Phosphorus sequestration in Fe-rich sediments from two Brazilian tropical reservoirs     

R. Fonseca  T. Canário  M. Morais  F.J.A.S. Barriga 《Applied Geochemistry》2011,26(9-10):1607-1622

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Sulfide oxidation as a process for the formation of copper-rich magmatic sulfides   总被引：1，自引：0，他引：1  

Cora C. Wohlgemuth-Ueberwasser  Raúl O. C. Fonseca  Chris Ballhaus  Jasper Berndt 《Mineralium Deposita》2013,48(1):115-127

Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic Cu/Fe ratio of these sulfides is typically less than unity. However, there are rare magmatic sulfide occurrences that are dominated by Cu-rich sulfides (e.g., bornite, digenite, and chalcopyrite, sometimes coexisting with metallic Cu) with atomic Cu/Fe as high as 5. Typically, these types of sulfide assemblages occur in the upper parts of moderately to highly fractionated layered mafic–ultramafic intrusions, a well-known example being the Pd/Au reef in the Upper Middle Zone of the Skaergaard intrusion. Processes proposed to explain why these sulfides are so unusually rich in Cu include fractional crystallization of Fe/(Ni) monosulfide and infiltration of postmagmatic Cu-rich fluids. In this contribution, we explore and experimentally evaluate a third possibility: that Cu-rich magmatic sulfides may be the result of magmatic oxidation. FeS-dominated Ni/Cu-bearing sulfides were equilibrated at variable oxygen fugacities in both open and closed system. Our results show that the Cu/Fe ratio of the sulfide melt increases as a function of oxygen fugacity due to the preferential conversion of FeS into FeO and FeO_1.5, and the resistance of Cu₂S to being converted into an oxide component even at oxygen fugacities characteristic of the sulfide/sulfate transition (above FMQ?+?1). This phenomenon will lead to an increase in the metal/S ratio of a sulfide liquid and will also depress its liquidus temperature. As such, any modeling of the sulfide liquid line of descent in magmatic sulfide complexes needs to address this issue.  相似文献   

Spatio-Temporal Patterns of Submerged Macrophytes in Three Hydrologically Altered Mediterranean Coastal Lagoons     

Patricia Prado  Nuno Caiola  Carles Ibáñez 《Estuaries and Coasts》2013,36(2):414-429

Rice cultivation in the Ebro Delta (Catalonia, Spain) has inverted the natural hydrological cycles of coastal lagoons and decreased water salinities for over 150 years. Adjustments in the water management practices—in terms of source and amount of freshwater inputs—have resulted in changes in the diversity, distribution and productivity of submerged angiosperms. Between the 1970s and late 1980s, a massive decline of the aquatic vegetation occurred in the Encanyissada–Clot and Tancada lagoons, but little information on the status is available after the recovery of macrophytes in the 1990s. Here, we evaluate the influence of salinity regimes resulting from current water management practices on the composition, distribution, seasonal abundance and flowering rates of submersed macrophytes, as well as on the occurrence of epiphyte and drift macroalgae blooms in three coastal lagoons. Our results show that Ruppia cirrhosa is the dominant species in the Encanyissada lagoon (185.97?±?29.74 g?DW?m^?2?year^?1; 12–27?‰ salinity) and the only plant species found in the Tancada lagoon (53.26?±?10.94 g?DW?m²?year^?1; 16–28?‰ salinity). Flowering of R. cirrhosa (up to 1,011?±?121 flowers?m^?2) was only observed within the Encanyissada and suggests that mesohaline summer conditions may favor these events. In contrast, low salinities in Clot lagoon (～3–12?‰) favor the development of Potamogeton pectinatus (130.53?±?13.79 g?DW?m²?year^?1) with intersperse R. cirrhosa (8.58?±?1.71 g?DW?m^?2) and mixed stands of P. pectinatus and Najas marina (up to ～57 g?DW?m^?2?year^?1) in some reduced areas. The peak biomasses observed during the study are 88 to 95 % lower than maximum values reported in the literature at similar salinities, and there is also little or no recovery in some areas compared to last reports more than 20 years ago. The main management actions to restore the natural diversity and productivity of submersed angiosperms, such as the recovering of the seagrass Zostera noltii, should be the increase of salinity during the period of rice cultivation, by reducing freshwater inputs and increasing flushing connections with the bays.  相似文献   

Effects of alkaline-activated fly ash and Portland cement on soft soil stabilisation     

Nuno Cristelo  Stephanie Glendinning  Lisete Fernandes  Amândio Teixeira Pinto 《Acta Geotechnica》2013,8(4):395-405

This paper studies the effects of sodium-based alkaline activators and class F fly ash on soil stabilisation. Using the unconfined compressive strength test (UCS), the effectiveness of this binder is compared with that of a common cement-based binder. Influence of the activator/ash ratio, sodium oxide/ash ratio and sodium hydroxide concentration was also analysed. Sodium hydroxide concentrations of 10, 12.5 and 15 molal were used for the alkaline-activated specimens (AA), with activator/ash ratios between 1 and 2.5 and ash percentages of 20, 30 and 40 %, relatively to the total solids (soil + ash). UCS was determined at curing periods of 7, 28, 90 and 365 days, and the most effective mixtures were analysed for mineralogy with XRD. The results showed a clear increase in strength with decreasing activator/ash ratio (up to a maximum of 43.4 MPa), which is a positive result since the activator is the most expensive component in the mixture. Finally, UCS results of the cement and AA samples, at 28 days curing, were very similar. However, AA results proved to be just between 20 and 40 % of the maximum UCS obtained at 1 year curing, while cement results at 28 days are expected to be between 80 and 90 % of its maximum.  相似文献   

Heavy metal accumulation in mangrove sediments surrounding a large waste reservoir of a local metallurgical plant, Sepetiba Bay, SE, Brazil     

E. F. Fonseca  J. A. Baptista Neto  C. G. Silva 《Environmental Earth Sciences》2013,70(2):643-650

Due to the growing rate of urbanization and a rapid and unplanned development in many tropical coastal areas, there continues to be an increasing concern in relation to the impact of anthropogenic activities on mangrove sediments. In southeastern Brazil, the Sepetiba Bay becomes an example of an ecosystem in the process of accelerated degradation. Previous studies highlighted the activities related with zinc processing by an industry on the Madeira’s Island as one of the main source of heavy metal to Sepetiba Bay. Despite the end of the industrial activities in the area, the waste reservoir became the main source of pollutant to the surrounding area. Analyses of Cd, Pb, Cu, Cr, Hg, Ni, Zn, particle size and nutrients of 20 sediment samples collected in the mangrove of the Madeira Island showed that the waste reservoir is the main source of contaminant to the mangrove. The statistic analyses showed that the moisture content and organic matter play an important role in the geochemical dynamic of heavy metal in the area.  相似文献   

Transition zone structure under a stationary hot spot: Cape Verde     

George Helffrich  Bruno Faria  João F.B.D. Fonseca  Alexandra Lodge  Satoshi Kaneshima 《Earth and Planetary Science Letters》2010,289(1-2):156-161

We report on a two-year seismic deployment in the Cape Verde Islands, one goal of which was to study the upper mantle to determine its structure under a hot spot that is stationary in the hot spot reference frame. We find from analysis of P-to-S receiver functions estimated from broadband seismic recordings that, within uncertainty, the time separation between the 410 and 660 km discontinuities is normal compared to radial earth models. Thus, to exist, even stationary hot spots do not require vertical thermal anomalies from deep melting sources anchored in the lower mantle or at the core–mantle boundary or their anomalies are narrower than ～ 250 km in the upper mantle.  相似文献   

Sensitivity analysis of a morphodynamic modelling system applied to a coastal lagoon inlet     

Sandra Plecha  Paulo A. Silva  Nuno Vaz  Xavier Bertin  Anabela Oliveira  André B. Fortunato  João M. Dias 《Ocean Dynamics》2010,60(2):275-284

This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the 2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period of 3 years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.  相似文献   

Seismic analysis of a building block     

Nuno Neves  António Arêde  Aníbal Costa 《Bulletin of Earthquake Engineering》2012,10(1):235-267

This paper reports on the study of the seismic response of an urban building block located in Faial, a town of the Horta Island of the Azores, Portugal. The work fits within the framework of studying strengthening schemes suitable for the reconstruction process of a town damaged by an earthquake action and includes numerical modelling of all the building blocks with calibration of material and structural parameters based on ambient vibration tests. The study aims at understanding a number of issues that are likely to influence the global behaviour of the block and the local response of individual buildings, namely the group effect of adjacent constructions, the in-plane stiffness of floors and/or roofs and the presence of possible localized strengthening interventions in selected parts of the block.  相似文献   

Mineralogy and geochemistry of trace metals and REE in volcanic massive sulfide host rocks,stream sediments,stream waters and acid mine drainage from the Lousal mine area (Iberian Pyrite Belt,Portugal)     

E. Ferreira da Silva  I. Bobos  J. Xavier Matos  C. Patinha  A.P. Reis  E. Cardoso Fonseca 《Applied Geochemistry》2009

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Mechanics of thick-skinned Variscan overprinting of Cadomian basement (Iberian Variscides)     

António Ribeiro  José Munhá  António Mateus  Paulo Fonseca  Eurico Pereira  Fernando Noronha  José Romão  José Rodrigues  Paulo Castro  Carlos Meireles  Narciso Ferreira 《Comptes Rendus Geoscience》2009,341(2-3):127-139

Remnants of the Cadomian basement can be found in the Iberian Variscides (IBVA) in several key sectors of its autochthonous units (composed of Neoproterozoic to Lower Palaeozoic metasedimentary sequences) and within the Continental Allochthonous Terrane (CAT). Comprehensive characterization of these critical exposures shows that the prevailing features are related to major geological events dated within the age range of 620–540 Ma. Indeed, near the Cambrian–Ordovician boundary, the IBVA Internal Zones experienced pervasive basement thinning and cover thickening, reflecting diffusive displacement of intracratonic rifting that continued until Lower Devonian times. In the thick-skinned Internal Zones, Helvetic/Penninic style nappes were generated, whereas flower upright axial structures developed along transpressive, intraplate shear zones. These features contrast with those preserved in the thin-skinned IBVA External Zones, dominated by décollements above (un-)deformed Palaeozoic and Cadomian basement. The inferred attenuation of rheological contrast between Cadomian basement and Palaeozoic cover can be explained by inherited fabrics due to thermal softening operated during the Cambrian–Lower Devonian extensional regime. Deeper décollements (and subsequent strain partitioning) are also expected to develop at the upper-lower crust (and at the Moho?) transition, as imaged by the available seismic profiling and MT surveys. The whole data implies a significant discontinuity between Cadomian and Variscan Cycles that should have constrained subsequent lithospheric evolution.  相似文献