EVOLUTION OF THE STRESS-FIELDS IN THE CARPATHO-PANNONIAN AREA DURING THE NEOGENE

Observations of microtectonic faults in and around the Pannonian basin suggest that the Tertiary evolution of the area was controlled by large-scale strike-slip fault activity. Statistical analysis of the fault pattern for different localities makes it possible to separate several conjugate sets of strike-slip faults and related dilatational and compressive structures. These stress fields have a distinct rotation pattern with time. Inversion of fault data suggests a characteristic rotation of the principal stress axes with time. Some rigid body rotations are indicated by paleomagnetic data. There are basically three contrasting mechanisms to explain this observation: (1) Appropriate rotation of the regional (e.g., European) stress field; (2) rotation of larger tectonic units (e.g., microcontinents) under a stable regional stress field; and (3) coherent rotation of smaller, detached continental blocks under a stable regional stress field. Our model for the Neogene tectonic evolution of the Pannonian area combines these mechanisms. Moderate microcontinent rotation may have occurred during the Paleogene-Early Miocene. In the early Middle Miocene, the microcontinents were dissected by a system of strike-slip and normal faults, created by a N-S compressive/E-W extensive stress field. Gravity spreading of the Pannonian units and block rotation within bounding strike-slip faults are suggested to explain rotated magnetic directions and fault patterns. In the Late Neogene, clockwise rotation of the general stress-field by at least 40-degrees is thought to be responsible for the reactivations of older strike-slip faults and for the creation of new sets. This change in the orientation of the stress field is related to the eastward and then southward shift of the Carpathian subduction activity.