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Evolution of the Bohemian Massif: Insights from numerical modeling
Maierová, Petra ; Čadek, Ondřej (advisor) ; Babuška, Vladislav (referee) ; Bina, Craig R. (referee)
The Bohemian Massif was consolidated during the Variscan orogeny (~400-300 Ma), which involved several oceanic subductions and collisions of continental micro-plates. The central part of the Bohemian Massif, the Moldanubian domain, shows a large accumulation of felsic high-pressure metamorphs. We present a numerical model of exhumation of these rocks due to continental collision and underthrusting. The key feature of the model is a felsic (light, rheologically weak and rich in radioactive elements) material in the lower crust of one of the colliding blocks. We examine the influence of the rate of convergence of the two blocks, radiogenic heating in the felsic lower crust and efficiency of erosion, on the model evolution and pressure-temperature conditions in the lower-crustal material. The models where the material is sufficiently weakened due to radiogenic heating show formation of an orogenic plateau, sedimentation in a foreland basin, and crustal thickening accompanied by gravity-driven exhumation of the lower crust and subsequent sub-horizontal flow in the middle crust. In colder and/or faster models, the thickening is dominated by folding. We correlate the tectonic style of these two types of models with differences between the high-grade rocks in the southern (Moldanubian) and northern (Sudetic) parts...
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Teleseismic Tomography of the Upper Mantle beneath the Bohemian Massif
Karousová, Hana ; Plomerová, Jaroslava (advisor) ; Růžek, Bohuslav (referee) ; Zahradník, Jiří (referee)
Passive seismic experiments, MOSAIC, BOHEMA I-III, EgerRift, or, PASSEQ, carried out in the region of the Bohemian Massif (BM), allowed a detailed study of velocity structure of the upper mantle. We present results of tomography studies of the upper mantle beneath the north-eastern and southern parts of the BM based on the data from the BOHEMA II and BOHEMA III experiments (2004-2006). Despite the fact that regions with the highest resolution of velocity perturbations differ in the models, tomography images are similar in overlapping parts. Models of the upper mantle show mostly low- velocity perturbations relatively to radially symmetric velocity model of the Earth beneath the BM. Limited high-velocity heterogeneity beneath the Moldanubian unit, extended in the NE-SW direction, reflects thickening of the lithosphere due to a collision of the BM with the Brunovistulian micro-plate during the Variscan orogeny. The tomography based on the data from the BOHEMA III experiment revealed significant high-velocity heterogeneity in the southern margin of the model with a subduction of the lithosphere beneath the Eastern Alps. Tomographic tests showed that effects of uncorrected velocity heterogeneities within the crust can appear as deep as 100 km and, therefore, they could lead to erroneous interpretation of...
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Paleoenvironmental record of carboniferous lacustrine deposits of central and western Bohemian basins: analysis and korealiton of mineral and biogenic proxies
Lojka, Richard ; Hradil, David (advisor) ; Hladil, Jindřich (referee) ; Janočko, Juraj (referee)
Ph.D. thesis represents summary of multidiciplinary palaeoenvironmental and palaeoclimatic research of the most significant Late Pennsylvanian lacustrine horizon of the central and western Bohemian basins - the Malesice Member of the Slaný Formation. Two cores from new shallow drills, situated 80 km apart, were analysed. Multidisciplinary approach is based on description of lamination structure and periodicity; mineral and isotopic composition of autigennic carbonates, namely siderite; compositiona of detrital minerals including clay mineral assemblages; and composition of autochthonous and allochthonous organic particles including palynospectra. Detailed analysis of drill cores lead to the identification of individual phases of lake development linked with lake-level fluctuation and water-column stratification, which were driven by a sume of precipitation and its seasonal distribution. Changes in precipitation also affected compostion and density of vegetational cover in the lake surroundings, weathering intesity of source rocks and degradation of organic matter in the drainage basin, and so precipitation affected final grain-size and composition of detrital material deposited in the lake. Beside common environmental signatures at both studied sites, there are also significant...
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Fabrics and geodynamic evolution of orthogneisses in the Moldanubian Zone
Kryl, Jakub ; Verner, Kryštof (advisor) ; Venera, Zdeněk (referee)
Fabrics and geodynamic evolution of Moldanubian orthogneisses English abstract The aim of this paper is a structural analysis of selected mostly Cambro-Ordovician orthogneisses cropping out in a part of high-grade rocks of western Moldanubian Zone. These rocks have been affected by HT-MP/LP metamorphism and the polyphase deformation during the Variscan orogeny. In the blaník orthogneisses, (Qtz + Kfs + Plg + Bt ± Ms ± Sill ± Ky) an early deformation banding dips steeply to SSE to ESE. These fabrics were overprinted by NW to N gently dipping foliation with well developed stretching lineations plunging to W. Rare kinematic indicators (e. g. fold and pressure shadows asymmetry) reveal a strong subvertical contraction and stretching in the ~N-S direction. Based on the microstructural analysis this contractional event was connected with the activity of "Grain Boundary Migration Recrystallization" (GBM). Ductile shear zones dipping to E, locally ESE or ENE were identified. Bechyně orthogneisses (Qtz + Kfs + Plg + Bt ± Ms) is a N-S elongated body with the presence of regional pervasive metamorphic foliation dipping homogenously under low angles from SSW to WNW . These foliations bear well developed mineral or stretching lineation of quartz, biotite and feldspar aggregates plunging to ~SW. In the blaník orthogneiss...
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Geological park of Charles University, Faculty of Science - web pages
Poláček, Boris ; Vondrovic, Lukáš (advisor) ; Trubač, Jakub (referee)
This bachelor's thesis is focused on the presentation of the Geological park of the Faculty of Science, Charles University in Prague. The ambition is to popularize significant architecture and evolution of the Bohemian massif. It consists of two different parts. The first is focused on general description of modern findings and opinions of regional zonality and petrological composition of the Bohemian massif. The second part is focused on the presentation of the Geological park and its brandnew website itself. This website has a clear goal to conduce to the popularization of the knowledge of geology of a significant part of our country as comprehensive as possible. Key words: geological park, Bohemian massif
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Preservation of HP minerals and textures in felsic and mafic granulites from the Rychleby Mts.
Schlöglová, Kateřina ; Faryad, Shah Wali (advisor) ; Kotková, Jana (referee)
Diploma thesis - Kateřina Schlöglová - 2011 1/2 English abstract Granulites of the Rychleby Mts. represent relics of high-pressure eclogite-facies metamorphic rocks that are scattered in various crustal and mantle segments of the Variscan orogen in central Europe. These rocks may provide important insights into early stages of Variscan plate convergence and burial as well as exhumation mechanisms. We use mineral assemblages and chemistry to reconstruct the pressure-temperature paths, mechanisms of melting, and conditions of mineral preservation of high-pressure granulites, as well as whole- rock geochemistry to aid in interpretation of granulite precursors and their geodynamic setting. The mafic granulites consist of garnet, omphacite, two feldspars, and quartz with accessory rutile and zircon. The peak assemblage was partly replaced by pargasitic amphibole and biotite. Garnet grains are zoned from Grs36Py10Alm54 (core) to Grs20Py38Alm42 (rim), and host inclusions of phengite, omphacite, unmixed feldspars, kyanite, and rutile. Omphacite composition varies from Di44Hd14Jd42 (inclusions in garnet) through Di63Hd20Jd17 (porphyroblasts) and Di63Hd24Jd13 (symplectitic intergrowths with plagioclase). Reintegrated composition of the feldspar porphyroblasts is Or43Ab53An04. The felsic granulite variety is composed...
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The Late Devonian to early Carboniferous kinematic evolution of the Teplá-Barrandian/Moldanubian boundary
Tomek, Filip ; Žák, Jiří (advisor) ; Babuška, Vladislav (referee)
ENGLISH ABSTRACT The Late Devonian to Early Carboniferous kinematic evolution of the Teplá-Barrandian/Moldanubian boundary The Staré Sedlo complex (SSC) is a relic of meta-igneous arc-related pluton in the southern part of the Sedlčany-Krásná Hora roof pendant, intruded by granitoids of the Central Bohemian Plutonic Complex along the boundary of Teplá-Barrandian (TBU) and Moldanubian units (MU), Bohemian Massif. The SSC mainly comprises deformed orthogneisses of calc-alkaline granodiorite to tonalite protoliths of Late Devonian age (380−365 Ma; Košler et al., 1993) that were commonly mingled with minor basic magmas. Locally preserved subhorizontal intrusive contacts of the orthogneisses against their meta-sedimentary host rock indicate that these magmas intruded as a sill complex. The SSC preserves a rather unusual flat-lying subsolidus foliation (dip <40ř) associated with subhorizontal ~NE-SW-trending mineral lineation. Mesoscopic structures, anisotropy of magnetic susceptibility (AMS), and deformational microstructures indicate prolate shape of the strain ellipsoid with dominant coaxial pure shear regime. The solid state microstructures record cooling of the orthogneiss protolith down to the ambient greenschist facies conditions followed by its static recrystallization due to the intrusion of the younger...
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Fabrics and emplacement of Weinsberg - type granitoids (Moldanubian Batholith)
Pour, Ondřej ; Verner, Kryštof (advisor) ; Buriánek, David (referee)
English abstract This diploma thesis is concerned with the brief introduction to the structures and fabrics in granitoid plutons. In the next part of this work are sumarized results of structural analyses of Weinsberg-type granite intrusion (Prášily and Strážný pluton) located in the SW part of high-grade rocks of the Moldanubian Zone. This research proceeded based on a combination of field structural data and results of AMS (Anisotropy of magnetic susceptibility) method. The emplacement and crystallization of both studied magmatic bodies took place in cooperation with the final phases of S3-fabrics development. This "bavarian phase" has a character of heterogenous deformation with indications of the dextral subhorizontal shear (WNW-ESE strike). During this event, syntectonic emplacement and internal fabrics development of strážný pluton took place at ~322 Ma. The transpression was followed by the localized transtension tectonics in NE direction, probably in cooperation with exhumation of high-grade metamorphic rocks of Bavarian terrane. In this phase, at ~320 Ma, the granitoids of Prášily pluton were emplaced into the considerably exhumed crust of the Moldanubian region.
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Response of selected rivers of the Bohemian Massif to lithological and structural conditions
Flašar, Jan ; Nývlt, Daniel (advisor) ; Kalvoda, Jan (referee)
Three groups of streams were selected in the area of the Bohemian Massif: the Berounka river with its source streams; the Vltava river with its tributaries the Malše and the Lužnice; the Labe river with its tributaries the Cidlina, the Bystřice and the Javorka. The lithological and tectonical influences to several parameters of the streams were studied. These parameters include: stream gradient, orientation of the stream and sinuosity of the stream. Data were obtained from digital elevation models, aerial photographs, topographical and geological maps. The longitudinal profiles of the streams (in the combination with geological cross-sections), the SL indexes and the gradient/sinuosity graphs were created on the basis of the obtained data. These tools were used for evaluation of the influence of lithology and the tectonics to the streams. The evolution of the streams and the stream-groups was evaluated and compared as well. A strong influence of lithology on the stream gradient was found on most of the analysed streams. The tectonic situation, on the contrary, had strong influence on the orientation of the streams, especially in the resistant rocks. Also, there were selected areas, where was a higher probability of quaternary vertical movements influencing the streams (mountainous areas of the Novohradské...
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