Abstract:
At least two supercontinents - Rodinia and Gondwana - have been proposed for the 1200-500 Ma time interval on the basis of stratigraphic, geochronological and paleomagnetic grounds. Although the exact configuration of Rodinia is still a matter of debate, both supercontinents are linked insofar as the demise of the older Rodinia begat the younger Gondwana. In order to constrain the paleogeographic transition between these two supercontinents, we evaluate an updated paleomagnetic database (148 poles) for Africa together with unpublished data from South America, using the Q-factor criteria of Van der Voo [Van der Voo, R., 1990. The reliability of paleomagnetic data. Tectonophysics 184, 1-9]. A postulated Grenvillian suture between Laurentia and the united Amazonia-West Africa craton is supported by comparing the Meso-Neoproterozoic drift history of these two cratons. Comparing this drift history with that of the remaining West Gondwanan cratonic elements: São Francisco-Congo, Kalahari, Rio de Plata, and Arabian-Nubian shield, reveals that these cratons were not part of Rodinia. The contrasting drift history of Laurentia cum Amazonia-West Africa with "central" West Gondwanan cratons São Francisco-Congo, Kalahari suggests the continued existence of at least two separate tectonic plates separated by an ocean basin. The assembly of central Gondwana, i.e. Kalahari, São Francisco-Congo, and the Arabia-Nubian shield was completed during latest Neoproterozoic times, as indicated by the approximation of ca. 550 Ma paleomagnetic poles. The collision of these central Gondwanan blocks with the Amazonia-West Africa craton appears to have occurred by mid-Cambrian times, after the opening of the Iapetus ocean basin between Laurentia and Amazonia-West Africa. We propose a scenario in which West Gondwana was formed through at least two distinct orogenic episodes: terranes and cratons accreting to the São Francisco-Congo craton in a series of collisions from 940 to 550 Ma, followed by the collision with Amazonia-West Africa and minor contiguous blocks (Rio Apa and Pampia) at ca. 520 Ma. West Gondwana was not a coherent tectonic unit before the end of Precambrian times, with a major mobile belt separating at least two separate continental masses. © 2006.
