Transamazonian orogeny in the southern Sao Francisco craton region, Minas Gerais, Brazil: evidence for Paleoproterozoic collision and collapse in the Quadrilatero Ferrifero

The Paleoproterozoic Transamazonian orogeny yielded a series of discrete orogens in Brazil. The present field study in the Quadrilatero Ferrifero (QF) indicates that the southern Sao Francisco craton region of the Brazilian highlands preserves a portion of one of these orogens, Two sets of Transamazonian structures occur in this region. The first consists of northwest-verging folds and thrusts affecting supracrustal sequences. It is suggested that this set formed in a fold-thrust belt setting shortly after 2.125 Ga, during the closure of a passive-margin basin that had initiated along the margins of a preexisting continental mass at ca 2.5 Ga. The second set consists of structures defining the prominent dome-and-keel architecture of the QF, This set, a consequence of the emplacement of basement domes against supracrustal rocks at 2.095 Ga, map reflect the consequences of orogenic collapse. Narrow, conglomerate-filled intermontane basins may have formed coevally with dome emplacement. Formation of an ocean basin east of the present-day Sao Francisco craton eventually occurred in Late Mesoproterozoic. In effect, the Transamazonian orogen of the QF represents the collision and collapse stages of a Paleoproterozoic Wilson cycle. The contractional phase of the Transamazonian orogeny probably represents accretion of an offshore are to the eastern and southeastern margin of the present-day Sao Francisco craton legion. The are. and an associated suture, may be traced in the Brasiliano (Pan African) orogen east of the Sao Francisco craton, northwards into the northeastern lobe of the SBo Francisco craton. Clearly, initial assembly of crustal;blocks to form a larger continent involving South America occurred during the Paleoproterozoic (2.1Ga). Post-Transamazonian rifting of this continent created the basins which were later inverted during the Brasiliano assembly of Gondwana. (C) 1998 Elsevier Science B.V.