Introduction

[2]  The problem of the paleomagnetic poles of the transitional Late Precambrian-Phanerozoic period of the geological history is one of the most acute and morbid problems of the Siberian Platform paleomagnetology. First, the location of these poles is highly necessary for the solution of a number of actual problems in modern geology and geophysics. Secondly, the data available for the terminal Vendian time (see a brief review in [Shatsillo et al., 2005]) and for the Early Cambrian are highly contradictory and are almost absent for the Late Riphean time (except for its beginning).

[3]  The location of the Vendian-Early Cambrian and Late Riphean paleomagnetic poles of the Siberian Platform is highly important for solving the problem of timing the breakup of the Late Proterozoic Rhodinia supercontinent and for testing the numerous hypotheses explaining the geological evolution of our planet at the Precambrian-Paleozoic boundary. The results of this work will allow us to reconstruct the positions of the Siberian and East European cratons relative to each other at the Precambrian-Phanerozoic boundary and to carry out the paleomagnetic testing of the competing basic hypotheses [Didenko et al., 1994; Mossakovskii et al., 1993; Sengör et al., 1993], describing the formation and evolution of the Central Asian foldbelt.

[4]  The results of the latest studies [Kazanskiy, 2002; Kravchinsky et al., 2001; Pavlov et al., 2002; Pisarevsky et al., 2000; Smethurst et al., 1998] prove the importance of correlating the Phanerozoic and Riphean curves of the apparent migration of the pole for the Siberian Platform, of choosing the direction of the normal polarity of the paleomagnetic vectors of Siberia in Precambrian time, of the rate of the horizontal movements of the Siberian Craton at the Precambrian-Paleozoic boundary, of the adequacy of the regional and global paleotectonic reconstructions available, to name but a few.

[5]  The lack of definiteness in the positions of the Vendian-Early Cambrian and Late Riphean poles of the Siberian Platform leads to the conventional minimization of the movements of the paleomagnetic poles in determining the polarity of the paleomagnetic trends during the Riphean. To sum up, in spite of having reliable data for the Middle and initial Late Riphean data for the Uchur-Maya and Turukhan regions, and for the Yenisey mountain range, we cannot be sure of the fact in which hemisphere the Siberian platform was situated in that time.

[6]  Kirschvink et al. [1997] offered an Inertial Interchange True Polar Wander (IITPW) hypothesis, growing more and more popular, which is based to a significant degree on the paleomagnetic data obtained by this author for the Lower Cambrian rocks of East Siberia. However, this hypothesis need be verified because of the indefinite choice of the paleomagnetic pole of that time. The IITPW hypothesis suggests that the redistribution of rock masses in the lithosphere and mantle during the Lower Cambrian caused a change in the Earth inertia axes: the axis corresponding to the maximum moment of inertia became an axis with the intermediate moment, and vice versa. The change of the axes caused a rapid (15-20 million years) displacement of the lithosphere and mantle relative to the Earth rotation axis, that is, caused a significant displacement of the pole relative to the surface of the planet, which in turn triggered the significant tectonic, paleogeographic, climatic, and biospheric reconstruction of the planet at the beginning of the Cambrian. Since the IITPW hypothesis implies the significant displacement of the paleomagnetic pole in Vendian-Early Cambrian time, we must have modern reliable data for the Vendian and Early Cambrian paleomagnetic poles, which will allow us to prove or discard this widely discussed hypothesis.

[7]  The collection of these data for the Siberian Platform and of similar data for the second half of the Late Riphean would be sufficient to test the IITPW hypothesis, to clarify the time of the final breakup of Rhodinia, to combine the Paleozoic and Riphean trends of the curve for the final migration of the Siberian pole, to determine the polarity of the Riphean paleomagnetic trends, and to advance substantially in the solution of other important problems.

[8]  The aim of this study was to determine the reliable Vendian paleomagnetic poles of the Siberian Platform for plotting the Siberian curve of the apparent pole migration, necessary for solving the problems mentioned above. For this purpose detailed paleomagnetic studies of Vendian reference rock sequences were performed in the southwest of the Siberian Platform. The results of these studies are reported in this paper.


RJES

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