Paleogene to Neogene kinematics of the Outer West Carpathian fold-and-thrust belt and Miocene strike-slip faulting at the front of the Magura superunit (Slovakia and Czech Republic)

The area of investigations covers the Outer West Carpathian (OWC) flysch units, which are referred to as theexternal fold and thrust belt of the West Carpathian orogen. The OWC is separated from the Central and InnerWest Carpathians by the Pieniny Klippen Belt (PKB). Kinematic data obtained from brittle structural analysesof outcrops within the OWC flysch units (Silesian-, Foremagura-, Magura- and Biele Karpaty unit; see Fig. 1for location of study area) depict a polyphase deformation history including several deformations, which couldbe correlated into the adjacent PKB to the South (see Beidinger et al., this volume). Four different deformations(DF1, DF2, DF3, DF4) are distinguished in the OWC- flysch units
The most prominent deformation D F1 is characterized by NNW-directed shortening, which formed the large-scale architecture of the roughly ENE-trending fold and thrust belt. The stratigraphic record found in thedifferent OWC flysch units indicates an in-sequence foreland-propagating thrust sequence. According to theages of the youngest overthrust sediments (Zytko et, al., 1989; Nemcok et al., 1998), thrusting progresses fromthe PKB into the OWC flysch during Paleocene/Eocene times and terminates in the most external flysch unitsclose to the Karpatian/Badenian stage boundary. We interpret foreland propagating, NNW-directed folding andthrusting to be responsible for the progressive steepening of units towards the internal parts of the orogenleading to subvertical to overturned positions in the innermost part of the fold and thrust belt.
Crosscutting relationships in outcrops give evidence that NNW-directed shortening (DF1) is followed by ENE-striking sinistral strike-slip faulting of DF2. This deformation is concentrated within the flysch units close to theboundary with the adjacent PKB. Structures there indicate sinistral strike-slip reactivation of the floor thrusts ofthe Bystrica and Biele Karpaty unit. Ad ditional ENE-striking strike-slip faults occur within the Biele Karpatyunit and in the PKB.Structures of D F1 and D F2 are further overprinted or cut by by map-scale (N)NE-striking sinistral strike-slipfaults attributed to NNE-directed shortening (DF3). DF3 strike-slip faults are linked with NNE-directed out-of-sequence thrusts. Structural data and geological maps show that NNE-directed out-of-sequence thrusts andkinematically linked strike-slip faults coincide with major bends at the fronts of the Magura and Bystrica unitsNNE of Žilina (SK; Fig. 1). The timing of D F3 is constrained by Egerian sediments, which are affected byNNE-directed shortening at the southern margin of the Silesian unit near Rožnov pod Radhoštěm (CZ). Furtherrecordings of NNE-directed shortening around the front of the Magura unit coincide with the bend of theMagura front from ENE-directed strike to ESE-directed strike near Valašske Meziřiči (Fig. 1). Structural datafrom outcrops in the Magura and Foremagura unit west of the bend depict sinistral strike-slip faulting sub-parallel to the ENE-striking Magura front Structures are interpreted as due to sinistral reactivation of the frontof the Magura unit. At the ESE-striking section of the Magura front, NNE-directed shortening is accomodatedby NNE-directed out-of-sequence thrusting. The situation is interpreted as a restraining bend formed by thebending of the front of the Magura unit. The interpretation is corroborated by map-scale ENE-striking faults,which splay off from the ESE-striking floor thrust of the Magura unit. The strike of these faults fits theexpected strike of Riedel-faults at a restraining bend of a sinistral strike-slip fault.Deformation D F4 within the flysch units is characterized by WNW-directed shortening and is restricted to thearea around the Magura front. This deformation is related to minor strain and appears as the youngestdeformation although no high-quality cross-cutting relationships could be identified in outcrops.The outcrop-derived deformation history is compared with the tectonic evolution in the Vienna Basin area,where seismic data provide excellent constraints for deformation ages (Hölzel et al., 2010). There, studies showthat Early Miocene NE-striking sinistral strike-slip faults are cut by NNE-striking Middle to Late Miocenesinistral strike-slip faults. Both types of strike-slip faults are related to distinct stages of the eastward lateralextrusion of the Eastern Alps towards the Pannonian region. The older NE-striking faults pre-date theformation of the pull-apart basin, whereas NNE-striking faults are linked to the pull-apart stage of the basinduring Middle to Late Miocene times. D F2 and D F3 identified in the Outer West Carpathians are thereforecorrelated to Miocene extrusion kinematics. We correlate the ENE-striking strike-slip faults recorded in theOWC (DF2) with the Early Miocene strike-slip faults found in the Vienna Basin. NNE-directed out-of-sequencethrusting and (N)NE striking strike-slip faults (DF3) are linked to the pull-apart stage of the Vienna Basin. Thesinistral strike-slip faults of DF3 at the Magura front are regarded as continuations of the of Middle to UpperMiocene strike-slip faults delimiting the Middle to Upper Miocene Vienna pull-apart basin towards theNorthwest.The proposed structural model suggests that structures of DF3 serve to accommodate the displacement of NNE-striking sinistral strike-slip faults delimiting extruding blocks to the Northwest. NNE-directed block-movementduring Middle to Late Miocene lateral extrusion is compensated by NNE-directed shortening and out-of-sequence thrusting at the leading edge of the fault blocks.