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Hydrodynamic and thermal mode ling of reactive flow in the surroundings of intrusions
Jandová, Tereza ; Dolejš, David (advisor) ; Bruthans, Jiří (referee)
English Summary Intrusion of magma into the Earth's crust is associated with significant thermal perturbations, release of aqeuous fluids and formation of hydrothermal system. In order to better understand the feedback relationships between fluid flow, thermal evolution and permeability variations, we have modeled conductive and advective cooling of a shallow- crustal pluton using the SHEMAT software. Our model represents a two-dimensional cross section through the lithosphere with homogeneous material properties, whebery the heat and mass conservation equations are solved by finite difference method. We first calculate the stable lithospheric geotherm by emplying constant basal thermal flow of 40 mW m-2 and a constant surface temperature. Subsequently, we consider a rectangular magmatic intrusion emplaced at 5-10 km depth, which forms a contact aureole by conductive cooling. With time, a mushroom-like shape of the contact aureole is predicted. Inclusion of aqueous fluid flow into the model causes only a small alteration of thermal evolution mainly because the permeability is low and the fluid mass is negligible due to very low density under hydrothermal conditions. In addition to thermal effects, we have explored variations in hydraulic head in order to address the ensuing effects on the flow velocity. The...
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Mineral assemblages and conditions of origin of metamorphic skarns in the Bohemian Massif
Bubal, Jan ; Dolejš, David (advisor) ; Pertoldová, Jaroslava (referee)
ENGLISH SUMMARY MINERAL ASSEMBLAGES AND CONDITIONS OF ORIGIN OF METAMORPHIC SKARNS IN THE BOHEMIAN MASSIF Calcic-iron skarns are a characteristic rock type of regional metamorphic complexes wirkude. In the Bohemian Massif, characteristic enrichment in Ca, Al, and Fe as well as mineral assemblages, textures are similar to their contact metamorphic counterparts but their origin remains unclear. In this thesis, we document petrography, mineral assemblages and chemistry of skarns and apply phase equilibrium models to reconstruct conditions of their formation. Skarns at Vlastějovice (Moldanubian zone), Malešov (Kutná Hora complex) and Měděnec (Saxothuringian zone) contain primary assemblage of garnet, clinopyroxene and magnetite, followed by crystallization of amphibole, epidote, formation of carbonate veins, and silicification. Some of these phenomena are related to the emplacement and fluid release from dykes of granitic pegmatites. Garnet represents the most abundant rock-forming minerals. Primary fine-grained aggregates (Gr30-50Alm30-40And10-30) are often recrystallized into euhedral grains or monomineralic masses with preserved chemical zoning (Gr05-30Alm1-30And40-90). At the Měděnec locality, garnets evolved towards andradite-skigaite composition. Clinopyroxene belongs to the diopside-hedenbergite series,...
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Numerical model for the origin of magmatic textures and its application to the Fichtelgebirge/Smrčiny granite batholith
Špillar, Václav ; Dolejš, David (advisor) ; Ježek, Josef (referee) ; Žák, Jiří (referee)
Magmatic processes are major agents responsible for the formation and differentiation of the Earth's crust. In contrast to extensive efforts to improve understanding and utility of igneous geochemistry, physical processes of magma differentiation and solidification remain largely unclear. Large variability of igneous textures provides record of these processes and intensive parameters governing the crystallization. In this thesis, we develop quantitative methods, which allow us to better interpret igneous textures in the framework of physics of solidification. We have developed a new three-dimensional model of crystallization from one- component melt driven by homogeneous and heterogeneous nucleation and crystal growth. The predicted textures are quantitatively characterized by crystal size distributions, spatial distribution functions and parameters representing grain contact relationships. The model employs high resolution in a large volume simulation domain in order to produce statistically stable results. Our simulations, performed for various functional forms of nucleation and growth rates with respect to time, imply that (i) crystals are ordered (anti-clustered) on short length scales. This reflects that other crystals already have a finite size at the time of nucleation of younger crystal,...
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Quantitative description of textures in volcanic rocks: Case study of trachybasalt from Dubičná
Ditterová, Hana ; Dolejš, David (advisor) ; Rapprich, Vladislav (referee)
- iii - ENGLISH ABSTRACT Quantitative description of textures, in particular, the distribution of grain sizes, is becoming a powerful tool for interpreting kinetic processes that govern crystallization of igneous rocks. Variation in grain size are frequently represented by logarithm of population density vs. linear crystal size, where the majority of igneous rocks forms a linear trend. Its slope provides an estimate of characteristic grain size, or growth rate and crystallization time, whereas the intercept provides the nucleation density. The log-linear trend is predicted to result from kinetic nucleation and growth processes only, whereas its modifications such as kinks or curvature are due to mechanical separation or accumulation of crystals, magma mixing or Ostwald ripening (coarsening) in the presence of melt. In order to investigate the true, three-dimensional crystal size distribution, the raw two-dimensional data acquired from thin sections or rock slabs must be processed by various stereological methods. We illustrate application of quantitative textural measurements to distribution and origin of clinopyroxene crystals in a trachybasaltic lava flow from Dubičná near Úštěk. This effusion belongs to Cenozoic volcanic products in the Bohemian Massif, specifically to its main Eocene-Miocene stage in...
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Reactive fluid flow and origin of the fracture-controlled greisens in the Horní Blatná granite pluton, Krušné hory Mts.
Heřmanská, Matylda ; Dolejš, David (advisor) ; Štemprok, Miroslav (referee)
Magmatic intrusions emplaced in the shallow continental crust are often associated with hydrothermal alteration and mineralization systems. Alteration zones and their assemblages can be described by means of reaction progress and this variable then used to calculate the time-integrated fluid fluxes, responsible for the mineral formation, if gradients in fluid composition, temperature and pressure are known or estimated. Two limiting cases of this approach have been applied in previous numerical models: (i) infiltration of aqueous fluid that is out of equilibrium with the host rocks, thus producing an alteration sequence as the fluid flux increases, and (ii) fluid flow in local equilibrium with host rocks, where mineral changes are induced by pressure and temperature gradients along the flow path. These two models generally yield results that differ by several orders of magnitude but are both in use for estimating fluid fluxes and transport properties in the lithosphere. We propose a combined model that evaluates the disequilibrium fluid infiltration and the pressure-temperature gradients simultaneously, and apply it to the interpretation of fracture-controled greisen alteration in the Horní Blatná granite pluton in the Krušné hory Mts. (Czech Republic). The Horní Blatná pluton is a composite...
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