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Deformation and petrological record of polyphase quartzo-feldspathic rocks in Erzgebirge, Bohemian Massif
Kryl, Jakub ; Lexa, Ondrej (advisor) ; Závada, Prokop (referee) ; Hasalová, Pavlína (referee)
The Erzgebirge dome, exposing Proterozoic - Early Palaeozoic metagranitoids and metasedimentary rocks of the Saxothuringian domain in the Bohemian Massif, is formed by a tectonic stack of several UHP-HP and HT units exhumed during the Variscan continental subduction-collision process. A systematic study of orthogneiss deformation microstructures carried out on a regional scale has been done to evaluate these units' extent and relative structural position in the subduction complex. Five different microstructural types have been distinguished, revealing two overprinting sequences with 1) coarse-grained microstructures in the parautochthonous Kateřina-Reitzenhain Dome and 2) fine- grained microstructures in the allochthonous HP-HT Gneiss Eclogite Unit I. P-T conditions of the individual overprinting microstructures calculated by conventional thermobarometry suggest continuous deformation during exhumation along two contrasting P-T paths. The warmer one in the parautochthonous unit showed exhumation from ~13.5 kbar and ~820 ◦C to ~3 kbar and ~500 ◦C, while the colder one in the allochthonous unit showed exhumation from ~16 kbar and ~740 ◦C to ~3 kbar and ~400 ◦C. The overprinting microstructures are associated with vertical shortening interpreted as ductile thinning. This deformation started at depths...
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Position of Saxonian granulite within the frame of European Variscides
Ramešová, Olga ; Jeřábek, Petr (advisor) ; Racek, Martin (referee)
The Saxonian Granulite Massif (the type granulite locality) is situated in the northwestern part of Bohemian Massif. It is an antiform with dome structure, which came to the surface from below SaxoThuringian Paleozoic units. It consits of high-pressure "Granulite core" with felsic and mafic granulites, which are surrounded by tectonic cover called "Schist mantle" of low-grade upper- crustal rocks. Massif is penetrated by several granite bodies. The Core and Mantle are separated by shear zone with a thickness of about 2 km. Geochronological dating of complex exhumation gives ages of about 340 Ma. The whole complex is affected by system of foliation and lineations. Massif was deeply buried, extremely heated and then exhumed with high exhumation rates during post collision extensional phase of the Variscan Orogeny.
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Structural evolution, magnetic fabric and mechanism of exhumation of the Podolsko complex
Burjak, Miroslav ; Žák, Jiří (advisor) ; Franěk, Jan (referee)
This thesis concentrates on a detailed field and structural analysis of the Podolsko complex, Moldanubian unit, Bohemian Massif, complemented by a microstructural study and analysis of magnetic susceptibility (AMS). The Podolsko complex occupies the footwall of a major Variscan normal shear zone and is juxtaposed against the southern to southeastern margin of the Central Bohemian Plutonic complex. During the field work, more than 160 outcrops were examined, the AMS samples were taken at 25 stations, and samples for microstructural studies were taken from 12 localities. On the micro-scale, leucocratic migmatites contain abundant garnet grains which may represent relics of an earlier (ultra-)high preassure metamorphic phase. Retrogression is obvious in other samples of biotite migmatites of the Moldanubian Variegated unit. The retrogression is marked by the presence of sillimanite and chlorite. The main tectonometamorphic event in the Podolsko complex is extensive migmatization coeval with formation of pervasive flat-laying fabric. This is corroborated by the AMS study which indicates concordant steep to flat-laying magnetic and mesoscopic foliations striking NNW-SSE. The AMS also shows that the subhorizontal N-S to NNW-SSE trending magnetic lineations in the Podolsko complex correspond to those in the...
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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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Structural evolution, magnetic fabric and mechanism of exhumation of the Podolsko complex
Burjak, Miroslav ; Žák, Jiří (advisor) ; Franěk, Jan (referee)
This thesis concentrates on a detailed field and structural analysis of the Podolsko complex, Moldanubian unit, Bohemian Massif, complemented by a microstructural study and analysis of magnetic susceptibility (AMS). The Podolsko complex occupies the footwall of a major Variscan normal shear zone and is juxtaposed against the southern to southeastern margin of the Central Bohemian Plutonic complex. During the field work, more than 160 outcrops were examined, the AMS samples were taken at 25 stations, and samples for microstructural studies were taken from 12 localities. On the micro-scale, leucocratic migmatites contain abundant garnet grains which may represent relics of an earlier (ultra-)high preassure metamorphic phase. Retrogression is obvious in other samples of biotite migmatites of the Moldanubian Variegated unit. The retrogression is marked by the presence of sillimanite and chlorite. The main tectonometamorphic event in the Podolsko complex is extensive migmatization coeval with formation of pervasive flat-laying fabric. This is corroborated by the AMS study which indicates concordant steep to flat-laying magnetic and mesoscopic foliations striking NNW-SSE. The AMS also shows that the subhorizontal N-S to NNW-SSE trending magnetic lineations in the Podolsko complex correspond to those in the...
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Position of Saxonian granulite within the frame of European Variscides
Ramešová, Olga ; Jeřábek, Petr (advisor) ; Racek, Martin (referee)
The Saxonian Granulite Massif (the type granulite locality) is situated in the northwestern part of Bohemian Massif. It is an antiform with dome structure, which came to the surface from below SaxoThuringian Paleozoic units. It consits of high-pressure "Granulite core" with felsic and mafic granulites, which are surrounded by tectonic cover called "Schist mantle" of low-grade upper- crustal rocks. Massif is penetrated by several granite bodies. The Core and Mantle are separated by shear zone with a thickness of about 2 km. Geochronological dating of complex exhumation gives ages of about 340 Ma. The whole complex is affected by system of foliation and lineations. Massif was deeply buried, extremely heated and then exhumed with high exhumation rates during post collision extensional phase of the Variscan Orogeny.
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Exhumation of mid-crustal rocks by a brittle-ductile unroofing mechanism, an example from the Veporic crystalline complex in the West Carpathians
Bukovská, Zita ; Jeřábek, Petr (advisor) ; Milovský, Rastislav (referee)
Study of the structural and metamorphic record of the eastern part of contact zone within Vepor and Gemer units in Central West Carpathians has interpreted the burial and exhumation in the evolution of alpine orogeny. The studied area is built by granitoid rocks of Vepor basement and metapelites of cover sequences both Vepor and Gemer units. Three structural fabrics have been identified in the area, which are correlated with so far described deformation stages. Higher metamorphosed rocks with presence of two generation garnets were found out within lower metamorphosed metapelites of cover sequences. From the garnet - biotite thermometry the metamorphic conditions for the rims were established to 550-580řC. Whereas muscovite and in some case chlorite, are the only metamorphic phases in neighbouring cover rocks. Three generations of white micas are documented within structural fabrics. The oldest muscovites, magmatic in origin (Ms1), younger phengites (Phg) present in fabrics S1 and youngest muscovites (Ms2) present in fabric S2. The study of quartz microstructures distinguished aggregates and from aggregates coming band microstructures. These are mostly found in deformed granitoids, sometimes also in cover quartzites and can have sigma-shape geometry. The aggregate microstructure, representing S1...
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