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Lithology, geochemistry and metamorphic evolution of northern Hammar Domain (East-African Orogeny)
Gashe, Negessa Gonfa ; Verner, Kryštof (advisor) ; Racek, Martin (referee)
in English The studied part of the Hammar Domain is composed of the Neoproterozoic basement rocks belonging to the Southern Ethiopian Shield (SES), partly covered by volcanic and volcanosedimentary deposits of the Main Ethiopian Rift (MER). The high-grade migmatite to migmatized biotite paragneiss and amphibolites were intruded by numerous peraluminous granite and granodiorite bodies and gabbros of metaluminous composition. The results of U/Pb zircon dating of granodiorite yielded at 507.7 ± 3.2 Ma, which is interpreted as the age of magma emplacement and crystallization. The P-T estimation reveal the peak P-T conditions at ca. 1.21 to 0.88 GPa and ca. 842 to 700 řC which were followed by retrograde part P-T path (from ca. 0.84 to 0.12 GPa) with decrease of temperature from ca. 700 to 464 řC. The emplacement of gabbro in syn-tectonic settings took place at P = ca. 0.87 to 0.93 GPa and T ca. 650 řC reflecting magma emplacement to ca. 30 km in depth. Next, the syn- to post- tectonic emplacement and crystallization of biotite and amphibole-bioitite granodiorite reveal P = 0.27-0.52 GPa and T ca. 720-836. The events described above were associated with the latter period of the East-African Orogeny, which resulted in overall consolidation of the Gondwana continent.
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Equilibrium conditions of minerals in Al-Mg-rich eclogite from Světlík (Moldanubian Zone)
Tecl, Martin ; Faryad, Shah Wali (advisor) ; Racek, Martin (referee)
English abstrakt This thesis focusses on textural relations of Al-Mg-rich kyanite eclogite from Světlík-Suš locality in the monotonous group of the Moldanubian Zone. Mineral analyses and compositional maps were used to analyze detail relations and reactions responsible for mineral formation and/or their decomposition. The analyzed minerals were then compared with the chemical composition of minerals from other eclogites and garnet pyroxenites from studied locality. Based on bulk rock chemistry and mineral analyses, the studied kyanite eclogite is comparable rather with garnet pyroxenite. Minerals stable under eclogite facies conditions in the rock were garnet, jadeite rich clinopyroxene, Cr-kyanite and Ce-rich clinozoisite/zoisite, which is transformed to tabular pseudomorphosis. The rock shows clear evidence of granulite facies overprint. In total 9 types of symplectites were distinguished. Most of them were created under granulite facies condition. Compositional maps obtained for the Cr-rich kyanites show diffusion of Cr from kyanite to garnet during the granulite facies conditions. Symplectites with clinopyroxene and orthopyroxene were transformed into amphiboles during the decompression to amphibolite facies conditions. Keywords: eclogite, microscopy, mineral chemistry
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Thermobarometry of garnet peridotites and granulites from the Blanský Les Massif
Urychová, Michala ; Faryad, Shah Wali (advisor) ; Racek, Martin (referee)
English abstract Granulites of Moldanubian Zone are usually characterized by the presence of HP/UHP rocks of mafic and ultramafic compositions. The relationships between UHP rocks and granulites and their metamorphic history are subjects of many discussions. The Blanský Les Granulite Massif is the largest body of this type and includes numerous budines and bodies of serpentinized garnet peridotites, pyroxenites and amphibolic eclogites. PT conditions of granulites and garnet peridotites were estimated using different thermobarometric calculations. Temperatures 850-1050řC and pressures 15-20 kbar were calculated for granulites and 800-1000řC/25-40 kbar were estimated for garnet peridotites. Similar to other granulite bodies in the Moldanubian zone, the Blanský Les Granulite Massif is interpreted either as a segment of orogenic root, which was exhumed by viscous flow from low crust or the rocks reached eclogite facies conditions in the subduction channel first and then were overprinted by granulite facies metamorphism. Maximum depths of emplacement of garnet peridotites and other UHP rocks into granulites are limited by their pressure conditions. For these granulites the pressure is 22 kbar.
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Record of Cambro-Ordovician Extension in the Teplá Crystalline Unit
Jašarová, Petra ; Racek, Martin (advisor) ; Kusbach, Vladimír (referee)
In my thesis I would like to summarize informations about SW part of the Teplá- Barrandian Unit. Particularly interesting situation is in the Teplá Crystalline Complex and Mariánské-Lázně Complex during Cambro-Ordovician rifting. At the beginning I will remind some basic information about Bohemian Massif (evolution and distribution). The next part of the thesis is dedicated to the west part of the Teplá-Barrandian Unit in the context of sedimentary record in the eastern part of the Unit. In two other captures is described Teplá Crystalline and Domažlice Crystalline Complex with emphasis on the plutons, which help us to reveal evolution of this area. In the third part of the thesis I will characterize Mariánské- Lázně Complex (lithology, dating and evolution). This complex was interpreted as a dismembered Cambro-Ordovician metaophiolite complex affected by Variscan subduction. But the latest studies show that the HP rocks protoliths are late Cadomian age, thus the eclogites probably originated during exhumation of this area. According to new results the Mariánské-Lázně Complex represent a metamorfic core complex and the Teplá Crystalline Complex is the detached roof of it. The corronitic metagabbros on the border between Mariánské-Lázně and Teplá Crystaline complex are generally interpreted to be...
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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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Fabrics of the Weinsberg granitoids on example of the Prášily pluton (Moldanubický plutonický komplex)
Pour, Ondřej ; Verner, Kryštof (advisor) ; Racek, Martin (referee)
This bachelor 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 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 internal fabrics and structures of the Prášily pluton reflect emplacement mechanisms, kinematic history and evolution of the regional strain field during Variscan orogeny at around 330 Ma. The examined area provides crucial constraints for the geodynamic models of geological evolution of deeper parts of the Variscan orogen in the SW part of the Bohemian Massif.
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From Cambro-Ordovician extension to Variscan orogeny - study from the contact of Teplá crystalline and Mariánské Lazně complex
Jašarová, Petra ; Racek, Martin (advisor) ; Janák, Marian (referee)
Coronitic metagabbros occur as small isolated bodies along the contact between the Mariánské Lázně and the Teplá crystalline complexesin the NW of the Bohemian Massif. Metagabbros show variable metamorphic and textural characteristics with respect to their magmatic mineral assemblage and degree of metamorphism. The aim of this study is to characterize mineralogical, chemical, and microstructural changes related to metamorphic changes in selected representative samples. In addition, the associated calculation of P-T conditions can help to clarify the evolution of the boundary of both units as well as to provide constraints on formation of corona microstructures. Magmatic mineral assemblages in the metagabbros formed by plagiocase, orthopyroxene, clinopyroxene, amphibole, biotite and ilmenite occasionally olivine,spinel or quartz are generally well preserved. Metamorphism is mainly reflected by formation of single or multiple coronas at the contact of plagioclase with other primary minerals, the most common constuents are amphibole, garnet and orthopyroxene. Progressive breakdown of the magmatic plagioklase is reflected by formation of mixture An40 and An90 plagioclase associated with spinel,corundum and occasionally kyanite. According to chemical composition metagabbros follow tholeiitic trend and...
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