AS TAFROGÊNESES SUPERPOSTAS ESPINHAÇO E SANTO ONOFRE, ESTADO DA BAHIA: REVISÃO E NOVAS PROPOSTAS

Abstract

The built up of the Espinhaco rift in the states of Bahia and Minas Gerais, took place along NS and NW-SE faults. In the State of Bahia the initial phase of the taphrogeny was marked by the Rio dos Remedios volcanism, dated at about 1750 Ma (U-Pb), and followed by the deposition of more than 5,000 meters of continental and shallow marine sediments. These units represent the Espinhaco supergroup in the northern part of the Espinhaco range and in the Chapada Diamantina plateau. A second extensional phase at the beginning of the Neoproterozoic, between 1000 and 900 Ma, lead to a new rifting episode in the area of the Espinhaco supergroup and its basement. Old faults of the former aborted Espinhaco rift were reactivated. A triple junction was developed in the southeastern margin of the Sao Francisco craton. In the lesser active arm of this junction the Santo Onofre rift was formed, penetrating the site of the Espinhaco supergroup in the State of Bahia. Along this neoproterozoic rift continental and marine sediments including turbiditic lobes were deposited. These units are represented by the redefined Santo Onofre group, which outcrops along the strike of the Espinhaco supergroup. The southern extension of the redefined Santo Onofre group is represented by the Macaubas group, in the upper Pardo river, northern Minas Gerais. Both southernly located limbs of the triple junction are represented by the assimetric Macaubas rift, which opens to the east to form a passive continental margin - the Aracuaf basin. In the Chapada Diamantina plateau, a discordance at the basis of the Morro do Chapeu formation, is interpreted to be genetically related to the deposition of the redefined Santo Onofre group. The Morro do Chapeu formation represents therefore also a neoproterozoic unit. On the other hand, the Tombador and Caboclo formations are mesoproterozoic platform sediments (∼1200-1000 Ma), probably related to a geodynamic event of grenvillian age.The closing of the Macaubas basin during the Brasiliano orogenesis, lead to the formation of the Aracuai belt and to the deformation of the Santo Onofre group along the so called Paramirim deformation corridor in the interior of the Sao Francisco craton. This deformation involved also the Espinhaco system and its basement.