Tertiary tectonic evolution of the Pannonian Basin system and neighbouring orogens: a new synthesis of palaeostress data

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Abstract Compilation of a microtectonic observation data base for most of the data measured in the Pannonian Basin and surrounding orogens permits a detailed reconstruction of the Tertiary stress field evolution. Combination of tectonic observations, borehole, gravity and seismic data, palaeogeographic and stratigraphic information led to an understanding of fault kinematics and description of the structural evolution in seven major tectonic episodes. The first two episodes depict the kinematics of the two major separated blocks, the Eastern Alpine-Western Carpathian-Northern Pannonian (Alcapa) and the Southern Pannonian-Eastern Carpathian (Tisza-Dacia) microplates. A Mid-Eocene to Early Oligocene N-S compression led to contractional basin formation both in the foreland (Western Carpathians) and hinterland (Hungarian Palaeogene basins) of the orogenic wedge. Due to oblique convergence, the Palaeogene basins are generally asymmetric and often dissected by dextral tear faults. Northward advance of the Adriatic promontory initiated the separation of the Alcapa from the Southern Alps and its eastward extrusion. This process probably started during latest Oligocene and reached its climax during the Early Miocene. The main displacement was accommodated by dextral slip along the Periadriatic and Mid-Hungarian shear zones and during and after this tectonic episode Alcapa suffered 50° CCW rotation. At about the same time period the Tisza-Dacia block also experienced rotation of 60–80°, but clockwise. These opposite rotations resulted in the marked actual deviation of earlier compression axes, which are now N or NW in the Eastern Alps, WNW-ESE in the Western Carpathian-Pannonian domain and NE-SW in the Tisza-Dacia domains. Termination of rotations can be considered as the time for final amalgamation of the two separate blocks and the beginning of extensional tectonics in a single Pannonian unit. The Pannonian Basin system was born by rifting of back-arc style during the late Early and Mid-Miocene time. Extension was controlled by the retreat and roll-back of the subducted lithospheric slab along the Carpathian arc. Two corners, the Bohemian and Moesian promontories formed gates towards this free space. At both the northern and southern corners, broad shear zones developed. The initial NE-directed tension was gradually replaced by a later E- to SE-directed tension as a consequence of the progressive termination of subduction roll-back along the arc from the Western Carpathians towards the Southern Carpathians. There is growing evidence that an E-W-oriented short compressional event occurred during the earliest Late Miocene but during the most of the Late Miocene extension was renewed. Starting from the latest Miocene roll-back terminated everywhere and a compressional stress field has propagated from the Southern Alps gradually into the Pannonian Basin, and resulted in Pliocene (?) through Quaternary tectonic inversion of the whole basin system.