U-Pb (zircon) ages of metabasic rocks of the Água Clara formation in the Araçaiba region-São Paulo (Brazil): preliminary data - Weber, Werner; Siga Júnior, Oswaldo; Sato, Kei; Basei, Miguel Angelo Stipp; Reis Neto, José Manoel dos (South American Symposium on Isotope Geology, 2003)