Rifting events in the southern sector of the Paramirim Aulacogen, NE Brazil: New geochronological data and correlations for the São Francisco – Congo paleocontinent

Abstract

The evolutionary history of the Paramirim Aulacogen is characterized by the superposition of rifts that developed from 1770 to 675 Ma. In the Northern Serra do Espinhaço Fold Thrust Belt, two units of this aulacogen were analyzed in the present study: the Algodão Formation (Espinhaço Supergroup) and the Santo Onofre Group (São Francisco Supergroup). In the study area, the Algodão Formation consists of alternating of quartzose to feldspathic metasandstones, sericitic metasandstones, oligomictic metaconglomerates, metasandstones and quartzites, laminated metapelites, metarhythmites and metasiltites, and quartzites. In turn, the Santo Onofre Group, the Serra da Garapa Formation was subdivided into two lithofacies associations. The first is composed predominantly by quartzites and hematite-rich, graphite-rich and/or manganese-rich metapelites and phyllites. The second lithofacies association comprises staurolite-garnet-quartz-biotite aluminous schist and quartzites. In the Boqueirão Formation predominates metasubarkoses and lithic metasandstones and metasiltites, besides oligomictic metamicroconglomerates. U-Pb geochronological studies (LA-ICPMS) were performed on detrital zircons from these units. Ages ranging were 2870 ± 17–1958 ± 18 Ma and 3177 ± 42–894 ± 38 Ma, respectively. The main primary sources were related to rocks from the basement of the Western Bahia orogeny, of siderian-orosirian age, as well as volcanites and plutonites, both mafic and felsic, with ages between ca. 1.7 and 0.8 Ga, related to the evolution of the precursor basins of the Araçuaí-West Congo Orogen. As secondary sources, results suggest Metavolcanosedimentary sequences and Greenstone Belts of Archean and Paleoproterozoic ages, as well as rocks from the Espinhaço Supergroup and Macaúbas Group. The lithofacies of Serra da Garapa formation, as well as the ages found in detrital zircons, suggest that this formation is chronocorrelate with Rio Peixe Bravo Formation of the Macaúbas Group. Together, these formations, and Matão and Duas Barras Formation represent the pre-glacial unit of the Santo Onofre-Macaúbas basin initiated in Tonian. Some characteristics suggest that the Boqueirão Formation may be correlated to some of the glacial units of this basin. This work suggests that the formations Fazendinha and Serra da Vereda are excluded from the Santo Onofre Group.