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Microtextures and compositional relations in multiple grown garnet formed during subduction of crustal and mantle rocks
Kulhánek, Jan ; Faryad, Shah Wali (advisor) ; Collett, Stephen (referee) ; Konrad-Schmolke, Matthias (referee)
English abstract Studies of rocks from high- to ultrahigh-pressure metamorphic environments in subduction zones play a crucial role in advancing our understanding of Earth's dynamic processes and geodynamic evolution. Such samples, which have experienced Earth's mantle conditions, provide valuable insights into the subduction and exhumation processes associated with the tectonic collision of lithospheric plates. By analysing the mineral assemblages, textures, and chemical compositions of these rocks, we can unravel the complex history of the subducted rocks and determine the pressure-temperature paths experienced during their formation. Additionally, the investigation of high- to ultrahigh-pressure metamorphic rocks aids in constraining the mechanical behaviour of subduction zones, deciphering the fluid-rock interactions and element cycling processes. Such studies contribute to our broader understanding of plate tectonics, the formation of mountain ranges, and the geodynamic processes that shape our planet. This research focuses on the investigation of metapelitic and metabasic rocks from the Saxothuringian zone of the Bohemian Massif and the Western Gneiss Region of the Norwegian Caledonides. The studied rocks have a shared history of being part of subducted material that experienced high- to...
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Equilibrium conditions of minerals in Al-Mg-rich eclogite from Světlík (Moldanubian Zone)
Tecl, Martin ; Faryad, Shah Wali (advisor) ; Racek, Martin (referee)
English abstrakt This thesis focusses on textural relations of Al-Mg-rich kyanite eclogite from Světlík-Suš locality in the monotonous group of the Moldanubian Zone. Mineral analyses and compositional maps were used to analyze detail relations and reactions responsible for mineral formation and/or their decomposition. The analyzed minerals were then compared with the chemical composition of minerals from other eclogites and garnet pyroxenites from studied locality. Based on bulk rock chemistry and mineral analyses, the studied kyanite eclogite is comparable rather with garnet pyroxenite. Minerals stable under eclogite facies conditions in the rock were garnet, jadeite rich clinopyroxene, Cr-kyanite and Ce-rich clinozoisite/zoisite, which is transformed to tabular pseudomorphosis. The rock shows clear evidence of granulite facies overprint. In total 9 types of symplectites were distinguished. Most of them were created under granulite facies condition. Compositional maps obtained for the Cr-rich kyanites show diffusion of Cr from kyanite to garnet during the granulite facies conditions. Symplectites with clinopyroxene and orthopyroxene were transformed into amphiboles during the decompression to amphibolite facies conditions. Keywords: eclogite, microscopy, mineral chemistry
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Solid phase inclusions in minerals from eclogites, peridotites and granulites in the Kutná Hora Complex
Jedlička, Radim ; Faryad, Shah Wali (advisor) ; Svojtka, Martin (referee)
Studium pevných inkluzí vybraných minerálů eklogitů, peridotitů a granulitů Kutnohorské oblasti English abstract Felsic granulites with lenses and boudins of garnet peridotites and eclogites, for which UHP conditions have been obtained, commonly occur in the Moldanubian Zone of the Bohemian Massif. However, it is not clear when and how the HP-UHPM rocks were emplaced into the host granulites. The most important question that remains is, whether the felsic granulites also experienced UHP metamorphism. By studying solid phase inclusions and compositional zoning in resistant phases as garnet, we provide evidence of prograde metamorphism of felsic rocks prior to their granulite facies overprint. Finding mono-mineral inclusion of Ti-rich phengite point to prograde evolution of the rocks.Polyphase inclusions of phengite and biotite indicate that it was previously Ti-poor phengite. Another important inclusion is graphite, which could be remnant of micro-diamond inclusion. Well-preserved prograde zoning of major elements in garnet from the felsic granulites is supported by zoning patterns of trace elements, such as titanium, chromium and yttrium and rare earth elements. Both these groups of elements remain heterogeneous at a micro-scale. The garnet profiles reveal that the rocks preserved signs of multiple stages...
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Thermobarometry of garnet peridotites and granulites from the Blanský Les Massif
Urychová, Michala ; Faryad, Shah Wali (advisor) ; Racek, Martin (referee)
English abstract Granulites of Moldanubian Zone are usually characterized by the presence of HP/UHP rocks of mafic and ultramafic compositions. The relationships between UHP rocks and granulites and their metamorphic history are subjects of many discussions. The Blanský Les Granulite Massif is the largest body of this type and includes numerous budines and bodies of serpentinized garnet peridotites, pyroxenites and amphibolic eclogites. PT conditions of granulites and garnet peridotites were estimated using different thermobarometric calculations. Temperatures 850-1050řC and pressures 15-20 kbar were calculated for granulites and 800-1000řC/25-40 kbar were estimated for garnet peridotites. Similar to other granulite bodies in the Moldanubian zone, the Blanský Les Granulite Massif is interpreted either as a segment of orogenic root, which was exhumed by viscous flow from low crust or the rocks reached eclogite facies conditions in the subduction channel first and then were overprinted by granulite facies metamorphism. Maximum depths of emplacement of garnet peridotites and other UHP rocks into granulites are limited by their pressure conditions. For these granulites the pressure is 22 kbar.
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Solid phase inclusions in minerals from eclogites, peridotites and granulites
Jedlička, Radim ; Faryad, Shah Wali (advisor) ; Jelínek, Emil (referee)
English abstract Felsic granulites in the Bohemian Massif are characterized by the presence of small (from decimetres to several houndred metres in size) boudins and lenses of garnet peridotites and high-pressure eclogites. Pressure conditions of the granulites and their mutual metamorphic history with garnet peridotites and eclogites are subject of long discussion. For this purpose, minerals and textures formed at peak pressure conditions were investigated using thin-sections and mineral separates of these rocks from the Kutná Hora complex. As all these rocks underwent granulite facies reequilibrium and subsequent cooling, most inclusions are transformed to lower pressure and temperature phases. In addition to olivine, orthopyroxene and clinopyroxene, garnet from garnet peridotites contains frequent chromium spinel. The host garnet around inclusions shows Cr-rich domains as result of diffusion from spinel to garnet. Rare ilmenite inclusions with high MgO content and pentlandite were also observed in garnet. Orthopyroxene in matrix and rims of large grains have low amounts of Al and the associated clinopyroxene has relatively high jadeite content. Two varieties of eclogites are present in the granulite: eclogites with pyroxenites and garnetites occur within or adjacent to garnet peridotites. Garnets of...
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Tracing of the pre-exhumation history of strongly re-equilibrated high-ultrahigh pressure rocks in a collision orogeny
Jedlička, Radim ; Faryad, Shah Wali (advisor) ; Janák, Marian (referee) ; Schertl, Hans-Peter (referee)
English abstract The investigation of high- to ultrahigh-pressure rocks in the Bohemian Massif occurring as small bodies enclosed in surrounding rocks with a low degree of metamorphism was always focused on their main metamorphic event in granulite facies conditions at very high temperatures. However, recent studies have shown that these rocks underwent a high-pressure metamorphism that preceded the subsequent high-temperature overprint and exhumation of those rocks. The scientific publications that comprise this dissertation thesis present petrological, mineralogical and geochemical research of these (ultra)high pressure rocks from various parts of the Bohemian Massif that have the potential to preserve information about their pre-exhumation history. The findings of the inclusions of high-pressure phases in metamorphic minerals and, in particular, the study of major and trace elements zoning in garnets together with thermodynamic modelling allowed us to describe new temperature-pressure conditions and to refine the metamorphic paths of these rocks. The felsic and mafic granulites of the Kutná Hora Complex in the Moldanubian Zone and the Rychleby Mountains in the East Sudetes preserve the evidence of prograde metamorphism. In addition to the inclusions of phengite and omphacite in the garnet cores, the...
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Geochemistry of upper mantle rocks from Kozákov and Horní Bory, Bohemian Massif
Ackerman, Lukáš ; Jelínek, Emil (advisor) ; Faryad, Shah Wali (referee) ; Becker, Harry (referee)
The purpose ofthis dissertation is geochemical study ofupper mantle rocks at two sites from diÍlěrent geological settings of the Bohemian Massif (Czech Repub|ic) - Koziíkov and Homí Bory. The first part of dissertation represents a review of petrological and geochemical studies of upper mantle Íocks found in the Bohemian Massi{ which have been pub|ished or presented so far' These include information about ýpe and occuÍTences of mantle{erived rock with individual Bohemian Massif units and summarized present state of knowledge on depletion and metasomatism ofthese rocks. The principal questions related to the mantle beneath the Bohemian Massif which remďn opened are presented at the end of this part. The most important paÍt of the dissertation represents three comprehensive papers on geochemical studies of upper mant|e rocks from Koziíkov and Horní Bory. In the second part, a geochemical study of major elements, trace elements, and Sr-Nd isotopes combined with mineral chemistry of upper mantle xenoliths from the Koziíkov volcano have been presented. This unique suite of xenoliths samples upper 2/3 of the upper mantle in this region and, therefore' provides a great possibility to study uppeÍ mantle composition variations with depth. The results show that upper mantle beneath Koziíkov volcano underwent...
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From microstructures to large-scale crustal deformations in collisional orogen: multidisciplinary approach
Franěk, Jan ; Schulmann, Karel (advisor) ; Faryad, Shah Wali (referee) ; Stünitz, Holger (referee) ; Whitechurch, Hubert (referee)
The thesis aims to compile response of deep-seated rocks to continental collision in the root zone of Variscan orogen exposed in Bohemian Massif. It treats the orogenic processes from the scale of microscopic grains constituting rocks through scale of individual outcrops to an overall view of ~4000 km2 large domain of the high-grade rocks. The thesis is divided into three chapters. The first represents an article summarizing study of structurally most complex area - Blanský les granulite massif - published in the Mineralogy and Petrology journal (2006). The second chapter unravels regional evolution of the south Bohemian Moldanubian domain and correlates the presented results with suitable studies from other orogenic regions or with numerical models of continental collisions. The related article will be submitted to Tectonics journal in June 2007. The last section focuses on the mechanisms of deformation in the felsic granulites and extrapolates the results to rheology of the Variscan lower crust and behavior of common felsic rocks under HT HP conditions. The corresponding paper will be submitted to Journal of Metamorphic Geology in the autumn 2007. The Bohemian massif represents the easternmost exposure of Variscan orogen in Europe. During the 380-300 Ma complex subduction - collision a ~300km...
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Mineral and chemical changes of magma crystallization during formation of post-Variscan intrusions and veins in the Moldanubian Zone of the Bohemian Massif
Kubínová, Šárka ; Faryad, Shah Wali (advisor) ; Rapprich, Vladislav (referee) ; Moyen, Jean-François (referee)
- 1 - English abstract The late-Variscan magnesium-rich potassic to ultrapotassic igneous rocks create numerous dykes, dyke swarms and several plutonic bodies at the boundary between the Moldanubian Zone and the Teplá-Barrandian Block of the Bohemian Massif. They represent a volumetrically smaller group of igneous rock but they are the key to understand generation of melt and processes of mantle metasomatism and shallow-level magma differentiation. In addition, they are considered as an indicator of the tectonic evolution of this part of the Bohemian Massif during the final stages of the Variscan orogenesis. Currently, they are the subject of discussion by several authors in terms of their genesis, emplacement time and geodynamic significance. The presented thesis is a compilation of four scientific publications that are aimed at the petrological study of selected (ultra)-potassic dyke rocks from several localities at the western border of the Moldanubian Zone. The study of mineral textures, mineral chemistry and whole-rock geochemistry together with magnetic fabrics, structural field relations and age determinations allowed us to describe the crystallization history of these rocks, discuss their evolution from melt generation to magma ascent and emplacement, and form the model of sequence of Variscan...
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