement for some of these tuffs. However, the subaqueous welding of pyroclastic deposits remains controversial.The Visean marine volcaniclastic formations of southern Vosges (France) contain several layers of rhyolitic and rhyodacitic ash-flow tuff. These deposits include, from proximal to distal settings, breccia, lapilli and fine-ash tuff. The breccia and lapilli tuff are partly welded, as indicated by the presence of fiamme, fluidal and axiolitic structures. The lapilli tuff form idealized sections with a lower, coarse and welded unit and an upper, bedded and unwelded fine-ash tuff. Sedimentary structures suggest that the fine-ash tuff units were deposited by turbidity currents. Welded breccias, interbedded in a thick submarine volcanic complex, indicate the close proximity of the volcanic source. The lapilli and fine-ash tuff are interbedded in a thick marine sequence composed of alternating sandstones and shales. Presence of a marine stenohaline fauna and sedimentary structures attest to a marine depositional environment below storm-wave base.In northern Anatolia, thick massive sequences of rhyodacitic crystal tuff are interbedded with the Upper Cretaceous marine turbidites of the Mudurnu basin. Some of these tuffs are welded. As in southern Vosges, partial welding is attested by the presence of fiamme and fluidal structures. The latter are frequent in the fresh vitric matrix. These tuff units contain a high proportion of vitroclasis, and were emplaced by ash flows. Welded tuff units are associated with non-welded crystal tuff, and contain abundant bioclasts which indicate mixing with water during flowage. At the base, basaltic breccia beds are associated with micritic beds containing a marine fauna. The welded and non-welded tuff sequences are interbedded in an alternation of limestones and marls. These limestones are rich in pelagic microfossils.The evidence above strongly suggest that in both examples, tuff beds are partly welded and were emplaced at high temperature by subaqueous ash flows in a permanent marine environment. The sources of the pyroclastic material are unknown in both cases. We propose that the ash flows were produced during submarine fissure eruptions. Such eruptions could produce non-turbulent flows which were insulated by a steam carapace before deposition and welding. The welded ash-flow tuff deposits of southern Vosges and northern Anatolia give strong evidence for existence of subaqueous welding. 相似文献
107.
Pierre Rochette Grard Fillion Jean-Luc Matti Marinus J. Dekkers 《Earth and Planetary Science Letters》1990,98(3-4)
A characteristic magnetic transition at 30–34 K is shown to provide a powerful tool for the identification of pyrrhotite with concentration down to 10 ppm through the same low-temperature techniques as applied to magnetite and hematite, extended down to liquid helium temperature. A review of rock magnetic and petrological data on pyrrhotite suggests that this mineral should be considered as a major carrier of paleomatnetic signals. Unblocking temperature up to 350°C and extreme resistance against AF may be encountered in fine grained pyrrhotite. 相似文献
108.
Laurent Turpin Michel Cuney Marc Friedrich Jean-Luc Bouchez Monique Aubertin 《Contributions to Mineralogy and Petrology》1990,104(2):163-172
Seventy samples of Hercynian peraluminous granites (Guéret, Millevaches and Saint Sylvestre massifs) and metamorphic units of the Limousin area were analysed for Rb–Sr and Sm–Nd. The source rocks of the peraluminous granites can be found in the metamorphic rocks of Limousin, among them meta-igneous rocks were largely predominent over meta-sedimentary rocks in the source of the three granites. Millevaches and Guéret granites were generated by the partial melting of rocks comprising meta-volcanics and meta-sediments, whereas the Saint Sylvestre granite was produced exclusively by the melting of late Precambrian granites. This leads to confusing T
DM
Nd
values, the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites, which leads to dramatic fractionation in Sm/Nd ratios. The data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates. Late Precambrian time seems, however, to have been a period of extensive crustal generation in Western Europe. 相似文献
109.
Par Jean-Luc Schneider Rudolf Maass Jean-Claude Gall Philippe Duringer 《International Journal of Earth Sciences》1989,78(2):555-570
Resumé L'existence d'une phase tectonique intraviséenne dans la chaîne varisque d'Europe a été admise par divers auteurs. Le présent travail apporte des précisions sur la nature de cet événement dans le Nord du Massif Central, les Vosges et la Forêt Noire, c'est à dire dans la zone interne varisque. Des données nouvelles concernent les Vosges et la Forêt Noire. Dans le domaine étudié, cet événement géodynamique n'est pas phcatif et se caractérise par une période d'instabilité au cours du Viséen supérieur qui conduit à d'importants phénomènes de resédimentation, résultats de l'érosion de paléoreliefs. Cette période d'instabilité se prolonge au cours du Viséen supérieur où une emersion généralisée se produit dans la zone moldanubienne. Dans les zones externes septentrionales, la déformation synmétamorphique qui se déplace vers l'extérieur de la chaîne est contemporaine de cet événement. Dans le massif armoricain (zone externe), il se traduit par des mouvements décrochants. Cet événement s'explique par un épaississement crustal, conséquence directe de la collision varisque et se traduit par un soulèvement qui précède la phase de déformation paroxysmale d'âge tardi-viséen et carbonifère supérieur.
The existence of an Intravisean tectonic phase in the variscan belt of Europe is admitted by some authors. The present work specifies the characteristics of such an event in the northern part of the French Massif Central, in the Vosges mountains and in the Black Forest, i.e. in the internal variscan zone. New data are given for the Vosges and the Black Forest. In the considered domain the geodynamic event does not have a folding effect. It leads to a period of instability during Late Visean, inducing important resedimentation processes as a result of erosion of the paleoreliefs. A generalized emersion of the Moldanubian Zone occurs at the same time. This event coincides with the migration toward the North of the syn-metamorphic deformation in the extern parts of the belt. In the Armorican Massif (external zone) strike slip faults are active during the same period. That event can be explained by the crustal thickening resulting from the variscan collision. The uplift preceds the paroxysmal Late Visean and Upper Carboniferous tectonic phase.
Zusammenfassung Verschiedene Autoren vertreten die Meinung, daß das mitteleuropäische Variszikum innerhalb des Visé von einer tektonischen Phase betroffen wurde. Die gegenwärtige Arbeit soll eine genauere Vorstellung von den Ereignissen geben, welche sich um diese Zeit im nördlichen Zentralmassiv, den Vogesen und dem Schwarzwald abspielten. Innerhalb des angeführten Bereiches läßt sich nirgends eine Faltung beobachten. Es handelt sich vielmehr um ein geodynarmsches Ereignis, welches sich im obereren Visé als eine Periode der Instabilität mit sehr beachtlichen Erosionen einerseits und ebenso bedeutenden Resedimentationen andererseits äußert. Diese Zeit der Instabilität mündet noch im Laufe des obersten Visé in einer allgemeinen Heraushebung des Moldanubikums. Das Intra-Visé Ereignis ist zeitgleich mit der nordwärtigen Wanderung der synmetamorphen Deformation in den externen Zonen. Im armorikanischen Massiv fällt es anscheinend mit bedeutenden Blattverschiebungen zusammen. Offensichtlich steht hinter den Vorgängen als Ursache eine relativ plötzliche Krustenverdickung im Zusammenhang mit der variszischen Kollision. Die Heraushebung geht der paroxysmalen Deformation im späten Visé bzw. frühen Oberkarbon voraus.
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110.
Jean-Luc Piveteau 《Geoforum》1975,6(2):105-112
The lack of any unified view amongst geographers in their conceptions of the articulation of Swiss space is evidence, in the dialectical sense, of the complexity of the reality. It is also, however, a sympton of methodological uncertainty. The purpose of this article is an analysis of this malaise, usually passed over in silence.The evolution of geography during the last hundred years cannot be easily defined, but against a general trend opposed approaches have always been present.The manner of conceiving Swiss space is still affected by the changes in the physiognomy of the country, but the analysis of reality and reality itself are out of phase.It appears possible that the presuppositions admitted by authors or the intellectual paths followed by them in regionalisation should be considered and treated as one of the fundamentals of all studies concerned with the organisation of space. 相似文献