Evolution of the transport direction of the Carpathian belt during its collision with the east European Platform

Abstract

The evolution of the Carpathians is in its final stage with intermediate seismic activity (70–200 km, M w = 4–7.7) localized beneath its southeastern salient (Vrancea zone). Our analysis, in the transition area between south Carpathians and east Carpathians, reveals that the termination of convergence is characterized by a clockwise rotation of the Carpathian belt transport direction. Using structural maps and cross sections, we show that this change of convergence direction had several structural consequences including (1) the Pliocene‐Quaternary activation of out‐of‐sequence structures in the southern east Carpathians and (2) the creation of dextral strike‐slip faults bounding the mobile belt to the west, in the south Carpathians. Our fracture analysis in syntectonic deposits allows us to distinguish and stratigraphically date two fanning stress patterns, corresponding to the two last transport directions of the Carpathian system (1) a Burdigalian to early Tortonian stress field with compression directions rotating along with the Carpathian curved orogenic belt but with transpression (NW–SE compression) and a low‐strain partitioning along east trending internal strike‐slip faults in the south Carpathians and (2) a late Tortonian to Pleistocene rotated and smaller radial stress pattern, with N–S compression in the south Carpathians. The rotation of the convergence direction is interpreted as the result of the Miocene migration and progressive collision of the Carpathian system with the thick crust of the NW trending Tornquist‐Teisseyre line and its prolongation in Romania. The area able to subduct, determined by thickness of crust entering the subduction zone, was progressively restricted to a foreland corner in front of the southeastern Carpathians. The progressive collision forced the convergence to slow down and rotate from eastward to southeastward in late Miocene. The Dobrogea hills in front of the latest migrating system may represent the late Neogene NE–SW flexural bulge of the subducting foreland panel. This clockwise rotation of the transport direction can be compared with the clockwise rotation that occurred in other subduction systems (Tyrrhenian subduction, Caribbean subduction, etc.) which were controlled by the location of oceanic versus continental crust in front of the orogenic belt.