Abstract
The data from 15 new K - Ar analysis are here presented for Precambrian rocks sampled in the Central Northern region of Brazil. The Guapore 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 Araxa Group in the Northern Goias State has been named on basis of lithologic and structural trends similarities with the Araxa Group, a unit defmed in the Western Minas Gerais State and extended untill Peixe region in Goias State. However, the vergences are in opposition, the metamorphic grade of that Araxa Group changes gradually to west into the Tocantins Group, and there is a belt of the Goiano Basal Complex separating the two Araxa units. So, the Authors proposes to abandon that correlation and introduces the name Estrondo Group for that unit in Northern Goias. 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.
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