National Repository of Grey Literature 9 records found  Search took 0.01 seconds. 
Deformation history and decomposition of ternary feldspar in the proto-phase of the Blanský les felsic granulite evolution
Jirků, Markéta ; Jeřábek, Petr (advisor) ; Závada, Prokop (referee)
This diploma thesis deals with the oldest recognized deformation microstructure of felsic granulites of Blanský les (southern Bohemian Massif) in order to understand their lower crustal deformation history later altered during exhumation. Moreover, the study is focused on decomposition of ternary feldspars in the proto-phase of evolution of granulite microstructure. Based on the structural and microstructural analyses of the less developed cleavage I. and the more developed cleavage II., it was possible to distinguish between two deformation structures. The S1 is defined by compositional banding of alternating quartz bands with bands rich in plagioclase, garnets and with porphyroclasts of alkaline feldspars. The S1 cleavage is transposed into the S2 cleavage. During intense reworking of S1 into S2, the quartz bands were decomposed and recrystallized into the ribbons. The feldspar thermometry of the cleavage I. and II. allowed to distinguish the three stages of decomposition of feldspars. A continuous temperature decrease was observed as reflected by the individual microstructures. The quantitative microstructural analysis indicate the shape preferred orientation of the grain boundaries of two-feldspar matrix. The shape preferred orientation of cleavage I. is controlled by the albite rim, however after its...
Characteristics of polyphase deformation in quartz microstructure: an example from the Krkonoše-jizera Unit
Očenášková, Eva ; Jeřábek, Petr (advisor) ; Závada, Prokop (referee)
Quartzite samples taken in the east part of Krkonoše-Jizera Massif belong to metasedimentary cover of paraautochtonous unit. Rocks underwent a polyphase deformation which established a strong shape preffered orientation (SPO) of quartz grains. In folded quartz veins, deformation overprint mechanisms and microstructure, CPO and SPO relations were studied. For determination of crystal preffered orientations (CPO) the method of computer integrated polarization microscopy (CIP) was used. Microstructural analysis was focused on grain sizes, aspect ratios, long axis orientations and their relation to the deformation overprint grade. Results implies that dominant mechanism of quartz grain recrystallization is grain boundary migration. Folds were created by simple shear in microscale. The deformation overprint grade is strongest in the top of the fold hinge, where grains achieve highest aspect ratios and sizes. In the lower parts of the fold hinge the original CPO is preserved in small grains and SPO has similar orientation to original CPO. During folding CPO and SPO rotated with shear direction in dependance on deformation overprint grade.
Textural analysis of granites from the Western Krušné hory/Erzgebirge pluton: implications for crystallization kinetics and crystal-melt interactions
Ditterová, Hana ; Dolejš, David (advisor) ; Závada, Prokop (referee)
Texture of igneous rocks, which includes size, shape and spatial distribution of grains, represents the final record of kinetic and mechanical processes operating during ascent and final emplacement of a magma. However, traditional geochemical approaches cannot assess and verify the physical processes of magma solidification, in particular, crystal nucleation and growth, textural coarsening, or mechanical crystal-melt interactions. In this work, I apply stereological methods to quantitatively characterize the textures and to interpret the crystallization history of granitic rocks in the Western Krušné hory/Erzgebirge and Vogtland. The Western Krušné hory/Erzgebirge granites consist of three suites: biotite granites (Kirchberg), muscovite-biotite microgranites (Walfischkopf), and topaz-zinnwaldite alkali- feldspar granites (Eibenstock), which consist of eight intrusive units and two aplite dyke sets. The entire granite sequence exhibits an extreme and nearly continuous differentiation range, but in detail the evolutionary trends of each suite are independent, and individual intrusive units are also clearly compositionally separated. The granites consist of 29-43 vol.% quartz, 20-30 vol. % plagioclase, 22-31 vol. % K-feldspar, 2-9 vol. % biotite, <2 vol. % muscovite, and minor topaz and apatite. All...
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...
Mechanisms of differentiation and emplacement of peraluminic granite magma: Říčany pluton, Bohemian Massif
Trubač, Jakub ; Žák, Jiří (advisor) ; Závada, Prokop (referee)
English abstrakt This thesis is focused on emplacement mechanisms of granitic magma into upper continental crust. The studied area is the Říčany pluton due to its unusual and asymmetric shape. Therefore, it represents a suitable intrusion for interpretation different models referring to emplacement of granitic magma. Common model for ascent of magma is incremental diking in present. The Říčany pluton of the Central Bohemian Plutonic Complex is a post-tectonic elliptical shallow-level intrusion emplaced into low-grade Neoproterozoic and Lowe Carboniferous times (~337 Ma). It comprises of outer, more fractionated, strongly porphyritic granite and inner, less evolved, weakly porphyritic granite. Mesoscopic foliation represents an onion-skin pattern and corresponds well to the magnetic (AMS) foliations. Magnetic lineation has a gentle dip (0-20ř) and closely parallels with the pluton contact in its outer part whereas the lineation dips steeply (60-70ř) with a variable trend in the pluton interior. Author interprets these fabrics as a result of a helical flow, which is a faster subvertical flow in the low-viscosity pluton centre being accompanied by a subhorizontal flow in the outer, higher-viscosity (phenocryst-rich) margin. The proposed scenario of the helical magma flow can provide a viable mechanism for the...
Plains volcanism in Tharsis region on Mars: Ages and Rheology of Eruption Products
Brož, Petr ; Hauber, Ernst (referee) ; Závada, Prokop (advisor)
Plains volcanism in Tharsis region on Mars: Ages and Rheology of Eruption Products Remote sensing data show clusters of low shield volcanoes in Tharsis volcanic province on Mars (Hauber et al., 2009). These low shield volcanoes and associated landforms are comparable with terrestrial plain-style volcanic products (Plescia, 1981) as defined by Greeley (1982) in the Snake River Plain in Idaho, which represents an intermediate style of volcanic activity ranging between flood basalts and the Hawaiian shields. While a number of recent studies addressed some aspects of low shield volcanoes, in particular their morphology, morphometry, and lava rheology, no systematic study including the chronology for the entire region of Tharsis is available so far. The goal of this work is to determine relative and absolute ages of low shield volcanoes and surrounding lava flows and their basic rheological properties. We used crater size-frequency distribution method (CSFD) developed by Hartman and Neukum (2001) and Ivanov (2001) for determination of absolute dating of the surface. For calculation of the rheological properties of the lava, we used methods established by Hiesinger et al. (2007). It is known that the low shield volcanoes on Mars consist of basaltic lavas that had low viscosities during their effusion, which can...

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1 Závada, Pavel
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