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Kinematic analysis of deformed quartzite from the Vysoký kámen: implications for development of the Saxothuringian orogenic wedge
Ildžová, Tamara ; Jeřábek, Petr (advisor) ; Jouvent, Marine (referee)
The Saxothuringian orogenic wedge is an impressive example of a collisional orogenic wedge formed during the Variscan orogeny in the Bohemian Massif. The Vysoký kámen area in the Erzgebirge Mountains (Saxothuringian Domain) represents a part of the outer wedge which was not subducted into the great depths during the evolution of the wedge. To better understand a polyphase deformation in this frontal part of the former accretionary wedge, the study focuses on macro and micro-scale analyses of deformed quartzite and quartz veins from the Vysoký kámen area. Two main deformation fabrics (S1 and S2) were formed under slightly different P-T conditions and linked to two deformation events (D1 and D2). The S1 fabric defined by coarse-grained recrystallised quartz grains and by axial planes of folded quartz veins is related to a simple shear regime but also shows stretching in the folds axes in the NS direction. This subhorizontal and gently eastward dipping metamorphic foliation is associated with deformation event D1 during which the area subducted. Minerals such as paragonite and rutile, and a higher silica content up to 3.17 a.p.f.u. recorded in micas reflect a subduction environment. The second deformation fabric S2, characterised by fine-grained recrystallisation, is generally identified as...
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Assembly of the Saxothuringian orogenic wedge: the Variscan P-T-t record of the metasediments of Erzgebirge, Bohemian Massif
Jouvent, Marine ; Lexa, Ondrej (advisor) ; Tichomirowa, Marion (referee) ; Pitra, Pavel (referee)
The formation of collisional orogenic wedges involves complex polyphase deformation and metamorphism. This study reveals the tectonic evolution, internal architecture and the timing of the Variscan orogenic wedge evolution in the Saxothuringian Domain (Bohemian Massif). The studied area is the Erzgebirge Crystalline Complex, characterized by numerous occurrences of the (U)HP rocks. In contrast, the surrounding metasediments have been scarcely studied, although they provide an important link between deep subduction and mid-crustal processes. Using field structural geology, petrology, thermodynamic modelling and geochronology (monazite U-Pb and mica 40 Ar/39 Ar dating), we constrained the P-T conditions and timing of four deformation events (D1-D4) identified by structural analysis. Several transects from the low-grade hanging wall phyllites to the footwall medium-grade micaschists have been investigated. The first M1-D1 event is characterized by HP-LT minerals (garnet, chloritoid, phengite, paragonite, and rutile) defining the S1 foliation with an M1 peak pressure conditions increasing from 13 kbar and 520řC in phyllites to 25 kbar and 560řC in micaschists. The corresponding geothermal gradient of 6-11řC/km is typical for subduction environments. The M2-D2 event corresponds to the deformation and...
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