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

Alfons Berger  Claudio L. Rosenberg 《Contributions to Mineralogy and Petrology》2003,144(4):416-427

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.  相似文献   

The Erzincan (Turkey) Earthquake (Ms 6.8) of March 13, 1992 and its Aftershock Sequence     

H. Grosser  M. Baumbach  H. Berckhemer  B. Baier  A. Karahan  H. Schelle  F. Krüger  A. Paulat  G. Michel  R. Demirtas  S. Gencoglu  R. Yilmaz 《Pure and Applied Geophysics》1998,152(3):465-505

—The Erzincan strike-slip earthquake of March 13, 1992 ruptured a section of the North Anatolian fault (NAF) at the northern margin of the Erzincan basin. The focal depth of about 10 km was less than given by ISC and NEIC. Erzincan and the surrounding villages were considerably damaged. In the Erzincan basin and in the neighbouring mountains a seismic network of ten stations was installed. It was operating continuously from March 21 through June 16, 1992. More than 3,000 aftershocks were recorded of which 505 could be located. The spectral parameters of 394 and the fault-plane solutions of 53 aftershocks were determined. For the given region the frequency dependent coda Q was derived as Q _c = 122 f ^0.68. The aftershock area increased with time, reflecting the process of stress redistribution. Some events clustered in the immediate vicinity of the town of Erzincan close to the epicentre of the main event and seem to trace the NAF. Their source mechanism is similar to that of the main event (strike slip). About 150 aftershocks clustered in the southeastern part of the Erzincan basin where a concentration of the events in a small volume of 5 × 5 × 3 km³ was observed. The majority of fault-plane solutions available for these aftershocks showed a normal faulting mechanism with an east-west directed extension. Most of the aftershocks southeast of the basin clustered between two lineaments that were mapped by satellite images. The P-wave velocity below the Erzincan basin, derived from travel-time residual analysis, is lower compared to areas NE and SW of the basin. Three-dimen sional stress modelling of the Erzincan region qualitatively explains the occurrence of the aftershocks southeast of the basin. The calculated displacement distribution which exhibits the north-westward motion of the basin and tension at its southeastern margin, caused by the Erzincan earthquake, is in agreement with derived fault-plane solutions.  相似文献   

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

Jean Pohl  Alfons Eckstaller  P. Blyth Robertson 《Meteoritics & planetary science》1988,23(3):235-238

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.  相似文献   

Internationale Arbeitsgemeinschaft für Cyanophytenforschung IAC     

Alfons Zehnder 《Aquatic Sciences - Research Across Boundaries》1964,26(1):147-164

Ohne Zusammenfassung  相似文献   

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

Alfons Zehnder  Dr. J. Komárek  Prof. Dr. S. Golubić  Prof. Dr. R. Y. Stanier  Dr. J. Komárek  Dr. J. Ludvík  Dr. L. Kováčik  Dr. Asta Almestrand  Prof. Dr. P. Compère  Dr. D. Mollenhauer  Dr. F. Hindák  Dr. T. P. Chang  Dr. Nagaraj Jeeji Bai  C. V. Seshadri  Dr. M. -E. Meffert  Dr. R. Oberhäuser  Dr. J. Overbeck  Dr. F. Hindák  Susan E. Campbell  Dr. Jaroslava Komárková  Dr. U. Uehlinger  Dr. F. Schanz  Dr. Alfons Zehnder 《Aquatic Sciences - Research Across Boundaries》1983,45(1):267-310

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).   相似文献   

Earthquake early warning for transport lines     

Désirée Hilbring  Tanja Titzschkau  Alfons Buchmann  Gottfried Bonn  Friedemann Wenzel  Eberhard Hohnecker 《Natural Hazards》2014,70(3):1795-1825

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.  相似文献