Tectonics of the consolidated basement of the Polish Carpathians

Abstract

Based on the results of magnetotelluric soundings a sketch of the main tectonic elements of the consolidated basement of the Polish Flysch Carpathians and a number of longitudinal profiles and cross-sections have been drawn. The sketch as well as the sections allowed for developing a concept about major tectonic pattern of the consolidated basement in this part of the Carpathians. Morphology of the consolidated basement surface of the Carpathians is very diversified. Depth to the top of the basement surface varies from several hundred meters in the western part of the Carpathians to around 20 km in the south-eastern part. Generally, the surface drops from the north-west toward the south-east. The drop is not uniform, and it has a discontinuous character. In the tectonics of the consolidated basement of the Carpathians, in the territory of Poland, three major elements influencing its structure are distinguished. These are two transverse, generally SW-NE oriented fault zones (A-A and B- B), where the basement is dipping eastward. The third element, of a comparable meaning to the other two, is a longitudinal zone of the basement dipping southward - "regional basement slope". The first of these large fault zones, the transverse and western-most one (A-A), runs from Babia Góra to the region of Rzeszotary. The dislocated area lying to south-east of the fault zone is lowered by about 8.5 km in its southern part and about 2 km in its northern part. The second, transverse B-B fault zone follows the Wysowa-Sędziszów Małopolski line. The dislocated area lying to the east of this fault zone is lowered by several kilometers to maximum of 12 km in the southern part. The entire eastern block is moved along the fault 40 km to the north. The B-B zone separates the central block from the eastern one. The third major tectonic element is the described earlier zone of the regional basement slope (Fig. 2). It is a longitudinal element which remodels the consolidated basement of the Carpathians in the southern direction. Along this zone, there is an abrupt block-wise lowering of the consolidated basement to the south. The two transverse dislocation zone A-A and B-B, discussed earlier, divide the consolidated basement of the Polish Carpathians into three regions. The western region located to the west of the A-A zone, the central region between the A-A and B- B zones, and eastern region located to the east of the last zone (B-B). The consolidated basement oj the western region is relatively shallow, at the depth from one to four kilometers. This region is technically calm. The central and eastern blocks are two-fold, separated by the regional basement slope into the elevated northern part and lowered southern part. An outlined general framework of the tectonics of the consolidated basement of the Polish Carpathians is a present-day representation, yet it was finally formed in the Neogene. We can assume that in the Early Neogene (probably at the turn oj the Oligocene and Miocene) the northern plate collided with the Carpathian block. In the Lower Miocene, along the boundary between the northern plate and the Carpathian block, the latter was dropped from a few kilometers in the west to several kilometers in the east. After the lower Miocene, probably at the Middle/Upper Miocene interface, the Carpathian block started to disjoin. It was fractured along the A-A zone and, in its eastern part, rotationally shifted by about 40 km to the north-east. In the west, the western block was jonned. The eastern part, apart from being shifted and rotated, was additionally lowered by a jew kilometers towards the south. In the Upper Miocene a fracture along the B-B zone took place, and, as in the previous stage, the eastern part was rotationally transferred by ca 40 km to the north-east. Thus, the net shift, along the A-A and B-B line was about 80 km. The eastern part was divided along the B-B line into the central and eastern blocks. The eastern block, moreover, is lowered by a few kilometers to the south. This process is accompanied by a development of a set of oblique slip faults of various directions.