Magma chambers and localization of deformation during thrusting     

Domenico Montanari  Giacomo Corti  Alexander Simakin 《地学学报》2010,22(5):390-395

Terra Nova, 22, 390–395, 2010 Abstract We present the results of coupled analogue and numerical models that provide new insights into the relationships between volcanoes and thrusts. The effects of both upper‐crustal magma chambers and the load of volcanoes on the geometry of thrust systems were investigated. Analogue modelling points to a strong influence exerted by a magma chamber on thrust geometry, which, as suggested by the numerical models used to rationalize these results, is related to the stress redistribution around the weak heterogeneity. The low‐viscosity body below a volcanic edifice localizes compressional deformation and causes a curvature of the thrusts towards the magma chamber, opposite to the direction of tectonic transport. In these conditions, the volcanic load has a negligible effect on the structural geometry. These results are in contrast with those of previous studies, where intrusions or the load of major volcanoes generated a curvature of the thrusts away from volcanic edifices in the direction of tectonic transport.  相似文献   

Megaflooding on Earth and Mars by Devon M. Burr,Paul A. Carling & Victor R. Baker     

Alexander Gershunov 《水文科学杂志》2013,58(7):1246-1247

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Thrust tectonics along the north-western continental margin of Sabah/Borneo   总被引：4，自引：0，他引：4  

Prof. Dr. K. Hinz  Dr. J. Fritsch  Dr. E. H. K. Kempter  Mr. A. Manaf Mohammad  Dr. J. Meyer  Mr. D. Mohamed  Dipl. Geophys. H. Vosberg  Dipl. Ing. J. Weber  Mr. J. Benavidez 《International Journal of Earth Sciences》1989,78(3):705-730

Widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north-west continental margin of Sabah. In contrast, interpretation of reflection seismic data acquired by BGR shows an autochthonous continental terrane comprising an Oligocene to Early Miocene carbonate platform being progressively overthrust by an allochthonous rock complex. Progressive compression resulted in the development of four structural zones: Imbricated thrust sheets (Zone III); two thrust sheet systems one on top of the other (Zone IV); a complex zone with multiphase deformation (Zone V); and piercement ridges (Zone VI).

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Zusammenfassung Nach herkömmlichen plattentektonischen Vorstellungen soll eine inaktive Subduktionszone am nordwestlichen Kontinentalrand von Sabah liegen. Reflexionsseismische Meßdaten der BGR zeigen jedoch, daß hier autochthone kontinentale Kruste mit einer oligozänen-frühmiozänen Karbonatplattform progressiv von einem allochthonen Gesteinsverband überschoben wird. Fortschreitender Zusammenschub seit dem frühen Miozän führte zur Anlage von vier Deformationszonen: Tekonische Schuppen (Zone III); zwei übereinander geschobene Verschuppungssysteme (Zone IV); Gürtel mit mehrphasiger Deformation (Zone V) und Durchspießungsstrukturen (Zone VI).

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Résumé Les modèles géodynamiques que l'on admet habituellement comportent une zone de subduction inactive le long de la marge continentale nord-occidentale de Sabah. Toutefois, des mesures de sismique-réflexion exécutées par le BGR font apparaître qu'à cet endroit, une croûte continentale autochtone, comportant une plateforme carbonatée oligocène à éomiocène, est chevauchée progressivement par un complexe allochtone. La compression, qui s'est manifestée progressivement depuis le Miocène inférieur, a engendré quatre zones structurales: un ensemble d'écailles tectoniques (zone III); deux systèmes de lames tectoniques charriés l'un sur l'autre (zone IV); une zone complexe à déformation multiphasée (zone V); des structures d'extrusion tectonique (zone VI).

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4829923 Sewage disposal     

Alexander G Copson  Mirza N Baig 《Marine pollution bulletin》1989,20(12):639

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Cumulate gabbros from the Southwest Indian Ridge, 54°S-7° 16′ E: implications for magmatic processes at a slow spreading ridge     

Peter S. Meyer  Henry J. B. Dick  Geoffrey Thompson 《Contributions to Mineralogy and Petrology》1989,103(1):44-63

A diverse volcanic and plutonic rock suite was recovered from the center of the 80 km long ridge segment of the Southwest Indian Ridge (54°S, 7°16 E) between the Islas Orcadas and Shaka Fracture Zones. The cumulus nature of the gabbroic rocks in the suite is indicated by phase, modal and cryptic layering, igneous lamination, and low incompatible element abundances. We present a mass-balance model for calculating the proportions and compositions of cumulus phases and crystallized intercumulus liquid from bulk-rock major element compositions. The model is based on the ability to define a compositional array of basaltic liquids and on the assumption that cumulus minerals are initially in equilibrium with trapped liquid. Calculated proportions of trapped liquid range from 3%–15%; values that are characteristic of adcumulates to mesocumulates. Models of postcumulus crystallization indicate significant enrichments of incompatible elements and buffering of compatible elements in residual trapped liquids, thus explaining the high TiO₂ contents observed in magnesian clinopyroxenes. Cumulus phase assemblages and compositions suggest solidification in shallow level magma chambers, but disequilibrium plagioclase compositions suggest some crystallization at greater depth. Furthermore, basalt compositions projected onto the olivine-clinopyroxenequartz pseudoternary suggest magma generation over a range of pressures (from less than 10 to greater than 20 kb) as well as polybaric fractional crystallization. We suggest that the Southwest Indian Ridge is characterized by low magma supply with small batches of melt that either ascend directly to the surface having undergone limited polybaric crystallization or are trapped in shallow crustal magma chambers where they evolve and solidify to form cumulate gabbros. The adcumulus nature of the gabbros investigated here suggests slow cooling rates typical of large intrusions implying relatively large, but ephemeral magma chambers below segments of the Southwest Indian Ridge.  相似文献   

Habitat partitioning between the xanthid crabsPanopeus herbstii andEurypanopeus depressus on intertidal oyster reefs (Crassostrea virginica) in southeastern North Carolina     

David L. Meyer 《Estuaries and Coasts》1994,17(3):674-679

The abundances of the xanthid crabsPanopeus herbstii andEurypanopeus depressus were examined relative to surface oyster shell cover, surface oyster cluster volume, subsurface shell content, substrate sand and silt composition, and oyster reef elevation. During August 1986 through July 1987, xanthid crabs were collected monthly from twelve 0.25 m²×15 cm deep quadrats, during low tide, from intertidal oyster reefs in Mill Creek, Pender County, North Carolina, USA, with respective quadrat details recorded. The abundance ofP. herbstii, and to a lesser degreeE. depressus, was positively correlated with surface shell cover. The abundance ofE. depressus, and to a lesser degreeP. herbstii, was positively correlated with surface cluster volume. The majority ofP. herbstii inhabited the subsurface stratum of the oyster reef, whereas the majority ofE. depressus inhabited the cluster stratum. Seasonality (i.e., temperature) appeared to influence the strata habitation of both species, with a higher incidence of cluster habitation during warmer months and a lower incidence during colder months. Crab abundance was not related to other factors examined, such as subsurface shell, substrate sand and silt composition, or elevation within the oyster reef. The analyses show thatP. herbstii andE. depressus have partitioned the intertidal oyster reef habitat, withE. depressus exploiting surface shell clusters andP. herbstii the subsurface stratum.  相似文献   

Analysis of swarms of high-frequency seismic events at Nevado del Ruiz volcano, Colombia (January 1986–August 1987): Development of a procedure     

Fernando C. Muoz  Alvaro E. Nieto  Hansjürgen Meyer 《Journal of Volcanology and Geothermal Research》1990,41(1-4)

The determination of signal properties like frequency, amplitude, “signature” of the sequence of arrivals of P- and S-phases and the subsequent computation of hypocenter parameters, are the steps of a procedure in the analysis of swarms of high-frequency seismic events from Nevado del Ruiz volcano, which could be useful in other volcanic areas. The use of this procedure on Ruiz data led to the determination of various seismic source volumes, which together with hypocenters of non-swarmed events and the identification of geological features such as faults which cross the area, alignment of domes and volcanic edifices, and the record of low-frequency seismic events not centered in the area of the active vent, suggest the existence of a magma chamber of a rather complex geometry. This hypothesis would suggest that magma, emplaced in zones of weakness (faults) that affect the area, may act as the source of seismic activity. This demands a revision of the methodology used in the deformation measurements, and in the analysis of released energy and event occurrence too. The relations between hypocenters (sources), location and relative energy of the swarms, as well as the general volcanic activity (tremor, ash and gas emission, deformation) could turn out to be a possible means to assist in the identification of premonitory activity and thus be relevant to the process of monitoring and forecasting.  相似文献   

European Environmental Research Organization (EERO)     

Alexander J. B. Zehnder 《GeoJournal》1990,22(4):438-438

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Hydrophobic and electrostatic parameters in bacterial adhesion   总被引：5，自引：0，他引：5  

Mark C. M. van Loosdrecht  Willem Norde  Johannes Lyklema  Alexander J. B. Zehnder 《Aquatic Sciences - Research Across Boundaries》1990,52(1):103-114

Recently it has been shown that the initial stages of bacterial adhesion to a model-surface of sulphated polystyrene can best be described using hydrophobic and electrostatic parameters. In the present study it is tested whether these parameters can generally be applied to predict bacterial adhesion by using (i) glass, as a model for hydrophilic and natural surfaces of silicates and oxides, (ii) polystyrene coated with proteins, as a model for a surface coated with an organic layer, and (iii) river Rhine sediment, as an example of a natural surface. Adhesion to glass was dominated by electrostatic interaction, whereas adhesion to polystyrene coated with various types of proteins depended on the surface characteristics of the bacteria and the type of protein. By relating Van der Waals interactions to hydrophobicity of the interacting species, the adhesion of bacteria to the various surfaces including the river Rhine sediments could be interpreted in terms of the DLVO-theory. It is therefore concluded that the conceptual principles of the DLVO-theory (interplay of Van der Waals and electrostatic interactions) are suitable to describe, at least qualitatively, the initial processes of bacterial adhesion to a wide range of surfaces.  相似文献   

Efficiency test of earthquake prediction around Thessaloniki from electrotelluric precursors     

K. Meyer  P. Varotsos  K. Alexopoulos  K. Nomicos 《Tectonophysics》1985,120(1-2)

Since the completion of the network in January 1983, the electric field of the earth has been continuously monitored at four sites near Thessaloniki, the capital of northern Greece. From the present study and from previous investigations by similar measurements in Greece, it is evident that transient changes of the electrotelluric field occur prior to earthquakes. The analysis of these electric forerunners leads in many cases to a successful prediction of the epicentral area, the magnitude and the time of the impending event. Predictions prior to regional earthquakes are issued and documented with telegrams.From November 1983 until the end of May 1984 twelve earthquakes (M_L > 3.5) occurred in the vicinity of Thessaloniki. Ten of these were predicted and warnings given by telegram, whereas two smaller seismic events were missed. Two additional predictions were unsuccessful. Independent of their magnitudes, predicted events took place within a time window of 6 hrs to 6 days after the observations of the electrotelluric anomalies. The accuracy of the predicted epicenters in eight cases is better than 100 km, which corresponds roughly to the mean distance between the electric stations. Magnitude estimates deviate by less than 0.5 magnitude units from the seismically observed ones.Considering the two largest earthquakes, it is shown that the probability of making each of these predictions by chance is of the order of 10⁻².  相似文献