Stratigraphy of the Pitangui synclinorium, northwest of the Quadrilátero Ferrífero mineral province - Brazil: magmatism and sedimentation from archean to Neoproterozoic

Abstract

The Pitangui Synclinorium is located in the northwestern portion of the Quadrilátero Ferrífero mineral province, São Francisco Craton, in southeast Brazil. It corresponds to a NW-SE-trending synformal structure composed of an Archean greenstone belt sequence, which is covered by Paleoproterozoic metasedimentary rocks to Neoproterozoic sedimentary rocks, and surrounded by Archean granite-gneiss complexes. This study reports the first detailed 1:25.000 scale geological mapping in the Pitangui Synclinorium and provides cartographic, stratigraphic and petrographic improvements, allowing the formalization of its lithostratigraphic units and unraveling the sedimentary and volcanic depositional environments. The Archean Pitangui greenstone belt occurs in most parts of the homonymous synclinorium, and is subdivided into the Pitangui Group and the Antimes Formation. The metavolcanosedimentary sequence of the Pitangui Group comprises basal mafic/ultramafic metavolcanic rocks with subordinate felsic/intermediate metavolcanic and metavolcaniclastic rocks of the Rio Pará Formation, suggesting a bimodal volcanism. It is followed by volcanogenic and chemical metasedimentary rocks of the Rio São João Formation, and pelitic to sandy metasedimentary rocks of the Onça do Pitangui Formation deposited in subaqueous environments mainly corresponding to submarine fan systems. The occurrence of clastic rocks increases towards the top of the sequence. The Antimes Formation comprises quartzites and metaconglomerates related to fluvial and fan delta depositional environments. The Pitangui greenstone belt is overlapped, in the central and northwest regions of the study area, by the Fazenda Tapera Formation, a Paleoproterozoic siliciclastic package containing arkosic metasandstones, metagreywackes and metarhythmites deposited in a shallow marine environment. Subordinated tuff layers occur as ash/fall deposits from distal volcanism. Neoproterozoic clastic-chemical sedimentary rocks of the Bambuí Group cover the northern portions of the synclinorium, and are mainly composed of diamictites, limestones, marls and rhythmites from the Carrancas (lacustrine or restricted marine), Sete Lagoas (shallow marine) and Serra de Santa Helena formations (deep water grading to prodelta and delta front). sequence of the Pitangui Group comprises basal mafic/ultramafic metavolcanic rocks with subordinate felsic/intermediate metavolcanic and metavolcaniclastic rocks of the Rio Pará Formation, suggesting a bimodal volcanism. It is followed by volcanogenic and chemical metasedimentary rocks of the Rio São João Formation, and pelitic to sandy metasedimentary rocks of the Onça do Pitangui Formation deposited in subaqueous environments mainly corresponding to submarine fan systems. The occurrence of clastic rocks increases towards the top of the sequence. The Antimes Formation comprises quartzites and metaconglomerates related to fluvial and fan delta depositional environments. The Pitangui greenstone belt is overlapped, in the central and northwest regions of the study area, by the Fazenda Tapera Formation, a Paleoproterozoic siliciclastic package containing arkosic metasandstones, metagreywackes and metarhythmites deposited in a shallow marine environment. Subordinated tuff layers occur as ash/fall deposits from distal volcanism. Neoproterozoic clastic-chemical sedimentary rocks of the Bambuí Group cover the northern portions of the synclinorium, and are mainly composed of diamictites, limestones, marls and rhythmites from the Carrancas (lacustrine or restricted marine), Sete Lagoas (shallow marine) and Serra de Santa Helena formations (deep water grading to prodelta and delta front).