Pre-Alpine high-pressure metamorphism in the Gemer unit: mineral textures and their geodynamic implications for Variscan Orogeny in the Western Carpathians

We report mineral textures of retrogressed eclogites from the gneiss–amphibolite complex, which is represented by a series of isolated bodies that were thrusted over the greenschist-facies Rakovec group in the Gemer unit (Western Carpathians). Peak pressure and temperature conditions of about 2.0 GPa and 650 °C are estimated for the eclogite-facies assemblage (omphacite, garnet and rutile). The eclogites show strong amphibolite-facies re-equilibration that is characteristic for the rest of gneiss–amphibolite complex rocks. Pressure and temperature conditions for both eclogite and subsequent amphibolite-facies stages are comparable with those reported from the retrogressed eclogites in the Vepor and Tatra units. The underlying Rakovec group rocks indicate greenschist-facies conditions, but relicts of high-pressure (blueschist facies) metamorphism are also preserved. The Pre-Alpine age of the eclogite-facies metamorphism in the gneiss–amphibolite complex and blueschist-facies metamorphism in the Rakovec group is confirmed by the presence of their pebbles in the overlaying upper Carboniferous conglomerates. The origin of eclogites and blueschists in the Gemer unit and their relationship to eclogites in the Vepor and Tatra units are discussed with respect to the subduction zone along which they originated, but also in relation to the high-pressure rocks occurring along the European Variscan Belt. As the whole Gemer unit underwent Alpine metamorphism, the retrogressed eclogites and associated gneisses were also studied to clarify possible degree of this metamorphic overprint in the gneiss–amphibolite complex rocks.