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Mass balance and major and trace element zoning in atoll garnet from eclogite facies metamorphism.
Kulhánek, Jan ; Faryad, Shah Wali (advisor) ; Svojtka, Martin (referee)
English abstract This work focuses on high pressure atoll garnet-bearing metabasites from the central part of Krušné hory Mts. in Saxothuringian zone of Bohemian Massif. Eclogite bodies are interpreted as a part of alochtonnous units, which were dragged into the high pressure conditions of subduction zone during a subduction of Saxothuringian oceanic crust under the Teplá-Barrandien Unit and subsequently they were exhumed into upper parts of subduction- collisional system. Main mineral assemblage of eclogites consists of omphacite, garnet, quartz and amphibole which replaces grains of omphacite. Minor minerals present are rutile, ilmenite, talc a chlorite. Zircon, apatite, paragonite, pyrite, plagioclase, albite and monazite are enclosed in porphyroblasts of garnets. Grains of garnet frequently form the atoll structures, where its central part of a grain is replaced by new minerals of matrix and rim part stays preserved. Based on compositional profiles and mapping of major and trace elements, two evolution phases of garnet were distinguished. Older garnet (I) forms mainly preserved cores of garnet and on the contrary younger garnet (II) is present on rims or also replaces garnet I in the core part of a grain. Garnet I has higher amounts of Ca and Mn but lower Mg and Fe than garnet II. Preserved grains of...
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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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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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Metamorphism and geodynamics of the Proterozoic Kabul Block: Preservation and modification of crustal fragments within an orogenic zone
Collett, Stephen ; Faryad, Shah Wali (advisor) ; Kotková, Jana (referee) ; Krenn, Kurt (referee)
The Kabul Block is a lenticular crustal fragment that, along with the Farah, Helmand, and Nuristan terranes, is situated within a tectonic zone known as the Afghan Central Blocks. The Afghan Cent- ral Blocks form within the collision zone between the Indian, Eurasian, and Arabian plates. The Kabul Block consists of a highly-deformed crystalline basement overlain by weakly-deformed Late Paleozoic- Mesozoic sediments. U/Pb SHRIMP analysis of zircon cores from the lowermost basement formations (the Sherdarwaza and/or Khair Khana) indicates the presence of a Neoarchean component (~ 2700 Ma), while the majority of zircon cores yield a range of Early Paleoproterozoic ages (2200 - 2500 Ma). The Sherdarwaza and Khair Khana Formations are comprised of migmatite and orthogneiss with minor marble, quartzite, and amphibolite that reached granulite-facies conditions. Conventional geother- mobarometry and phase equilibria modelling on well preserved granulite-facies assemblages indicates that the rocks reached conditions of approximately 850 řC at up to 7 kbar of pressure. Textural relations indicate that this was a strongly temperature dominated event. U/Pb SHRIMP dating of zircon rims and U-Th-Pb dating of monazite inclusions in granulite-facies garnet suggest that this event occurred in the late...
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Reconstruction of PT path in the eclogites facies micaschists from the Krušné Hory
Kulhánek, Jan ; Faryad, Shah Wali (advisor) ; Racek, Martin (referee)
English abstract This work focuses on garnet bearing micaschist in the vicinity of the Měděnec village on the czech side of the Krušné hory Mountains (Saxothuringian Zone, Bohemian Massif). Micaschist is a part of nappe units with eclogites which reached high pressure conditions during subduction of the Saxhothuringian plate beneath the Teplá-Barrandien unit and they were subsequently exhumed into the upper parts of this subduction-collisional system. The rock-forming minerals present in micaschist are phengite, quartz and porphyroblastic garnet with inclusions of quartz, rutile, phengite, paragonite, apatite, monazite, florencite, zircon, chlorite, chloritoid, ilmenite, titanite, Co-arsenopyrite and graphite. Small amount of kyanite, retrograde chlorite and tourmaline are present in the matrix. Detailed chemical composition of garnet was studied using compositional maps of major and trace elements. The garnet shows prograde zoning with decrease of Mn and Ca and increase of Fe and Mg from the core towards the rim. Pressure and temperature conditions of the micaschist were calculated using thermodynamic modeling in Perple_X in the system of MnNCKFMASHTO. Based on the pseudosection, the mineral assemblage with kyanite is stable at higher pressure above 18 kbar and 600 řC. The pressure-temperature path of...
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Structural and petrological characterization of Melechov massif host-rock migmatites
Zelinková, Tereza ; Lexa, Ondrej (advisor) ; Faryad, Shah Wali (referee)
English abstract This work deals with the structural and petrological characteristics of migmatites surrounding Melechov massif near Humpolec. The aim was to assess the existence of multiple anatectic events that could be caused by intrusion of late granites. The results are based on fieldwork, petrographic observations in thinsections of the collected rocks, study of major minerals chemistry in both melanosome and the leucosome of selected migmatites and a comparison of bulk chemical analyses of selected samples. Studied migmatites are characterized by SSW-NNE oriented migmatitic vertical banding S2, which is intensively transposed into subhorizontal foliation S3 via folding and solid state deformation. Rocks of all studied sites bears common mineral assamblage (Bt + Crd + Sil + Pl + Kfs + Qtz + Ms + Mag). While overall chemical analysis of selected samples do not vary significantly, the chemistry of biotite and cordierite exhibits a significant increase in xMg a slight decrease in Ti from the first to the third locality. Chemistry of other rock-forming minerals do not vary significantly. These differences correlate well with different modal abundance of magnetite, which reaches up to 3% on the locality TM3. Based on the obtained data it can be stated that the studied rocks form a homogeneous domain of the...
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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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Preservation of HP minerals and textures in felsic and mafic granulites from the Rychleby Mts.
Schlöglová, Kateřina ; Faryad, Shah Wali (advisor) ; Kotková, Jana (referee)
Diploma thesis - Kateřina Schlöglová - 2011 1/2 English abstract Granulites of the Rychleby Mts. represent relics of high-pressure eclogite-facies metamorphic rocks that are scattered in various crustal and mantle segments of the Variscan orogen in central Europe. These rocks may provide important insights into early stages of Variscan plate convergence and burial as well as exhumation mechanisms. We use mineral assemblages and chemistry to reconstruct the pressure-temperature paths, mechanisms of melting, and conditions of mineral preservation of high-pressure granulites, as well as whole- rock geochemistry to aid in interpretation of granulite precursors and their geodynamic setting. The mafic granulites consist of garnet, omphacite, two feldspars, and quartz with accessory rutile and zircon. The peak assemblage was partly replaced by pargasitic amphibole and biotite. Garnet grains are zoned from Grs36Py10Alm54 (core) to Grs20Py38Alm42 (rim), and host inclusions of phengite, omphacite, unmixed feldspars, kyanite, and rutile. Omphacite composition varies from Di44Hd14Jd42 (inclusions in garnet) through Di63Hd20Jd17 (porphyroblasts) and Di63Hd24Jd13 (symplectitic intergrowths with plagioclase). Reintegrated composition of the feldspar porphyroblasts is Or43Ab53An04. The felsic granulite variety is composed...
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