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The Early Palaeozoic break-up of northern Gondwana, new palaeomagnetic and geochronological data from the Saxothuringian Basin, Germany

Schätz, M., T. Reischmann, J. Tait, V. Bachtadse, H. Bahlburg, and U. Martin (2002), The Early Palaeozoic break-up of northern Gondwana, new palaeomagnetic and geochronological data from the Saxothuringian Basin, Germany, International Journal of Earth Sciences, 91(5), 838-849.

Abstract
Early Palaeozoic volcanic and sedimentary rocks from the Saxothuringian Basin (Franconian Forest, northern Bavaria) have been subjected to detailed radiometric and palaeomagnetic studies in order to determine the tectonic environment and geographic setting in which they were deposited. Two hand samples were collected from the as yet undated pyroclastic flow deposits for Pb-207/Pb-206 age dating. Radiometric results for these samples, obtained by the single-zircon evaporation technique, are identical within error, and the mean age of all measured grains is 478.2+/-1.8 Ma (n=11). This age is considered to be primary and firmly constrains the eruption of the ignimbrites and formation of the subaqueous pyroclastic flows as having occurred in Early Ordovician (Arenig) times. Palaeomagnetic studies were carried out on these Early Ordovician volcanic rocks, and also on the biostratigraphically dated, Late Ordovician (Ashgillian) Dobra sandstones. The volcanic rocks carry up to three directions of magnetisation. The poorly defined, low and intermediate unblocking temperature directions are thought to represent secondary overprint directions of post-Ordovician age. The high temperature component, however, identified at temperatures of up to 580 degreesC, is of mixed polarity and passes the fold test with 99% confidence. The overall mean direction after bedding correction is 189degrees/76degrees. alpha(95)=11.6degrees, k=44.7 (25 samples, five sites), and is considered to be primary and Early Ordovician in origin. It yields a palaeo-south pole at 24degreesN and 007degreesE, which translates into palaeolatitudes of 63degrees+21.7degrees/-17.3degrees S for the Saxothuringian Terrane. Samples from, the Late Ordovician Dobra sandstone are generally very weakly magnetised. A high temperature D component of magnetisation can be identified in some samples and yields a mean direction of 030degrees/-58degrees, alpha(95)=18.5degrees, k=25.7 (15 samples, four sites) after bedding correction. The Arenig palaeomagnetic results indicate high palaeolatitudes, but separation from northern Gondwana. This is in basic agreement with data from elsewhere in the Armorican Terrane Assemblage, all of which suggest high southerly palaeolatitudes in the Early Ordovician. The geochemical signatures of these rocks indicate emplacement in an extensional environment. These new data, therefore, are interpreted as marking the onset of rifting of Saxothuringia from the north African margin of Gondwana, and the start of the relative northward migration of the Saxothuringian Terrane. Although the Late Ordovician palaeomagnetic results presented here are only poorly constrained, they suggest an intermediate palaeolatitude for Saxothuringia in Ashgillian times, in good agreement with Late Ordovician palaeomagnetic data from the Barrandian.
BibTeX
@article{id168,
  author = {M. Sch{\"a}tz and T. Reischmann and J. Tait and V. Bachtadse and H. Bahlburg and U. Martin},
  journal = {International Journal of Earth Sciences},
  number = {5},
  pages = {838-849},
  title = {{The Early Palaeozoic break-up of northern Gondwana, new palaeomagnetic and geochronological data from the Saxothuringian Basin, Germany}},
  volume = {91},
  year = {2002},
  language = {en},
}
EndNote
%0 Journal Article
%A Schätz, M.
%A Reischmann, T.
%A Tait, J.
%A Bachtadse, V.
%A Bahlburg, H.
%A Martin, U.
%D 2002
%N 5
%V 91
%J International Journal of Earth Sciences
%P 838-849
%T The Early Palaeozoic break-up of northern Gondwana, new palaeomagnetic and geochronological data from the Saxothuringian Basin, Germany
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Printed 15. Dec 2019 04:09