THE RIO-DOCE OROGENY, SOUTHEASTERN BRAZIL

The Neoproterozoic-Eopaleozoic superposed orogenic system of Southeastern Brazil, which was active during the Brasiliano-Pan-African Cycle during the assembly of this sector of the Gondwana Supercontinent, includes distinct terranes such as the Guanhaes, Curitiba, Apiai-Guaxupe and Serra do Mar microplates and the Juiz de Fora Thrust Belt. These orogenic systems also affected the reworked border of the Sao Francisco Craton. The collisional or ocean plate subduction-controlled ''Brasiliano I'' Orogeny was responsible for the generation of fold belts along the southeastern border of the Sao Francisco Craton, the accretion of different microplates and the formation of a magmatic are associated with the roots of a northwestward trending thrust belt. The ''Brasiliano I'' evolution occurred during the Neoproterozoic and by 600 Mn was already in a post-orogenic stage in the Apiai-Guaxupe Microplate, with the intrusion of rapakivi-like granitoids. The Rio Doce Orogeny is best characterized in the Serra do Mar Microplate by a magmatic are, active between 590 and 570 Ma, with batholithic calc-alkaline plutonism exhibiting subduction zone components and a chemical zonation indicative of northwest-ward subduction. The collisional stage (550-530 Ma) accounted for the accretion of the Serra do Mar Microplate to the former orogenic domains. Anatexis of mostly metasediments producing peraluminous migmatites and granites, began at the calc-alkaline magmatic are stage and culminated during crustal thickening associated with the northwesterly piling-up of large thrust slices. The post-collisional plutonism (520-480 Ma) is characterized by plutons and dikes of mainly alkali-calcic granitoids enriched in incompatible elements.