Two neoproterozoic crustal accretion events in the Brasilia belt, central Brazil

摘要

New U-Pb and Sm-Nd isotopic data for orthogneiss and granitoid rocks from the Neoproterozoic Goias magmatic arc in western Goias constrain the geological evolution of this juvenile crust in the western Brasilia belt. Orthogneiss rock samples have U-Pb crystallization ages of 804 +- 6, 669 +- 3, 662 +- 12, 634 +- 8, 630 +- 5, and 637 +- 20 Ma and show ε_(Nd)(T) values between + 2.8 and - 15.1. Rock units with negative ε_(Nd)(T) are more frequent in the eastern part of the studied area to the south of Anicuns, which indicates the presence of older continental crust in that part of the arc. Metagranitoids have ages of 821 +- 10, 810 +- 10, 792 +- 5, 790 +- 12, 782 +- 14, 748 +- 4, and 614 +- 5 Ma and ε_(Nd)(T) values between +5.1 and -3.7. The data presented here, combined with those in the literature, suggest that igneous activity in the Goias magmatic arc took place in two episodes: between ca. 0.89 and 0.8 Ga, probably in intraoceanic settings, and between ca. 0.66 and 0.60 Ga, likely in an active continental margin at the end of the Brasiliano orogeny.