Variability of strain partitioning in rheologically weak zones: Inferences from a kinematic study in the southeastern Dinarides

Previous studies have shown that syn- and post-orogenic deformation typically reactivates inherited rheologically weak zones, such as pre-existing regional nappe contacts or weak sedimentary layers. In contrast, partitioning of strain has been less quantified by observational studies analysing the internal structure of these weak zones. A good example to study such deformation is provided by the SE Dinarides Mountains of Europe, where deformation is localised within stratigraphic layers composed of deep-water sediments that were repeatedly (re-)activated by deformation episodes associated with changes in tectonic regimes. Here, Cretaceous–Paleocene foredeep turbidites presently exposed in the footwall of the East Bosnian-Durmitor thrust have been affected by successive stages of deformation with different kinematics or tectonic styles during the switch from Cretaceous–early Oligocene thrusting to Oligocene–Miocene extension and post-9 Ma transpression. To understand the mechanisms of strain partitioning, a field kinematic study was performed in Montenegro and the SE part of Bosnia and Herzegovina. The results demonstrate that although reactivation took place within this weak stratigraphic horizon, different styles of deformation are observed at higher resolution, controlled by structural inheritance and geodynamic evolution. While the thrusting (re-)activation was distributed and partitioned by different mechanisms along the orogenic strike, the subsequent extension was localised mostly in the southeast, controlled by slab tearing and detachment. Strike-slip structures crosscutting the northwestern parts of the studied area developed during the last stages of tectonic plate convergence, controlled by a more external localisation of transpressional indentation in the orogenic system. The overall analysis allows a better understanding of the regional-scale strain distribution based on deformation within rheologically weak zones, and provides a novel structural solution for the SE Dinarides.