Contrasting deformation styles along an active thrust belt front - the external Dinarides and Hellenides

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The fold-and-thrust belt of the Dinarides-Hellenides on the Balkan Peninsula is a rare example of active continental subduction. We propose to study its active tectonics in an area of transient kinematics between southern Croatia, Montenegro and northern Albania. Several anomalous features characterize this area and need clarification: (a) northward-diminishing seismic moment release, (b) northward disappearance of a continental lithospheric slab and (c) northward end of syn-collisional extension related to subduction rollback. The study area hosted numerous historical earthquakes as well as one of the strongest instrumentally recorded earthquakes in Europe (Montenegro 1979, MW 7.1). GPS studies indicate convergence between Adria and Eurasia at rates of 4-5 mm yr-1, largely accommodated within the external thrust belt. Long-term convergence rates, by contrast, remain unconstrained. We aim to characterize the structural basis of this transient kinematic behaviour in a two-fold approach: (1) Balanced cross sections in two regional transects on either sides of the orogen-perpendicular Skutari-Pec Fault, which delimits syn-collisional extension to the north, will allow quantifying the overall Cenozoic crustal shortening as well as the contribution of rollback-triggered extension in the transect south of the Skutari-Pec Fault. (2) Presently active structures will be identified by tectonic geomorphological and paleoseismological studies. Emphasis will be given to quantifying rates of surface uplift and active folding in the adjacent coastal areas by dating Quaternary aggradational river terraces affected by river incision and fold growth. In combination with constraints on geometries of active faults, this will allow estimating fault slip rates on a 10-100 kyr time scale. These slip rate estimates will provide average values across many seismic cycles compared to GPS-derived convergence rates that are valid only for the last 1-2 decades, i.e., a seismically quiet period since the 1979 event. The comparison of long-term and short-term slip rates can potentially highlight locked faults and is hence of relevance for assessing the seismic hazard. Our study will also contribute towards a better understanding of continental subduction and thrust belt propagation in areas characterized by low plate convergence rates.