Lattice vibration spectra. LXVIII. Single-crystal Raman spectra of marcasite-type iron chalcogenides and pnictides,FeX2 (X=S,Se, Te; P,As, Sb)

Single-crystal Raman spectra of marcasite-type FeS₂, FeSe₂, and FeTe₂ and loellingite-type FeP₂, FeAs₂, and FeSb₂ are presented and discussed with reference to the energies of the two X-X stretching modes v _x-x (A _g, B _1g) and the four X₂ librations Rx₂ (A _g, B _1g, B _2g, B _3g). The main results obtained are that (i) the intraionic X-X bonds of FeS₂ marcasite and FeS₂ pyrite are nearly equal in strengths (mean values of the S-S stretching modes 418 and 420 cm^-1, respectively) and (ii) the interactions of the metal ions and the dumbbell-like X₂ units increase on going from the chalcogenides to the respective pnictides and from FeS₂ marcasite to pyrite (as shown from the frequencies of the X₂ librations).     

Development of a High Magnification Enlarger

Visual interpretation forms the basis for many operational applications of remote sensing. Suitable enlargement of remotely sensed data by optical projection is a basic requirement for visual interpretation. High Magnification Enlarger (HME) is a versatile interpretation aid developed for achieving wide-ranging scale transfer and variable-magnification display from a standard 24 cm format transparency. It operates on the principle of optical projection and is configured as a vertical column mounted unit. Low-distortion, high-quality enlarging lenses coupled with accuracy of alignment ensure accurate reproduction of the scale and the finer details from the input image transparency. Maximum user convenience is achieved by motorization of various controls.     

Heavy metal pollution in the Arcachon Basin (France) : Bonding states

Information available (since 1977) from a great many recent surveys on the Arcachon Basin has enabled us to determine three characteristic environments and study the behaviour of heavy metals (Ni, Cu, Zn, Pb, Cd, Hg). The relationship between heavy metals and grain-size fractions has been determined after having specified whether metals were preferentially organically or inorganically bound. This study has allowed us to establish the origin (natural or anthropogenic) of metallic enrichment and assess the extent of pollution.     

Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences

A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite. The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage. This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.     

Selective feeding and grazing rates of oyster (Crassostrea virginica) larvae on natural phytoplankton assemblages

Results of laboratory feeding experiments suggest that oyster (Crassostrea virginica) larvae select small phytoplanktonic organisms (<10 μm) over larger-celled forms from natural estuarine assemblages, but that little selection occurs within the small phytoplankton fraction. Laboratory-reared larvae grazed each of five small-celled phytoplankton groups enumerated (coccoids, centrate diatoms, pennate diatoms, dinoflagellates, and flagellates) at rates proportional to phytoplankton group densities in controls (no larvae added). Larval grazing rates (number of cells removed per larva per hour) were inversely proportional to both larval density and experimental duration.     

Sulfide and platinum mineralization in the Merensky Reef: evidence from hydrous silicates and fluid inclusions

The base metal sulfides of the Merensky Reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates. Biotite and phlogopite crystallized in the vicinity of sulfides from a volatile-enriched highly fractionated intercumulus melt. Amphibole, chlorite, and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase. Biotite is often accompanied by zircon, rutile, and quartz. Accessory quartz hosts a complex suite of H₂O-NaCl-(CaCl₂)-CO₂-CH₄ fluid inclusions which have thus far not been described from the Merensky Reef. The earliest fluid inclusion compositions are NaCl-(H₂O) with less than 10 vol.% water; CO₂ coexisting with a halite daughter crystal and brine; and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations. The maximum trapping temperature is around 730° C at 4 to 5 kb pressure. Later inclusion generations are H₂O-NaCl, CO₂-H₂O, and pure CO₂ and CH₄. The presence of Cl-rich fluids during the intercumulus stage of the crystallizing Merensky Reef is directly related to the mode of sulfide precipitation. Prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as H₂S. Sulfur saturation causes reaction of H₂S with oxides of the silicate melt to form a sulfide melt plus water. During reaction the magma is enriched in water until a separate fluid unmixes. It carries all compounds with high fluid/melt partition coefficients, as well as metals capable of forming OH- and Cl-complexes. Precious metals are assumed to have fractionated into the Cl-rich fluid as Cl-complexes rather than being dissolved in the sulfide melt. During the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets. The model proposed explains the distribution pattern of platinum-group minerals in the Merensky Reef better than any orthomagmatic mineralization concept offered so far.     

A comparison of two avalanche-models with exemplary avalanches of Tyrol and Switzerland and the effects to hazard zoning

For the purposes of a thesis at the Institute of avalanche and torrent control at the university of agriculture in Vienna a comparison of two avalanche-models, a hydraulic one from Voellmy/Salm/Gubler and a statistical one from Laatsch/Zenke/Dankerl with exemplary exactly known avalanches of Tyrol and Switzerland was started in 1993. The result of this work was that both models failed by the calculation of avalanches with high recurrence intervals (over 300 years). For the calculation of avalanches with recurrence intervals under 300 years the results of both models are regular. The conclusion is that a combination of two models i.e. a hydraulic one improved by statistical calculations will be the best.