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COBERTURAS METASSEDIMENTARES DO PROTEROZÓICO MÉDIO: OS GRUPOS ARAÍ E PARANOÁ NA REGIÃO DE NIQUELÂNDIA - COLINAS, GOIÁS

1988; Sociedade Brasileira de Geologia; Volume: 18; Issue: 1 Linguagem: Inglês

10.25249/0375-7536.19881815462

2177-4382

Reinhardt A. Fuck, Onildo João Marini, Marcel Auguste Dardenne, Almir Neves De Figueiredo,

Fish biology, ecology, and behavior

In the Niquelândia-Colinas, Goiás, Middle Proterozoic Araí Group nonconformably overlies granite-gneiss basement and remains of the possibly Early Proterozoic Ticunzal Formation. The Araí rocks comprise the lower Arraias Formation of quartzite, feldspathic quartzite, and metaconglomerate, and the upper Traíras Formation of carbonatic metapelite, calcschist, chlorite schist, and marble lenses, bearing greenschist facies mineral parageneses. Proeminent deformation structures are the domal shape outlined by the structural high of basement rocks and the large 5-20° S20W plunging asymmetric folds. The latter have not been recognized within the younger Paranoá Group metasediments which unconformably overly the Araí Group. The Paranoá Group is divided into two sequences. The lower is made of five psamitic and pelitic units, with the discontinuous São Miguel metaconglomerate at the base. The upper sequence comprises four mostly pelitic and carbonatic units, with less important psamitic layers. The rocks have been metamorphosed to the biotite zone of the greenschist facies. Deformation is represented by an earlier phase of tight to isoclinal folding with axial-plane schistosity, possibly coeval with large nearly N-S trending thrusts verging towards the east. These structures are refolded by asymmetric to reverse chevron folds with north-south axial-plane crenulation cleavage. The latest phases are of SW plunging open folds, and large vertical folds with sub-horizontal E- W trending axes. The lower psamo-pelitic sequence correlates with the unmetamorphosed Paranoá Group outcropping near Alto Paraíso de Goiás, to the east of the study area. The dominantly pelitic and carbonatic upper sequence is equivalent to the Minaçu Formation described further to the northwest. Stratigraphic relations between these sequences and their natural division in easily recognized units allow their characterization as groups of formations conferring supergroup rank to the Paranoá.