Duplex structures within the Świątkowa Wielka tectonic window (Beskid Niski Mts.,Western Carpathians, Poland): structural analysis and photointerpretation

Abstract

A tectonic window within the Magura nappe, situated near the village of Świątkowa Wielka in the Western Carpathians, reveals the Grybów unit overthrust in turn on the Dukla nappe. The thrust-sliced folds exposed in the tectonic window make up a classical interthrust contractional duplex. Its origin is related to the presence of a step in the basement beneath the Magura nappe. The Magura nappe is folded and thrust-faulted and cut, together with the Grybów unit by right-lateral strike-slip faults oriented NNW and left-lateral ones, oriented NE and NNE. A part of these faults have been reactivated as dip-slip faults. The differences in the structural directions between the window series and the Magura nappe indicate that fold oriented E-W had originated and have been partly thrust-faulted during the first phase under the influence or the Magura nappe overriding from the south to the north. 1lte first stage was concluded in early Sarmatian time. The second stage involved deceleration of the Magura nappe starting from its front and additional forward movement of the southern part, which changed the direction of its movement to SSW-NNE when it overrode the step in the basement, thus completing the formation of the interthrust contractional duplex. This stage teminated with the formation of the post-thrusting strike-slip faults. During the last stage, at the end of Neogene, the area was subject to post-orogenic uplift and related reactivation of part of the strike-slip faults as dip-slip ones.