(U-Th)/He Geochronology Constraints on Lateritic Duricrust Formation on the Guiana Shield

Thick regoliths developed under tropical climate, namely, laterites, resulting from long-term and pronounced geochemical mineralogical rearrangement of the parent rock in response to environmental changes. Little information is available on timing laterite bauxite formations, especially chronology main weathering episodes responsible for lateritic cover formation Guiana shield. For this purpose, we focused both bauxitic duricrusts over Paleoproterozoic Greenstone Belt Brownsberg, Suriname. The duricrust samples have a relatively simple mineralogy (i.e., goethite, gibbsite, hematite, kaolinite) but reveal, when observed at microscopic scale, complex history with multiple dissolution/reprecipitation. (U-Th)/He dating 179 Fe-oxides subsamples shows that sampled top Brownsberg plateau ages ranging <0.8 Ma ∼19 Ma. In contrast, extracted detrital boulders collected downslope indicate up 36 This age discrepancy may episode physical erosion affected region between ca. 30 20 Consistently, mountaintop indicates younger phase formation, recementing fragments preexisting material older than ∼15 Geochronological data also reveal long-lasting until present day, generations successive cycles dissolution reprecipitation associated redox cycles. led remobilization apparent enrichment some immobile elements, such as REE, aluminum, vanadium, mountaintop. Our geochronological, mineralogical, study Fe- Al-crusts mountain provide constraints evolution conditions prevailing since early Oligocene