Estratigrafia, tectônica e geocronologia U-Pb (LA-ICP-MS) em zircão detrítico dos grupos Rio Preto e Santo Onofre, faixa Rio Preto e norte do Corredor Paramirim Bahia e Piauí/Brasil

Abstract

At the Rio Preto Fold and Thrust Belt and the northern Paramirim Corridor two important Proterozoic metasedimentary sequences crops out: the Santo Onofre and Rio Preto Groups. The Rio Preto Group, which compose the homonymous fold-thrust belt on the northwestern limit of the São Francisco Craton, is composed of the Formosa Formation (schist, garnet schist, quartzite, chlorite-sericite schist and ferriferous quartz schist) and the Canabravinha Formation (quartzite, micaceous quartzite, metarhytmite, phylite, schist and metaturbidite). The Santo Onofre Group outcrops exclusively on the Paramirim Corridor and is composed by quartzite, and subordinately sericitic phylite, hematitic, carbonaceous or Mn-rich. Both groups are considered as the sedimentary register of rift basins deformed and metamorphosed under green schist facies during the Brasiliano/Pan-African Orogenesy. In the research área, two deformacional trends are observed: the Rio Preto Fold and Thrust Belt, structured in an assimetric divergente fan, NE-SW directed, and the Paramirim Corridor, with N-S striking layers and foliations. Three deformation phases were recognized, from wich the main D2 phase is responsible for the NE-SW and N-S structuration. In this work, we present 427 new U-Pb ages of detrital zircons from these units. The new data presented allow to determine a maximu age of deposition of ca. 912 Ma for the Canabravinha Formation, ca. 965 Ma for the Formosa Formation and ca. 971 Ma for Santo Onofre Group. The zircon age spectra showed sources from Tonian to Paleoarchean, with major contribution from tonian, statherian and ryacian rocks. This work suggests two neoproterozoic rift basins formed by Rio Preto Group and Santo Onofre Group, probably correlated with the pre-glacial units of the Macaúbas Group, at the Araçuaí belt. The Santo Onofre Group, mostlyformed by sand-rich rocks, would represent a less tectonically active, shallow plataformal marine environment, and the Rio Preto Group, with metadiamictites, quartzites, pelitic and rhythmitic rocks would represent a shallow to deep marine environment related with sedimentary gravity flows.