Understanding the kinematic evolution of asymmetric extensional basins during the Miocene evolution of the Dinarides The case study of the Konjic basin, Bosnia and Herzegovina

Abstract

Tectonic inversion of extensional basins in intramontane settings is by favoured the weaknesses of the inherited nappe stack and depends on the direction of contraction applied to the structural grain. Many such intramontane basins (i.e. Konjic Basin) are observed in the Dinarides, that have an asymmetric extensional architecture and are poorly understood. The aim of this study is to study the evolution of asymmetric extensional basins in the intramontane setting of the Dinarides, focussing on inherited weakness zones. We achieve this objective by interpreting field kinematic data collected in one of these basins, Konjic, located in the central part of the orogenic belt. Our results demonstrate an early-middle Miocene NE-SW oriented extension followed by a post- middle Miocene N-S transpression that inverted the basin, characterised by dextral strike-slip and high-angle reverse faults. In terms of sedimentation, the Miocene extension was associated with a deepening stage of the basin characterized in the north east by syn-deposition of clastic wedges in the hanging-wall of normal faults. This deepening was correlated outside the basin with the uplift by exhumation of the Mid-Bosnian Schist Mountains (MBSM) in the footwall of large offsets (>10 m) normal faults. The second phase of extension was associated with normal faulting with smaller offset located mainly in the vicinity of the basin centre. The overall extensional episode was followed by the post – Middle Miocene inversion, resulting in controlling deformation by rheological inheritance instead of structural. This has novel inferences to favouring inversion deformation as a result of orientation of the former normal faults to the newly imposed stress field. The sequence of extension and subsequent inversion acting oblique to the Dinaridic trend, and rheological inherited weaknesses are responsible for the current asymmetric geometry of the Konjic Basin