40Ar-39Ar dating of the Inner Carpathians Variscan basement and Alpine mylonitic overprinting

Abstract The 40 Ar- 39 Ar dating method has been applied to mylonitic rocks from the Carpathian mountains. These are Variscan metamorphic and magmatic rocks that were overprinted during the Alpine orogeny. The Inner Western Carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike-slip and normal faulting, resulting in the formation of mylonitic rocks. Precise stratigraphie ages provide clear constraints for the geodynamic interpretation related to the succession of Alpine events, such as the pre-Gosauian phase, during the Turonian (90 Ma). The 40 Ar- 39 Ar method allows to define the age of the ancient Variscan basement and the ages of the Alpine overprinting. In the High and Low Tatras, mineral ages of around 340–350 Ma are yielded by gneisses, micaschists and amphibolites, providing a younger limit for the Variscan metamorphism. The emplacement/cooling of the Variscan granites is defined between 305 and 335 Ma. These rocks are overprinted by several Alpine tectonothermal events. The major events are dated at 65 and 86–88 Ma during which the mylonites were generated. An older event, around 140 Ma earlier, defined by the Rb-Sr method, is now confirmed by the 40 Ar- 39 Ar method. Dating of phengites extracted from high-pressure metamorphic Triassic rocks from the Kosice area yields new data for the age of this event, at 155 Ma.