Paleomagnetic and Geological Constraints on the Amazon Craton in Rodinia and Gondwana Supercontinents

The assembly of Rodinia along the North American Grenville mobile belt was marked by the collision between Amazonia and Laurentia. Paleomagnetic data from the SW Amazon craton suggest net left-lateral motion between Amazonia and Laurentia, reflective of a transpressive collision. Geological evidence for this motion includes portions of Amazonian crust stranded within the North American craton, notably the Blue Ridge province of the southern Appalachians, as well as thermochronological histories. The final, post-Grenvillian (<1.0 Ga) plate configuration is clouded by uncertainty in the Laurentian apparent polar wander path. The break-up of Rodinia is mostly unconstrained by paleomagnetic data from South America. Neoproterozoic-Cambrian, rift-related sediments from the Amazon side outcrop in the 90º curved Paraguai belt along the SE margin of the Amazon craton. These sediments comprise, from bottom to top, a >10 km package of clastic sediments (Cuiabá Gp.) unconformably overlain by the 3-4 kms of the Alto Paraguai Gp, which contains a Snowball Earth lithological sequence, i.e. banded iron formation, glacial diamictites, and overlying cap carbonates, reportedly of Marinoan age. Paleomagnetic study of bituminous limestones in the cap carbonate reveals a post-folding remagnetization carried by magnetite and/or pyrrhotite. The paleomagnetic direction from this secondary component was acquired at ca. 525 Ma, according to a reference pole reported by Trindade et al (EPSL, 2006). The co-variation in the declination of this remagnetization with the strike of the Paraguai fold- -thrust belt suggests that the belt's curvature is a secondary feature, acquired during the collision of the Amazon craton with the São Francisco-Congo craton sometime after the mid-Cambrian. This late Cambrian age for the amalgamation of West Gondwana is supported by existing paleomagnetic data, as well as new U-Pb zircon ages from post-tectonic granites and rhyolites along the inferred suture zone.