Agradecimentos: This work was partially funded by grants #2013/16382-0 to WP and #2010/10754-4 São Paulo Research Foundation (FAPESP), CAPES AUXPE 2043/2014 and CNPq grant 454609/2014-0 to GAH and CNPq-PQ 304934/2014-3 to RIFT. Plinio Jaqueto helped in magnetic mineralogy measurements. We thank Prof. Igor Pacca for suggesting the Jesuit Missions as an archeointensity target. A pre-submission reading by Andrew Biggin and two editorial reviews by Greig Paterson and an anonymous colleague helped in improving the paper Ver menos

Abstract: South America contributes only a small fraction of the global archeomagnetic data. Recent work in the region has expanded significantly the previous database with new data being generated from Chile, Argentina, Northeast and Southeast Brazil. We report here new results from Jesuit Missions in South Brazil, at the triple border with Argentina and Paraguay. Our archeological collection comprises a total of 24 fragments of baked clay construction materials from three Jesuit Missions, São Luiz Gonzaga 1657–1687 AD (3 fragments), São João Batista 1667–1697 AD (4 fragments) and Santo Ângelo 1676–1706 AD (17 fragments). Archeointensity determinations were performed with the double-heating technique in its modified form, with pTRM checks and pTRM tail checks. Measurements were complemented by anisotropy and cooling-rate corrections. A total of 24 specimens (11 fragments) passed strict quality selection, corresponding to a success rate of 45%. We also performed an experimental test for the 6-specimen average anisotropy correction technique and we show that it does not correct for the effects of TRM anisotropy. Results were similar within error for the three missions: São Luiz Gonzaga (40.2±2.4 µT), São João Batista ((39.1±1.6 µT) and Santo Ângelo (41.1±2.0 µT). These data were then compared with the most reliable data from South America, after a critical assessment of the current database. According to our analysis, only 39 intensity data for the continent can be considered as high-quality, most within the last 700 years; only three data were retained for older periods (800–1100 AD). The filtered data match reasonably well the available models for the past five centuries. A combined curve for South and Southeast Brazil plus Argentina plot systematically below relocated data from NE Brazil and Chile. These differences are likely due to complexities in the geometry of the field in South America not appropriately accounted for by a simple axial dipole. Our analysis highlights the need for high-quality data for the continent Ver menos