Geophysical Journal | 2004 volume 26 1

The problem of Proterozoic paleomagnetic key poles for the Ukrainian Shield

© Kravchenko S.N.

   Thorough laboratory experiments and mineralogical analyses indicate the primary origin and stability of the remanent magnetization of the Proterozoic anorthosites from the Ukrainian Shield. Information on the U-Pb dates of rocks and the blocking temperature of ferromagnetic are used to determine the age of this remanence. For slow cooling intrusion such as the Korosten Pluton this procedure should be carried out routinely because U-Pb dates are not equivalent to the time of remanence acquisition. The age of characteristic remanent magnetization is (1647+10) Ma. For the first time a key palaeomagnetic pole has been obtained for the Mesoproterozoic from anorthosites of the Ukrainian Shield. It is situated at: Plat=30,0 N, Plon=178,0 E, α95=3,4 exactly coinciding with the mean key pole (Plat=28 N, Plon=177 E, A95=4,6) from 1630-1648 Ma dykes of Fennoscandia. In contrast to earlier palaeomagnetic results, in this study it was obtained much more clear indication of the time when these two segments of the East European Craton were already a single tectonic unit. The reliability of geodynamic inferences greatly increases if they are based on key paleopoles.

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