Structural evolution of the Fatric Unit in the Malé Karpaty Mountains (Slovakia) during the Cretaceous–Early Neogene Alpine Orogeny: Insights from field-based orientation analysis

This study investigates the internal deformation of the Fatric Unit in the Malé Karpaty Mountains during the Alpine orogeny, with the aim of clarifing the structural evolution and thrusting history of the Vysoká and Zliechov nappes. A comprehensive dataset of primary and deformation-related planar structures was collected and analysed to reconstruct the tectonic evolution of the Fatric Unit. Three main Alpine deformation phases (DA1 –DA3 ) were identified, reflecting significant changes in the regional stress field. (1) The earliest phase (DA1) is associated with northwest-directed thrusting and NW–SE crustal shortening during the Eo-Alpine orogeny, as documented by asymmetric folds, stretching lineations, and large-scale recumbent folding. (2) The subsequent phase (DA2) reflects a shift to a W–E compression axis during the Late Cretaceous to Early Eocene and is expressed by the development of extensional structures, predominantly calcite-filled veins. (3) The youngest phase (DA3) records a return to the N–S-oriented compression associated with south-vergent backthrusting during the Late Oligocene to Early Miocene, probably related to the soft docking of the ALPACA Mega-Unit with the European Platform. Overall, the tectonic analysis of the Fatric Unit in the Malé Karpaty Mts. characterises three principal Alpine deformation stages of the Western Carpathians by constraining their timing and kinematics.