SUPERCONTINENTS DURING THE PROTEROZOIC - A PALEOMAGNETIC SURVEY

Palaeomagnetic data are used to construct the positions of continents during Proterozoic. The data have been compiled from literature, from Global Paleomagnetic Data Base and from theses. Applying stringent reliability criteria, the assemblies of cratons at twelve slots in the 2.45-1.00 Ga period have been constructed. The continents lie predominantly in low to intermediate latitudes. The sedimentological indicators of palaeoclimate are consistent with magnetic latitudes, with the exception of the Early Proterozoic, when low latitude glaciations took place. The continental configurations are generally in agreement with geological models of their evolution. The data suggest that three landmasses existed during Proterozoic. The oldest Kenorland broak up during 2.45-2.10 Ga as manifested by dykes and sedimentary basins on many continents. The global 13C-excursion occurred during this break up, although the exact cause for the 13C-anomaly is unknown. The second landmass is Hudsonland which existed from 1.83 to ca. 1.50-1.25 Ga. The configuration of the continents forming Hudsonland is different than the previously proposed supercontinent Columbia. The Neoproterozoic supercontinent Rodinia was formed by continent-continent collisions during ~ 1.10-1.00 Ga and involved most continents. A new model for its assembly is presented, which suggest that multiple Grenvillian collisions took place during 1.10-1.00 Ga. The position of Kalahari is problematic since its Grenvillian belts are oceanwards. The position of Siberia is also problematic since geological data indicate that it is circumferenced by oceanic rocks. It is not known with which continent Baltica collided during its amalgamation with Rodinia. We have proposed that the counter continent was Congo/São Fransisco but there is no geological support for this. Another possibility is Amazonia. The configurations of Kenorland, Hudsonland and Rodinia are different pointing to variable tectonic styles in their formation, reflecting perhaps changes in sizes and thicknesses of the cratons as well as changes in thermal conditions of the mantle through time. References: L.J., Pesonen, S.-Å ., Elming, S. Mertanen, S. Pisarevsky, M.S. D´Agrella-Filho, J. Meert, P. Schmidt, N. Abrahamsen, G. Bylund, 2003. Tectonophysics, v. 375, 289-324.