Time Constraints for the Formation of the Archean Rio Maria Crust, Southeastern Amazonian Craton, Brazil

Abstract

The Rio Maria area (southeastern Carajás metallogenic province, Brazil) consists of a typical Archean Au-bearing granite-greenstone association intruded by Paleoproterozoic anorogenic granites. U-Pb analyses were performed on single zircon grains from the main Archean units of this area in order to elucidate the history of formation and evolution of the continental crust in this part of the southeastern Amazonian Craton. The Arco Verde metatonalite yielded one of the oldest U-Pb zircon ages from the Amazonian Craton (2957 +25/−21 Ma). Zircons from a meta-rhyodacite from the greenstone belt of the Lagoa Seca Group (Andorinhas Supergroup) are dated at 2904 +29/−21 Ma. This sequence is crosscut by Archean granitoids, such as the Rio Maria granodiorite, emplaced at 2874 +9/−10 Ma. These results suggest a short time interval (∼100 Ma) for crustal evolution of the Rio Maria area.