Abstract
Due to the lack of reliable paleomagnetic data from Armorica for mid‐Ordovician to Late Devonian times, the drift history for this tectonic element is poorly understood. In order to help rectify this problem, a paleomagnetic study of Upper Silurian volcanic, intrusive and sedimentary rocks from the Barrandian Basin of the Central Bohemian Massif (Czech Republic) has been carried out. This basin comprises a sequence of unmetamorphosed lower Paleozoic rocks, the folding of which has an uppermost age limit of Early Carboniferous. Stepwise thermal demagnetization of the samples collected (182 samples from 21 sites), and principal component analysis of both great circle and stable endpoint data reveal a total of three directions of magnetization. The first (labelled A) is in the direction of the present‐day local Earth's magnetic field (D/I = 360°/67°) and is thus interpreted as being of recent origin. The other two directions, termed B and C, comprise the intermediate and high blocking temperature directions respectively. The overall in situ mean direction obtained for B, identified between 150° and 320°C, is 195°/−8° (D/I), k = 18.5, α95 = 13.2° (eight sites). It fails the fold test and yields an in situ paleo‐south pole position of 42°S, 354°E. This coincides with the Late Carboniferous segment of the apparent polar wander (APW) path for stable Europe and is considered to be a secondary overprint of this age. The third magnetization (termed C) is identified between 320° and 600°C, gives an overall mean direction of 208°/−40°, k = 96.8, α95 = 5.7° (eight sites), after bedding correction. It passes fold and reversal tests on both local and regional levels and is interpreted as representative of the Late Silurian paleofield direction in the Bohemian Massif; it yields a paleo‐pole position of 55°S, 325°E. Assuming a normal polarity, the inclination value obtained translates into paleolatitudes of 23°S for this part of Armorica and implies a position adjacent to the southern margin of Baltica. This therefore indicates closure of the intervening ocean by Late Silurian times. However, adopting this polarity also implies large‐scale (up to 140°) anticlockwise rotations of the Bohemian Massif prior to deformation in the Early Carboniferous.
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