Jointing in the Dukla Nappe (Outer Carpathians, Poland): an attempt at palaeostress reconstruction

The joint network in the portion of the Dukla Nappe studied originated in two stages showing different orientations of the stress field axes. The older, compressive stage I was characterised by a N45°E-orientated (at present coordinates) horizontal s1, and formation of the diagonal, shear (SL and SR) joint system. The younger, extensional stage II was characterised by vertical s1 and horizontal, N35°E-orientated (also at present coordinates) s3, suitable for formation of the fold-parallel joints. At the turn of the first stage, under diminishing horizontal compression (s1 trending N35°E), the cross-fold T joints developed. The orientation of the maximum compression axis changed between stages I and II. The first stage probably commenced while strata which were not fully lithified underwent shortening, and lasted until the termination of nappe emplacement. The second stage, in turn, is associated with post-orogenic collapse of the Carpathians, whose onset in the study region began at least in Late Miocene times.