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From deposition to caldera resurgence: pyroclastic density current dynamics as revealed by magnetic anisotropy of the Teplice rhyolite, Bohemian Massif
Vitouš, Petr ; Tomek, Filip (advisor) ; Mlčoch, Bedřich (referee)
Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...
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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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From deposition to caldera resurgence: pyroclastic density current dynamics as revealed by magnetic anisotropy of the Teplice rhyolite, Bohemian Massif
Vitouš, Petr ; Tomek, Filip (advisor) ; Mlčoch, Bedřich (referee)
Better understanding of pyroclastic density current (PDC) dynamics is one of the key volcanological focuses, as PDCs represent one of the most life-threatening volcanic hazards. PDCs associated with explosive collapse calderas are difficult to observe and examine directly, and thus research of internal architecture of calderas and their PDC deposits is focused on extinct and partly eroded volcano-plutonic systems. Such a case is the Late-Carboniferous Altenberg-Teplice caldera in NW Bohemian Massif, which exposes a large body of ignimbrites (deposits of the PDC) called Teplice rhyolite (an intra-caldera fill). This body is well exposed on the southern flank of the Krušné hory/Erzgebirge Mts., mainly its members: Teichweg, Lugstein-Pramenáč, Vlčí kámen-Medvědí vrch and Přední Cínovec. As these ignimbrites appear macroscopically isotropic, I employed the Anisotropy of magnetic susceptibility (AMS) in order to quantify their internal structure. A total of 1232 specimens from 63 sampling stations were analyzed for the AMS, complemented by susceptibility vs. temperature variations and petrographic observations. Obtained AMS data, carried by a mixture of paramagnetic ferrosilicates and low-Ti titanomagnetite, indicate various processes recorded in ignimbrites. The relatively oldest and moderately welded Teichweg...
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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...
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