A combined structural and sedimentological study of the Inner Carpathians at the northern rim of the Transylvanian basin (N. Romania)

By integrating detailed structural and sedimentological field-work with paleomagnetic data, this thesis provides constraints for the reconstruction of the Late Tertiary tectonic history of the nner Carpathians in Northern Romania. Central for the understanding of the formation of the Carpathians is the emplacement history of crustal blocks into the so-called ‘Carpathian embayment’. This large-scale bight in the European continental margin is situated between the Bohemian and Moesian promontories. Roll - back of the (partly?) oceanic crust formerly occupying the Carpathian embayment, combined with lateral escape due to indentation in the Eastern Alps are thought to be the driving forces for this emplacement. The irregular shape of the European continental margin ultimately led to the formation of a highly bent orogen, the Carpathians. The study area is a key area for the understanding of the tectonic processes during this emplacement, since it is situated at a triple point where three of the major continental bocks (ALCAPA, Tisza and Dacia) meet. During the time interval covered by this study, the Tisza and Dacia blocks are considered firmly attached to each other, representing one single block. A large fault zone between the ALCAPA block and the Tisza-Dacia block, termed Mid-Hungarian fault zone, accommodated most of the complex deformation caused by their contemporaneous invasion into the Carpathian embayment. During emplacement corner effects at the Bohemian and Moesian promontories resulted in large differential rotations of the invading blocks. The juxtaposition of the Tisza-Dacia block and the ALCAPA block along the MidHungarian fault zone resulted in the formation of a flexural basin on the northern part of Tisza-Dacia. The filling of this basin started in Oligocene times, developing from flysch units into Burdigalian-age molasse-type deposits. The last moment of thrusting of ALCAPA related units onto Tisza-Dacia is reflected by the Early Burdigalian SE - directed emplacement of unmetamorphic flysch nappes (Pienides) onto the autochthonous cover of Tisza-Dacia. Back-arc type extension leading to the formation of the Pannonian basin is in the study area only weakly documented as SW-NE extension. Roughly perpendicular ‘soft collision’ of Tisza-Dacia with the European margin leads to transpressional deformation in the study area after 16 Ma. Due to migration of slab retreat, the convergence direction of Tisza-Dacia becomes more oblique, initiating a deformation stage characterized by transtension (NW – SE extension). The northern rim of Tisza-Dacia is ‘fitted’ to the European continental margin by E-W trending, sinistral strike slip faults coupled to SW – NE trending normal faults. This process leads to a weak (~20°-30°) counterclockwise rotation as well as accelerated uplift of the northern part of Tisza-Dacia. After 16 Ma deformation in the study area is located within the Tisza-Dacia block, but most likely connected to the Mid-Hungarian fault zone.