Tectonic and paleogeographic interpretation of the paleomagnetism of Variscan and pre-Variscan formations of the Bohemian Massif, with special reference to the Barrandian terrane

Paleomagnetic data from Variscan and pre-Variscan formations of the Bohemia n Massif (BM) have been interpreted tectonically, and paleogeographically e valuated with respect to the European paleomagnetic results. The interpreta tion of data from the BM was preceded by the evaluation of the effect of th e Trans-European Suture Zone (TESZ) on the dispersion of the European paleo magnetic pole positions during the Variscan orogeny. Stability of the Europ ean lithospheric plate is well documented by paleomagnetic results for the Early Permian to the Quaternary rocks of the regions between the Ural Mount ains and Great Britain, north of the Alpine tectonic brit. For the Late Car boniferous and earlier times, the stable plate is defined in the regions NE of the TESZ in the East European Craton only. Late Carboniferous and older rocks from the regions SW of the TESZ, largely occupied by the West-Europe an Variscides, show tectonic deformations controlled by prominent horizonta l rotations. These rotations can be studied on a theoretical model simulati ng the distribution of pole positions controlled by rotation of rock format ions about a vertical axis. In the BM, horizontal paleotectonic rotations a re well documented for Variscan and pre-Variscan rocks: they reach several tens of degrees (up to 180 degrees in extreme cases) of mostly clockwise se nse. The study of the tectonics anal paleogeography of Cambrian to Devonian formations of the Barrandian area, which is considered a peri-Gondwana ter rane with affinities to Armorica, may serve as a case history of the study of a terrane incorporated into a stable lithospheric plate. Here, the Barra ndian terrane became a part of the European Plate as a component of the eme rging Pangea supercontinent in the final phase of the Variscan orogeny. Hig h, almost peri-polar paleolatitudes for the Cambrian rocks of the Barrandia n area are - within the limits of data scatter - in agreement with the pres umed position of Gondwana and Armorica. Rocks of Ordovician age did not pro duce consistent results; they will require further paleomagnetic and paleoc limatologic studies in relation to the data for the Late Cambrian and Early Silurian rocks of the Barrandian area. The analysis of data presented here shows that paleomagnetic declinations of Variscan and pre-Variscan formati ons reflect paleotectonic rotations following the formation of the respecti ve rocks including rotations induced by the Variscan orogeny and rotation o f the European Plate to which the rocks became incorporated. Therefore, pal eomagnetic declination of none of the pre-Variscan formations can be identi fied with paleotectonic rotation either of the Barrandian terrane or even o f the whole BM. Magnitudes of horizontal paleotectonic rotations in the BM affected by Variscan tectonism are notably similar to those in the Western Carpathians affected by Alpine deformation. Senses of rotation are, however , different with clockwise rotation prevailing in the BM, and counterclockw ise rotations prevailing in the Western Carpathians. Recognition of the eff ect of horizontal rotations of rock formations, if located in tectonically mobile belts and incorporated into a stable plate during their later histor y, should be respected while deriving the apparent polar wandering path (AP WP). (C) 2001 Elsevier Science B.V. All rights reserved.