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Jean-Marie Dautria Jean-Michel Liotard Danièle Briot 《Comptes Rendus Geoscience》2004,336(11):971-981
Sr and Nd isotopic compositions of one trachyte, eight phonolites and five basalts have been measured. The isotopic characteristics of the trachyte can be explained by a combined assimilation–fractional crystallization process within an upper crustal magmatic chamber. Some phonolites display isotopic signatures identical to basalts, suggesting that they have been protected against any crustal assimilation during their formation. Some others have low Sr contents, whereas they are enriched in radiogenic Sr (0.70451<87Sr/86Sri<0.71192), and display basaltic 143Nd/144Nd ratios. Both observations could be explained by very strong alkali feldspar fractionation and by subsequent very low assimilation of surrounding rocks (between 0.3 and 4%) during intrusion. To cite this article: J.-M. Dautria et al., C. R. Geoscience 336 (2004). 相似文献
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Radovan Pipík Anne-Marie Bodergat Danielle Briot Michal Ková? Ján Král’ Grzegorz Zielinski 《Journal of Paleolimnology》2012,47(2):233-249
The Turiec Basin (TB) of Slovakia formed in the Miocene when the West Carpathians escaped from the Alpine region. The 1,250-m-thick
sedimentary Neogene fill of the basin preserved fossil leaves as well as endemic bivalves, gastropods, and ostracodes. The
paleolimnologic changes recorded in the TB infill were derived from the most abundant fossils, the ostracodes. Five contemporaneous
ostracode assemblages within the Late Miocene lacustrine system were distinguished through statistical analysis. These assemblages
have low species similarity, between 2.1 and 24.1%, and are recognized by shape differences among the Candoninae. The ostracode
assemblages, mollusca fossils, and Sr-isotope ratios suggest a low-salinity environment at the beginning of the Late Miocene,
during a brief connection with the Central Paratethys. When the connection ceased, the basin became an isolated freshwater
lake, with five zones differentiated ecologically and bathymetrically using the ostracode assemblages. Taxonomic comparison
of the faunas of the TB and the freshwater to brackish Neogene basins of Europe demonstrates the endemic character of the
TB ostracode fauna. The biologic characteristics of the ostracode families, along with the geology of the lake basin, suggest
that the longevity of the Late Miocene lake probably exceeded 1 Ma. 相似文献
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Ph. Briot 《Mineralium Deposita》1982,17(1):151-157
Résumé L'étude du calcrete uranifère de Yeelirrie, en Australie Occidentale (46000 tonnes d'U3O8 estimées), minéralisé en carnotite, a permis de préciser la genèse de tels gîtes. Les calcretes se présentent en corps lenticulaires dans la partie axiale des chenaux de drainage en amont d'une structure verrou, constituée par une remontée du socle ou un retrécissement du chenal. La présence de structures verrous a déterminé l'existence de légères dépressions en amont, temporairement inondées, où se localise le dépôt d'un calcrete d'origine sédimentaire. Dans un second temps, la structure barrage a provoqué le ralentissement de l'écoulement de la nappe. Une nappe fixe se créee, sursaturée en sels dissous, provoquant l'épigenèse et la dolomitisation de la partie du calcrete proche du verrou, avec dépôts d'uranium, de vanadium (carnotite) et de strontium (célestite). Des gîtes de type calcrete sont connus également en Mauritanie et en Namibie. Ainsi, les calcretes sont, dans les domaines évaporitiques intracontinentaux, des sites favorables au piègeage de l'uranium. Si leur genèse est différente, leur localisation dans des zones stables à climat aride ou semi-aride est une caractéristique commune.
The study of the Yeelirrie uraniferous calcrete of the Western Australia, containing abundant carnotite, has allowed interpretation of the genesis of the main ore concentrating processes within this type of deposit (46000 tons of estimated U3O8). The calcretes are found as lenses within the axial parts of certain channels. They are situated upstream with respect to local barriers formed by uplifted basement blocks or by local constrictions of the channel. The presence of such constrictions has allowed development of minor upstream depressions which were temporarily flooded, and within which the sedimentary calcrete has formed. Subsequently, the constriction has caused a slowing of phreatic water circulation. The stabilised phreatic lense, supersaturated with respect to dissolved salts, has provoked the epigenesis and dolomitization of the original calcrete situated in the proximity of the dam. Uranium and vanadium (carnotite) as well as strontium (celestite) are concentrated through this process. Uranium ore concentrations of the calcrete type are known also in Mauritania and Namibia. Thus, calcretes within intracontinental evaporitic areas form favourable traps for the concentration of uranium. Although of possible different origin, the concentration of ore within the stable areas of arid to semi-arid regions is a common characteristic of this type of deposit.相似文献
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Sr and Nd isotopic compositions have been determined on basaltic and acid trachyandesites (BTA-ATA) from the Sancy volcano (Mont-Dore massif, France). These represent more than 80% of the lavas erupted during its activity between 0.9 and 0.2 Ma. These lavas have been recently interpreted as the result of two-component magma mixing during and after repeated injections of basaltic magmas in trachytic reservoirs. Magmatic heterogeneities in the ATA's (large to small enclaves, banded lavas, megacrysts…) testify to the mingling event. Complete mixing is supposed to have been achieved in the “hybrid” BTA's which contain sanidine, plagioclase and clinopyroxene megacrysts in disequilibrium with their host. The megacrysts are interpreted as relicts of the trachytic end-member. Isotopic data on basic comagmatic enclaves and host ATA matrix samples from three different cycles of mingling (succession of heterogeneous pyroclastics, heterogeneous ATA lava flows or domes and occasionally homogeneous BTA lava flows) are not incompatible with two component mixing but could just reflect the heterogeneity of the analysed samples. However, the BTA's have Sr contents and Sr isotopic ratios which are too high to be simple binary mixing products between the postulated end-members. Three hypotheses are considered to explain this discrepancy: (1) the analysed end-members are not those involved in BTA genesis, (2) some crustal contamination occurred during and after the mixing event, (3) Sr-rich sanidine xenocrysts with radiogenic 87Sr/86Sr have been assimilated and digested in the BTA's. In this third hypothesis that I favour, it is not necessary to resort to magma mixing to explain the genesis of the BTA's: assimilation of xenocrysts by basaltic, hawaiitic or mugearitic magmas accounts for both mineralogical disequilibria and isotopic characteristics of these lavas. 相似文献
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Petrological and geochemical relationships between pyroxene megacrysts and associated alkali-basalts from Massif Central (France) 总被引：2，自引：0，他引：2
Major, trace element, and REE analyses, as well as Sr isotopic ratios, have been obtained on twelve clinopyene megacrysts and phenocrysts and their alkali-basalt hosts from the French Massif Central. Equilibrium between crystals and host was examined based on petrographic and geochemical data.Two types of pyroxenes are recognized: the acmite-bearing clinopyroxenes, rich in incompatible elements and the salitic clinopyroxenes, poor in incompatible elements. 87Sr/ 86Sr isotopic data reveal no significant difference between clinopyroxenes and host lavas: they are in apparent isotopic equilibrium. The Sr isotopic ratios of the two types of pyroxenes are also quite similar. However pyroxene crystals from the first group are not in equilibrium with their host; they have crystallized at high-pressure from differentiated alkali-lavas and have been incorporated in a more primitive magma. Pyroxene crystals from the second group are in apparent equilibrium with their host lava; they have crystallized at various pressures. For the latter, distribution coefficients are proposed for compatible elements, trace elements and REE. 相似文献
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Mineralium Deposita - Les paramètres physico-chimiques (pH, Eh, T, conductivité, alcalinité) des eaux de 31 puits ont été mesurés dans le chenal du calcrete... 相似文献
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