Post‐Great Oxidation Event Orosirian–Statherian iron formations on the São Francisco craton: Geotectonic implications

Abstract

The protocratonic core of the São Francisco craton assembled during the 2.1–2.0 Ga Transamazonian orogeny. Orosirian Fe‐rich sequences that extend from the northwestern border of the São Francisco protocraton (Colomi Group) to the southeast under the Espinhaço Belt (the < 1.99 Ga Serra da Serpentina Group) record the opening of an intracratonic basin with the episodically developed ferruginous waters prior to the initiation of the Espinhaço rift at 1.8 Ga. Ferruginous conditions developed again during deposition of the Canjica Iron Formation of the < 1.7 Ga Serra de São José Group in the Espinhaço rift (contemporaneously with felsic magmatism; Conceição do Mato Dentro Rhyolite and Borrachudos Granitic Suite) and extensive sandstones of the < (1666 ±32) Ma Itapanhoacanga and < (1683 ±11) Ma São João da Chapada Formations. In the upper São João da Chapada Formation, banded hematitic phyllite also records input of Fe‐rich fluids. The young age of these iron formations with respect to the conventionally accepted 1.88 Ga age for the youngest shallow‐marine Paleoproterozoic iron formations, the apparent absence of granular facies (granular iron formations), and yet shallow‐water (above fair‐weather base) depositional environment indicate that an unusual setting developed in a large basin after the Great Oxidation Event, in the aftermath of the Transamazonian orogeny. We propose that mantle plumes led to the opening of a previously unrecognized rift system, that could have caused the magmatism, supplied hydrothermal Fe and led to the opening of the Espinhaço, Pirapora, and Paramirim rifts, later obliterated by the Araçuaí orogenic belt during the Neoproterozoic to Early Paleozoic Brasiliano orogeny. The rift system did not develop into an open continental margin but probably evolved into a broad sag basin, stretching across the São Francisco and Congo cratons.

Hydrologic Alteration and Enhanced Microbial Reductive Dissolution of Fe(III) (hydr)oxides Under Flow Conditions in Fe(III)-Rich Rocks: Contribution to Cave-Forming Processes

“…The Southern Espinhaço Mountain Range (SE) of southeastern Brazil contains commercially important, high-grade iron ore hosted by the Serra da Serpentina Group, a stratigraphic unit which includes the iron-rich Serra do Sapo Formation (Auler et al, 2019). These sedimentary units were formed by the precipitation of Fe(III) and Si phases from solution during the Proterozoic Eon (Weber et al, 2006;Rosière et al, 2019;Silveira Braga et al, 2021). Iron ores can include magnetite (Fe 3 O 4 ), hematite (α-Fe 2 O 3 ), or a ferric oxyhydroxide like goethite (α-FeOOH) or limonite (FeO(OH)•n(H 2 O), and highgrade ore averages between 60 and 67% Fe (Dorr, 1964;Beukes et al, 2003;Rolim et al, 2016).…”

Detrital zircon records of the Paleo-Mesoproterozoic rift-sag Tamanduá Group in its type-section, Northern Quadrilátero Ferrífero, Minas Gerais, Brazil

“…The opening of the Espinhaço basin is related to the crustal stretching in the aftermath of Minas accretionary orogeny (Machado and Abreu-Bentivi 1989). The crustal stretching may be the result of far-field stress (Danderfer Filho et al 2015) or mantle plumes (Rosière et al 2019). The Espinhaço basin fill-succession comprises three tectonostratigraphic megasequences, Lower Espinhaço (1.80-1.68 Ga), Middle Espinhaço (1.60-1.38 Ga), and Upper Espinhaço (1.2-0.9 Ga), which represent stages of the rift to sag basin (Chemale Jr. et al 2012).…”

Thematic section: Special topics in 4th IGS ‘Precambrian World 2’

“…Rosière, Bekker, Rolim, and Santos (2019) reports the development of ferruginous conditions in an intracratonic basin along the eastern margin of the São Francisco protocraton, straddling the Orosirian‐Statherian boundary after the termination of the 2.1–2.0 Ga Trans‐Amazonian orogeny, with the occurrence of Fe‐rich sequences that extend from the northwestern cratonic border to the Southeast under the Espinhaço Belt (the < 1.99 Ga Serra da Serpentina Group). The presence of iron formations of this age indicates the development of an unusual setting in a large basin after the Great Oxidation Event.…”