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Neogene structural development in the border zone between Alps, Dinarides and Pannonian Basin (NW Croatia)

The border zone between the Alps, Dinarides and Pannonian Basin provides a remarkable opportunity to test and improve current knowledge on the orogenic history of the European Alpine belt. This is mostly due to the fact that four major tectonic boundaries join here, i.e. the Periadriatic (Insubric) lineament=PAL, the Mid-Hungarian line=MHL, Sava=SaF and the Drava=DF faults (Fig. 1). At least three of them (PAL, MHZ and SaF) separate tectonic and/or paleogeographic domains that experienced quite different kinematics and style of deformation during the Eoalpine and Neoalpine orogenic stages. In this study we analysed Neogene structures obtained from seismic lines crossing the area and those found on outcrops, supplemented by geological-mapping data. As a result three major extensional events are separated, each of them followed by a period of inversion. The first extensional event (Early Miocene) was governed by a normal displacement along gently dipping, NNW- striking faults that accommodated ENE directed extension. It was, at least in part, synchronous with the NW-SE shortening. The second extensional event (Middle Miocene) was characterised by WNW-ESE (E-W?) to NW-SE directed extension generated by NE-striking conjugate and NNW-oriented normal faults. This extension was localised within transtensional zones bounded by NE-striking sinistral strike-slip faults. Again, this event was followed by a new generation of NE-striking thrusts related to the end-Sarmatian shortening. The last (Late Miocene) E-W to WNW-ESE directed extension was achieved by normal displacement along NE- and NNW-striking faults, followed by a final shortening that had the strongest impact on the structural setting of the study area. This resulted in formation of numerous compression related structures including large map-scale folds, basement pop-ups and inverted former basins. This last, N-S to NW-SE directed shortening started in late Early, or early Late Pontian and continued up to the present time as indicated by geometry, onlap and thickness patterns of the youngest syn-tectonic basin fill. When taking into account much wider surrounding area, it seems that inverted structures related to this latest shortening are arranged in practically all, often perpendicular directions, centred at the eastern end of the PAL. To explain this fan-like pattern of synchronous inversions we proposed a thought-experience model that supposed a bulk counterclockwise rotation combined with the northwestward shift of the Dinaridic block with respect to the more stable and rigid Alpine buttress.

structural analysis; Alps; Dinarides; Pannonian Basin; Neogene

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