Paleostress reconstruction of the southeast Ukrainian Outer Carpathians

Abstract

ABSTRACT The paleostress analysis of the southeast part of the Ukrainian Outer Carpathians (UOC) was carried out with the separation and stress inversion TR method (TRM). The analysis includes site and bulk stress tensors through which the late-orogenic processes of the frontal part of UOC can be better described. In particular, three bulk compressive stress regimes dated to Miocene describe a compressional deformation that changes progressively from real to hybrid. The first stress regime is a pure compression and changes progressively to transpression, while the trend of the greatest principal stress axis ( constantly remains ENE-WSW (065°), perpendicular to the main trend of the UOC. This progressive deformation spans the Late Burdigalian to Sarmatian period and reflects the driving stresses during the Alcapa and Tisza-Dacia mega-units drifting and docking with the Eastern European Platform. During the transpressional stress regime, the thrust displacements waned, and transfer (strike-slip) faults accommodated the deformation. The third stress regime is also a hybrid compression, i.e. transpression, but the greatest principal stress axis () trends NNE-SSW (029°). It reflects the post-docking deformation giving rise to mesoscale NW-WNW thrusts and transfer (strike-slip) faults. However, these thrusts and strike-slip faults have not modified the NNW-SSE rectilinear trend of the UOC. This hybrid compression outlasted the Late Miocene (Latest Sarmatian–Early Maeotian), and it is related to the separation and left-lateral movement of the Tisza-Dacia plate from the Alcapa plate. In addition, two extensional stress regimes with the least principal stresses () trending NE-SW and NW-SE have been defined. We interpret them to represent subsidiary stresses in the Carpathians’ uppermost part due to orogen collapse both normal and parallel to the orogen after the Late Miocene.