The Rio Salitre Volcano-Sedimentary Succession, São Francisco Craton, Eastern Brazil: Record of a Siderian-Orosirian tectonic cycle

Abstract

The basement of the São Francisco Craton in eastern Brazil records a complex history of growth and deformation that extends from the Paleoarchean up to the Orosirian Period. It hosts a segment of the Minas-Bahia Orogen, likely developed during the Orosirian assembly of the Central African block, a continental mass that would encompass the São Francisco-Congo, Borborema, Trans-Saharian, Rio de la Plata, and Kalahari shield provinces of South America and Africa. Aiming to unravel the tectonic scenarios of the Minas-Bahia Orogen generation, we conducted a stratigraphic, structural, geochemical, and geochronological study of the Rio Salitre belt of the Gavião microcontinent, the largest terrane of the Minas-Bahia Orogen exposed in the northern São Francisco craton. The Rio Salitre succession comprises a basal sedimentary unit (A), a middle volcano-sedimentary package (B), and an upper clastic sedimentary assemblage (C). Intruded by small granitic bodies and diabase dikes of unknown age, and unconformably covered by Meso- to Neoproterozoic strata, the Rio Salitre succession experienced two phases of deformation, a WNW-ESE contraction, followed by a left-lateral transtensional shearing that led to the development of a large-scale synformal keel, bound on all sides by basement uplifts. U-Pb zircon dating reveals Neoarchean (2666 ± 13 Ma) and Orosirian (1936 ± 21 Ma) maximum depositional ages, respectively, for Units A and C, and a Rhyacian depositional age of c. 2200 Ma for Unit B calc-alkaline to shoshonitic metatuffs. Our results point to a three-stage tectonic evolution of the Gavião microcontinent. Unit A represents the fill of an interior depocenter likely connected to a continental margin after 2666 Ma, whereas Unit B records its conversion into an extensional back-arc basin in the time interval of 2200 and 2100 Ma. Eventually, the Rio Salitre Basin evolved into a retro-foreland depocenter and received the clastic wedge of Unit C, accumulated after the collision of the various components of the Minas Bahia orogen. Our findings support a correlation between the Rio Salitre succession and classic Paleoproterozoic units of the São Francisco, Congo, and Kalahari cratons, thus favoring the existence of the Orosirian Central African paleocontinent.