Cenozoic stress field and jointing in the outer West Carpathians, Poland

Abstract

The Polish segment of the outer Carpathians fold-and-thrust belt is composed of a number of North-verging nappes. Preliminary studies of joint patterns within different lithostratigraphic units of these nappes, as well as within discordantly overlying younger strata, enable one to constrain the Late Cretaceous through Quaternary stress fields of that region. In the medial segment of the area studied, joints have been analysed in several nappes, most of the data coming from the Magura Nappe. In the latter one, joint pattern suggests diversified orientation of the reconstructed maximum stress axes, depending on the age of strata. The maximum stress axis inferred from the position of the acute bisector between conjugate Coulomb-shear or hybrid-shear fractures is oriented N-S within the Turonian-Campanian, NNE-SSW in the Maastrichtian, ENE-WSW in the Palaeocene, and NNW-SSE within the Eocene through Miocene strata. The maximum stress axes reconstructed for post-Cretaceous strata of other nappes in the eastern part of the area studied are oriented NNE-SSW to NE-SW, being nearly perpendicular to the fold axes. On the other hand, the Pliocene molasses of the Inner Carpathians display joint patterns indicative of the NE-SW oriented maximum stress axis, which coincides with that in the eastern segment of the Polish outer Carpathians, both in the Paleogene strata and in the unconformably overlying Middle Miocene molasses.