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Textural analysis of granites from the Western Krušné hory/Erzgebirge pluton: implications for crystallization kinetics and crystal-melt interactions
Ditterová, Hana ; Dolejš, David (advisor) ; Závada, Prokop (referee)
Texture of igneous rocks, which includes size, shape and spatial distribution of grains, represents the final record of kinetic and mechanical processes operating during ascent and final emplacement of a magma. However, traditional geochemical approaches cannot assess and verify the physical processes of magma solidification, in particular, crystal nucleation and growth, textural coarsening, or mechanical crystal-melt interactions. In this work, I apply stereological methods to quantitatively characterize the textures and to interpret the crystallization history of granitic rocks in the Western Krušné hory/Erzgebirge and Vogtland. The Western Krušné hory/Erzgebirge granites consist of three suites: biotite granites (Kirchberg), muscovite-biotite microgranites (Walfischkopf), and topaz-zinnwaldite alkali- feldspar granites (Eibenstock), which consist of eight intrusive units and two aplite dyke sets. The entire granite sequence exhibits an extreme and nearly continuous differentiation range, but in detail the evolutionary trends of each suite are independent, and individual intrusive units are also clearly compositionally separated. The granites consist of 29-43 vol.% quartz, 20-30 vol. % plagioclase, 22-31 vol. % K-feldspar, 2-9 vol. % biotite, <2 vol. % muscovite, and minor topaz and apatite. All...
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Mineral assemblages, alteration reactions and transport model of the greisen formation in the Horní Blatná granite pluton, Krušné hory Mts.
Heřmanská, Matylda ; Dolejš, David (advisor) ; Štemprok, Miroslav (referee)
English abstract Hydrothermal systems related to highly evolved granitic magmas host diverse mineralization styles and provide an important source of economic metals. This master thesis concentrates on description and interpretation of geological structure, petrographic and textural variability, alteration zoning and calculation of time-integrated fluid fluxes recorded in highly evolved granites and tin-mineralized greisens of the Horní Blatná massif in the Western Krušné hory pluton. The massif is a composite intrusion, which consists of a large number of intrusive units emplaced during two stages. The first stage is represented by sparsely porphyritic fine-grained low-lithian annite granites that can be correlated with marginal granites (G2) of the Fichtelgebirge (Smrčiny) batholith or with intermediate granites (Walfischkopf type) of the Western Krušné hory (Erzgebirge) pluton. Intrusive batches of the second stage progressively evolve from medium- to coarse-grained serial high-lithian annite and zinnwaldite granites with topaz and rare tourmaline towards aphyric fine-grained zinnwaldite (or trilithionite) granites. This suite corresponds to the EIB2 and EIB3 facies of the younger intrusive complex in the Western Krušné hory (Erzgebirge) pluton and it can be compared to the G3 Waldstein and G4 units in...
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Geochemistry and origin of skarns of the Bohemian Massif
Bubal, Jan ; Dolejš, David (advisor) ; Houzar, Stanislav (referee)
Calcic-iron skarns are one of the characteristic part of the regional metamorphic complexes of the Bohemian Massif. Their mineral assemblages, structures and significant enrichment of Ca, Al and Fe were previously interpreted to be primary (exhalation sediment) or secondary (metasomatic carbonates). In this project, which consists of three sub-studies will focus on the geochemical composition of skarn as the main arguments for the discussion of their origin. Malešov deposit belongs to the typical calcic-iron skarns whose mineral assemblages are not very different from similar skarns associations in the Bohemian massif. It consists of lenticular body that is stored in gneiss and migmatites of the Kutná Hora crystalline complex. On the deposit prevails garnet-pyroxen skarn, less abundantly represented garnet and magnetite skarns and skarns replacement by amphibole or epidote. Fine-grained garnet skarns are formed by isotropic dark red garnet (Adr78-88Prp0-0.3), while in massive garnet rocks garnet grains form the core (Adr13-38Prp2.5), which envelop newly formed garnet (Adr28-66Prp1.6). In association with them is often pyroxene (Hd60-90) which can be replaced by hastingsite amphibole composition. Other minerals present are magnetite, Fe-epidote, calcite and albite. Magnetite and pyroxene skarns are...
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Differentiation and crystallization of evolved granitic melts, the Říčany pluton, central Bohemian Massif
Jandová, Tereza ; Dolejš, David (advisor) ; René, Miloš (referee)
Evolved silicic rocks display a variety of igneous textures, which can provide important information on crystallization kinetics and rheology in natural magma chambers. Individual kinetic effects such as diffusion rate, nucleation rate, growth rate and post-solidification modifications are likely to be reflected in the modal and textural appearance of the resulting rock. This work focuses on characterization and interpretation of solidification textures in a 600 m wide and 5 km long body of highly evolved, boron-rich aplites and pegmatites at the southern endocontact of the Říčany granite pluton (Central Bohemian Plutonic Complex). This rock suite is associated with biotite Říčany granite, hosting microgranite and aplite dyke swarm, and it is built up by massive tourmaline aplites, layered aplites with tourmaline-rich or locally garnet-rich bands, pegmatite pockets, pegmatite layers with unidirectional solidification textures (comb layers), megacryst zones (analogous to stockscheider), and late pegmatite dykes discordant to layering. Textural as well as modal variations are usually sharp and observable megascopically as well as on the microscale. All aplites and pegmatites usually contain similar proportions of quartz, albite-rich plagioclase, K-feldspar, various proportions of tourmaline (up to...
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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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