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Geological Society, London, Special Publications; 2009; v. 323; p. 145-163;
DOI: 10.1144/SP323.7
© 2009 Geological Society of London

Articles

Palaeomagnetism and U-Pb dates of the Palaeoproterozoic Akitkan Group (South Siberia) and implications for pre-Neoproterozoic tectonics

Alexei N. Didenko1,6,*, Vladimir Y. Vodovozov2,7, Sergei A. Pisarevsky3, Dmitry P. Gladkochub4, Tatyana V. Donskaya4, Anatoly M. Mazukabzov4, Arkady M. Stanevich4, Elena V. Bibikova5 & Tatyana I. Kirnozova5

1 Geological Institute of the Russian Academy of Sciences, 7, Pyzhevsky Lane, 119017 Moscow, Russia
2 Institute of Physics of the Earth of the Russian Academy of Sciences, 10 Bol. Gruzinskaya Street, 123995 Moscow, Russia
3 School of Geosciences of the University of Edinburgh, the King's Buildings, West Mains Road, Edinburgh EH9 3JW, UK
4 Institute of the Earth's Crust of the Siberian Branch of the Russian Academy of Sciences, 128, Lermontova Avenue, 664033 Irkutsk, Russia
5 Vernadsky Institute of geochemistry and analytical chemistry of the Russian Academy of Sciences, 19, Kosygina Street, 117975 Moscow, Russia
6 Institute of Tectonics and Geophysics of the Eastern Branch of the Russian Academy of Sciences, 65, Kim Yu. Chen Street, 680063 Khabarovsk, Russia
7 Lomonosov Moscow State University, Faculty of Geology, 1 Leninskiye Gory, 119899 Moscow, Russia

* Corresponding author (e-mail: alexei_didenko{at}mail.ru)

We present new geochronological and palaeomagnetic results from the late Palaeoproterozoic Akitkan Group in South Siberia. The zircon U–Pb conventional age of the rhyodacite from the upper part of the group is 1863±9 Ma and the age of the dacite from the lower part of the group is 1878±4 Ma. Palaeomagnetic study of sedimentary and some igneous rocks from the upper part of the group isolated a high-temperature characteristic component (D=193°, I=19°, k=51, {alpha}95=7°) which is supported by two of three applied conglomerate tests. However, the third intra-formational conglomerate test demonstrates a contaminating overprint of uncertain nature for a part of our collection. The analysis of data suggests that this overprint occurred at time when the geomagnetic field's direction was similar to that at the time of the deposition. Therefore the corresponding palaeomagnetic pole (22.5 °S, 97.4 °E, dp=1.5°, dm=2.8°) may be considered as representative for the deposition time. Palaeomagnetic study of the sediments in the lower part of the Akitkan Group isolated a stable primary remanence (D=189°, I=8°, k=111, {alpha}95=5°) supported by positive intra-formational conglomerate and fold tests. The palaeomagnetic pole (30.8 °S, 98.7 °E, dp =2.5°, dm=5.0°) is nearly coeval with the 1879 Ma Molson B pole from the Superior craton. We used these two poles to compare the relative position of Siberia and the Superior craton in the late Palaeoproterozoic. It is different from their reconstruction around 1000 Ma. This demonstrates their relative movements in the Mesoproterozoic.