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EVOLUÇÃO SEDIMENTAR E TECTÔNICA DA BACIA METASSEDIMENTAR DO RIO PARDO: UMA SÍNTESE

1999; Sociedade Brasileira de Geologia; Volume: 29; Issue: 3 Linguagem: Inglês

10.25249/0375-7536.199929339344

2177-4382

Augusto José Pedreira,

Geochemistry and Geologic Mapping

The Rio Pardo Metasedimentary Basin (≈15° 40' S / 39° 20' W), is divided into two sub-basins. The northeastern sub-basin deposited on the southeastern edge of the Sao Francisco Craton, and the southwestern underwent folding during construction of the Ara?uai Fold Belt, of Brasiliano age. The Rio Pardo Group fills the basin and comprises, from base to top, of the Panelinha Formation, the Itaimbe Subgroup, and the Salobro Formation. The former is composed of conglomerates, breccias, arkoses and graywackes. The Itaimbé Subgroup contains the Camaca (pelites and carbonates), Água Preta (phyllites), Santa Maria Eterna (sandstones and conglomerates), and the Serra do Paraiso (limestones and dolomites) formations that are laterally gradational. The Salobro Formation, unconformably deposited on the Itaimbé Subgroup, consists of polymitic conglomerates, arkoses and graywackes. The main depositional phase of these sediments was during the compressional episode of the Neoproterozoic Brasiliano Cycle. A northeast-southwest gravimetric profile along the basin shows a flexure of the basement north of the Pardo River, generating a foredeep containing the Salobro Formation. After their deposition, the sediments were subjected to three deformational episodes: the first and the second consist of coaxial folding and thrusts with northeast directed tectonic transport; in the third episode, the tectonic transport is from west to east. The main mineral resources presently exploited in the basin are the Serra do Paraiso Formation carbonates and, occasionally, diamonds of the Salobro Formation. The Rio Pardo Metasedimentary Basin evolved from an intracontinental rift system filled by alluvial fans and fluvial systems of the Panelinha Formation, unconformably overlain by the Itaimbé" Subgroup sediments. In this subgroup, the Camaca, Serra do Paraiso and Santa Maria Eterna formations respectively represent the deposition in muddy and carbonatic tidal flats, and beaches, and the Agua Preta Formation by turbidites of the basin's deeper parts. The Itaimbe' Subgroup sediments were involved in the Araguaf belt folding, with subsequent uplift and erosion, and deposited as the Salobro Formation into the foredeep formed by the crustal flexure north of the Pardo River in a foreland basin setting.