Geological control of young orogenic mountain morphology: From geomorphological analysis to reinterpretation of geology of the Outer Western Carpathians

Abstract The paper presents a new concept of geological control of the Outer Western Carpathians (OWC) morphology. The establishment of the Carpathians' morphology dates back to the stage of evolution of sedimentary basin, when huge blocks of solidified rock massifs were gravitationally displaced into the foreland sedimentary basins, forming finally isolated hills. The altitudinal difference between the Beskidy Mts. and the Carpathian foothills is caused by the structural positions of these two segments of rock massifs within the orogenic megastructure during the compressional stage. Indeed, the tectonic elements that formed during the earliest stage of compression took (and still take) the highest structural and altitudinal position, whereas the elements incorporated into the orogen as the last have taken a lower topographic position, forming a belt of foothills. Therefore, this difference in topography is not related to rock resistance only, as was previously thought. The rotation of the Carpathian blocks during the orogenic thrusting and the formation of strike-slip fault zones parallel to the Carpathian tectonic thrusts formed a flower structure, which has played a significant role in morphology (insular character of). During the stage of secondary tectonic deformation – including the rotation of the Carpathian tectonic segments, strike-slip faulting and the radial extension and large extensional collapse of the Carpathian massifs – the principal features of the Carpathian relief as well as the main river valleys were formed. Gravitational collapse resulted in back-thrusting and the tectonic exhumation of the Carpathian massifs, which helps to explain the problem of seemingly large denudation of the Carpathian overburden of a thickness estimated at several kilometres. Chaotic complexes (synsedimentary and syntectonic melanges), which frequently occur in the Carpathians, are very important for the Carpathian morphology and river valley development (controlled not only by faults) as well as the formation of isolated hills. Analysis of the Carpathian morphology supported by the Bouguer's gravity anomalies map, and geological data allow us to present a new hypothesis that the Carpathians were formed as a huge regional flower structure, without the participation of subduction, which has formerly been considered to play the crucial role in the formation of the Carpathian orogen.