HR: 0800h
AN: GP21A-07    [Abstracts]
TI: New Paleomagnetic Data for the Middle Cambrian and Middle Ordovician of the Siberian Platform: Llandeilian Magnetostratigraphy and new Evidence for Relative Rotations Between the Aldan and Anabar-Angara Blocks
AU: Pavlov, V E
EM: pavlov-home@rambler.ru
AF: Russian Academy of Science, Bolshaya Grusinskaya 10, Moscow, 123995, Russian Federation
AU: Gallet, Y
EM: gallet@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, UMR CNRS 7154, 4 place Jussieu, , Paris cedex 5, 75252, France
AU: * Bachtadse, V
EM: valerian@lmu.de
AF: Geophysics Section, Department for Earth and Environmental Sciences, Ludwig- Maximilians-Universität, Theresienstr. 41, München, 80333, Germany
AU: Mikhailov, V
AF: Russian Academy of Science, Bolshaya Grusinskaya 10, Moscow, 123995, Russian Federation
AB: Whether Siberia acted a s a coherent black throughout the Phanerozoic or whether significant rotations occurred in early Paleozoic times between the Anabar-Aldan and Angara blocks is still a matter of debate and it has argued repeatedly that differences in the Apparent Polar Wander Paths from both blocks result from incorrect correlations between sections from the two regions. Addressing this problem a detailed palaeomagnetic study combined with high resolution magnetostratigraphy was carried out on sedimentary sections of mid Cambrian and Llandeillian age along the rivers Lena, Maya, Kulumbe, and Stolbovaya, where a total of 150 oriented hand samples were collected. In addition, a section of llandeilian age was sampled near St. Petersburg, on the Russian Platform in order to obtain a magnetostratigraphic reference profile for further correlation. In all sections the material sampled are either redbeds or greyish, fine grained sediments. Stepwise thermal demagnetization experiments reveal a rather simple directional spectrum in almost all samples studied. after removal of recent magnetizations, and occasionally intermediate components of magnetization, a high temperature component is identified, either carried by magnetite and/or hematite. The resulting mean directions are of dual polarity, pointing either to the south (north) and up (down) as in the case of the Cambrian sections or more to the east (west) or southeast (northwest) and up (down) as in the case of the sections of Llandeilian age. However, no directions of normal polarity have been identified in the lower two thirds of the Llandeilo. Positive reversal and fold tests clearly demonstrate the primary character of these magnetizations. The resulting magnetostratigraphy has been used to unambiguously correlate the sections from Anabar-Angara and Aldan. As a result, we note significant differences in declination in the order of 20° between sections from both blocks which is indicative for early Paleozoic rotations and can be can be linked to the opening of the intervening, v-shaped Vilyui basin. The resulting Euler pole of rotation is located close to the northern shore of lake Baikal and is in good agreement with data from deep sounding seismic experiments which have been used for estimates of crustal thinning in the Vilyui basin.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1535 Reversals: process, timescale, magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly