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Structural and Petrophysical Characterisation of Granite Intended for Radioactive Waste Stocking
Staněk, Martin ; Lexa, Ondrej (advisor) ; Žák, Jiří (referee) ; David, Christian (referee)
Structural and petrophysical analysis have been conducted within the Melechov massif with focus on structures controlling the porosity, permeability and thermal conductivity of the rock. The structure of the massif has been constrained based on extensive dataset including AMS and field structural measurements of ductile and brittle structures. Maps and stereograms have been constructed to display the magnetic fabrics and the fracture system of the studied massif. The fracture system of the massif has been described by two principal and two supplementary sets of joints and by faults formed mainly by joint reactivation or less frequently formed as shear fractures. The measured petrophysical data have been used to characterize the effect of fracturing and alteration on pore space geometry and in turn on permeability, thermal conductivity and elastic properties of the studied granite. Distinct petrophysical properties have been identified for pristine granite, for fractured fresh granite as well as for fractured granite altered by Fe-oxide, chlorite and clay minerals. Relations between the measured petrophysical properties have been explained in terms of evolution of the rock pore space. A detailed microstructural study combined with multidirectional P-wave velocity measurements at high confining pressure and...
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Numerical simulations of geodynamic processes
Krýza, Ondřej ; Lexa, Ondrej (advisor) ; Ježek, Josef (referee)
ENGLISH ABSTRACT The aim of this work is to provide a basic overview in numerical modeling of geodynamic processes. Therefore, work is divided into two main parts that almost independently describe its main topic. Both parts are designed to allow reader easily locate sources for more detailed and deeper description of the problem. The first part deals with the mathematical and physical apparatus, which is used to describe the geodynamic processes and their formalization due to the application for the construction of mathematical models. This section is mainly based on the description of conservation laws and related equations (continuity equation, Navier-Stokes equations, heat transfer equation) and also gives an overview of relations describing the force interactions in solids and rheology. The second aspect of this work is explanation of the principle of numerical methods (finite differences, finite volumes, finite elements and spectral methods) and their brief overview. In this part, the work is focused on finite differences, a description of which is the main topic of this part. In last chapter of this work, an example of the implementation of finite difference method for modeling of the thermal evolution of fold structures is given. We elaborate simple kinematic and thermal model to simulate time and...
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Mechanisms of granite fracturing and their implications for origin of gold-bearing veins in Mokrsko deposit
Švagera, Ondřej ; Lexa, Ondrej (advisor) ; Franěk, Jan (referee)
The stress concept in geology is widely used for analysis and description of tectonic events. These can be documented directly in the field or by interperetation of results gained by laboratory analysis. The expressions of brittle tectonics and geological events linked with them are often important clues leading to understanding processes giving unique forms to many localities. The origin of gold-bearing veins in Mokrsko deposit is result of long-lasting tectonic processes. During these were created at least 4 generations of brittle structures. The proximity of Variscides is the source of this brittle fracturing. Sázava pluton intruded during the syn- orogenic phase and in the Slapy apophysis of Sázava pluton started the circulation of fluids because of the contact metamorphism. These fluids were using pre-existing EW joint systems. After that, the precipitation of minerals rich in Bi-Te-Cu gave origin to the local gold-bearing mineralization. This mineralisation is partly bound to the quartz-veins localized on Mokrsko- Západ. Their thickness is often in sub-milimeter scale with very regular spacing.
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Quantification of fabrics and magmatic textures of rhyolite extrusive domes
Hrudková, Kristýna ; Lexa, Ondrej (advisor) ; Závada, Prokop (referee)
Bubbles in rhyolites are being formed during ascension of rhyolite magma up to the surface. That is beacuse of decreasing content of dissolved water in melt. Stability of bubbles is kept constant because of their own internal pressure, which they are able to sustain for a long period. Some bubbles can occure after the fragmentation of magma in extrusive bodies on the surface. Bubbles created this way have very small size and they don't participate in fragmentation. In my thesis I'm dealing with internal structure of some rhyolite magmatic bodies and description of mechanisms of bubble formation. Furthermore I will concentrate on methods of quantification of the internal structure of extrusive domes, i.e. the AMS magnetic minerals population structure and texture analysis of rock incisions. Texture analysis was concentrated on some aspects, which could help us to assess the extent of distribution of bubbles in strips. In conclusion, I compare the results of these methods to evaluate the importance of individual structural elements for structural-geological interpretation. We investigated samples from extrusive rhyolite body, which are being formed during the gradual egression of magma on the surface. We were investigated bubbles and their realtions between each other by using several methods. On the...
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Quantitative correlation of textural data obtained with CIP and EBSD method
Slunská, Petra ; Lexa, Ondrej (advisor) ; Machek, Matěj (referee)
Since 2011, the Institute of Petrology and Structural Geology, Charles University in Prague, worked with CIP - Computer Integrated Polarization microscopy as fast, inexpensive measurement of c-axis orientation of uniaxial minerals, mostly quartz in high definition. CIP method is developed from the early nineties in Switzerland (Heilbronner & Pauli 1993) and later in many other workplaces. The aim of this work was testing and calibration of optical and camera equipment to verify the accuracy and reliability of data obtained. Served as an independent measurement of EBSD (Electron Backscatter Diffraction) data obtained from the same part of the studied thinsections. The data obtained were analyzed by quantitative analysis of microstructures (PolyLX - MATLABTM toolbox; Lexa 2003). The samples used for testing the methodology mentioned were taken on the profile of Hvězdná and Zdobnice near Rokytnice in the Eagle Mountains by contact orlica-snieznik complex and its mantle. Field studies showed the existence of west dipping shear zone along the said contact and deformed orthogneiss show a macroscopic superposition of several deformation events. The resulting frequency histograms similarities and differences of angles c-axes and angles misorientace grains have a high consensus in the azimuthal criterion, axes...
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Polyphase structural evolution of superstructure and infrastructure in orogenic zones
Peřestý, Vít ; Lexa, Ondrej (advisor) ; Pitra, Pavel (referee)
Polyphase structural evolution of superstructure and infrastructure in orogenic zones Proterozoic basement rocks of the Teplá-Barrandian Unit (TBU) are affected by two main tectono-metamorphic events. The central and SW part of the TBU is a well-preserved relict of Cadomian episode. On the other hand, the western margin of the TBU shows superposition of polyphase early-varicsan deformation and metamorphism onto the pre- variscan fabric. The Střela river profile in the northern part of Teplá Crystalline Complex (TCC) exposes a continuous crustal section through western margin of the TBU from the low-grade phyllites (near biotite izograd) in the east to the high-grade rocks of kyanite zone at the contact with high-pressure Mariánské-Lázně Complex (MLC). Three main deformation events were distinguished in the studied area and the cross-section is interpreted as a fossil (devonian) suprastructure-infrastructure transition zone preserved in the carboniferous TBU superstructure. The oldest pre-variscan D1 phase produced flat-lying metamorphic foliation showing normal metamorphic zonation from the very low-grade in the upper part to at least garnet zone in the structurally lower part. Large scale upright folding of prevariscan foliation S1 occurred during early-variscan D2 event. Tight F2 folds were...
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Structural evolution of infra- and superstructure boundary in orogens
Peřestý, Vít ; Lexa, Ondrej (advisor) ; Franěk, Jan (referee)
ENGLISH ABSTRACT This work focuses on structural and deformational aspects of the crust development during orogeny, based on historical suprastructure/infrastructure concept. The uppermost suprastructure is dominated by steep fabrics, which evolved in a brittle regime within early stages of orogeny, and which sustain almost unchanged for the whole period of orogenic evolution. On the other hand, the infrastructure is located in the lower crust, where ductile processes dominate. Because the ductility is a thermally activated process, sufficiently long time is needed to heat the lower crust, and therefore the infrastructure is younger than suprastructure. Gently to shallowly dipping structures develop as a consequence of ductile flow. The aim of this study is to describe processes on the suprastructure/infrastructure boundary. Position of this boundary is closely related to brittle/ductile transition, and so that a brief introduction to rheology is included. Rheological boundaries are often places of high strain and high displacement gradients, which must be somehow accomodated. One possibility is to lose communication between adjacent levels and create a detachment plane, which is commonly supposed in the conventional thrust tectonics model. The other possibility is, that layers are at least partially...
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Geologický výzkum Antarktidy
Masarykova univerzita, Přírodovědecká fakulta, Brno ; Univerzita Karlova v Praze, Přírodovědecká fakulta, Praha ; Česká geologická služba, Praha ; Holub, František V. ; Kadlec, Jaroslav ; Svojtka, Martin ; Máčka, Zdeněk ; Jeřábek, Petr ; Žák, Jiří ; Lexa, Ondrej ; Klán, Petr ; Košler, Jan ; Mlčoch, Bedřich ; Nývlt, Daniel ; Mixa, Petr
Závěrečná zpráva popisuje výsledky čtyřletého projekt, kterých bylo dosaženo v jednotlivých dílčích úkolech: 1. Studium zdrojových oblastí a glacifluviálních a morénových sedimentů na ostrově James Ross ve vztahu k paleoklimatologickému a paleogeografickému vývoji oblasti; 2. Organické průmyslové polutanty - jejich koncentrace, chování a degradace v prostředí Antarktidy; 3. Geomorfologický výzkum kamenných ledovců, periglaciálních a paraglaciálních fenoménů na ostrově James Ross; 4. Podrobné geologické mapování území projektovaného biologického monitoringu; 5. Tektono-metamorfní vývoj hornin akrečního prizmatu Trinity Peninsula Group; 6. Magmatické stavby antarktického batolitu (sev. část Graham Land) a způsob jeho vmístění; Sedimentologický a geomorfologický záznam zalednění na ostrově James Ross a jejich korelace s vývojem zalednění v průlivu Prince Gustav.
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Geologický výzkum Antarktidy
Masarykova univerzita, Přírodovědecká fakulta, Brno ; Univerzita Karlova v Praze, Přírodovědecká fakulta, Praha ; Česká geologická služba, Praha ; Klán, Petr ; Máčka, Zdeněk ; Košler, Jan ; Mlčoch, Bedřich ; Nývlt, Daniel ; Jeřábek, Petr ; Žák, Jiří ; Lexa, Ondrej ; Mixa, Petr
V roce 2005 proběhly dvě terénní expedice. Hlavními cíli v této etapě byl geologický výzkum v širším okolí stavby stanice, který navazoval na předchozí, loňskou etapu a zahrnoval témata: Podrobné geologické mapování území širšího okolí budoucí stanice pro potřeby projektovaného biologického monitoringu; Studium zdrojových oblastí tillů a glacifluviálních sedimentů na ostrově James Ross ve vztahu k paleoklimatologickému a paleogeografickému vývoji oblasti; Geomorfologický výzkum kamenných ledovců, periglaciálních a paraglaciálních fenoménů na ostrově James Ross; Vývoj zalednění na ostrově James Ross, studium glaciálních a glacimarinních sedimentů terciérního i kvartérního stáří a zalednění; Paleoklimatická rekonstrukce během holocénu; Organické průmyslové polutanty - jejich koncentrace, chování a degradace v prostředí Antarktidy.
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