Reavaliação e novos dados geocronológicos (Pb/Pb e K/Ar) da região do quadrilátero ferrífero e adjacências

Abstract

Geochronological investigations have clarified the geodynamic process and ages of the Rio das Velhas Supergroup and Minas Supergroup, two of the main stratigraphic units of the Quadrilátero Ferrífero, Minas Gerais, Brazil. . The best characterized geologic event (U/Pb in zircon crystals) is related to deposition, metamorphism and magmatism of the Rio das Velhas Supergroup. The magmatic event of the Rio das Velhas Supergroup occurred between 2.78 Ga and 2.73 Ga. The volcanic rocks of the Nova Lima Group, the basal unit of the Rio das Velhas Supergroup, have an Archaean age of ca 2.77 Ga. Pb/Pb dates on carbonate rocks of the Minas Supergroup yield an age of 2.42 Ga. Intrusive granitoids in the basal units of the Minas Supergroup have yielded a U/Pb zircon date of 2.612 Ga and Pb/Pb zircon date of 2.608 Ga. Transamazonian magmatism is well represented by granite emplacement along crustal discontinuities at ca 2.120 Ga. The vergence and metamorphic polarity of the Archaean and Paleoproterozoic orogenies are still controversial. The Brasiliano cycle was responsible for isotopic rejuvenation of the K/Ar system by partial or total argon losses.