Chemical mass balance of calcrete genesis on the Toledo granite (Spain)   总被引：2，自引：0，他引：2  

Arnaud Chiquet  Fabrice Colin  Bruno Hamelin  Annie Michard  Daniel Nahon   《Chemical Geology》2000,170(1-4):19-35

The chemical mass balance of calcrete genesis is studied on a typical sequence developed in granite, in the Toledo mountains, Central Spain.

Field evidence and petrographic observations indicate that the texture and the bulk volume of the parent rock are strictly preserved all along the studied calcrete profile.

Microscopic observations indicate that the calcitization process starts within the saprolite, superimposed on the usual mechanisms of granite weathering: the fresh rock is first weathered to secondary clays, mainly smectites, which are then pseudomorphically replaced by calcite. Based on this evidence, chemical mass transfers are calculated, assuming iso-volume transformation from the parent rock to the calcrete.

The mass balance results show the increasing loss of matter due to weathering of the primary phases, from the saprolite towards the calcrete layers higher in the sequence. Zr, Ti or Th, which are classically considered as immobile during weathering, are also depleted along the profile, especially in the calcrete layer. This results from the prevailing highly alkaline conditions, which could account for the simultaneous precipitation of CaCO₃ and silicate dissolution.

The calculated budget suggests that the elements exported from the weathering profile are provided dominantly by the weathering of plagioclase and biotite. We calculate that 8–42% of the original Ca remains in granitic relics, while only 15% of the authigenic Ca released by weathering is reincorporated in the calcite. This suggests that 373 kg/m² of calcium (i.e., three times the original amount) is imported into the calcrete from allochtonous sources, probably due to aeolian transport from distant limestone formations.  相似文献   

Photoelectric observations of CH Cygni during the explosive phases of 1967–68     

Bruno Cester 《Astrophysics and Space Science》1969,3(1):198-204

Observations made at Trieste in 1967 and 1968 of CH Cygni reveal a strong variability, particularly in U colour. From the observed colours, a suggestion is made about the existence of a hot companion which could be a subdwarf.Presented at the Trieste Colloquium on Mass Loss from Stars, September 12–16, 1968.  相似文献   

Precision measurement of the Sun's gravitational field by means of the twin probe method     

Bruno Bertotti  Giuseppe Colombo 《Astrophysics and Space Science》1972,17(1):223-237

An accurate measurement of the gravitational field of the Sun, needed for the verification of the theories of gravitation, requires the use of a geodesic test body. To eliminate the effect of non-gravitational forces (mainly the solar radiation pressure) we propose to use two twin space probes, whose surface has identical geometrical and optical properties, but with different mass. Their differential motion leads to the determination of the motion of an ideal geodesic point. We discuss in detail the various conditions which are needed to ensure the required degree of identity and submit as a possible solution two cylindrical probes, whose sides are covered by cavities to make them absorbing, rotating at a fast rate around an axis orthogonal to the ecliptic plane. We discuss briefly also the accuracy in the determination of the parameters of the metric field of the Sun obtainable from range measurements.Work done at the European Space Research Institute, Frascati, Italy  相似文献   

Sediments and pollution in the Northern Adriatic Sea: a statistical analysis     

Pietro Mantovan  Laura Menegazzo Vitturi  Bruno Pavoni  Sandro Rabitti 《Continental Shelf Research》1985,4(3):321-340

Data concerning grain-size distribution, mineralogy, geochemistry, and chlorinated hydrocarbon concentrations, obtained from 246 surface sediment samples collected in the Northern Adriatic sea (Italian area), provide the basis for a multivariate statistical analysis which evaluates the influence of riverine inputs, the differences among various depositional environments and the presence of polluted zones.Cluster analysis applied to grain size has identified nine groups of lithotypes associated with the morphology and the hydrology of the basin.In the Gulf of Venice, principal component analysis on clay minerals and carbonates has permitted recognition of two main areas located north and south of the Brenta river. More subareas correspond to other lithological types.Principal component analysis of nine metal (Hg, Cd, Cu, Pb, Cr, Zn, Fe, Ni, and Co) concentrations reveals that the studied sea area is more complex from the geochemical point of view. Three geochemical zones related to riverine inputs, different lithotypes and specific forms of contamination are identified. High pollution of both halocarbons and heavy metals is associated with fine grain size.  相似文献   

Multiphase model for inclusion‐reinforced geostructures: Application to rock‐bolted tunnels and piled raft foundations     

Bruno Sudret  Patrick de Buhan 《国际地质力学数值与分析法杂志》2001,25(2):155-182

A multiphase model is proposed to describe the mechanical behaviour of geomaterials reinforced by linear inclusions. This macroscopic approach considers the reinforced soil or rock mass as the superposition of continuous media. Equations of motion and constitutive laws of the model are first derived. Its implementation in a finite element computer code is then detailed. A modified implicit algorithm for elastoplastic problems is proposed. The model and its implementation are fully validated for rock‐bolted tunnels (comparison with scale model experiments) and piled raft foundations (comparison with the classical ‘hybrid method’). The Messeturm case history is finally presented to assess the handiness of the approach for real structures. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Carbon and oxygen diffusion in calcite: Effects of Mn content and P H2O     

Andreas K. Kronenberg  Richard A. Yund  Bruno J. Giletti 《Physics and Chemistry of Minerals》1984,11(3):101-112

The diffusion rates of carbon and oxygen in two calcite crystals of different Mn contents have been studied between 500° and 800° C in a CO₂-H₂O atmosphere (P _{CO 2}=1?5 bars, P _H2_O=0.02?24 bars) labeled with ¹³C and ¹⁸O. Isotope concentration gradients within annealed specimens were measured using a secondary ion microprobe by depth profiling parallel and perpendicular to the c axis. Despite the anisotropic structure of calcite, the diffusion of carbon and oxygen are both very nearly isotropic. Least-squares fitting of the carbon data to an Arrhenius relation gives an activation energy of 87±2 kcal/mole, with D ₀ terms dependent only slightly upon direction: 1 $$D_{\text{0}} {\text{(}}\parallel c{\text{) = }}\left( {9\frac{{ + 12}}{{ - 5}}} \right){\text{x10}}^{\text{2}} cm^2 /s$$ , 2 $$D_{\text{0}} {\text{(}} \bot c{\text{) = }}\left( {5\frac{{ + 6}}{{ - 3}}} \right){\text{x10}}^{\text{2}} cm^2 /s$$ . These results are in close agreement with previous determinations. Results for oxygen diffusion, however, give D values much larger than those previously reported for dry conditions; at 650° to 800° C the D values are two orders of magnitude larger. The diffusion of oxygen, unlike carbon, is strongly dependent on water pressure, as well as Mn content, and does not fit an Arrhenius relation over the entire temperature range. On the basis of these observations and considerations of the defect chemistry of calcite, it is proposed that carbon migrates as a Frenkel pair. The diffusion of oxygen, however, appears to be more complicated and may depend upon several simultaneous mechanisms.  相似文献   

Systematique U-Pb et Evolution du Gisement d'Uranium de Lodève (France)     

Joël R. Lancelot  Bruno de Saint André  Henri de la Boisse 《Mineralium Deposita》1984,19(1):44-53

Résumé Considérée comme syngénétique ou diagénétique précoce, la minéralisation uranifère de la couche 0 de l'Autunien du bassin de Lodève a été étudiée par la méthode U-Pb sur roches totales. Les données U-Pb démontrent l'existence de perte en radon, principalement dans la chaine de désintégration de ²³⁸U, et l'intérêt de l'utilisation du couple ²⁰⁷Pb-²³⁵U pour la détermination des âges de cristallisation des concentrations uranifères. Pour la couche 0, deux phases de remobilisation de l'uranium et du plomb ont pu être déterminées respectivement à 173±6 Ma et 108±5 Ma. La plus ancienne de ces deux phases est la plus marquée dans les échantillons étudiés, dont les systèmes U-Pb ne montrent pas la mémoire d'une concentration uranifère permienne. La première mobilisation de l'uranium et du plomb s'est faite lors d'une phase de distension à 160–170 Ma, affectant la croûte continentale du Sud du Massif Central. Cette phase a provoqué la circulation de fluides minéralisés et est marquée par une recristallisation des illites des pélites permiennes entre 100 et 200 °C (du fait de l'élévation du gradient géothermique) et par la mise en place d'un volcanisme d'origine mantellique daté à 155±6 Ma. La composition isotopique en plomb d'une galène de l'Autunien du Lodévois, est analogue à celles des feldspaths des granitoïdes du Massif Central français et à celles des galènes des minéralisations stratiformes de Pb-Zn des Causses, ce qui fournit un argument pour faire dériver au moins une partie des métaux en traces dans les pélites autuniennes de l'altération de la croûte continentale hercynienne environnante.

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In the Lodeve basin, the uraniferous mineralization associated with the autunian pelitic layer 0 is usually considered as syngenetic or early diagenetic. U-Pb isotopic data performed on U bearing whole rocks demonstrate occurrence of radon losses, mainly in the ²³⁸U decay series; the ²⁰⁷Pb-²³⁵U geochronometer is particularly suitable to date U-Pb systems disturbed by such radon losses. For the autunian layer 0, two U-Pb mobilization phases have been respectively recognized at 173±6 Ma and 108±5 Ma. The oldest phase is the most clearly expressed in the studied samples, no memory of a permian age could be recognized in the U-Pb systems. The first U-Pb mobilization occurred 170 Ma ago, during a distension phase of the continental crust. This phase induced circulations of mineralized fluids, illite recristallization in the permian pelites at temperatures ranging from 100 to 200 °C and emplacement of a mantellic volcanism recently dated at 155±6 Ma. A galena from the Autunian of the Lodeve basin, the feldspars of the surrounding variscan granitoïds and galenas of mesozoïc stratiform deposits in the Causses, present similar Pb isotopic composition, which is in agreement with the hypothesis that some metals of the autunian pelites originated in the surrounding weathered variscan continental crust.

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Structural modifications in clinopyroxene solid solutions: The Ca-Mg and Ca-Sr substitutions in the diopside structure     

Piera Benna  G. Chiari  E. Bruno 《Mineralogy and Petrology》1987,36(1):71-84

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On the advection of turdidity in the saint lawrence middle estuary     

Bruno d'Anglejan 《Estuaries and Coasts》1981,4(1):2-15

The suspension transport away from the extensive turbidity zone of the St. Lawrence estuary is largely determined by the channel topography. The suspended sediments are advected downstream by a 40 km long turbid plume which takes its source in a turbidity maximum at the head of the estuary and flows downstream partly confined by the South Channel. During the ebbing phase of tidal cycles, the turbid waters of the plume are forced downstream through narrow converging sections of the channel, and slowed down through more opened diverging regions, particularly down-stream of the St. Roch Traverse. These, large fluctuations in stratification modulate the vertical transport of suspended material from the bottom to the surface layer. Midway down the estuary, dispersion of the plume occurs along a frontal zone which seasonally migrates 30 km or more in response to changes in fresh water discharge. The plume is reinforced and the turbidity gradient is intensified by local injections of inshore waters from Ste. Anne Bay, a subtidal platform highly enriched in suspended material by intertidal exchanges with large mudllats. Lateral erosion of the plume and cross-channel transport of suspended matter from the South into the North Channel is made possible by large horizontal shears developing in the central part of the middle estuary during the early flood. These are created by a one-hour tidal phase difference between the North and the South Channel.  相似文献   

Fractionation of carbon and hydrogen isotopes by methane-oxidizing bacteria   总被引：1，自引：0，他引：1  

Dennis D. Coleman  J.Bruno Risatti  Martin Schoell 《Geochimica et cosmochimica acta》1981,45(7):1033-1037

Carbon isotopic analysis of methane has become a popular technique in the exploration for oil and gas because it can be used to differentiate between thermogenic and microbial gas and can sometimes be used for gas-source rock correlations. Methane-oxidizing bacteria, however, can significantly change the carbon isotopic composition of methane; the origin of gas that has been partially oxidized by these bacteria could therefore be misinterpreted.We cultured methane-oxidizing bacteria at two different temperatures and monitored the carbon and hydrogen isotopic compositions of the residual methane. The residual methane was enriched in both ¹³C and D. For both isotopic species, the enrichment at equivalent levels of conversion was greater at 26°C than at 11.5°C. The change in δD relative to the change in δ¹³C was independent of temperature within the range studied. One culture exhibited a change in the fractionation pattern for carbon (but not for hydrogen) midway through the experiment, suggesting that bacterial oxidation of methane may occur via more than one pathway.The change in the δD value for the residual methane was from 8 to 14 times greater than the change in the δ¹³C value, indicating that combined carbon and hydrogen isotopic analysis may be an effective way of identifying methane which has been subjected to partial oxidation by bacteria.  相似文献