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Structural evolution, magnetic fabric and mechanism of exhumation of the Podolsko complex
Burjak, Miroslav ; Žák, Jiří (advisor) ; Franěk, Jan (referee)
This thesis concentrates on a detailed field and structural analysis of the Podolsko complex, Moldanubian unit, Bohemian Massif, complemented by a microstructural study and analysis of magnetic susceptibility (AMS). The Podolsko complex occupies the footwall of a major Variscan normal shear zone and is juxtaposed against the southern to southeastern margin of the Central Bohemian Plutonic complex. During the field work, more than 160 outcrops were examined, the AMS samples were taken at 25 stations, and samples for microstructural studies were taken from 12 localities. On the micro-scale, leucocratic migmatites contain abundant garnet grains which may represent relics of an earlier (ultra-)high preassure metamorphic phase. Retrogression is obvious in other samples of biotite migmatites of the Moldanubian Variegated unit. The retrogression is marked by the presence of sillimanite and chlorite. The main tectonometamorphic event in the Podolsko complex is extensive migmatization coeval with formation of pervasive flat-laying fabric. This is corroborated by the AMS study which indicates concordant steep to flat-laying magnetic and mesoscopic foliations striking NNW-SSE. The AMS also shows that the subhorizontal N-S to NNW-SSE trending magnetic lineations in the Podolsko complex correspond to those in the...
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Magnetic fabric, magma flow and tectonic deformation in volcano-plutonic systems
Tomek, Filip ; Žák, Jiří (advisor) ; Lexa, Jaroslav (referee) ; Petronis, Michael (referee)
Magnetic fabric, magma flow and tectonic deformation in volcano-plutonic systems ABSTRACT This Ph.D. thesis aims to investigate dynamics of emplacement and tectonic history of selected volcano-plutonic complexes in a continental magmatic arc and back arc setting. The thesis presents new data sets from five field areas, presented in separate chapters, which could be viewed as representing a vertical sections through upper part of an intermediate to felsic magmatic system. From top to bottom in this ‛imaginary' vertical system, the examined units are: (1) andesitic lava domes and (2) sub-volcanic magma chambers (<3 km deep) of the Miocene Štiavnica volcano- plutonic complex, Western Carpathians (Slovakia), (3) Shellenbarger pluton (<3 km depth) within the mid-Cretaceous Minarets caldera, Sierra Nevada batholith in California (USA), and ~7-10 km deep granitoids of (4) Lower-Cretaceous Wallowa batholith, Blue Mountains province in Oregon (USA) and (5) Late Devonian Staré Sedlo complex, central Bohemian Massif (Czech Republic). The research incorporates extensive field and structural data, supported by analysis of igneous textures and anisotropy of magnetic susceptibility (AMS). The latter is further accompanied by detailed examination of magnetic mineralogy using thermomagnetic measurements and optical and back...
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The Late Devonian to early Carboniferous kinematic evolution of the Teplá-Barrandian/Moldanubian boundary
Tomek, Filip ; Žák, Jiří (advisor) ; Babuška, Vladislav (referee)
ENGLISH ABSTRACT The Late Devonian to Early Carboniferous kinematic evolution of the Teplá-Barrandian/Moldanubian boundary The Staré Sedlo complex (SSC) is a relic of meta-igneous arc-related pluton in the southern part of the Sedlčany-Krásná Hora roof pendant, intruded by granitoids of the Central Bohemian Plutonic Complex along the boundary of Teplá-Barrandian (TBU) and Moldanubian units (MU), Bohemian Massif. The SSC mainly comprises deformed orthogneisses of calc-alkaline granodiorite to tonalite protoliths of Late Devonian age (380−365 Ma; Košler et al., 1993) that were commonly mingled with minor basic magmas. Locally preserved subhorizontal intrusive contacts of the orthogneisses against their meta-sedimentary host rock indicate that these magmas intruded as a sill complex. The SSC preserves a rather unusual flat-lying subsolidus foliation (dip <40ř) associated with subhorizontal ~NE-SW-trending mineral lineation. Mesoscopic structures, anisotropy of magnetic susceptibility (AMS), and deformational microstructures indicate prolate shape of the strain ellipsoid with dominant coaxial pure shear regime. The solid state microstructures record cooling of the orthogneiss protolith down to the ambient greenschist facies conditions followed by its static recrystallization due to the intrusion of the younger...
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Analog modeling of subduction zone processes
Tkáčiková, Tatiana ; Žák, Jiří (advisor) ; Krýza, Ondřej (referee)
Subduction zones, domains where oceanic lithosphere is subducted into the mantle beneath an overriding plate, are one of the most dynamic tectonic environments. A wide range of the long-lasting subduction-zone processes may be suitably reproduced and studied through analog modeling and thus may be directly observed in laboratory, though at time and length scales that differ fundamentally from nature. The main goals of this Bachelor thesis are first to provide an overview of large-scale architecture of subduction zones, to present an overview of the published analog experimental methods, and then to discuss the main outcomes of analog modeling of subduction zones and accretionary prisms. The thesis also summarizes the main mechanical parameters of materials used in the analog modeling. Furthermore, a set of simple experiments were performed, with the main goal to model formation of basalt-bearing mélanges during subduction of seamounts and volcanic belts that may occur on ocean floor and are commonly incorporated into accretionary wedges as dismembered Ocean Plate Stratigraphy (OPS).
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Processes of cumulate formation in mafic intrusions
Linzerová, Dominika ; Špillar, Václav (advisor) ; Žák, Jiří (referee)
Igneous cumulates and their parental intrusions are best known amongst geologist for their economical profitability as the main source of platinum group elements. However, beyond the scope of mining interests, cumulate rocks represent one of the most complicated and least understood topics in igneous petrology. Their formation is assumed to be driven by fractional crystallization of mostly mafic parental magmas, achieved by a separation of crystals from their surrounding liquid. In this work, I review the extend of current knowledge regarding the wide variety of possible formation processes, as well as the common properties and settings of cumulates and means of their classification. In order to demonstrate the operation of the reviewed processes we carried out a series of high temperature experiments, investigating a behaviour of two different crystal suspensions over a period of 20 hours. Experiments were performed in a classic 1-atm. furnace at 1350 and 1390 řC, using a 10 wt. % and 60 wt. % mixtures of natural olivine and synthetic haplobasaltic glass. In a liquid rich environment, we observed a progressive formation of a cumulate layer by crystal settling, while in contrast, the suspension containing 60 wt. % of olivine effectively inhibited all movement aside from expansion of bubbles trapped...
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