The data from 15 new K - Ar analysis are here presented for Precambrian rocks sampled in the Central Northern region of Brazil. The Guaporé Craton presents K - Ar ages consistent to the Transamazonic Cycle and the available results allow us to generalize the influence of this cycle to all the eastern edge of the craton. For the Goiano Basal Complex we obtained an age attributable to the Transamazonic Cycle, an assemblage of data related to an isotopic rejuvenation during the Brazilian Cycle, an an intermediate result. The so-known Araxá Group in the Northern Goiás State has been named on basis of lithologic and structural trends similarities with the Araxá Group, a unit defmed in the Western Minas Gerais State and extended untill Peixe region in Goiás State. However, the vergences are in opposition, the metamorphic grade of that Araxá Group changes gradually to west into the Tocantins Group, and there is a belt of the Goiano Basal Complex separating the two Araxá units. So, the Authors proposes to abandon that correlation and introduces the name Estrondo Group for that unit in Northern Goiás. It makes part of the Paraguay - Araguaia Folding Belt, corresponding to its internal zone. The K - Ar ages for gneisses and schists to Estrondo Group varies from 426 to 581 m.y.
