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Petrogenesis and evolution of the Davle Volcanic Complex
Santolík, Václav ; Ackerman, Lukáš (advisor) ; Krmíček, Lukáš (referee)
The Davle Volcanic Complex (DVC) situated in the Teplá-Barrandian unit (TBU) of the Bohemian Massif, is considered as a Neoproterozoic-Cambrian magmatic arc that developed on the northern active margin of Gondwana supercontinent during Cadomian accretionary orogeny. This study combines data obtained from fieldwork, petrography, rock-forming mineral microanalysis, major and trace element analysis, Sr-Nd-Pb isotopic systematics and U-Pb zircon geochronology in order to reveal the petrogenesis and evolution of the DVC. At least three-stage metamorphism including Cadomian seafloor alteration, Variscan regional metamorphism as well as contact metamorphism related to the emplacement of the Central Bohemian Plutonic Complex affected the DVC. The studied rocks follow calc-alkaline trend whereas tholeiitic trend previously reported is rather related to younger magmatic events. The northern part of the DVC is dominated by felsic subvolcanic (plagiogranite), volcanic (dacite- rhyolite) and pyroclastic (dacitic-rhyolitic tuffs and breccias) rocks with a few outcrops of basaltic andesite-andesite pillow lavas documenting the subaqueous activity of the DVC. These rocks are Na-rich, but K-poor, the plagiogranite contains albite most likely primary in origin, and exhibit highly radiogenic εNd values (~ +6 to +11),...
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Formation of realgar at the Mokrsko
Rodovská, Zuzana ; Drahota, Petr (advisor) ; Filippi, Michal (referee)
Summary: Throughout the world there are many places with a high concentration of arsenic in water. In the Czech Republic is such a place the area of Mokrsko, where arsenic in groundwater reaches the values, which are well above recommended limits for drinking water. On the studied locality arsenic is bound to secondary minerals containing iron; however, in the reducing conditions of the fluvial sediments arsenic is bound to newly-formed realgar accumulations associated with organic matter. Aim of this diploma thesis was to characterize realgar from this locality and try to determine the way and conditions of its origin. For the purpose of research, realgar and pore- water have been sampled, using lysimeters and rhizon samplers. Specimen of realgar was characterized by numerous standard techniques (XRD, SEM, TEM, chemical and isotopic composition). Water samples have been analysed for As, F and S species. Analysis of realgar using XRD, SEM and TEM techniques confirmed the presence of nanocrystalline realgar, forming clusters and needle like aggregates. Domination of divalent iron and reduced form of As3+ (4,3-7,3 mg/L) in similar concentrations has been observed within the pore- water samples. The concentration of dissolved sulfide was very low (cca 30 µg/L), on the other hand, content of sulphate was always...
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