Redox potential measurements and Mössbauer spectrometry of Fe adsorbed onto Fe (oxyhydr)oxides     

Ewen Silvester  Laurent Charlet  Antoine Géhin  Emmanuelle Liger 《Geochimica et cosmochimica acta》2005,69(20):4801-4815

The redox properties of Fe^II adsorbed onto a series of Fe^III (oxyhydr)oxides (goethite, lepidocrocite, nano-sized ferric oxide hydrate (nano-FOH), and hydrous ferric oxide (HFO)) have been investigated by rest potential measurements at a platinum electrode, as a function of pH (−log₁₀[H⁺]) and surface coverage. Using the constant capacitance surface complexation model to describe Fe^II adsorption onto these substrates, theoretical values of the suspension redox potential (E_H) have been computed, under the assumption that Fe^II adsorption occurs at crystal growth sites of the substrate surface. Good agreement between calculated and experimental E_H values is observed for nano-FOH and HFO, however the redox potentials measured for lepidocrocite and goethite are significantly more oxidizing than predicted. Mössbauer spectroscopic analysis of ⁵⁷Fe^II adsorbed onto HFO and goethite shows that in both cases the adsorbed ⁵⁷Fe^II is incorporated into the crystal structure of the substrate, in broad agreement with the thermodynamic model, but is almost completely oxidized to ⁵⁷Fe^III. The mechanism by which the adsorbed ⁵⁷Fe^II is oxidized is not resolved in this work, but is thought to be due to electron transfer to the substrate, rather than a net oxidation of the suspension. The disagreement between experimental and calculated rest potential measurements in the goethite and lepidocrocite systems is thought to be due to the poor electrochemical equilibration of these suspensions with the platinum electrode, rather than a failure of the thermodynamic model. The model developed for the redox potential of adsorbed Fe^II allows direct assessment of the reactivity of this species towards oxidized pollutants.  相似文献   

Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene–Udine sector, NE Italy)     

F. Galadini  M. E. Poli  A. Zanferrari 《Geophysical Journal International》2005,161(3):739-762

  相似文献   

Morphometric analysis of magmatic enclaves: a tool for understanding magma vesiculation and ascent   总被引：3，自引：0，他引：3  

D. Perugini  G. Poli  N. Prosperini 《Lithos》2002,61(3-4):225-235

The extent of deformation of magmatic enclaves that occur in different portions of the Khaggiar endogenous lava dome (Island of Pantelleria, Italy) has been quantified using two morphometric techniques: thin-plate splines and fractals. Deformation of enclaves decreases from the outer portions of the dome to the more internal portions, defining two exponential trends. The amount and distribution of vesicles have also been quantified using image analysis of digital images obtained by a scanning electron microscope. The variation of deformation of enclaves correlates with the variation of their vesicle content, suggesting that deformation and vesiculation are related. We envisaged a continuous feedback system between vesiculation of enclaves and radial forces exerted by the surrounding host magma during the growth of the dome. These relationships are used as dynamic markers to infer the eruptive style of the endogenous dome. In particular, it is suggested that the variation of vesicularity of enclaves is related to the pressure exerted by magma on the extrusion vent. This resulted in enclaves being more vesicular and more deformed in the outer portions of the dome that emplaced first and at lower pressure, and less vesicular and less deformed in the more internal portions that emplaced later and at higher pressure. We interpret the occurrence of the two trends in the variation of deformation and porosity as related to two main eruptive pulses of dome growth.  相似文献   

Impact of ocean optical properties on seasonal SST: results with a surface ocean model coupled to the LMD AGCM     

Emmanuelle Cohen-Solal  Hervé Le Treut 《Climate Dynamics》1996,12(6):417-433

As the accuracy of ocean models improves, determination of the solar irradiance within the ocean may become important to simulate precisely the seasonal evolution of the SST. As ocean optical properties are not well documented in space and time, we have undertaken a sensitivity study to measure the corresponding SST uncertainties at a global scale using a model coupling the LMD AGCM with an integral mixed layer model and a thermodynamic sea ice representation. The downwelling irradiance formulation is that of Paulson and Simpson which has been tuned for the five water types of the Jerlov classification. Two sensitivity, and academic, experiments corresponding to a uniformly clear ocean or turbid ocean are carried out. Turbid waters exhibit, in general, a stronger seasonal cycle of the SST of about 2°C. The sensitivity is far from uniform, with a maximum in the subtropics and the mid-latitudes of the summer hemisphere. It corresponds precisely to the area in which the observed optical properties present a large temporal variability which is therefore likely to have an action on the seasonal cycle of the ocean surface temperatures. We perform a decomposition of the model sensitivity in four terms, corresponding to the direct impact of the water type change, feedback due to the mixed layer change, feedback due to the surface solar irradiance change, and feedback due to the non solar heat fluxes change. The first two terms dominate the SST change. The direct effect tends to increase the warming of the mixed layer. In addition, the mixed layer depth diminishes because of a higher stabilizing effect of solar radiation on the TKE budget. This tends to increase further summer warming of the SST as well as their winter cooling.  相似文献   

Tertiary anorogenic granites of the western border of the Yemen Plateau     

G. Capaldi  S. Chiesa  P. Manetti  G. Orsi  G. Poli 《Lithos》1987,20(6):433-444

North Yemen (Y.A.R.) was affected, from 30 to 20 Ma ago, by intense magmatic activity (Trap Series), contemporary with the main tensional tectonic phases of the Afro-Arabian Plate. In the Trap activity, two main phases have been recognized; the former, mainly basaltic, between 30 and 26 Ma; and the second, mainly acidic, between 23 and 20 Ma. During the latter period of activity, a basaltic dyke swarm and stock-like bodies and dykes (granophyres) were emplaced along the escarpment and coastal plain. Some granitic bodies intruded the Trap Series towards the end of the first phase and during the second one.

On the basis of geochemical and petrological data, the Tertiary granites of Yemen belong to alkaline or peralkaline associations of A-type. The textural characteristics indicate that the granites are either hypersolvus or subsolvus. The mafic mineral assemblages allow three main types of granites to be distinguished by their different environments of crystallization.

As regards the origin of these kinds of granites, several hypotheses account for the peculiarities observed. The lack of crustal xenoliths, the preliminary data on the Sr isotopic ratio, the data on major and trace elements point to a direct origin by fractional crystallization, without substantial crustal interaction. This agrees well with the strong tensile tectonics, linked with the uplift of the Afro-Arabian dome and with the lithosphere thinning, which provide a minimal opportunity for interaction of the magmas with the crust.  相似文献   

South Aegean volcanic arc: Geochemical variations and geotectonic implications     

F. Innocenti  P. Manetti  A. Peccerillo  G. Poli 《Bulletin of Volcanology》1981,44(3):377-391

The Aegean volcanic arc is one of the most important geological structure of the Mediterranean area. It is a belt of volcanic centers consisting of products ranging from basaltic, andesitic, dacitic to rhyolitic in composition, all of them displaying a typical calc-alkaline chemical character. The most abundant rock types are represented by andesites and dacites. Minor amounts of basalts and rhyolites occur mainly in the central-eastern sector of the arc. The REE, Rb, Sr, Ba, Th, Ta, Hf, Zr, Ni, Co, V and Cr abundances determined in 27 representative samples from different centers suggest that: 1) the intermediate and acidic terms are products of crystal/liquid fractionation processes starting from basic parent magmas: 2) large variations in incompatible elements occur in the most basic samples that are interpreted as evidence for heterogeneously LIL element-enriched mantle source; 3) plagioclase played a role in the evolution of the volcanic centers of the eastern and central arc different from that played in the volcanoes of the western sector. Along the arc, the differences in the distribution of lithological types, in the volumes of erupted material, in the volcanological characteristics of the different centers as well as in the patterns of trace element distribution in the volcanites are considered to be connected with the prevailing tectonic regime affecting the various sectors of the arc.  相似文献   

The composition of nanogranitoids in migmatites overlying the Ronda peridotites (Betic Cordillera,S Spain): the anatectic history of a polymetamorphic basement     

Antonio Acosta-Vigil  Amel Barich  Omar Bartoli  Carlos J. Garrido  Bernardo Cesare  Laurent Remusat  Stefano Poli  Caroline Raepsaet 《Contributions to Mineralogy and Petrology》2016,171(3):24

  相似文献   

The Upper Miocene magmatism of the Island of Elba (Central Italy): compositional characteristics,petrogenesis and implications for the origin of the Tuscany Magmatic Province     

Giampiero Poli  Angelo Peccerillo 《Mineralogy and Petrology》2016,110(4):421-445

  相似文献   

Influence of landscape morphology and vegetation cover on the sampling of mixed plutonic bodies     

D. Perugini  M. Petrelli  G. Poli 《Mineralogy and Petrology》2007,90(1-2):1-17

Summary A plethora of evidence indicates that magma mixing processes can take place at any evolutionary stage of magmatic systems and that they are extremely common in both plutonic and volcanic environments. Furthermore, recent studies have shown that the magma mixing process is governed by chaotic dynamics whose evolution in space and time generates complex compositional patterns. The fact that magma mixing processes can produce igneous bodies exhibiting a large compositional complexity brings up the key question about the potential pitfalls that may be associated with the sampling of these systems for petrological studies. In particular, since commonly only exiguous portions of the whole magmatic system are available as outcrops for sampling, it is important to address the point whether the sampling may be considered representative of the complexity of the magmatic system. Here, we attempt to address this crucial point by performing numerical simulations of magma mixing processes in 3D, and by evaluating the best conditions for sampling by considering different landscape morphologies and percentages of vegetation cover. It is shown that the goodness of sampling is strongly dependant on the roughness of the landscape, with highly irregular morphologies being the best candidates to give the most complete information on the whole magma body. Vegetation cover, on the contrary, does not appear to significantly influence the representativeness of sampling.  相似文献   

U-Pb SHRIMP zircon dating of andesite from the Dolomite area (NE Italy): geochronological evidence for the early onset of Permian Volcanism in the eastern part of the southern Alps     

Dario Visonà  Anna Maria Fioretti  Maria Eliana Poli  Adriano Zanferrari  Mark Fanning 《Swiss Journal of Geoscience》2007,100(2):313-324

The Athesian Volcanic District (AVD), a thick sequence of andesitic to rhyolitic lava and ignimbrite, overlies both the Variscan basement of the Dolomites and, where present, the continental basal conglomerate of Upper Carboniferous(?) to Early Permian age. This volcanic activity is known to mark the margin of the intra-Pangea megashear system between Gondwana and Laurasia, the onset age of which is determined in this study.SHRIMP U-Pb dating on zircon from Ponte Gardena/Waidbruck (Isarco/Eisack valley) basaltic andesite yields an age of 290.7 ± 3 Ma, providing the oldest record of andesite volcanic activity yet documented in the AVD. Two younger dates (279.9 ± 3.3 and 278.6 ± 3.1 Ma) obtained for the andesitic necks of M. dei Ginepri (Eores/Aferer valley) and Col Quaternà (western Comelico), respectively, probably represent a second pulse of andesite magmatic activity.Near Chiusa/Klausen, the volcanoclastic deposits at the bottom of the Funes/Villnöss valley volcano-sedimentary complex only contain detrital zircons, dated at 469 ± 6 Ma; these probably derive from erosion of Paleozoic porphyroids. Other zircons from the same sediments and inherited cores of magmatic andesite crystals give Paleoproterozoic (1953.6 ± 22.1, 1834.6 ± 69.3, 1773.6 ± 25.1 Ma), Early Neoproterozoic (1015 ± 14 Ma) and Late Neoproterozoic (728.4 ± 9.6, 687.6 ± 7.6 Ma) ages. These ancient detrital and inherited zircon ages fit the model that envisages the Dolomite region as being tectonically coherent with Africa, at least until the Lower Permian.  相似文献