The structural pattern and tectonic evolution of the Muráň fault revealed by geological data, fault-slip analysis, and paleostress reconstruction (Western Carpathians)

Abstract

The Muráň fault is perhaps the most distinctive, steeply-dipping, brittle structure in the Western Carpathians. An analysis of brittle deformation was used to gain the succession of tectonic evolution of the Muráň fault by paleostress tensors. Movement on this fault depended on spatial orientation of the principal paleostress axes representing the paleostress fields. The kinematic analysis of fault-slip data confirmed the predominant strike-slip nature of the fault during the entire history, which had sometimes been disrupted by quiescence periods or normal faulting. The Muráň fault may be as old as 85 Ma and originated as a ductile shear zone in deeper crust. It is possible to consider the Muráň fault as sinistral transpressional strike-slip fault during the latest Cretaceous to earliest Paleocene. During this time period, with given orientation of the paleostress field, the fault originated as a semi-brittle to brittle shear zone. A significant re-organization of the paleostress field was carried out approximately on the boundary of the Paleocene and Eocene periods. During this deformation, movement on the Muráň fault changed to dextral, and the secondary positive and negative flower structures in Mesozoic rocks were most likely formed in this time as well. These structures originated after the Danian, since sediments of the Gosau Group are incorporated into these structures. In the late Eocene, activity of the Muráň fault gradually began to decrease, and the fault structure is more or less covered by the upper Eocene transgressive deposits of the Central Carpathian Paleogene Basin. The Neogene evolution is characterised by a continuous change of the orientation of the principal maximum axis σ1 (SHmax, respectively) from the NW–SE through N–S to NE–SW position. The Muráň fault started to become sinistral transpressional to transtensional up to a normal fault, however, the movement along the fault was only several tens of metres. The Quaternary period is characterised by an extensional tectonic regime with the orientation of principal least axis σ3 in the WNW–ESE direction. Late Pleistocene to Holocene normal faulting is indicated by borehole analysis in the alluvial planes of the Rimava and Muráň rivers.