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Russian Geology and Geophysics

2005 year, number 4

PALEOMAGNETIC DIRECTIONS FROM NERSA INTRUSIONS OF THE BIRYUSA TERRANE, SIBERIAN CRATON, AS A REFLECTION OF TECTONIC EVENTS IN THE NEOPROTEROZOIC

D.V. Metelkin, I.V. Belonosov, D.P. Gladkochub*, T.V. Donskaya*, A.M. Mazukabzov*, and A.M. Stanevich*
Institute of Geology, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
* Institute of the Earth's Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Neoproterozoic, paleomagnetic pole, Siberian craton, Rodinia
Pages: 395-410

Abstract

New paleomagnetic data have been obtained from the Neoproterozoic subvolcanic intrusions which are widespread in the Biryusa terrane of the southwestern margin of the Siberian craton. The mafic dike swarms called the Nersa complex are rift-related subvolcanics, which could be used as indicators of the initial stage of the Neoproterozoic breakup of the Rodinia supercontinent. Two stable components of magnetization from the Nersa intrusions and Neoproterozoic sedimentary rocks of the Karagas Group were obtained. One of them is possibly a synfolding component related to the Early Paleozoic deformation processes. The other is the characteristic component of remanent magnetization, with the site-mean direction characterized by D s = 146.4, I s = 11.0, and α95 =13.3}>. The nature of this component is disputable. On the one hand, it can locate Siberia in the Late Neoproterozoic, but on the other hand, it also can reflect the Early Paleozoic remagnetization processes. Detailed analysis of the data, including results of reversal, baked-contact, and fold tests, suggests that the paleomagnetic directions could be of primary origin. We have tested the new paleomagnetic pole for its correspondence to some alternative tectonic reconstructions of Rodinia and believe that Siberia had an equatorial position and its modern southern margin was oriented to Laurentia during Neoproterozoic time.