Tectonics of the Beskid Wyspowy Mountains (Outer Carpathians, Poland)

Abstract

The structure of the Magura Nappe, within the zone of maximal bending of the Western Outer Carpathians, is described; investigations were concentrated mainly in the Beskid Wyspowy Subunit. A zone, bounded to the north and south by duplexes, comprises large characteristic synclines (Śnieżnica, Lubogoszcz, Szczebel, Klimas, Łopień, Ćwilin, Luboń Wielki). These appear on maps as isolated “island mountains”, in the Beskid Wyspowy Subunit. These synclines contrast strongly with the belt-like distribution of regional folds to the west and east of the area. The synclinal massifs developed gradually. Fold belts several hundred metres long developed in the first phase of overthrusting of the Magura Nappe, with horizontal N–S compression dominant.Thrusts separating the individual subunits developed when the face of the overthrusting Magura Nappe stopped and the stress continued to push its southern parts forwards. The next phase, with continuing horizontal N–S stress included the development of strike-slip faults and the bending of the Carpathian Arc, resulting in extension of this part of the orogen. The syncline zone within the Beskid Wyspowy Subunit underwent disintegration and particular blocks became independent. Rotation of blocks with individual synclines took place along fault zones. In the part of the Polish Outer Carpathians investigated this stage is also characterised by a change of compression from N–S to NNE–SSW. Due to the uplift of this part of the Carpathians, strike-slip faults changed into dip-slip faults in the terminal part of this phase.