Późnokarbońska aktywność przesuwcza strefy granicznej bloków górnośląskiego i małopolskiego

Jerzy Żaba



The edge (boundary) zone of the Małopolska Block (MB) and of the Upper Silesia Block (USB) is cut by two major, transcontinental fault zones: the Hamburg-Kraków and the Szczecin-Kraków-Presov lineaments (Fig. 1). A long lasting tectonic activity of both these fault zones had an important impact on polyphase structural evolution of the edge zone area. Of particular intensity was their Late Carboniferous strike-slip motions, closely related to granitoid intrusions as well as to the accompanying ore mineralisations. The Late Carboniferous deformation comprised three stages during which a progressive rotation of horizontal compression axis took place. During the pre-intrusive stage, dated as posterior to Namurian A, under dextral transpressive regime conditions (NNE-SSW directed compression) the NE margin of the Upper Silesia Block was uplifted and overthrust along a high-angle reverse faults upon the edge of the Małopolska Block (Fig. 2). This produced fold and thrust structures (Figs 3 and 4) as well as Riedel shears and normal faults (Fig. 2) in the Palaeozoic strata. During the syn-intrusive stage, postdating the Westphalian B, in conditions of dextral transtension (NNW -SSE directed compression) granitoid bodies were emplaced in active, extensional shear zones (Figs 5-7), into voids produced in – between en - echelon trains of penetrative P shears. The plutons intruded as well into pull-apart zones. These processes were accompanied by formation of R' and X shears. During the post-intrusive stage, which occurred at the turn of Westphalianand Stephanian and, most probably, also in the early Stephanian, under conditions of dextral simple shearing regime followed by dextral transpression (with horizontal compression axis direction oriented at first submeridianally, next replaced by NNE-SSW direction), the granitoids and their matle rocks were deformed (Figs 8-11). At that time several tectonic events produced folds, reverse faults and thrusts, parallel to analogousstructures that had formed earlier during the pre-intrusivestage. A significant proportion of then generated faults were reactivated and rejuvenated older discontinuities. A saturated fault network developed at that stage. The main part was played at that time by the Szczecin-Kraków-Presov fault zone. The displacements on the Hamburg-Kraków fault zone in the vicinities of Lubliniec were of the transpressive type, with initially sinistral strike-slip sense (at the pre-intrusive stage), being then replaced by dextral (at syn-intrusive stage) and, eventually, again by sinistral sense of motion (at the post-intrusive stage). At the syn-intrusive stage, at the same time when along the NE boundary of the Upper Silesia Block grainitoid plutons intruded under extensional regime, the western edge of this block was overriden, under compressional regime, by Early Carboniferous sediments of the Moravo-Silesian zone. The recently suggested Early Carboniferous large-scale strike slip faulting in the Sudetes (Aleksandrowski 1990, 1994) along crustal discontinuities of the same direction (NW-SE to WNW-ESE) as those in the area under discussion, seems, therefore, to have migrated northwards in the Late Carboniferous and concentrated on the Odra fault zone and its continuation into the boundary faults between the Małopolska and Upper Silesia Blocks.

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