AR-40-AR-39 DATING OF THE INNER CARPATHIANS VARISCAN BASEMENT AND ALPINE MYLONITIC OVERPRINTING

The Ar-40-Ar-39 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 West ern Carpathians are conventionally described as a nappe pile formed by northward movement and then subjected to intense strike-slip and norm al faulting, resulting in the formation of mylonitic rocks. Precise st ratigraphic ages provide clear constraints for the geodynamic interpre tation related to the succession of Alpine events, such as the pre-Gos auian phase, during the Turonian (90 Ma). The Ar-40-Ar-39 method allow s to define the age of the ancient Variscan basement and the ages of t he Alpine overprinting. In the High and Low Tatras, mineral ages of ar ound 340-350 Ma are yielded by gneisses, micaschists and amphibolites, providing a younger limit for the Variscan metamorphism. The emplacem ent/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 myloni tes were generated. An older event, around 140 Ma earlier, defined by the Rb-Sr method, is now confirmed by the Ar-40-Ar-39 method. Dating o f phengites extracted from high-pressure metamorphic Triassic rocks fr om the Kosice area yields new data for the age of this event, at 155 M a.