1. School of Geosciences University of the Witwatersrand PO WITS Johannesburg 2050 South Africa
2. Laboratory of Geochronology Institute of Geosciences University of Brasília Campus Universitario Darcy Ribeiro, Asa Norte, CEP Brasília 70910‐900 Brazil
3. Geophysics Institute of Geosciences University of Brasília Campus Universitario Darcy Ribeiro, Asa Norte Brasília CEP: 70910‐900 Brazil