Stratigraphy and geochronlogy of the Guarinos greenstone belt, Goiás, Brazil

The Guarinos greenstone belt is one of the three low metamorphic grade supracrustal rocks assemblage rimmed by orthogneissesof Central Brazil’s Archean Block northern limits. The investigation of the stratigraphy of those greenstone beltsstarted by the end of 1970’s and underwent improvements during the years as a result of detailed geological mapping. Thelatest and accepted stratigraphic model for the Guarinos greenstone belt refers its supracrustal rocks under the GuarinosGroup, which is subdivided into the Serra do Cotovelo (metakomatiites), Serra Azul (metabasalts), São Patricinho (maficmetaturbidites), Aimbé (BIF) and Cabaçal (carbonaceous phyllites and impure metarenites) formations. Detailed geologicmapping (1:10,000) and drill-cores during an exploration program by Yamana Desenvolvimento Mineral S.A. in the areaallowed a better definition of the metasedimentary package of the Cabaçal Formation, which is here formally proposed tobe subdivided into a Lower Member of carbonaceous phyllites with basalt lava flows and gondite lenses interlayers, anIntermediate Member of gondite, iron formation, metachert and massive barite lenses, and an Upper Member of carbonaceous phyllites with minor metachert lenses. The impure metarenites, formerly considered as part of the Cabaçal Formation, are proposedunder the Mata Preta Formation, which is laterally interfingered with the Cabaçal Formation. U-Pb LA-ICP-MS geochronologicaldata of detrital zircon grains from the São Patricinho mafic metaturbidites and the impure metarenites of the Mata Preta formationsindicate that the major source-area of the clastic load had a Siderian to Rhyacian age, with minor contribution from Archean rocks.From the rock assemblage of both units and their contact relationships it is concluded that the basin stage they represent evolved duringthe world-wide Anoxic Oceanic Event (AOE) that took place during the 2.2 to 2.06 Ga, represented by the carbonaceous phyllites ofthe Cabaçal Formation, coeval with the erosion of a magmatic arc that derived the immature clastic load of the Mata Preta Formation