Equilibration Scales in Silicic to Intermediate Magmas Implications for Experimental Studies   总被引：5，自引：0，他引：5  

Pichavant  Michel; Costa  Fidel; Burgisser  Alain; Scaillet  Bruno; Martel  Caroline; Poussineau  Stephane 《Journal of Petrology》2007,48(10):1955-1972

Experimental phase equilibrium studies are increasingly beingused for the determination of intensive variables (P, T, fH₂O,fO₂ ) in silicic to intermediate magmas. In contrast, silicicigneous bodies are now perceived as open, periodically recharged,systems involving only limited chemical equilibration. Thus,the use of laboratory-determined crystal–liquid equilibriumdata needs clarification. Here we review the field, petrologicaland geochemical evidence concerning states and scales of chemicalequilibrium in silicic magma bodies. It is concluded that totalchemical equilibrium is generally not the rule. However, a subsystemin local equilibrium (the reactive magma) can be identified.Equilibration scales in silicic magmas are rate-limited eitherby diffusive flux in crystals (DICL regime) or by diffusiveflux in the melt (MD regime). The recognition that equilibriumin magmas is limited to a reactive subsystem requires phaseequilibrium studies to be chemically scaled. Experiments, eitherof total or partial equilibrium type, should aim at a closereproduction of equilibrium states specific to natural systems.The laboratory reconstruction of the natural equilibrium statesguarantees a precise determination of the pre-eruptive parametersand a reliable application of the experimental data to activevolcanic systems. KEY WORDS: silicic magmas; chemical equilibrium; timescales; experimental studies  相似文献   

Quantifying garnet-melt trace element partitioning using lattice-strain theory: new crystal-chemical and thermodynamic constraints   总被引：1，自引：0，他引：1  

Wim van Westrenen  David S. Draper 《Contributions to Mineralogy and Petrology》2007,154(6):717-730

  相似文献   

Effects of orientation on the diffusive properties of fluid-filled grain boundaries during pressure solution     

R. van Noort  C. J. Spiers  C. J. Peach 《Physics and Chemistry of Minerals》2007,34(2):95-112

An unresolved issue in the study of pressure solution in rock materials is the dependence of grain boundary structure and diffusive properties on the mutual orientation of neighbouring grain lattices. We report electrical measurements yielding the diffusivity of differently oriented halite–glass and halite–halite contacts loaded in the presence of brine. The halite–glass contact experiments show pressure solution of the halite and an effect of halite lattice orientation on grain boundary transport. Post-mortem observations show an orientation-dependent grain boundary texture controlled by the periodic bond chains in the halite structure. It is inferred that this texture determines the internal grain boundary structure and properties during pressure solution. In the halite–halite experiments neck-growth occurred, its rate depending on twist-misorientation. The results imply that deformation by pressure solution may lead to lattice-preferred orientation development, and that polymineralic rocks may deform faster at lower stresses than monomineralic rocks.  相似文献   

First evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) from the Ionian Zone,western continental Greece     

Vassilis Karakitsios  Harilaos Tsikos  Yvonne van Breugel  Lyda Koletti  Jaap S. Sinninghe Damsté  Hugh C. Jenkyns 《International Journal of Earth Sciences》2007,96(2):343-352

Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes) and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate—black shale succession of the Ionian Zone (western Greece), provide the first evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich (44.5 wt% TOC), carbonate-free black shale, near the Cenomanian–Turonian boundary within the Vigla limestone formation (Berriasian–Turonian). Compared to the ‘Bonarelli’ black-shale interval from the type locality of OAE2 in Marche–Umbria, Italy, this black shale exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched δ¹³C values for both bulk organic matter (−22.2‰) and specific organic compounds are up to 5‰ higher than those of underlying organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian–Turonian black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N₂-fixing cyanobacteria in Cretaceous oceans during the Cenomanian–Turonian and early Aptian oceanic anoxic events.  相似文献   

Problems in predicting the mobility of slow-moving landslides   总被引：4，自引：0，他引：4  

Th.W.J. van Asch  L.P.H. Van Beek  T.A. Bogaard 《Engineering Geology》2007,91(1):46-55

This paper discusses problems in predicting the mobility of slow-moving landslides. Three case studies are presented here where research has been carried out by the Utrecht University: The La Valette landslide complex in the French Alps, the La Mure landslide in the French pre-Alps near Grenoble and the Hau landslide in Switzerland.To predict field velocities of these slow-moving landslides the viscosity parameters of the material of these landslides were determined by strain-controlled tests in a ring shear apparatus based on Bishop's design at Utrecht University. The viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field. This discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid, wavy slip surface and/or by convergent flow effects. The associated gain in strength results in a higher apparent viscosity.A more detailed analysis is made for the movements of the La Valette landslide. Observed velocities at the La Valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level. This deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under (partly) undrained conditions. The emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides.  相似文献   

On the spreading mechanism of shallow groundwater in the Hinterland of the Dutch Dune hill area     

C. van den Akker 《Engineering Geology》2007,91(1):72-77

The low lying Western part of the Netherlands is protected from the sea by a 5 km wide stretch of dunes rising to some 50 m of height. The fresh water pocket in the dunes overlies saline groundwater and a brackish transition zone. There was during a century an extraction of fresh groundwater for drinking water, supported by artificial infiltration. This has been stopped some 30 years ago. The consequent wetting of the valuable farm area (flower cultures) behind the dunes is stronger and more extensive than could be expected from mere replenishment of the fresh water zones in the dunes. It is shown in this paper that the lateral shear flows in the brackish and saline groundwater area have displaced (and are displacing) the interfaces vertically downward. The effect of more fresh and less saline groundwater in an arbitrary groundwater column is an (extra) rise of the groundwater head of the upper fresh water part. The described slow process will continue for decades until a new equilibrium has been established. In the mean time the inner dune farm area will have to cope with a surprisingly strong and extensive water level rise.  相似文献   

The organizational paradox in advertising and the reconfiguration of project cooperation     

Caroline von Bernuth 《Geoforum》2007,38(3):545-557

In recent literature, projects are mostly seen as an efficient form of organization which is particularly suited for mastering tasks of high complexity and creativity and adapting to changing economic and institutional conditions. This paper challenges the assumption that inter-firm projects are persistent organizational arrangements of production in the advertising industry and presents a novel argument about the potential threats to forms of project organization in crisis situations. By exploring the cases of Frankfurt/Main and Leipzig (East Germany), we show that the organization of production is substantially affected by periods of economic crisis or political transformation. We demonstrate that inter-firm projects might be replaced by more durable organizational configurations or might not be viewed as viable options in situations of severe rupture. This applies particularly to the cooperative arrangements in the creative process and leads to an organizational paradox. Although creativity is often a pivotal force to gain competitive advantage, the advertising agencies respond to the challenges of crises by reducing cooperation with external partners to a minimum and sometimes fully rely on in-house personnel. This threatens the potential of the respective firms to develop innovative and creative ideas which would enable the firms to acquire new customers and market segments. Instead of trying to overcome crises by focusing on their creative capabilities, many advertising agencies develop a cost-cutting strategy and rely on more durable network-forms of organization instead of inter-firm projects.  相似文献   

Rotation-Variant Template Matching for Supervised Hyperspectral Boundary Detection   总被引：1，自引：0，他引：1  

van der Werff  H. van Ruitenbeek  F. van der Meijde  M. van der Meer  F. de Jong  S. Kalubandara  S. 《Geoscience and Remote Sensing Letters, IEEE》2007,4(1):70-74

  相似文献   

Mapping East African tropical forests and woodlands — A comparison of classifiers     

Grace Nangendo  Andrew K. Skidmore  Henk van Oosten 《ISPRS Journal of Photogrammetry and Remote Sensing》2007,61(6):393-404

In mapping the forest–woodland–savannah mosaic of Budongo Forest Reserve, Uganda, four classification methods were compared, i.e. Maximum Likelihood classifier (MLC), Spectral Angle Mapper (SAM), Maximum Likelihood combined with an Expert System (MaxExpert) and Spectral Angle Mapper combined with an Expert System (SAMExpert). The combination of conventional classifiers with an Expert System proved to be an effective approach for forest mapping. This was also the first time that the SAMExpert had been used in the mapping of tropical forests. SAMExpert not only maps with high accuracy, but is also fast and easy to use, making it attractive for use in less developed countries. Another advantage is that it can be executed on a standard PC set up for image processing.Combining the conventional classifiers (MLC and SAM) with the Expert System significantly improved the classification accuracy. The highest overall accuracy (94.6%) was obtained with SAMExpert. The MaxExpert approach yielded a map with an accuracy of 85.2%, which was also significantly higher than that obtained using the conventional MLC approach.The SAMExpert classifier accurately mapped individual classes. Of the four classes of woodland mapped, the Open Woodland (with Terminalia) and Wooded Grassland classes were more accurately mapped using SAMExpert. The Open Woodland had been previously identified by ecologists, but had never been mapped.  相似文献   

Clearance rates of Cerastoderma edule under increasing current velocity     

S. Fernandes  P. Sobral  L. van Duren 《Continental Shelf Research》2007

Estimates of clearance rates (CR) of Cerastoderma edule (300 ind. m⁻²) as a function of free-stream current velocity (U) (from 5 to 40 cm s⁻¹) were compared between a small annular (60 l) and a large racetrack (8850 l) flume with different hydrodynamic conditions. Results showed that the flumes differ considerably in their hydrodynamic characteristics. The relationship between CR and U is different in the two flume tanks, however there appears to be a straightforward unimodal trend between CR and shear velocity (U_*). It was found that the cockles themselves influence the benthic boundary layer (BBL) characteristics, by causing steeper velocity gradients and increasing the mixing over the cockle bed compared to bare sediment. This provides new evidence on how endobenthic organisms can affect the BBL. However, the influence of CR on U_* could not be quantified because these parameters have interactive effects that cannot be dissociated.  相似文献