Intense weathering attending the emergence of the southeast Amazonian Craton during the Neoarchean

Sedimentological evidence and detrital zircon provenance analysis show that the Amazonian Craton, Brazil, was subjected to large-scale subaerial erosion by c. 2.7 Ga. To assess weathering conditions attending the emergence of the Amazonian Craton, we used the chemical composition of terrigenous sediments deposited in the Carajás Basin, SE Amazonian Craton, between c. 2.7 and 2.6 Ga. Results from 41 samples collected in two drill cores along 150 and 250 m thick intervals show that emerged lands have been affected by strong chemical weathering conditions, similar in intensity to those occurring in the present-day inter-tropical belt. These intense chemical weathering conditions were probably due to the conjunction of warm temperatures ( potentially as high as 22 ± 3°C), abundant precipitation (mean annual precipitation estimated at 1540 ± 150 mm) and high atmospheric CO2 content ( pCO2 ≥ 10 times the present atmospheric level) that enhanced the chemical alteration of labile minerals. These intense weathering conditions contrast with those inferred in other cratons, which suggests that regionally contrasted climates existed during the Neoarchean.