Tectonic and paleogeographic interpretation of the paleomagnetism of Variscan and pre-Variscan formations of the Bohemian Massif, with special reference to the Barrandian terrane
M. Krs et al., Tectonic and paleogeographic interpretation of the paleomagnetism of Variscan and pre-Variscan formations of the Bohemian Massif, with special reference to the Barrandian terrane, TECTONOPHYS, 332(1-2), 2001, pp. 93-114
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.