Palaeomagnetic constraints for Variscan mobilism of the Upper Silesian and Małopolska Massifs, sonthern Poland

Abstract

Palaeomagnetic results from the NE part of the Upper Silesian Massif (USM) have been interpreted as evidence for the final amalgamation of this block with Baltica by the Givetian (J. Nawrocki, 1993a,b). This paper aims to indicate, however, that closer analysis of palaeomagnetic results reported by J. Nawrocki has shown their applicability to a wide scope of mobilistic interpretations. It will be substantiated that palaeopole D (5°S/313°E) obtained for the Givetian dolostones of the Siewierz area can not represent the Givetian palaeopole for Baltica (by extrapolation - for the Old Red Continent – ORC), as was postulated by J. Nawrocki (l993a,b), because this conclusion results in confusing Middle Devonian palaeogeographic configuration of ORC, in which Eifelian-Givetian oolite and evaporites of Laurentia would be deposited in palaeolatitudes over 50°S. It will also be presented that juxtaposition of pole D with the current palaeomagnetic data for the Middle-Late Devonian poles of ORC reveals ca. 30° misfit, pole D being shifted to the NW. This implies clockwise rotation of USM in Variscan times. Taking into account that pole D is similar to the palaeopoles of the Early Carboniferous reported from some Variscan blocks of Western Europe, approximately the same acquisition time is suggested for the corresponding natural remanent magnetization (NRM). An origin of this and other intemediare/hard components of NRM are tentatively attributed to a conjectural, pulsative epigenetic mineralization during the time spanning from the Tournaisian to the Bashkirian (360-305 Ma). Finally, the inadequacy of palaeopole D for disproving the hypothesis of strike-slip displacement of Małopolska Block along the SW margin of Baltica in Devonian time will be shown.