A contribution to better understanding of structural characteristics and tectonic phases of the Boč region, Periadriatic Fault Zone

Abstract

The aim of this study was to determine properties of the tectonic contact between Permian/Mesozoic limestones and less competent Miocene clastites on the northeastern foothill of the Boč Mt. Because fault planes significantly mark the relief, this contact was studied by a detailed structural mapping, which showed that the Boč Mt. is limited by subvertical faults in its northeastern part. To ensure that mapped subvertical contact is compatible with regional geodynamics of the area, additionally paleostress analysis of fault-slip data was performed. Four individual paleostress tensor groups were documented in a wider Boč area and compared by published structural data from the border zone between Alps, Dinarides and Pannonian Basin. The oldest paleostress tensor group (Phase 1) is likely of Lower and Middle Miocene age and indicates SW-NE extension accommodated by W-E to WNW-ESE striking normal faults. Phase 2 can be correlated with Middle to Late Miocene NW-SE to WNW-ESE directed extension accommodated by NNE-SSW striking normal faults. Phase 3 is correlated with Late Miocene W-E directed contraction accommodated by N-S striking sinistral faults and NNE-SSW to NE-SW striking dextral faults. The youngest paleostress tensor group (Phase 4) fits well with Pliocene to Quaternary NNW-SSE to N-S directed contraction accommodated by NW-SE to W-E striking dextral faults and NE-SW striking reverse faults. Since the documented paleostress phases fits well with the geodynamic processes of the Alps-Dinarides-Carpathians territory the subvertical border in the northeastern part of Boč Mt. seems to be an acceptable structural solution. The study is important because the study area is located at interaction zone between two major Alpine fault systems: the Periadriatic and the Lavanttal faults. IzvlečekGlavni namen raziskave je bil ugotoviti značaj tektonskega kontakta, ki poteka vzdolž severovzhodnega pobočja Boča v coni Periadriatskega in Labotskega preloma. Ker gre za kontakt med permskimi/mezozojskimi apnenci in manj kompetentnimi miocenskimi klastiti, prelomne ploskve, ki predstavljajo kontakt enot, v reliefu značilno izstopajo. Zato je raziskava temeljila na natančnem strukturnem kartiranju območja, ki je pokazalo, da je Boč na severovzhodnem delu omejen s subvertikalnimi prelomi. Rezultati terenskega kartiranja se ujemajo z regionalno geodinamiko območja, ki je bila preverjena s paleonapetostno analizo opazovanih zdrsov ob prelomnih ploskvah. V širši okolici Boča so bile dokumentirane štiri skupine paleonapetostnih tenzorjev, ki so bile nato primerjane z objavljenimi strukturnimi podatki iz prehodnega območja med Alpami, Dinaridi in Panonskim bazenom. Najstarejša faza (Faza 1) je najverjetneje spodnje do srednjemiocenske starosti in odraža ekstenzijo ozemlja v smeri SW-NE, ki jo vidimo na normalnih prelomih s slemenitvijo W-E do WNW-ESE. Fazo 2 lahko primerjamo s srednje do zgornjemiocensko ekstenzijo ozemlja v smeri NW-SE do WNW-ESE, ki se odraža na normalnih prelomih s slemenitvijo NNE-SSW. Faza 3 je primerljiva ...