Slab tearing or slab retreat as triggers of extension at the Dinaric-Hellenic transition?

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This project will show how Earths crust responds to an along-strike transition from roll-back subduction of continental lithosphere to oblique continent-continent collision. Lateral transitions in subduction mode are relevant because they coincide with marked differences in earthquake activity, with attendant hazards for society in coastal and mountainous areas. Specifically, we will test the hypothesis that a change in subduction mode along the Dinaric-Hellenic chain of SE Europe involved late orogenic extension which migrated in the direction either of slab tearing or of slab roll-back and arcuation.Investigation will initially focus on the junction of the Dinarides and Hellenides, where our preliminary work has revealed both orogen-parallel and -normal extensional faults that overprint and reactivate older thrusts. This is an auspicious place to start because it coincides with a first-order difference in geophysically imaged mantle structure, from a SSE-dipping continental slab beneath the northwestern Hellenides currently retreating to the SW, to a shorter slab beneath the Dinarides with little or no retreat. Our work so far suggests that the crustal structure at this transition is marked by a transverse normal fault (the Shkoder-Peja Normal Fault or SPNF) that accommodates increasing amounts of orogen-parallel extension along its strike from SW to NE, where it bounds the Mio-Pliocene Kosovo (Metohia) Basin. However, the SPNF is only one of several faults in this area whose age and kinematics are key to understanding whether crustal extension is related to the Hellenic roll-back subductions, to slab delamination or break-off beneath the Dinarides, or to some combination of these mechanisms. Investigation will also cover three other locations in the Dinarides-Hellenides where along-strike changes in stratigraphy and nappe structure coincide with orogen-perpendicular faults. If so, the Dinaric-Hellenic transition is possibly unique in recording the along-strike response of the lithosphere to changing modes of plate convergence.To realize these goals, we will combine state-of-the-art dating methods (apatite-fission track- and -helium analyses of faulted blocks, detrital thermochronology in fault-bounded sedimentary basins) and well-established structural techniques (fault-slip analysis, fabric mapping).