Post-metamorphic palaeofluid evolution of the Mecsekalja Zone metamorphic complex

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The thesis held in hand discusses the post-metamorphic palaeofluid evolution of the crystalline metamorphic rocks of the Mecsekalja Zone, near Ófalu village, south Hungary. The rocks of the study area now observable at surface outcrops were metamorphosed ca. 300 ma ago. During its uplift history a complex stress evolution must have worked upon the rock mass, the most momenta of which can hardly be recognized, and the most phases of which possibly did not leave an inquirable clue. Crystalline rocks can be considered impermeable, and it is the deformation of the rock that enhances the efficiency of fluid flow, both at the micro- and the mesoscale. The stress activated microscale porosity is testified by fluid inclusion planes in granites and also by rock mechanic experiments. Veins of different configurations are the mesoscale product of deformation and subsequent fluid flow in the newly grown fracture porosity. The above considerations suggest that the uplift history of the Ófalu metamorphic complex is also a complex palaeofluid history, the momenta of which are determined by the obscure stress history of the Mecsekalja Zone. These momenta can be reconstructed by minerals that were precipitated from fluids, i.e. vein minerals or minerals that are obviously not part of the original mineral assemblage and the hydrothermal origin of which can be reasonably assumed, e.g. microcrack calcite in a quartzofeldspathic gneiss. The present thesis is an attempt to reconstruct the phases of the fluid evolution during the post-metamorphic history of the Mecsekalja Zone metamorphic zone and to extract the nexus of these with the application of the available methods and data, i.e. textural analysis (augmented with cathodoluminescence microscopy), fluid inclusion microthermometry and stable isotope measurements.

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