CURRENT STATUS OF PRECAMBRIAN PALEOGEOGRAPHIC RECONSTRUCTIONS

Paleomagnetism remains the only quantitative method available to produce global Precambrian paleogeographic reconstructions. Many high-quality paleopoles were used to construct Phanerozoic APWPs for the majority of continents, and there is a general agreement about Phanerozoic tectonic history. In contrast, Neoproterozoic and older paleomagnetic data are scarce and commonly controversial, and it is impossible at this stage to apply the traditional APWP method owing to time gaps of more than 100 million years between some data points. Such gaps lead to paleomagnetic problems of longitudinal uncertainty and polarity ambiguity. The latter is of particular importance, because even high-quality results can be used to support remarkably different paleogeographic models by choosing alternative polarity options. Thus, for the Rodinia supercontinent in late Mesoproterozoic and early Neoproterozoic time, there are four alternative Australia-Laurentia reconstructions, at least six proposed positions of Siberia, and several for Baltica, Kalahari, Amazonia, and Congo. The proliferation of alternative models will continue until the problems of Precambrian paleomagnetic data are resolved. Meanwhile, the only way to achieve any progress in Precambrian paleogeography lies in strong integration with the geological data, including matching areas from now widely separated continents, and documenting paleopositions of passive and active paleoceanic margins, paleoclimatic indicators, and major magmatic events (LIPs) etc. However, the reliable Precambrian paleomagnetic data are numbered and the geological, geochronological, geochemical and other data are likewise insufficient for robust paleoreconstructions. On an optimistic note we can predict that this situation will be improving shortly. There are several examples where new precise dating has attracted paleomagnetists to study, or re-study, some Precambrian rocks employing modern techniques and obtaining robust and well-dated paleopoles. There are also several examples of old paleomagnetic studies that produced promising results, but cannot pass reliability criteria due to poor statistics, lack of field tests, incomplete demagnetizations etc. These should be primary goals for paleomagnetic reinvestigation.