Uskoki przesuwcze strefy krawędziowej bloków górnośląskiego i małopolskiego

Jerzy Żaba



The boundary zone between two basement blocks (Fig. 1) of regional size, Małopolska (MB) and Upper Silesia (USB) is dissected by two major, transcontinental fault zones: the Hamburg-Kraków and the Szczecin-Kraków-Prešov lineaments (Fig. 4). The segment of the Hamburg-Kraków fault zone extending from Kraków to Lubliniec (Kraków-Lubliniec fault zone, after Buła [11]) separates the Upper Silesia from the Małopolska blocks. This fault, most probably of Early Paleozoic or even Late Proterozoic foundations, showed particularly intense tectonic activity at the end of Silurian and during the Late Carboniferous. Close to Kraków the fault zone turns to ESE, plunging below the Carpathian frontal thrust. This seems to suggest that the crystalline basement of the Upper Silesia block (or Bruno-Vistulicum in a broader sense) which occurs below the Outer Carpathian nappe pile and the underlying Late Paleozoic through Cenozoic cover, extends further to the east (Fig. 4) than was previously assumed [16]. The present-day map-view shape of the Kraków-Lubliniec zone seems to have mostly resulted from high-angle overthrusting of the NE margin of the Upper Silesia block onto the SW edge of the Małopolska block. The overthrusting took place after the Namurian A under the Late Carboniferous dextral transpressive regime. It is along this fault line that all the known granitoid plutons are located. With no exception they occur within the NE (Małopolska) side of this fault zone (Figs 2 and 3). The Szczecin-Kraków-Prešov fault zone transects the marginal area of the basement ofthe Upper Silesia block. It can be traced on gravimetric maps and topographic surface maps showing condensed topographic contours. Towards the SE it continues into the Carpathian nappes (Fig. 4). This fault zone was produced (or reactivated) after the above mentioned overthrusting took place, being, however, not younger than Westphalian B times. The direct effects of the dextral shearing in the Palaeozoic cover of the Upper Silesia block are deflections in axial trends of somewhat older folds and thrust lines (Fig. 3). The Szczecin-Kraków-Prešov fault zone showed a prolonged tectonic activity supposedly extending until the recent times. In the boundary zone of the Małopolska and Upper Silesia blocks both major fault zones occur very close to each other (the maximum distance between the two is 10 km), nearly coinciding near to Myszków, Zawiercie and Kraków. In the latter cases the widths of the direct, combined fault zone approximates 2 km. The strike-slip fault zones played a long-lasting and important metallogenic role in the region. A direct spatial relationship to those major faults in shown, as well, by granitoid plutonism. At the end of the Variscan cycle, due to polyphase evolution of the Late Carboniferous, dextral, britte strike-slip zone the regional fault network became so multidirectional and complex that during the younger deformation events was only able to be reactivated along various older anisotropy directions (Fig. 2). It was thus characterized by typical features of a saturated fault network.