Provenance of the Buritirama Formation reveals the Paleoproterozoic assembly of the Bacajá and Carajás blocks (Amazon Craton) and the chronocorrelation of Mn-deposits in the Transamazonian/Birimian system of northern Brazil/West Africa.

Abstract

The Mn-bearing Buritirama Formation along the homonymous ridge consists of a 40 km long by ca. 3 km wide NW-SE trending unit that limits the northern border of the Archean Carajás domain with the Paleoproterozoic Bacajá domain in the southeastern Amazon Craton. The Buritirama Formation type section is arranged in four imbricated thrusts that individualize three main stratigraphic units: Lower Unit, Intermediate Unit and Upper Unit. Detrital U-Pb zircons ages from the Lower Unit and Upper Unit record the prevalence of Neoarchean populations, suggesting the Carajás block as the main sedimentary source for the Buritirama basin. However, minor Paleoproterozoic populations attributed to the Bacajá block are also recognized, defining a maximum depositional age at ca. 2186 Ma. The anorogenic Buritirama metagranite occurs at the local basement, represents a probable precursor stage of the Buritirama rift and yielded a Concordia age of 2549 ± 5.9 Ma (U-Pb).

Supported by these new geochronological data, a framework model for the evolution of the Buritirama basin is proposed. Contrary to previous interpretations, the basin was active until at least the Rhyacian, representing a platformal setting fringing the northern margin of the Carajás block. A regional metamorphic event (ca. 2.06 Ga) records the closure of the basin during the Transamazonian Orogeny and the amalgamation of the Bacajá and Carajás blocks. The depositional age bracketed in between 2.3 and 2.1 Ga links the Buritirama Mn deposit (southeastern Amazon Craton) with those of Serra do Navio (Amapá Block, northeastern Amazon Craton) and Nsuta (West African Craton), suggesting: (i) widespread chronocorrelation of Mn-bearing sequences in the continental-scale Rhyacian Transamazonian/Birimian orogenic system, and (ii) formation of the primary carbonate ores under the influence of a major global manganese deposition episode.