PENNINIC WINDOWS AT THE EASTERN END OF THE ALPS AND THEIR RELATION TO THE INTRA-CARPATHIAN BASINS

The deformation history of the Penninic windows at the eastern end of the Alps is related to Oligocene dextral transpression in the Eastern Alps and Miocene formation of the intra-Carpathian basins. Ductile flow of Penninic rocks resulted in subhorizontal ENE trending pure shear crustal thinning. Omission of parts of the tectonostratigraphy and excision of Tertiary metamorphic isograds indicate normal displacements between Penninic and Austro-Alpine units overprinting the Alpine nappe edifice. Later NW-SE compression is by folding and causes sigmoidal trajectories of earlier foliations in the Penninic units. Finally, E-W extension led to a conjugate set of steep faults. These deformations occurred on the decompression path of Tertiary metamorphism. E-W extension along the eastern margin of the Alps resulted from instability of overthickened crust and repeated episodes of Oligocene and Miocene continental escape during compression of the Alpine wedge against the E-W trending European foreland. Material is transported laterally eastward, away from a zone of collision and toward the intra-Carpathian region, which acted as a geometrically unconstrained interface to the Alpine orogenic wedge. The final E-W extensional event is attributed to the final phase of uniform E-W extension of the intra-Carpathian region. © 1990.