GEOCRONOLOGIA DE ROCHAS GRANÍTICAS E GNÁISSICAS DA REGIÃO DE ARENÓPOLlS-PIRANHAS, GOIÁS

Resumo

Geochronologic dating of granites and gneisses from the Arenópolis-Piranhas region put into evidence that important late-to-post-tectonic granitic magmatism took place during the latest phases of the Brasiliano Cycle in southwestem Goiás. The foliated granite of the Caiapó River has an age of 568 ± 10 Ma and initial Sr⁸⁷/Sr⁸⁶ ratio of 0.7039 ± 0.0001, the Serra do Iran granite 564 ± 5 Ma with initial Sr⁸⁷/Sr⁸⁶ ratio of 0.70499 ± 0.00072, and the Serra Negra granite hás a conventional age of 524 ± 16 Ma The initial Sr⁸⁷/Sr⁸⁶ ratíos of these rocks suggest that they represent an important episode of addition of new mantle derived material to the continental crust during the Late Precambrian and Early Phanerozoic.