In the context of radioactive waste repository in geological formation, kaolinite-metallic iron interaction in chlorine solution was conducted in batch experiments, under anoxic conditions at 90 °C during 9 months. After a mineralogical characterization at a global scale, products were analyzed at the micrometer and nanometer scales by X-ray absorption spectroscopic techniques (XAS and STXM). Absorption at Al, Si and Fe edges was investigated to have a complete overview of the distribution and status of constituting elements. Whereas Si K-edge results do not evidence significant evolution of silicon status, investigations at Al K-edge and Fe L-edges demonstrate variations at aggregate and particle scales of IVAl:VIAl and Fe2+:Fe3+ ratios. Spectroscopic data evidence the systematic crystallization of Fe-serpentines onto the remaining particles of kaolinite and the absence of pure species (kaolinite or Fe-serpentines). Combination of spatially resolved spectroscopic analyses and TEM-EDXS elemental distribution aims to calculate unit cell formulae of Fe-serpentines layers and abundance of each species in mixed particles. For most of the investigated particles, results reveal that the variations of particles composition are directly linked to the relative contributions of kaolinite and Fe-berthierine in mixed particles. However, for some particles, microscale investigations evidence crystallization of two other Fe-serpentines species, devoid of aluminum, cronstedtite and greenalite. 相似文献
In the Pointe Géologie area (66°40 S; 140°00 E; Terre Adélie, East Antarctica), the Paleoproterozoic basement consists in a migmatitic complex of metasedimentary origin. Metasediments underwent a thermal event, leading to the high-grade amphibolite facies assemblages biotite–cordierite–sillimanite and to dehydration melting reactions at 4–6 kbar and 700±50 °C, followed by retrogression in greenschist facies.
In most of the archipelago, K-feldspar gneisses (KFG) are characterized by a Sil+Crd+Kfs+Bt assemblage and many K-feldspar-rich leucosomes. Locally, a spectacular rock type occurs as North dipping bands of about 10 m thick and consists in nodular gneisses (NG) that display less abundant, K-feldspar-poor leucosomes.
Commonly, the retrograde imprint facies is quite weak in KFG and only expressed by sporadic Bt–Ms±And equilibrium assemblage, whereas it developed more extensively in NG. A pseudosection calculated at constant P=4 kbar shows that the differences between NG and KFG assemblages can be considered to be mainly driven by difference in H2O proportions and much less by differences in FeO/MgO or K2O/MgO ratios. The hydrated assemblage (Bt–Ms nodules) in NG requires at least 10–20% more H2O than the Crd+Kfs+Sil/And assemblage does in KFG. Parageneses and mineral compositions indicate that this difference in H2O occurred early in the history, at least as early as the anatectic stage. Therefore, differences between NG and KFG are related to the variation in partial melting features (water distribution, proportion of melt extraction), which appears to be spatially controlled by cryptic tectonic structures. The particular shape and orientation of NG bands are interpreted as a complex history of melt extraction in the Pointe Géologie area which could involve a two stage melting process. 相似文献
Although seawater concentration of tributyltin (TBT) should decrease when the direct inputs from ship hulls will cease after the incoming world ban of organotin-based antifouling paints in 2003 or later, the TBT environmental issue will still be present for decades as contaminated sediments in shallow waters will be acting as a long-lasting reservoir for TBT and its degradation products. The lost of TBT to the atmosphere by volatilization has already been proposed as a part of its molecular motion through the aquatic environment but most recent calculated values of water-to-air rate of exchange of TBT (from 20 to 510 nmol m−2 year−1) do not take into account the potential contribution of aerosols ejection to the atmosphere upon bubbles bursting, an important process for pollutants transport in the marine environment. In this work, an experimental approach to measure the seawater-to-air flux of TBT mediated by bubbles bursting is described, and the influence of phytoplankton cells and dissolved organic matter from exudates and culture weathering on flux rates was assessed. The results demonstrate that TBT can be transferred from water to air via the ejection of droplets from bubbles bursting and that cell density strongly affected the transfer. Under a bubbling regime, the water-to-air flux (pmol TBT cm−2 min−1 level) is estimated up to 1000-fold the flux measured for the molecular diffusion and volatilization under static quiescent conditions. The surface microlayer acted as a transient boundary between the water column and the atmosphere where the dynamic of TBT accumulation has the same trend as the dynamic of TBT ejection. This physical transfer mechanism might be of high significance in nearshore environments, harbors, and shallow channels where clouds of bubbles generated in the wake of large ships play an important role for the atmosphere/seawater chemical exchanges. 相似文献
The distribution of iron atoms in the octahedral sheet of a series of dioctahedral smectites with varying unit-cell composition and iron content was investigated by Fe K-edge XAS spectroscopy. First-step analysis reveals that the patterns corresponding to backscattering by atoms located between 3 and 4 Å from the absorbing atom are very sensitive to the relative amount of light (Si, Al, Mg) and heavy (Fe) atoms. Detailed modelling of this domain then provides valuable information on the number of iron atoms surrounding octahedral iron. By comparing the number of iron neighbours deduced from EXAFS with that determined from unit-cell composition assuming a statistical distribution, three groups of montmorillonites can be distinguished: (1) clay samples from Wyoming display an ordered distribution of iron atoms; (2) clay samples from Georgia, Milos, China and Washington exhibit a close to random distribution of iron atoms; (3) clay samples from North Africa, Germany, Texas and Arizona display extensive iron clustering. These results complement previously obtained IR results and show that the combination of these two spectroscopic techniques could provide an additional crystal-chemistry-based framework for typological analysis of montmorillonite deposits. 相似文献
The inherited localization model for shear zone development suggests that ductile deformation in the middle and lower continental crust is localized on mechanical anisotropies, like fractures, referred to as shear zone brittle precursors. In the Neves area (Western Tauern Window, Eastern Alps), although the structural control of these brittle precursors on ductile strain localization is well established, the relative timing of the brittle deformation and associated localized fluid flow with respect to ductile deformation remains in most cases a matter of debate. The present petrological study, carried out on a brittle precursor of a shear zone affecting the Neves metagranodiorite, aims to determine whether brittle and ductile deformations are concomitant and therefore relate to the same tectonic event. The brittle precursor consists of a 100–500 µm wide recrystallized zone with a host mineral‐controlled stable mineral assemblage composed of plagioclase–garnet–quartz–biotite–zoisite±white mica±pyrite. Plagioclase and garnet preserve an internal compositional zoning interpreted as the fingerprint of Alpine metamorphism and fluid–rock interactions concomitant with the brittle deformation. Phase equilibrium modelling of this garnet‐bearing brittle precursor shows that metamorphic garnet and plagioclase both nucleated at 0.6 ± 0.05 GPa, 500 ± 20°C and then grew along a prograde path to 0.75 ± 0.05 GPa, 530 ± 20°C. These amphibolite facies conditions are similar to those inferred from ductile shear zones from the same area, suggesting that both brittle and ductile deformation were active in the ductile realm above 500°C for a depth range between 17 and 21 km. We speculate that the Neves area fulfils most of the required conditions to have hosted slow earthquakes during Alpine continental collision, that is, coupled frictional and viscous deformation under high‐fluid pressure conditions ~450°C. Further investigation of this potential geological record is required to demonstrate that slow earthquakes may not be restricted to subduction zones but are also very likely to occur in modern continental collision settings. 相似文献
Despite the key importance of altered oceanic mantle as a repository and carrier of light elements (B, Li, and Be) to depth, its inventory of these elements has hardly been explored and quantified. In order to constrain the systematics and budget of these elements we have studied samples of highly serpentinized (>50%) spinel harzburgite drilled at the Mid-Atlantic Ridge (Fifteen-Twenty Fracture zone, ODP Leg 209, Sites 1272A and 1274A). In-situ analysis by secondary ion mass spectrometry reveals that the B, Li and Be contents of mantle minerals (olivine, orthopyroxene, and clinopyroxene) remain unchanged during serpentinization. B and Li abundances largely correspond to those of unaltered mantle minerals whereas Be is close to the detection limit. The Li contents of clinopyroxene are slightly higher (0.44-2.8 μg g−1) compared to unaltered mantle clinopyroxene, and olivine and clinopyroxene show an inverse Li partitioning compared to literature data. These findings along with textural observations and major element composition obtained from microprobe analysis suggest reaction of the peridotites with a mafic silicate melt before serpentinization. Serpentine minerals are enriched in B (most values between 10 and 100 μg g−1), depleted in Li (most values below 1 μg g−1) compared to the primary phases, with considerable variation within and between samples. Be is at the detection limit. Analysis of whole rock samples by prompt gamma activation shows that serpentinization tends to increase B (10.4-65.0 μg g−1), H2O and Cl contents and to lower Li contents (0.07-3.37 μg g−1) of peridotites, implying that—contrary to alteration of oceanic crust—B is fractionated from Li and that the B and Li inventory should depend essentially on rock-water ratios. Based on our results and on literature data, we calculate the inventory of B and Li contained in the oceanic lithosphere, and its partitioning between crust and mantle as a function of plate characteristics. We model four cases, an ODP Leg 209-type lithosphere with almost no igneous crust, and a Semail-type lithosphere with a thick igneous crust, both at 1 and 75 Ma, respectively. The results show that the Li contents of the oceanic lithosphere are highly variable (17-307 kg in a column of 1 m × 1 m × thickness of the lithosphere (kg/col)). They are controlled by the primary mantle phases and by altered crust, whereas the B contents (25-904 kg/col) depend entirely on serpentinization. In all cases, large quantities of B reside in the uppermost part of the plate and could hence be easily liberated during slab dehydration. The most prominent input of Li into subduction zones is to be expected from Semail-type lithosphere because most of the Li is stored at shallow levels in the plate. Subducting an ODP Leg 209-type lithosphere would mean only very little Li contribution from the slab. Serpentinized mantle thus plays an important role in B recycling in subduction zones, but it is of lesser importance for Li. 相似文献
Several classes of cosmic objects, such as Young Stellar Objects, Active Galactic Nuclei, Micro-Quasars, Pulsars and probably Gamma Ray Bursts, display powerful winds and jets; for some of them the flow is even ultrarelativistic. For all these classes of objects, the magnetic field is supposed to play a major role in launching and collimating the flow, together with the angular momentum transfer. It probably plays an important role for the turbulent transport in accretion disks also. Regarding the high energy radiation of relativistic jets and the cosmic ray generation, the magnetic field is of course the acceleration agent and could produce the Ultra High Energy Cosmic Rays in some extragalactic objects. The main growth points of these topics are presented, mostly in the case of black hole environments; the case of Young Stellar Objects is more complicated because of the interaction of the stellar magnetosphere with the accretion disk, and the models for this interaction are not yet founded on a reliable theory. 相似文献