40 Ar/ 39 Ar ages of the aluminio (Serra do Itaberaba group) and hermida (Itapira group) amphibolite centra, portion of the Ribeira belt, Brazil: preliminary inferences - Oliveira, Marcos Aurelio Farias de; Souza, S. C. A.; Teixeira, Wilson; Vasconcelos, Paulo Marcos (South American Symposium on Isotope Geology, 2003)