Strain-partitioning and mechanics of deformation during oblique indentation: Inferences from the SE external Dinarides post- middle Miocene evolution

Late-stage orogenic evolution often leads to multiple segmented slab systems, where the relative motion along oblique plate boundaries partitions the crustal strain into strike-slip and reverse faulting. The strain partitioning patterns and mechanics of deformation are thought to be closely related to the rheology inherited from previous tectonic events that affected various orogenic areas. The SE External Dinarides is one place to study such strain partitioning in a less understood tectonic setting. The Dinarides orogenic build-up is characterised by top SW thrusting during Late Cretaceous to Oligocene times. Subsequently, the N to NE indentation of the Adria microplate took place in this area after an early - middle Miocene period of generalized extension and was characterised by N-S to NNE-SSW oriented contraction, which is oblique to the inherited NW-SE oriented structural grain. We have studied the interplay between various structures creating strain partitioning during the Adria indentation in a SE External Dinarides region situated between the Trebinje city in SE Bosnia and Herzegovina and the Tivat city of SW Montenegro.

The post- middle Miocene orogenic evolution is characterised by regional NNW-SSE to N-S dextral strike-slip faulting associated with strain partitioning by the reactivation of NW-SE inherited rheological weak zones (former thrusts, nappe contacts or rheologically weak sediments). Kinematic analyses along individual structures define the strain partitioning pattern by a number of fault groups. The kinematically constrained mechanics of deformation (correlated to strain partition groups) in focus areas depict a gradual SE-ward transfer of deformation in the external thrust sheets of Montenegro. Such migration of deformation is done by an interplay between strike-slip, high-angle reverse faults and thrusts, which are locally associated with moderate block rotations (CW and CCW). The overall analysis demonstrates that oblique motions in advanced orogenic stages do not constrain a single paleostress field, and therefore they should be analysed by an improved kinematic approach aimed to understand strain partitioning and their effects superposed over an inherited structural grain.