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Weathering geochronology of a deep (> 120 m) lateritic profile in northern Brazil

Tropical weathering leads to the formation of deep weathering profiles called laterites. The Guiana shield has been tectonically stable and in tropical latitudes supposedly since the Cretaceous, allowing the formation of very deep (> 100 m) and old (tens of Ma) lateritic profiles.

In this contribution we present a coupled data set of kaolinite electron paramagnetic resonance (EPR) ages and (U-Th)/He ages of supergene hematite and goethite from a deep (> 120 m) weathering profile exposed in an open pit gold mine in the northern Brazilian state of Amapá. Coupling of the two methods which target different components of the lateritic profile allows us to reconstruct the formation and evolution of the presented profile throughout the entire Cenozoic. While (U-Th)/He ages on supergene hematite and goethite from the ferruginous duricrusts on the top of the profile record three discrete weathering events during the Late Cretaceous/Early Paleocene, Oligocene and Middle Miocene, kaolinite ages allow an insight into the vertical evolution of the profile. The oldest kaolinites, which are very well-ordered, are preserved in the saprolitic part of the profile whereas the kaolinites in the top of the profile show very recent (< 5Ma) rejuvenation. Disordered kaolinite captured in the lateritic duricrust was protected from this rejuvenation.


Beatrix Heller1, Thierry Allard2, Caroline Sanchez3, Guilherme Taitson Bueno4, Jean-Yves Roig5, Cécile Gautheron3
1GEOPS, Université Paris-Saclay, CNRS, France;IMPMC, Sorbonne Université, CNRS, IRD, MNHN, France; 2IMPMC, Sorbonne Université, CNRS, IRD, MNHN, France; 3GEOPS, Université Paris-Saclay, CNRS, France; 4Universidade Federal de Goiás, Brazil; 5BRGM, France
GeoMinKöln 2022