THE RIBEIRA FOLDED BELT

A tectonic differentiation along the coastal region of South America between Bahia State, Brazil, and Uruguay is observed on a longitudinal as well as on a transversal direction, Longitudinally, a Northern Segment is distinguished from a Southern Segment. The first, with a relatively simple megastructure, presents the Paraiba do Sul Folded Belt [Transamazonic Cycle, 1800-2200 m.y.] later remobilized during the Brazilian Cycle (450-650 m.y.), and the infrastructure of the Ribeira Folded Belt of Brazilian age. The Southern Segment is structurally more complex and is in itself a zoned entity, presenting from NW to SE the Apiai Folded System, the Joinvile Median Massif, the Tijucas Folded System, the Pelotas Median Massif and the Eastern Uruguay Folded System. A characteristic of the Folded Systems are ectinitic rocks from the greenschist and amphibolite facies, migmatized in some regions. The Joinvile Central Massif presents mainly gneissic-migmatitic sequences, partly related to the Brazilian Cycle, while others are of earlier consolidation [Transamazonic Cycle or even older). The Pelotas Central Massifis constituted by migmatitic units of Brazilian age, corresponding to a zone of early consolidation. The two longitudinal segments are separated by a wide zone of transcurrent faulting - the Sao Paulo Transcurrence Zone - with a dextral horizontal displacement of about 300 km. The Transcurrence Zone may have influenced the present setting by a vertical component. The Sao Roque Group is restricted to this Zone and cannot be considered a prolongation of the Acungui Group. The authors consider it rather a separate entity, originally constituting another Folded System to the NW of the Acungui Group.