Internationale Arbeitsgemeinschaft für Cyanophytenforschung IAC

Ohne Zusammenfassung     

Symposium über Fragen der Cyanophytentaxonomie im Seenforschungsinstitut der ETHZ/EAWAG in Kastanienbaum (Schweiz), 2.–15. August 1979 Verhandlungsbericht

The 8th Symposium of the International Association for Cyanophyte Research IAC was attended by 29 specialists from 11 countries. The 19 oral presentations and discussions centered on the following themes: The basic principles of cyanophyte taxonomy (3 lectures), systematic problems of certain taxonomic groups (5 lectures), morphology (6 lectures) and ecology (5 lectures). The intensive discussions between representatives of the classical (european) taxonomic treatment of cyanophytes (based on morphological and ecological characteristics) and those representing the bacteriological study of ‘cyanobacteria’ were especially valuable. The central theme of the meeting was, however, the mutual microscopic study and discussion of problematic blue-greens from natural habitats, that were mostly collected during the three field trips into different areas of central Switzerland (Grimsel-Gotthard-Nufenen. Klewenalp. Gerzensee).      

Preservation of chemical residue-melt equilibria in natural anatexite: the effects of deformation and rapid cooling

A combined petrologic, textural and chemical approach is used to interpret the relationship between chemical exchange and deformation during partial melting of a granodioritic gneiss in the contact aureole of the Bergell Pluton (Central Alps). In contrast to most regional metamorphic anatexites, chemical equilibrium between residue and segregated melt was attained and preserved by several elements, as shown by their present distribution. Equilibrium involved both the major and the trace elements hosted in the rock-forming minerals and the light rare earth elements (LREE), hosted primarily in allanite. Equilibrium with respect to LREEs was achieved because allanite had a reactive behaviour during water-present melting, in contrast to the refractive behaviour of xenotime, which mostly controls the distribution of the HREE's. The attainment and preservation of equilibrium between leucosome and residue requires peculiar boundary conditions. We propose that the achievement of equilibrium between melt and residue was promoted by deformation, operating via a mechanism of melt present granular flow (i.e. dissolution-accommodated grain-boundary sliding active during partial melting). Microstructural observations indicate that melt-present granular flow was the dominating deformation mechanism in these anatexites. The preservation of residue-melt equilibrium is inferred to result from rapid cooling under contact metamorphic conditions and from the lack of deformation below the solidus.     

Gravity and Magnetic Investigations in the Haughton Impact Structure,Devon Island,Canada

Abstract— The results of a new gravity survey show that the Haughton impact structure is associated with a 24 km diameter negative Bouguer gravity anomaly with a maximum amplitude of ?12 mgal. A local minimum with a half-width of 2 km and an amplitude of ?4 mgal is located at the center of the structure. A positive magnetic total field anomaly with a half-width of 0.6 km and an amplitude of 700 nT coincides with the local central gravity anomaly. The overall negative gravity anomaly is explained by lowered rock densities due to impact-related fracturing in the crater area. The central gravity and magnetic anomalies are believed to be due to highly shocked and heated sedimentary and crystalline basement rocks forming the unexposed peak of the central uplift in the Haughton impact structure.     

Shallow landslides triggered by rainfalls: modeling of some case histories in the Reggiano Apennine (Emilia Romagna Region, Northern Italy)

On April 10–11, 2005, the Emilia Romagna Apennine was affected by an intense rainfall event that triggered dozens of soil slips in the Province of Reggio Emilia. These shallow landslides occurred mainly on slopes of cultivated lands, often blocking roads, causing damages to crops and economic loss. Based on the analysis of an inventory of aerial photographs, it was possible to locate 45 sites where soil slips have occurred. In this paper, the area of study is described from a geological and climatic point of view. The authors analyze both the predisposing factors, related to the morphology of the territory, and the phenomena triggering factors, related to the rain trend. Once the geometrical features and characteristics of the soil slopes were available, a physically based triggering model, recently developed by the authors, was locally applied at each site. The model, which is based on the limit equilibrium method and on the hypothesis of infinite slope, is briefly described. It assumes a partial saturation condition of the soil and provides the safety factor of each slope as a function of time-variable rainfall intensity. The choice of the input parameters of the model is explained in detail. It is underlined, in particular, how the only parameter that has been determined through a procedure of back analysis, i.e., the discharge capability, is comparable to the typical permeability values obtained through field measurements by other authors, for similar kinds of soils and conditions. In this article, the results of the application of our model to the study areas, within a three-year time frame, are presented. Furthermore, on the basis of the analysis carried out, some observations on the operating mode of the model are carried out and its ability to predict a phenomenon triggering is evaluated.     

Cathodoluminescence,fluid inclusion and stable C–O isotope study of tectonic breccias from thrusting plane of a thin-skinned calcareous nappe

Basal hydraulic breccias of alpine thin-skinned Muráň nappe were investigated by means of cathodoluminescence petrography, stable isotope geochemistry and fluid inclusions analysis. Our study reveals an unusual dynamic fluid regime along basal thrust plane during final episode of the nappe emplacement over its metamorphic substratum. Basal thrusting fluids enriched in ¹⁸O, silica, alumina, alkalies and phosphates were generated in the underlying metamorphosed basement at epizonal conditions corresponding to the temperatures of 400–450°C. The fluids fluxed the tectonized nappe base, leached evaporite-bearing formations in hangingwall, whereby becoming oversaturated with sulphates and chlorides. The fluids further modified their composition by dedolomitization and isotopic exchange with the host carbonatic cataclasites. Newly formed mineral assemblage of quartz, phlogopite, albite, potassium feldspar, apatite, dravite tourmaline and anhydrite precipitated from these fluids on cooling down to 180–200°C. Finally, the cataclastic mush was cemented by calcite at ambient anchizonal conditions. Recurrent fluid injections as described above probably enhanced the final motion of the Muráň nappe.     

Dating emplacement and evolution of the orogenic magmatism in the internal Western Alps: 1. The Miagliano Pluton

The Canavese Line in the Western Alps represents the position in the Alpine chain, where alkaline and calc-alkaline magmatism occur in close spatial and temporal association. In addition to available data on the alkaline Valle del Cervo Pluton, we present petrological and geochemical data on the Miagliano tonalite. The latter is of special interest, because it is located in the south-eastern side of the Canavese Line, in contrast to most Periadriatic Plutons. The dioritic to tonalitic rocks of the Miagliano Pluton represent an intermediate stage of a calc-alkaline differentiation, demonstrated by relics of two different pyroxenes as well as the texture of allanite. Hornblende barometry indicates pressures of ~0.46?GPa consistent with the presence of magmatic epidote. Field relationships between the two Plutons, the volcanic and volcaniclastic rocks of the Biella Volcanic Suite and numerous dykes cross-cutting the different units, allow reconstruction of a more refined chronology of the calc-alkaline and alkaline magmatic series. High precision zircon geochronology yields an age of 33.00?±?0.04?Ma for the central tonalitic part of the Miagliano Pluton and 30.39?±?0.50?Ma for the granitic core of the Valle del Cervo Pluton. The difference in age combined with cooling data and intrusion depth indicates dissimilar tectonic transport east and west of the Canavese Line. The earlier emplaced Miagliano Pluton has to be exhumed from an intrusion depth of ~12?C15?km, whereas the neighbouring and younger Valle del Cervo Pluton is exhumed from a depth of 5?C7?km. This tectonic scenario is related to upper crustal rigid block rotation responsible for the burial of the lowermost Rupelian paleosurface of the Sesia?CLanzo Zone. Thus, the new ages constrain the paroxysm of the orogenic magmatism in the internal Western Alps to an extremely short lapse of time in the first half of the Rupelian.     

Earthquake early warning for transport lines

This paper analyzes the potential of earthquake early-warning systems for transport lines. The interdisciplinary work focuses on rapidly producing an alert map during an ongoing earthquake as well as providing a damage map immediately after the strong-motion phase that visualizes potential damages to the railway infrastructure. In order to meet these application requirements, a service-oriented architecture based on geospatial standards is specified. This ensures the portability of the system architecture to different geographic regions as well as a potential transfer to other natural disasters and infrastructure systems. The first part of the paper describes the standard-based services of the system architecture together with design principles that are useful for the realization of early-warning systems. In the second part of the paper, an online demonstrator for the exemplary test area in the federal state of Baden-Württemberg, Germany, is presented. The system architecture of the demonstrator includes an earthquake early-warning methodology based on artificial neural networks and an infrastructure-specific damage assessment. The third part of the paper analyzes the potential of implementing low-cost sensors in the track, which would provide a dense network directly at the railway infrastructure.