Agradecimentos: We would like to thank the following archeologists, architects and museum curators for providing the archeological samples and for their illuminating discussions: Neuvânia Ghetti, Jackeline Macedo, Ana Sampaio, Regiane Gambim, Margarida Andreatta, Anicleide Zequini, Janete Gutierre, Guilherme Michelin, José Candeias, Paulo Zanettini and Camila Moraes. We also thank the Instituto do Patrimônio Histórico e Artístico Nacional (IPHAN), Museu de Arqueologia e Etnologia da Universidade de São Paulo (MAE/USP), Universidade Estadual Júlio de Mesquita Filho (UNESP) and Instituto Chico Mendes de Conservação da Biodiversidade (ICMBIO) for institutional supports. The authors are also very grateful to Gauthier Hulot for our fruitful discussions, Monika Korte for kindly providing the geomagnetic coefficients of the CALS3k models and Ruven Pillay for his help on the manuscript. We further thank the three anonymous reviewers for their helpful comments on the paper. This work was supported by the FAPESP (grant 2005/57782-4) and CAPES (international grant 3971/08-2) to G.A. Hartmann; and CNPq (Research Fellowship to R.I.F. Trindade, C. Etchevarne and M.C. Afonso) and partly financed by the INSU-CNRS program "SYSTER". This is IPGP contribution no. 3145 Ver menos

Abstract: We report new archeointensity data obtained from the analyses of baked clay elements (architectural and kiln brick fragments) sampled in Southeast Brazil and historically and/or archeologically dated between the end of the XVIth century and the beginning of the XXth century AD. The results were determined using the classical Thellier and Thellier protocol as modified by Coe, including partial thermoremanent magnetization (pTRM) and pTRM-tail checks, and the Triaxe protocol, which involves continuous high-temperature magnetization measurements. In both protocols, TRM anisotropy and cooling rate TRM dependence effects were taken into account for intensity determinations which were successfully performed for 150 specimens from 43 fragments, with a good agreement between intensity results obtained from the two procedures. Nine site-mean intensity values were derived from three to eight fragments and defined with standard deviations of less than 8%. The site-mean values vary from ~ 25 µT to ~ 42 µT and describe in Southeast Brazil a continuous decreasing trend by ~ 5 µT per century between ~ 1600 AD and ~ 1900 AD. Their comparison with recent archeointensity results obtained from Northeast Brazil and reduced at a same latitude shows that: (1) the geocentric axial dipole approximation is not valid between these southeastern and northeastern regions of Brazil, whose latitudes differ by ~ 10°, and (2) the available global geomagnetic field models (gufm1 models, their recalibrated versions and the CALSK3 models) are not sufficiently precise to reliably reproduce the non-dipole field effects which prevailed in Brazil for at least the 1600–1750 period. The large non-dipole contribution thus highlighted is most probably linked to the evolution of the South Atlantic Magnetic Anomaly (SAMA) during that period. Furthermore, although our dataset is limited, the Brazilian archeointensity data appear to support the view of a rather oscillatory behavior of the axial dipole moment during the past three centuries that would have been marked in particular by a moderate increase between the end of the XVIIIth century and the middle of the XIXth century followed by the well-known decrease from 1840 AD attested by direct measurements Ver menos