Paleomagnetism of the Upper Riphean Lakhandinskaya Group in the Uchuro-Maiskii area and the hypothesis of the Late Proterozoic supercontinent

The results of paleomagnetic studies on rocks of the Neryuenskaya and Ignik anskaya Formations of the Late Riphean Lakhandinskaya Group (the Uchuro-Mai skii Righean hypostratotype, southeastern Siberian Platform) are presented. The direction of the inferred characteristic component of magnetization is independent of magnetic mineralogy and persists over at least a few tens o f kilometers but varies, on a significant level, from the bottom to top of the section. The data obtained indicate a prefolding age of the characteris tic component. The paleomagnetic poles from the study rocks clearly differ from younger pales of the Siberian Platform. All these data point to the fa ct that the inferred characteristic component was acquired at the time of o r shortly after the deposition of the Lakhandinskaya Group. Taking into acc ount recent paleomagnetic data on the Middle Riphean Malginskaya Formation, results of this current work suggest, depending on the choice of the paleo magnetic direction polarity, two possible scenarios for relative movements of the Siberian Platform and Laurentia in a 1100-1000-Ma interval. One of t hese scenarios contradicts the hypothesis on Siberia as a part of the Rodin ia supercontinent. The second scenario, which implies a variation in the ge nerally accepted polarity for one of the cratonic blocks considered, is in a good agreement with this hypothesis but requires a coincidence of norther n Laurentia with south-southeastern Siberia, rather than with its northern part, as is assumed in most reconstructions.