Pre-Variscan geological events in the Austrian part of the Bohemian Massif deduced from U–Pb zircon ages     

Gertrude?FriedlEmail author  Fritz?Finger  Jean-Louis?Paquette  Albrecht?von?Quadt  Neal?J.?McNaughton  Ian?R.?Fletcher 《International Journal of Earth Sciences》2004,93(5):802-823

In an attempt to elucidate the pre-Variscan evolution history of the various geological units in the Austrian part of the Bohemian Massif, we have analysed zircons from 12 rocks (mainly orthogneisses) by means of SHRIMP, conventional multi-grain and single-grain U–Pb isotope-dilution/mass-spectrometry. Two of the orthogneisses studied represent Cadomian metagranitoids that formed at ca. 610 Ma (Spitz gneiss) and ca. 580 Ma (Bittesch gneiss). A metagranite from the Thaya batholith also gave a Cadomian zircon age (567±5 Ma). Traces of Neoproterozoic zircon growth were also identified in several other samples, underlining the great importance of the Cadomian orogeny for the evolution of crust in the southern Bohemian Massif. However, important magmatic events also occurred in the Early Palaeozoic. A sample of the Gföhl gneiss was recognised as a 488±6 Ma-old granite. A tonalite gneiss from the realm of the South Bohemian batholith was dated at 456±3 Ma, and zircon cores in a Moldanubian metagranitic granulite gave similar ages of 440–450 Ma. This Ordovician phase of magmatism in the Moldanubian unit is tentatively interpreted as related to the rifting and drift of South Armorica from the African Gondwana margin. The oldest inherited zircons, in a migmatite from the South Bohemian batholith, yielded an age of ca. 2.6 Ga, and many zircon cores in both Moravian and Moldanubian meta-granitoid rocks gave ages around 2.0 Ga. However, rocks from the Moldanubian unit show a striking lack of zircon ages between 1.8 and 1.0 Ga, reflecting an ancestry from Armorica and the North African part of Gondwana, respectively, whereas the Moravian Bittesch gneiss contains many inherited zircons with Mesoproterozoic and Early Palaeoproterozoic ages of ca. 1.2, 1.5 and 1.65–1.8 Ga, indicating a derivation from the South American part of Gondwana.  相似文献   

Un programme de photographie en lumière monochromatique des émissions coronales pour la période 1973–1976     

Jean-Louis Leroy  Jean Rösch 《Solar physics》1970,15(2):383-386

A Cooperative international program is suggested for monochromatic coronal photography by means of interference filters.  相似文献   

Element Mobility in Melts during Successive Intrusions of Crustal-derived Magmas and Sn-W Mineralization     

Jean-Louis Vigneresse 《Resource Geology》2006,56(3):293-314

Abstract. Continental collisions are the place where granitic plutons result from the melting of crustal components. Granitic plutons are built up by successive input of magma with a variable composition and hence temperature and chemistry. The intrusion of a new magma batch has consequences on the element mobility in the melt. Diffusion in already formed crystals is limited, due to the short time interval between magma input, and because of the low values of element diffusivity in solids. Because the new magma is generally hotter than the magma chamber, the temperature in the contact zone is modified. It activates diffusion by and modifies its characteristic length for element mobility in the melt. A new intrusion also modifies the partition coefficients, decreasing compatibility and increasing the incompatibility. The change in temperature has also effects on fluid exsolution controlled by crystallization, or second boiling. The present paper examines the intrusion of magma (fel‐sic or mafic) into a felsic magma chamber with a time interval of 30 ky. The intrusion of magma with similar composition, hence low (±100d?C) temperature difference has few effects. The diffusion lengths for elements rarely exceed one order of magnitude. The fluids released by the cooling magma are balanced by their reincorporation into the warming magma. In contrast, the intrusion of mafic magma into felsic magma chamber results in temperature difference that can reach ±300d?C. It may change the diffusion length up to two orders of magnitude for elements having large activation energy. Partition coefficients also vary by more than one order of magnitude. The effect is enhanced in the warming felsic magma, and damped in the mafic magma. In consequence elements like As, Sn, Sr, W, Zr are driven from the mafic magma toward the felsic magma. The release of H₂O and CO₂ are balanced between the two magma types. However the mafic magma releases an important amount of S that cannot re‐dissolves into the felsic magma and remains in the fluid phase. This simple model also addresses processes acting during ore formation. In particular, it examines the behavior of ions with a four valences state, as Sn and W, which has implications on the incorporation of other elements sharing a similar structure. It points out the necessity of external factors (S, halogens content and redox conditions) for controlling ore formation.  相似文献   

Commentaire à la note intitulée Synergie entre la télédétection multispectrale et les données de terrain pour la conception d'un nouveau modèle géodynamique d'ouverture du bassin paléozoïque des Jebilet centrales (Maroc), de A. El Harti et al. [C. R. Geoscience 336 (2004) 1311–1320]     

Abderrahim Essaifi  Jean-Louis Lagarde  Ramon Capdevila 《Comptes Rendus Geoscience》2006,338(5):386-388

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Were the 2.1-Gyr fossil colonial organisms discovered in the Francevillian basin (Palaeoproterozoic,Gabon) buried by turbidites?     

Olivier Parize  Jean-Louis Feybesse  François Guillocheau  Thierry Mulder 《Comptes Rendus Geoscience》2013,345(2):101-110

The Francevillian series (Gabon) in which the Earth's oldest large colonial organisms were recently discovered (El Albani et al., 2010) were deposited 2 Gyr ago. These series are usually interpreted as a fining-upward basin-fill sequence composed by five superimposed lithological terms noted FA to FE. New studies initiated by AREVA, allowed new data to be collected on the southwestern edge of the Francevillian basin, particularly on newly excavated outcrops. Facies interpretations show that the Poubara sandstones and associated shales and black shales (upper part of FB,FB2a), correspond to turbidites deposited on an upper slope rather than one a shelf, submitted to tidal currents or storm wave action. These new interpretations based on facies association, sedimentary geometries, and basin evolution show that the depositional environment could be a turbidite lobe set at a palaeobathymetry deeper than 200 m.  相似文献   

On some early attempts to determine the variation of the magnetic force with distance     

Mickaël Mussard  Jean-Louis Le Mouël  Jean-Paul Poirier 《Comptes Rendus Geoscience》2013,345(5-6):225-229

We describe two experiments made by the 18th-century physicists Francis Hauksbee and Pieter van Musschenbroek, designed to find the dependence of the magnetic force on distance. From the experimental results, given in the form of tables, the authors did not infer any simple law. We calculated the values obtained by assuming that the force varies as the inverse square of the distance and found a good agreement with their results. It therefore appears that these remarkable experiments could have provided an experimental proof of the law.  相似文献