Crustal response to slab tearing and detachment: Inferences from the kinematics of the Dinarides-Hellenides transition

Complex slab tearing mechanisms are often associated with a lateral transition from continental indentation to subduction of oceanic or thinned continental lithosphere. These geodynamic conditions lead to the formation of crustal transfer zones associated with significant strain partitioning. A key area to study such mechanisms is the transition between the Dinarides and Hellenides mountain chains in southeastern Europe, affected by the indentation of the Adriatic continental microplate. Similar to other Mediterranean orogens, the slab roll-back was accompanied by a migration of the orogenic shortening towards the foreland and a coeval back-arc extension that reactivated inherited orogenic nappe contacts. Along the strike of the orogen, the Dinarides slab detached during Oligocene – early Miocene times, while the Hellenides subduction continued its evolution up to the present day. The transfer of deformation takes place along various structures in the transition zone between the Dinarides and Hellenides, from areas that underwent significant Adriatic indentation following the detachment of the subducted slab to the others where the retreat of the Aegean slab continues. We have performed a field kinematic and microstructural study in the less understood segment of the Dinarides-Hellenides transition in northern Montenegro to analyse the mechanism of strain partitioning in the Dinarides nappe stack related to along-strike changes in slab kinematics. The results demonstrate that the previously defined scissor-mechanism of extensional deformation in the neighbouring Hellenides is transferred dominantly to a newly documented large offset shear zone. This structure accommodates orogen-perpendicular extension by reactivating inherited Cretaceous – Paleocene nappe contacts, forming a major post-Eocene detachment and extensional klippens, which are cross-cut by late-stage brittle normal faults. When combined with the known structure of the neighbouring Hellenides, these results infer that the Oligocene – early Miocene slab-detachment of the Dinarides orogenic segment was accommodated at crustal levels by generalised bi-directional extension, exhuming mid-crustal levels in the footwall of major structures and accommodating the transition from Adriatic indentation to the continued subduction recorded by the Hellenides.