Integrating kinematics, mechanics of deformation, thermal modelling and diagenesis in orogenic systems: the Dinarides example

Abstract

Continental collision and subduction dynamics are often the main tectonic processes responsible for the formation of mountain belts. Understanding the mechanics of deformation across collisional orogens is of prime importance in order to determine the mountains architecture and the associated deep mantle-scale geodynamic processes. The Dinarides orogen is a world-class example of a collisional orogen that was affected by a number of critical processes driving mountain building and subsequent collapse during its Jurassic-Eocene evolution associated with the convergence between Europe- and Adriatic derived units. Such processes include linked migration of slab and magmatism during continental collision, indentation of continental micro-plates, changes in polarities in respect to neighboring orogens or transfer of deformation between active areas driving the distribution of present-day seismicity and crustal stresses. All these processes are critical for the evaluation of geo-resources in the upper crustal domain and their quantification is important to be ported to the understanding of other orogens worldwide. The large-scale kinematic evolution of the Dinarides has been obtained by an extensive surface kinematic study performed in the less known area of the external Dinarides. By correlating the kinematics with available geophysical and evolutionary constraints, we constructed two large-scale, kinematically controlled regional transects. The results demonstrate a long-lived evolution of shortening that affected the Dinarides lower orogenic plate. While the Late Jurassic-earliest Cretaceous deformation was associated with an earlier obduction moment, the latest Cretaceous onset of continental collision has gradually focused deformation at inherited rheological weakness zones. We show that shortening was interrupted by a period of Miocene extension that affected all orogenic areas. The extension was followed by renewed shortening, which started during the late Miocene and remains presently active. These results indicate a lower plate crustal accretion mechanism that was spatially and temporally connected with gradual slab retreat in the Dinarides. The structural and kinematic effects of the post- middle Miocene Adriatic indentation in the NW-SE oriented Dinarides structure have been analysed in more detail. This deformation induced a characteristic coherent regional system of large offset dextral strike-slip faults, which transfer gradually their offsets to thrusts and high-angle reverse faults. By linking the data in a regional context, the post-middle Miocene Dinarides fault system seems to accommodate the differential motion between the N- ward Adriatic indentation in the Alps and the rapid S- to SW- ward movement of a Hellenides area situated SE of the Kefalonia Fault driven by the Aegean slab-roll back. The effects of the kinematic, structural and regional geodynamics on the thermal, fluid-flow and organic matter maturity evolutions were further explored by the means of a numerical modelling study performed on a kinematically controlled cross-section. The modelling results demonstrate that deformation-, burial- and exhumation-, and erosion- and sedimentation- rates significantly contribute to changes in the thermal/maturity distribution across the orogen. In addition, petrographic and geochemical (stable oxygen and carbon isotopic) investigations of samples that were taken from major fault contacts, demonstrate the significant impact of the tectonic-induced paleo-fluid flow on the diagenetic evolution of rocks across the external Dinarides.