Characterisation of deformation and flow mechanics around porphyroclasts in a calcite marble ultramylonite by means of EBSD analysis   总被引：1，自引：0，他引：1  

Michel Bestmann  David J. Prior  Bernhard Grasemann 《Tectonophysics》2006,413(3-4):185-200

This paper studies the flow heterogeneity around porphyroclasts associated with greenschist facies deformation of a calcite marble shear zone. Microstructural data from electron backscatter diffraction analyses (EBSD) are used to constrain the flow mechanics of this dominantly non-coaxial type of deformation. The microstructure of the undisturbed ultramylonite (grain-size range 5–100 μm, mean 40 μm) is interpreted to represent steady-state (time-independent) flow conditions with flow planes parallel to the shear zone boundary. Single calcite porphyroclasts (grain-size 1–3 mm) caused flow perturbation in the fine-grained marble ultramylonite. It is the shape, in particular, of these rigid porphyroclasts that controls their rotational behaviour during deformation and, therefore, the development of specific flow fabrics. The flow planes around elongated-rhomboidal, stable porphyroclasts change the orientation to become roughly parallel to the porphyroclast margin, whereas the geometry of flow planes around nearly equant, rotating porphyroclasts describes a δ-type flow pattern. We infer that to some extent decoupling at the clast–matrix interface has occurred to guarantee a stable orientation of elongated porphyroclasts, but was not sufficient to reduce the rotation rate of equant clasts to zero. According to the flow deflection, the general crystallographic preferred orientation (CPO) with its single c-axis maximum perpendicular to the flow plane is rotated about an axis which is (sub)parallel to the kinematic rotation axis of the shear zone. Ultramylonite microstructures, CPOs and misorientation data are best explained by the dual operation of grain-size-insensitive (dislocation creep with recovery and recrystallization) and grain-size-sensitive (diffusion creep) mechanisms. The limited grain-size reduction around porphyroclasts suggests that the grain-size-insensitive mechanisms controlled rheology.  相似文献   

Laterally constrained inversion of helicopter-borne frequency-domain electromagnetic data     

Bernhard Siemon  Esben Auken  Anders Vest Christiansen 《Journal of Applied Geophysics》2009,67(3):259-268

Helicopter-borne frequency-domain electromagnetic (HEM) surveys are used for fast high-resolution, three-dimensional resistivity mapping. Standard interpretation tools are often based on layered earth inversion procedures which, in general, explain the HEM data sufficiently. As a HEM system is moved while measuring, noise on the data is a common problem. Generally, noisy data will be smoothed prior to inversion using appropriate low-pass filters and consequently information may be lost.For the first time the laterally constrained inversion (LCI) technique has been applied to HEM data combined with the automatic generation of dynamic starting models. The latter is important because it takes the penetration depth of the electromagnetic fields, which can heavily vary in survey areas with different geological settings, into account. The LCI technique, which has been applied to diverse airborne and ground geophysical data sets, has proven to be able to improve the HEM inversion results of layered earth structures. Although single-site 1-D inversion is generally faster and — in case of strong lateral resistivity variations — more flexible, LCI produces resistivity — depth sections which are nearly identical to those derived from noise-free data.The LCI results are compared with standard single-site Marquardt–Levenberg inversion procedures on the basis of synthetic data as well as field data. The model chosen for the generation of synthetic data represents a layered earth structure having an inhomogeneous top layer in order to study the influence of shallow resistivity variations on the resolution of deep horizontal conductors in one-dimensional inversion results. The field data example comprises a wide resistivity range in a sedimentary as well as hard-rock environment.If a sufficient resistivity contrast between air and subsurface exists, the LCI technique is also very useful in correcting for incorrect system altitude measurements by using the altitude as a constrained inversion parameter.  相似文献   

The western end of the Eoalpine High‐Pressure Belt (Texel unit,South Tyrol / Italy)          下载免费PDF全文

Hannah Pomella  David Flöss  Romed Speckbacher  Peter Tropper  Bernhard Fügenschuh 《地学学报》2016,28(1):60-69

Eclogites in the Texel Unit (Eastern Alps; South Tyrol, Italy) represent the westernmost outcrops of the E–W striking Eoalpine High‐Pressure Belt (EHB). East of the Tauern Window, the EHB forms part of a Cretaceous intracontinental south‐dipping subduction/collision zone; however, the same nappe stack displays a northwest dip at its western end. This prominent change in dip direction gave rise to discussions on the general setting of the Eoalpine collision. Based on our own observations and literature data, we present a new tectonic model for the western end of the EHB. Due to the special situation of this area at the tip of the Southalpine indenter, originally south(east) dipping structures became overturned, and former thrusts appear as normal faults (e.g. Schneeberg fault zone) while former normal faults presently display thrust geometries (e.g. Jaufen fault). Thus, we explain the current configuration with a coherent Eoalpine subduction direction.  相似文献   

A comparison of helicopter-borne electromagnetics in frequency- and time-domain at the Cuxhaven valley in Northern Germany     

Annika Steuer  Bernhard Siemon  Esben Auken 《Journal of Applied Geophysics》2009,67(3):194-205

Two different airborne electromagnetic methods were applied in the same area: the frequency-domain helicopter-borne electromagnetic (HEM) system operated by the Federal Institute for Geosciences and Natural Resources, Germany, and the time-domain SkyTEM system of the HydroGeophysics Group at the University of Aarhus, Denmark. For verification of and comparison with the airborne methods, ground-based transient electromagnetics and 2-D resistivity surveying were carried out. The target of investigation was the Cuxhaven valley in Northern Germany, which is a significant local groundwater reservoir. The course of this buried valley was revealed by drillings and the shape was determined by reflection seismics at several cross sections.We applied electrical and electromagnetic methods to investigate the structure of the valley filling consisting of gravel, sand, silt and clay. The HEM survey clearly outlines a shallow conductor at about 20m depth and a deeper conductor below 40m depth inside the valley. This is confirmed by 2-D resistivity surveying and a drilling. The thickness of the deeper conductor, however, is not revealed due to the limited investigation depth of the HEM system. The SkyTEM survey does not resolve the shallow conductor, but it outlines the thickness of the deeper clay layer inside the valley and reveals a conductive layer at about 180m depth outside the valley. The SkyTEM results are very consistent with ground-based transient electromagnetic soundings.Airborne electromagnetic surveying in general has the advantage of fast resistivity mapping with high lateral resolution. The HEM system is cost-efficient and fast, but the more expensive and slower SkyTEM system provides a higher depth of investigation. Ground-based geophysical surveys are often more accurate, but they are definitively slower than airborne surveys. It depends on targets of interest, time, budget, and manpower available by which a method or combination of methods will be chosen. A combination of different methods is useful to obtain a detailed understanding of the subsurface resistivity distribution.  相似文献   

Methodische Verbesserungen bei der routinemäßigen Schlämmanalyse von Ton- und Bodenproben     

Bernhard Mattiat 《Contributions to Mineralogy and Petrology》1964,10(2):216-224

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Stabilität einer Rutschscholle unter Einstau     

Bernhard Albiker 《Rock Mechanics and Rock Engineering》1977,9(4):173-181

ZusammenfassungStabilität einer Rutschscholle unter Einstau Die Elta, linker Seitenzufluß der Donau auf der Höhe Tuttlingen, sollte an der topografisch günstigsten Stelle zur Errichtung eines 12 Mio m³ großen Speichers abgesperrt werden. Die geologische Vorerkundung ergab Hinweise auf eine erfolgte Rutschung größerer Kubatur im linken Hangbereich. Die danach angesetzte Erkundung zeigte, daß eine Scholle aus Gesteinen des Weißen Jura unter Ausbildung einer Gleitfläche auf dem unterlagernden Braunen Jura abgeglitten war. Mit dem Teileinstau dieser Hangpartie mußte befürchtet werden, daß die Scholle erneut in Bewegung geraten und in das Becken gleiten würde (Vergleichssituation zu Vajont). Die bodenmechanische Berechnung ergab für den Lastfall der schnellen Senkung des Beckenspiegels eine nicht ausreichende Standsicherheit der Scholle, weshalb die Sperrstelle aufgegeben werden mußte.

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SummaryStability of a Rock Slide in a Reservoir The Elta, left tributory river of the upper Danube should have been dammed up at the topographically most suitable location in order to erect a reservoir for water supply of 12 mio. m³ in volume. Since the topography of the valley part in consideration showed some peculiarities, a more detailed geological survey was undertaken. Due to geo-morphological aspects on the left slope part of the valley expecially in the area of the dam abutment in prospection a former landslide was indicated. More detailed ascertainments showed that a stratum of malm had performed a slideway on the dogger yielding the actual morphological position.In projecting the basin it had to be taken into consideration the possibility of a renewed sliding expecially in the state of lowering the water table (comparative situation to Vajont).Indeed the soil mechanical safety determination of the slope part in consideration verified a not sufficient stability in the state of repeated sudden drow down of the water table in the basin. Due to this result one had to renounce on the realization of the project.

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RésuméStabilité d'un éboulement dans un bassin On devait construire un barrage sur la Elta (affluent gauche du Danube, à la hauteur de Tuttlingen), à l'endroit le plus favorable du point de vue topographique, afin de créer un réservoir de 12 Mio. m³. Le sondage géologique préalable a fourni des indications au sujet d'un glissement de cubage assez important, s'étant produit dans la région pentue gauche.Le sondage effectué par la suite montra qu'une masse de pierres du Jura Blanc s'était détachée en ferment une surface glissante sur le Jura Brun qui se trouve à la base. Avec le remplissage du bassin partiel il était à craindre que la masse ne se mît de nouveau en mouvement et ne glissât dans le bassin (Situation comparable à Vajont).Les calculs de la mécanique du sol n'ont pas révélé une sécurité suffisant de la stabilité de la masse, dans le cas d'une baisse rapide du niveau du bassin, c'est pourquoi on a dû renoncer à un barrage à cet endroit.

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Mit 8 Abbildungen  相似文献   

Ammoniten-Ökologie am Beispiel des Oberjura     

Prof. Dr. Bernhard Ziegler 《International Journal of Earth Sciences》1967,56(1):439-464

Zusammenfassung In vielen Fällen beeinflussen äußere Faktoren das Vorkommen der Ammoniten. Im Oberjura spielt die Wassertiefe eine große Rolle, daneben tritt die Wassertemperatur. Voraussetzungen der ökologischen Analyse sind bodenbezogenes Leben der Tiere und postmortale Autochthonie der Schalen. Methoden und Fehlerquellen werden besprochen. Aus der ökologischen Bindung vieler Ammoniten ergeben sich Folgen, vor allem für Stratigraphie, Phylogenie und Ontogenie.

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In many cases external factors determine the occurence of the ammonites. In the Upper Jurassic the depth of the sea is of great importance, as well as the temperature of the water. Ecological analysis requires life of the animals close to the sea floor, and that the shells are autochthonous.Methods and sources of errors are discussed. The dependence on environment of many ammonites has consequences, especially for stratigraphy, phylogeny and ontogeny.

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Résumé Souvent des facteurs extérieurs déterminent la présence des ammonites. Dans le Jurassique Supérieur la profondeur de la mer joue un grand rôle, aussi bien que la température de l'eau. L'analyse écologique doit supposer que les animaux vivent près du fond de la mer et que les coquilles sont autochtones. Les méthodes et les sources d'erreurs sont discutées. La dépendance des ammonites de leur milieu a des conséquences avant tout pour la stratigraphie, la phylogénie et l'ontogénie.

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Die Reaktion 2 Zoisit+1 CO2 ⇌ 3 Anorthit+1 Calcit+1 H2O     

Bernhard Storre  Karl -Heinz Nitsch 《Contributions to Mineralogy and Petrology》1972,35(1):1-10

The equilibrium conditions of the following reaction 2 zoisite +1 CO₂?3 anorthite+1 calcite+1 H₂O 2 Ca₂Al₃[O/OH/SiO₄/Si₂O₇]+1 CO₂?3 CaAl₂Si₂O₈+1 CaCO₃+1 H₂O have been determined experimentally at total pressures of P _j= 2000 bars, P _f =5000 bars, and P _f =7000 bars. Owing to the vertical position of the equilibrium curves in isobaric T- \(X_{{\text{CO}}_{\text{2}} }\) diagrams, the composition of the binary H₂O-CO₂ fluid phase coexisting with zoisite is independent of temperature in the temperature interval investigated. According to our experiments, orthorhombic zoisite is only stable in equilibrium with a fluid phase at a concentration of CO₂ which is less than, respectively, ca. 2 Mol% CO₂ at P _f =2000 bars, ea. 6 Mol% at P _f =5000 bars, and ca. 10 Mol% at P _f =7000 bars. Thus, the fluid phase coexisting with zoisite is rich in H₂O. While this is independent of temperature the experimental data demonstrate that the influence of pressure cannot be neglected: With increasing pressure the concentration of CO₂ of the fluid phase coexisting with zoisite can rise a little. The position of the reaction studied, which is independent of temperature and exhibits small values of \(X_{{\text{CO}}_{\text{2}} }\) ,leads to two important petrogenetic conclusions:

1. The occurrence of zoisite is an indicator for a CO₂-poor and H₂O-rich fluid composition during metamorphism of marly calcsilicates.
2. If the concentration of CO₂ of the fluid phase coexisting with zoisite exceeds the equilibrium value of \(X_{{\text{CO}}_{\text{2}} }\) calcite+anorthite+H₂O is formed from zoisite+CO₂. Thus, a considerable increase in the anorthite-content of plagioelase is possible.

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Aerial perspective for shaded relief     

Bernhard Jenny  Tom Patterson 《制图学和地理信息科学》2021,48(1):21-28

ABSTRACT

Aerial perspective is an essential design principle for shaded relief that emphasizes high elevation terrain using strong luminance contrast and low elevations with low contrast. Aerial perspective results in a more expressive shaded relief and helps the reader to understand the structure of a landscape more easily. We introduce a simple yet effective method for adding aerial perspective to shaded relief that is easy to control by the mapmaker.  相似文献   

Terrain generalization with line integral convolution     

Bernhard Jenny 《制图学和地理信息科学》2021,48(1):78-92

ABSTRACT

Line integral convolution is a technique originally developed for visualizing vector fields, such as wind or water directions, that places densely packed lines following the direction of movement. Geisthövel and Hurni adapted line integral convolution to terrain generalization in 2018. Their method successfully removes details and retains sharp mountain ridges; it is particularly suited for creating generalized shaded relief. This paper extends line integral convolution generalization with a series of enhancements to reduce spurious artifacts, accentuate mountain ridges, control the level of detail in mountain slopes, and preserve sharp transitions to flat areas. The enhanced line integral convolution generalization effectively removes excessive terrain details without changing the position of terrain features. Sharp mountain ridgelines are accentuated, and transitions to flat waterbodies and valley bottoms are preserved. Shaded relief imagery derived from generalized elevation models is visually pleasing and resembles manually produced shaded relief.  相似文献